# NetCDF C Interface Guide

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## The NetCDF C Interface Guide

This document describes the C interface to the netCDF library; it applies to netCDF version 4.1.1 and was last updated on 31 January 2010.

For a complete description of the netCDF format and utilities see The NetCDF Users Guide.

--- The Detailed Node Listing ---

Use of the NetCDF Library

Datasets

Groups

Dimensions

User Defined Data Types

Compound Types Introduction

Variables

Reading and Writing Character String Values

Attributes

Next: Datasets, Previous: Top, Up: Top

## 1 Use of the NetCDF Library

You can use the netCDF library without knowing about all of the netCDF interface. If you are creating a netCDF dataset, only a handful of routines are required to define the necessary dimensions, variables, and attributes, and to write the data to the netCDF dataset. (Even less is needed if you use the ncgen utility to create the dataset before running a program using netCDF library calls to write data.) Similarly, if you are writing software to access data stored in a particular netCDF object, only a small subset of the netCDF library is required to open the netCDF dataset and access the data. Authors of generic applications that access arbitrary netCDF datasets need to be familiar with more of the netCDF library.

In this chapter we provide templates of common sequences of netCDF calls needed for common uses. For clarity we present only the names of routines; omit declarations and error checking; omit the type-specific suffixes of routine names for variables and attributes; indent statements that are typically invoked multiple times; and use ... to represent arbitrary sequences of other statements. Full parameter lists are described in later chapters.

Next: Reading Known, Previous: Use of the NetCDF Library, Up: Use of the NetCDF Library

### 1.1 Creating a NetCDF Dataset

Here is a typical sequence of netCDF calls used to create a new netCDF dataset:

             nc_create           /* create netCDF dataset: enter define mode */
                  ...
                nc_def_dim       /* define dimensions: from name and length */
                  ...
                nc_def_var       /* define variables: from name, type, ... */
                  ...
                nc_put_att       /* put attribute: assign attribute values */
                  ...
             nc_enddef           /* end definitions: leave define mode */
                  ...
                nc_put_var       /* provide values for variables */
                  ...
             nc_close            /* close: save new netCDF dataset */

Only one call is needed to create a netCDF dataset, at which point you will be in the first of two netCDF modes. When accessing an open netCDF dataset, it is either in define mode or data mode. In define mode, you can create dimensions, variables, and new attributes, but you cannot read or write variable data. In data mode, you can access data and change existing attributes, but you are not permitted to create new dimensions, variables, or attributes.

One call to nc_def_dim is needed for each dimension created. Similarly, one call to nc_def_var is needed for each variable creation, and one call to a member of the nc_put_att family is needed for each attribute defined and assigned a value. To leave define mode and enter data mode, call nc_enddef.

Once in data mode, you can add new data to variables, change old values, and change values of existing attributes (so long as the attribute changes do not require more storage space). Single values may be written to a netCDF variable with one of the members of the nc_put_var1 family, depending on what type of data you have to write. All the values of a variable may be written at once with one of the members of the nc_put_var family. Arrays or array cross-sections of a variable may be written using members of the nc_put_vara family. Subsampled array sections may be written using members of the nc_put_vars family. Mapped array sections may be written using members of the nc_put_varm family. (Subsampled and mapped access are general forms of data access that are explained later.)

Finally, you should explicitly close all netCDF datasets that have been opened for writing by calling nc_close. By default, access to the file system is buffered by the netCDF library. If a program terminates abnormally with netCDF datasets open for writing, your most recent modifications may be lost. This default buffering of data is disabled by setting the NC_SHARE flag when opening the dataset. But even if this flag is set, changes to attribute values or changes made in define mode are not written out until nc_sync or nc_close is called.

Next: Reading Unknown, Previous: Creating, Up: Use of the NetCDF Library

### 1.2 Reading a NetCDF Dataset with Known Names

Here we consider the case where you know the names of not only the netCDF datasets, but also the names of their dimensions, variables, and attributes. (Otherwise you would have to do "inquire" calls.) The order of typical C calls to read data from those variables in a netCDF dataset is:

             nc_open                /* open existing netCDF dataset */
                  ...
                nc_inq_dimid        /* get dimension IDs */
                  ...
                nc_inq_varid        /* get variable IDs */
                  ...
                nc_get_att          /* get attribute values */
                  ...
                nc_get_var          /* get values of variables */
                  ...
             nc_close               /* close netCDF dataset */

First, a single call opens the netCDF dataset, given the dataset name, and returns a netCDF ID that is used to refer to the open netCDF dataset in all subsequent calls.

Next, a call to nc_inq_dimid for each dimension of interest gets the dimension ID from the dimension name. Similarly, each required variable ID is determined from its name by a call to nc_inq_varid Once variable IDs are known, variable attribute values can be retrieved using the netCDF ID, the variable ID, and the desired attribute name as input to a member of the nc_get_att family (typically nc_get_att_text or nc_get_att_double) for each desired attribute. Variable data values can be directly accessed from the netCDF dataset with calls to members of the nc_get_var1 family for single values, the nc_get_var family for entire variables, or various other members of the nc_get_vara, nc_get_vars, or nc_get_varm families for array, subsampled or mapped access.

Finally, the netCDF dataset is closed with nc_close. There is no need to close a dataset open only for reading.

Next: Adding, Previous: Reading Known, Up: Use of the NetCDF Library

### 1.3 Reading a netCDF Dataset with Unknown Names

It is possible to write programs (e.g., generic software) which do such things as processing every variable, without needing to know in advance the names of these variables. Similarly, the names of dimensions and attributes may be unknown.

Names and other information about netCDF objects may be obtained from netCDF datasets by calling inquire functions. These return information about a whole netCDF dataset, a dimension, a variable, or an attribute. The following template illustrates how they are used:

             nc_open                   /* open existing netCDF dataset */
               ...
             nc_inq                    /* find out what is in it */
                  ...
                nc_inq_dim             /* get dimension names, lengths */
                  ...
                nc_inq_var             /* get variable names, types, shapes */
                     ...
                   nc_inq_attname      /* get attribute names */
                     ...
                   nc_inq_att          /* get attribute types and lengths */
                     ...
                   nc_get_att          /* get attribute values */
                     ...
                nc_get_var             /* get values of variables */
                  ...
             nc_close                  /* close netCDF dataset */

As in the previous example, a single call opens the existing netCDF dataset, returning a netCDF ID. This netCDF ID is given to the nc_inq routine, which returns the number of dimensions, the number of variables, the number of global attributes, and the ID of the unlimited dimension, if there is one.

All the inquire functions are inexpensive to use and require no I/O, since the information they provide is stored in memory when a netCDF dataset is first opened.

Dimension IDs use consecutive integers, beginning at 0. Also dimensions, once created, cannot be deleted. Therefore, knowing the number of dimension IDs in a netCDF dataset means knowing all the dimension IDs: they are the integers 0, 1, 2, ...up to the number of dimensions. For each dimension ID, a call to the inquire function nc_inq_dim returns the dimension name and length.

Variable IDs are also assigned from consecutive integers 0, 1, 2, ... up to the number of variables. These can be used in nc_inq_var calls to find out the names, types, shapes, and the number of attributes assigned to each variable.

Once the number of attributes for a variable is known, successive calls to nc_inq_attname return the name for each attribute given the netCDF ID, variable ID, and attribute number. Armed with the attribute name, a call to nc_inq_att returns its type and length. Given the type and length, you can allocate enough space to hold the attribute values. Then a call to a member of the nc_get_att family returns the attribute values.

Once the IDs and shapes of netCDF variables are known, data values can be accessed by calling a member of the nc_get_var1 family for single values, or members of the nc_get_var, nc_get_vara, nc_get_vars, or nc_get_varm for various kinds of array access.

Next: Errors, Previous: Reading Unknown, Up: Use of the NetCDF Library

### 1.4 Adding New Dimensions, Variables, Attributes

An existing netCDF dataset can be extensively altered. New dimensions, variables, and attributes can be added or existing ones renamed, and existing attributes can be deleted. Existing dimensions, variables, and attributes can be renamed. The following code template lists a typical sequence of calls to add new netCDF components to an existing dataset:

             nc_open             /* open existing netCDF dataset */
               ...
             nc_redef            /* put it into define mode */
                 ...
               nc_def_dim        /* define additional dimensions (if any) */
                 ...
               nc_def_var        /* define additional variables (if any) */
                 ...
               nc_put_att        /* define additional attributes (if any) */
                 ...
             nc_enddef           /* check definitions, leave define mode */
                 ...
               nc_put_var        /* provide values for new variables */
                 ...
             nc_close            /* close netCDF dataset */

A netCDF dataset is first opened by the nc_open call. This call puts the open dataset in data mode, which means existing data values can be accessed and changed, existing attributes can be changed (so long as they do not grow), but nothing can be added. To add new netCDF dimensions, variables, or attributes you must enter define mode, by calling nc_redef. In define mode, call nc_def_dim to define new dimensions, nc_def_var to define new variables, and a member of the nc_put_att family to assign new attributes to variables or enlarge old attributes.

You can leave define mode and reenter data mode, checking all the new definitions for consistency and committing the changes to disk, by calling nc_enddef. If you do not wish to reenter data mode, just call nc_close, which will have the effect of first calling nc_enddef.

Until the nc_enddef call, you may back out of all the redefinitions made in define mode and restore the previous state of the netCDF dataset by calling nc_abort. You may also use the nc_abort call to restore the netCDF dataset to a consistent state if the call to nc_enddef fails. If you have called nc_close from definition mode and the implied call to nc_enddef fails, nc_abort will automatically be called to close the netCDF dataset and leave it in its previous consistent state (before you entered define mode).

For netCDF-4/HDF5 format files, define mode is still important, but the user does not have to called nc_enddef - it is called automatically when needed. It may also be called by the user.

In netCDF-4/HDF5 files, there are some settings which can only be modified during the very first define mode of the file. For example the compression level of a variable may be set only after the nc_def_var call and before the next nc_enddef call, whether it is called by the user explicitly, or when the user tries to read or write some data.

At most one process should have a netCDF dataset open for writing at one time. The library is designed to provide limited support for multiple concurrent readers with one writer, via disciplined use of the nc_sync function and the NC_SHARE flag. If a writer makes changes in define mode, such as the addition of new variables, dimensions, or attributes, some means external to the library is necessary to prevent readers from making concurrent accesses and to inform readers to call nc_sync before the next access.

Next: Compiling, Previous: Adding, Up: Use of the NetCDF Library

### 1.5 Error Handling

The netCDF library provides the facilities needed to handle errors in a flexible way. Each netCDF function returns an integer status value. If the returned status value indicates an error, you may handle it in any way desired, from printing an associated error message and exiting to ignoring the error indication and proceeding (not recommended!). For simplicity, the examples in this guide check the error status and call a separate function, handle_err(), to handle any errors. One possible definition of handle_err() can be found within the documentation of nc_strerror (see nc_strerror).

The nc_strerror function is available to convert a returned integer error status into an error message string.

Occasionally, low-level I/O errors may occur in a layer below the netCDF library. For example, if a write operation causes you to exceed disk quotas or to attempt to write to a device that is no longer available, you may get an error from a layer below the netCDF library, but the resulting write error will still be reflected in the returned status value.

Previous: Errors, Up: Use of the NetCDF Library

### 1.6 Compiling and Linking with the NetCDF Library

Details of how to compile and link a program that uses the netCDF C or FORTRAN interfaces differ, depending on the operating system, the available compilers, where the netCDF library and include files are installed, and whether or not you are using shared libraries. Nevertheless, we provide here examples of how to compile and link a program that uses the netCDF library on a Unix platform, so that you can adjust these examples to fit your installation.

Every C file that references netCDF functions or constants must contain an appropriate #include statement before the first such reference:

         #include <netcdf.h>

Unless the netcdf.h file is installed in a standard directory where the C compiler always looks, you must use the -I option when invoking the compiler, to specify a directory where netcdf.h is installed, for example:

         cc -c -I/usr/local/netcdf/include myprogram.c

Alternatively, you could specify an absolute path name in the #include statement, but then your program would not compile on another platform where netCDF is installed in a different location.

Unless the netCDF library is installed in a standard directory where the linker always looks, you must use the -L and -l options to link an object file that uses the netCDF library.

If the netCDF library was configured with the –enable-shared flag, and the operating system supports shared libraries, then it should be possible to link an application program using a relatively simple command. For example:

         cc -o myprogram myprogram.o -L/usr/local/netcdf/lib -lnetcdf

It should be noted that on some operating systems, when using shared libraries, the application itself may need to be compiled using some form of PIC (position independent code) flag; the particular flag will depend on the C compiler used. You should try it first without any PIC flag, and if that fails, then check with the system administrator about the proper form of PIC flag to use.

In addition, for some C compilers (e.g. Sun's cc compiler) it is necessary to specify runtime paths to the relevant libnetcdf.so. This can be accomplished in one of two ways.

1. Add the path to the directory containing libnetcdf.so to the LD_LIBRARY_PATH environment variable. This path is searched at runtime to locate any needed shared library. This might be accomplished, for example, by the following shell command (assuming that libnetcdf.so is in /usr/local/netcdf/lib).

                 LD_LIBRARY_PATH="/usr/local/netcdf/lib:$LD_LIBRARY_PATH"
                 export LD_LIBRARY_PATH

2. Set the so-called runtime path when the application is linked so that the absolute paths of all needed shared libraries is included in the application binary. For gcc under Linus, this is usually automatic. For C compilers on Solaris (and probably other operating systems) the runtime path must be specified at link time. The command in this case might look like this.

                 cc -o myprogram myprogram.o -L/usr/local/netcdf/lib -lnetcdf -R/usr/local/netcdf/lib

   Note that the -R flag is also C compiler dependent. For gcc and Linux, for example, the specification is usually of this form.

                 cc ...  -Wl,-rpath,/usr/local/netcdf/lib

   Other compilers may use other flags to specify this. Check with the local system administrator.

If shared libraries are not supported or are not being used for some reason, then it is necessary to include all the dependent libraries in the compile command. For example, for a netCDF-4 enabled library, it will be necessary to link with two HDF5 libraries, at least one compression library, and (on some systems) the math library.

         cc -o myprogram myprogram.o -L/usr/local/netcdf/lib -L/usr/local/hdf5/lib -lnetcdf -lhdf5_hl -lhdf5 -lz

Other configuration features (e.g. DAP support or parallel IO) may require additional libraries.

A complete list of necessary libraries can be obtained by executing the “nc-config –libs” command. For example:

         ./nc-config --libs

might return something like this:

         -L/tmp/install/spock/lib -lnetcdf -L/upc/share/stdinstall/local/spock/lib
         -lhdf5_hl -lhdf5 -L/upc/share/stdinstall/local/spock/lib -lz -lm
         -L/upc/share/stdinstall/local/spock/lib -lcurl -L/usr/kerberos/lib64
         -L/upc/share/stdinstall/local/spock/lib
         -lidn -lssl -lcrypto -lldap -lrt -lssl -lcrypto -ldl -lz -lz

Obviously there is some redundancy in this list, so it can be reduced somewhat to produce this slightly simpler list.

         -L/tmp/install/spock/lib -lnetcdf
         -L/upc/share/stdinstall/local/spock/lib -lhdf5 -lhdf5_hl -lz -lcurl
         -L/usr/kerberos/lib64 -lcrypto -lssl
         -ldl -lidn -lldap -lm -lrt

Next: Groups, Previous: Use of the NetCDF Library, Up: Top

## 2 Datasets

This chapter presents the interfaces of the netCDF functions that deal with a netCDF dataset or the whole netCDF library.

A netCDF dataset that has not yet been opened can only be referred to by its dataset name. Once a netCDF dataset is opened, it is referred to by a netCDF ID, which is a small non-negative integer returned when you create or open the dataset. A netCDF ID is much like a file descriptor in C or a logical unit number in FORTRAN. In any single program, the netCDF IDs of distinct open netCDF datasets are distinct. A single netCDF dataset may be opened multiple times and will then have multiple distinct netCDF IDs; however at most one of the open instances of a single netCDF dataset should permit writing. When an open netCDF dataset is closed, the ID is no longer associated with a netCDF dataset.

Functions that deal with the netCDF library include:

- Get version of library.
- Get error message corresponding to a returned error code.

The operations supported on a netCDF dataset as a single object are:

- Create, given dataset name and whether to overwrite or not.
- Open for access, given dataset name and read or write intent.
- Put into define mode, to add dimensions, variables, or attributes.
- Take out of define mode, checking consistency of additions.
- Close, writing to disk if required.
- Inquire about the number of dimensions, number of variables, number of global attributes, and ID of the unlimited dimension, if any.
- Synchronize to disk to make sure it is current.
- Set and unset nofill mode for optimized sequential writes.
- After a summary of conventions used in describing the netCDF interfaces, the rest of this chapter presents a detailed description of the interfaces for these operations.

Next: parallel access, Previous: Datasets, Up: Datasets

### 2.1 NetCDF Library Interface Descriptions

Each interface description for a particular netCDF function in this and later chapters contains:

- a description of the purpose of the function;
- a C function prototype that presents the type and order of the formal parameters to the function;
- a description of each formal parameter in the C interface;
- a list of possible error conditions; and
- an example of a C program fragment calling the netCDF function (and perhaps other netCDF functions).

The examples follow a simple convention for error handling, always checking the error status returned from each netCDF function call and calling a handle_error function in case an error was detected. For an example of such a function, see nc_strerror.

Next: nc_strerror, Previous: Interface Descriptions, Up: Datasets

### 2.2 Parallel Access for NetCDF Files

To use parallel access, open or create the file with nc_open_par (see nc_open_par) or nc_create_par (see nc_create_par).

The mode flag NC_PNETCDF will be automatically turned on for classic or 64-bit offset files opened or created with the parallel access functions.

The following example shows the creation of a file using parallel access with a netCDF-4/HDF5 file, and how a program might write data to such a file.

         #include "netcdf.h"
         #include <mpi.h>
         #include <assert.h>
         #include "hdf5.h"
         #include <string.h>
         #include <stdlib.h>

         #define BAIL(e) do { \
         printf("Bailing out in file %s, line %d, error:%s.\n", __FILE__, __LINE__, nc_strerror(e)); \
         return e; \
         } while (0)

         #define FILE "test_par.nc"
         #define NDIMS 2
         #define DIMSIZE 24
         #define QTR_DATA (DIMSIZE*DIMSIZE/4)
         #define NUM_PROC 4

         int
         main(int argc, char **argv)
         {
             /* MPI stuff. */
             int mpi_namelen;
             char mpi_name[MPI_MAX_PROCESSOR_NAME];
             int mpi_size, mpi_rank;
             MPI_Comm comm = MPI_COMM_WORLD;
             MPI_Info info = MPI_INFO_NULL;

             /* Netcdf-4 stuff. */
             int ncid, v1id, dimids[NDIMS];
             size_t start[NDIMS], count[NDIMS];

             int data[DIMSIZE*DIMSIZE], j, i, res;

             /* Initialize MPI. */
             MPI_Init(&argc,&argv);
             MPI_Comm_size(MPI_COMM_WORLD, &mpi_size);
             MPI_Comm_rank(MPI_COMM_WORLD, &mpi_rank);
             MPI_Get_processor_name(mpi_name, &mpi_namelen);
             printf("mpi_name: %s size: %d rank: %d\n", mpi_name,
                    mpi_size, mpi_rank);

             /* Create a parallel netcdf-4 file. */
             if ((res = nc_create_par(FILE, NC_NETCDF4|NC_MPIIO, comm,
                                      info, &ncid)))
                 BAIL(res);

             /* Create two dimensions. */
             if ((res = nc_def_dim(ncid, "d1", DIMSIZE, dimids)))
                BAIL(res);
             if ((res = nc_def_dim(ncid, "d2", DIMSIZE, &dimids[1])))
                BAIL(res);

             /* Create one var. */
             if ((res = nc_def_var(ncid, "v1", NC_INT, NDIMS, dimids, &v1id)))
                BAIL(res);

             if ((res = nc_enddef(ncid)))
                BAIL(res);

             /* Set up slab for this process. */
             start[0] = mpi_rank * DIMSIZE/mpi_size;
             start[1] = 0;
             count[0] = DIMSIZE/mpi_size;
             count[1] = DIMSIZE;
             printf("mpi_rank=%d start[0]=%d start[1]=%d count[0]=%d count[1]=%d\n",
                    mpi_rank, start[0], start[1], count[0], count[1]);

             /* Create phony data. We're going to write a 24x24 array of ints,
                in 4 sets of 144. */
             printf("mpi_rank*QTR_DATA=%d (mpi_rank+1)*QTR_DATA-1=%d\n",
                    mpi_rank*QTR_DATA, (mpi_rank+1)*QTR_DATA);
             for (i=mpi_rank*QTR_DATA; i<(mpi_rank+1)*QTR_DATA; i++)
                data[i] = mpi_rank;

             /*if ((res = nc_var_par_access(ncid, v1id, NC_COLLECTIVE)))
               BAIL(res);*/
             if ((res = nc_var_par_access(ncid, v1id, NC_INDEPENDENT)))
                BAIL(res);

             /* Write slabs of phony data. */
             if ((res = nc_put_vara_int(ncid, v1id, start, count,
                                        &data[mpi_rank*QTR_DATA])))
                BAIL(res);

             /* Close the netcdf file. */
             if ((res = nc_close(ncid)))
                 BAIL(res);

             /* Shut down MPI. */
             MPI_Finalize();

             return 0;
         }

Next: nc_inq_libvers, Previous: parallel access, Up: Datasets

### 2.3 Get error message corresponding to error status: nc_strerror

The function nc_strerror returns a static reference to an error message string corresponding to an integer netCDF error status or to a system error number, presumably returned by a previous call to some other netCDF function. The list of netCDF error status codes is available in the appropriate include file for each language binding.

### Usage

         const char * nc_strerror(int ncerr);

`ncerr`
  An error status that might have been returned from a previous call to some netCDF function.

### Errors

If you provide an invalid integer error status that does not correspond to any netCDF error message or or to any system error message (as understood by the system strerror function), nc_strerror returns a string indicating that there is no such error status.

### Example

Here is an example of a simple error handling function that uses nc_strerror to print the error message corresponding to the netCDF error status returned from any netCDF function call and then exit:

         #include <netcdf.h>
            ...
         void handle_error(int status) {
         if (status != NC_NOERR) {
            fprintf(stderr, "%s\n", nc_strerror(status));
            exit(-1);
            }
         }

Next: nc_create, Previous: nc_strerror, Up: Datasets

### 2.4 Get netCDF library version: nc_inq_libvers

The function nc_inq_libvers returns a string identifying the version of the netCDF library, and when it was built.

### Usage

         const char * nc_inq_libvers(void);

### Errors

This function takes no arguments, and thus no errors are possible in its invocation.

### Example

Here is an example using nc_inq_libvers to print the version of the netCDF library with which the program is linked:

         #include <netcdf.h>
            ...
            printf("%s\n", nc_inq_libvers());

Next: nc__create, Previous: nc_inq_libvers, Up: Datasets

### 2.5 Create a NetCDF Dataset: nc_create

This function creates a new netCDF dataset, returning a netCDF ID that can subsequently be used to refer to the netCDF dataset in other netCDF function calls. The new netCDF dataset opened for write access and placed in define mode, ready for you to add dimensions, variables, and attributes.

A creation mode flag specifies:

- whether to overwrite any existing dataset with the same name,
- whether access to the dataset is shared,
- whether this file should be in netCDF classic format (the default), the new 64-bit offset format (use NC_64BIT_OFFSET), or NC_NETCDF4 for a netCDF-4/HDF5 file.

### Usage

NOTE: When creating a netCDF-4 file HDF5 error reporting is turned off, if it is on. This doesn't stop the HDF5 error stack from recording the errors, it simply stops their display to the user through stderr.

         int nc_create (const char* path, int cmode, int *ncidp);

`path`
  The file name of the new netCDF dataset.
`cmode`
  The creation mode flag. The following flags are available: NC_NOCLOBBER, NC_SHARE, NC_64BIT_OFFSET, NC_NETCDF4, NC_CLASSIC_MODEL.

  Setting NC_NOCLOBBER means you do not want to clobber (overwrite) an existing dataset; an error (NC_EEXIST) is returned if the specified dataset already exists.

  The NC_SHARE flag is appropriate when one process may be writing the dataset and one or more other processes reading the dataset concurrently; it means that dataset accesses are not buffered and caching is limited. Since the buffering scheme is optimized for sequential access, programs that do not access data sequentially may see some performance improvement by setting the NC_SHARE flag. This flag is ignored for netCDF-4 files. (See below.)

  Setting NC_64BIT_OFFSET causes netCDF to create a 64-bit offset format file, instead of a netCDF classic format file. The 64-bit offset format imposes far fewer restrictions on very large (i.e. over 2 GB) data files. See Large File Support.

  A zero value (defined for convenience as NC_CLOBBER) specifies the default behavior: overwrite any existing dataset with the same file name and buffer and cache accesses for efficiency. The dataset will be in netCDF classic format. See NetCDF Classic Format Limitations.

  Setting NC_NETCDF4 causes netCDF to create a HDF5/NetCDF-4 file.

  Setting NC_CLASSIC_MODEL causes netCDF to enforce the classic data model in this file. (This only has effect for netCDF-4/HDF5 files, as classic and 64-bit offset files always use the classic model.) When used with NC_NETCDF4, this flag ensures that the resulting netCDF-4/HDF5 file may never contain any new constructs from the enhanced data model. That is, it cannot contain groups, user defined types, multiple unlimited dimensions, or new atomic types. The advantage of this restriction is that such files are guaranteed to work with existing netCDF software.

`ncidp`
  Pointer to location where returned netCDF ID is to be stored.

### Errors

nc_create returns the value NC_NOERR if no errors occurred. Possible causes of errors include:

- Passing a dataset name that includes a directory that does not exist.
- Specifying a dataset name of a file that exists and also specifying NC_NOCLOBBER.
- Specifying a meaningless value for the creation mode.
- Attempting to create a netCDF dataset in a directory where you don't have permission to create files.

### Return Codes

`NC_NOERR`
  No error.
`NC_ENOMEM`
  System out of memory.
`NC_EHDFERR`
  HDF5 error (netCDF-4 files only).
`NC_EFILEMETA`
  Error writing netCDF-4 file-level metadata in HDF5 file. (netCDF-4 files only).

### Examples

In this example we create a netCDF dataset named foo.nc; we want the dataset to be created in the current directory only if a dataset with that name does not already exist:

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
         if (status != NC_NOERR) handle_error(status);

In this example we create a netCDF dataset named foo_large.nc. It will be in the 64-bit offset format.

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_create("foo_large.nc", NC_NOCLOBBER|NC_64BIT_OFFSET, &ncid);
         if (status != NC_NOERR) handle_error(status);

In this example we create a netCDF dataset named foo_HDF5.nc. It will be in the HDF5 format.

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_create("foo_HDF5.nc", NC_NOCLOBBER|NC_NETCDF4, &ncid);
         if (status != NC_NOERR) handle_error(status);

In this example we create a netCDF dataset named foo_HDF5_classic.nc. It will be in the HDF5 format, but will not allow the use of any netCDF-4 advanced features. That is, it will conform to the classic netCDF-3 data model.

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_create("foo_HDF5_classic.nc", NC_NOCLOBBER|NC_NETCDF4|NC_CLASSIC_MODEL, &ncid);
         if (status != NC_NOERR) handle_error(status);

A variant of nc_create, nc__create (note the double underscore) allows users to specify two tuning parameters for the file that it is creating. These tuning parameters are not written to the data file, they are only used for so long as the file remains open after an nc__create. See nc__create.

Next: nc_create_par, Previous: nc_create, Up: Datasets

### 2.6 Create a NetCDF Dataset With Performance Options: nc__create

This function is a variant of nc_create, nc__create (note the double underscore) allows users to specify two tuning parameters for the file that it is creating. These tuning parameters are not written to the data file, they are only used for so long as the file remains open after an nc__create.

This function creates a new netCDF dataset, returning a netCDF ID that can subsequently be used to refer to the netCDF dataset in other netCDF function calls. The new netCDF dataset opened for write access and placed in define mode, ready for you to add dimensions, variables, and attributes.

A creation mode flag specifies whether to overwrite any existing dataset with the same name and whether access to the dataset is shared, and whether this file should be in netCDF classic format (the default), or the new 64-bit offset format.

### Usage

         int nc__create(const char *path, int cmode, size_t initialsz,
                        size_t *bufrsizehintp, int *ncidp);

`path`
  The file name of the new netCDF dataset.
`cmode`
  The creation mode flag. The following flags are available: NC_NOCLOBBER, NC_SHARE, and NC_64BIT_OFFSET, NC_NETCDF4, NC_CLASSIC_MODEL.

  Setting NC_NOCLOBBER means you do not want to clobber (overwrite) an existing dataset; an error (NC_EEXIST) is returned if the specified dataset already exists.

  The NC_SHARE flag is appropriate when one process may be writing the dataset and one or more other processes reading the dataset concurrently; it means that dataset accesses are not buffered and caching is limited. Since the buffering scheme is optimized for sequential access, programs that do not access data sequentially may see some performance improvement by setting the NC_SHARE flag. This flag is ignored for netCDF-4 files. (See below.)

  Setting NC_64BIT_OFFSET causes netCDF to create a 64-bit offset format file, instead of a netCDF classic format file. The 64-bit offset format imposes far fewer restrictions on very large (i.e. over 2 GB) data files. See Large File Support.

  A zero value (defined for convenience as NC_CLOBBER) specifies the default behavior: overwrite any existing dataset with the same file name and buffer and cache accesses for efficiency. The dataset will be in netCDF classic format. See NetCDF Classic Format Limitations.

  Setting NC_NETCDF4 causes netCDF to create a HDF5/NetCDF-4 file.

  Setting NC_CLASSIC_MODEL causes netCDF to enforce the classic data model in this file. (This only has effect for netCDF-4/HDF5 files, as classic and 64-bit offset files always use the classic model.) When used with NC_NETCDF4, this flag ensures that the resulting netCDF-4/HDF5 file may never contain any new constructs from the enhanced data model. That is, it cannot contain groups, user defined types, multiple unlimited dimensions, or new atomic types. The advantage of this restriction is that such files are guaranteed to work with existing netCDF software.

`initialsz`
  On some systems, and with custom I/O layers, it may be advantageous to set the size of the output file at creation time. This parameter sets the initial size of the file at creation time.
`bufrsizehintp`
  The argument referenced by bufrsizehintp controls a space versus time tradeoff, memory allocated in the netcdf library versus number of system calls.

  Because of internal requirements, the value may not be set to exactly the value requested. The actual value chosen is returned by reference.

  Using the value NC_SIZEHINT_DEFAULT causes the library to choose a default. How the system chooses the default depends on the system. On many systems, the "preferred I/O block size" is available from the stat() system call, struct stat member st_blksize. If this is available it is used. Lacking that, twice the system pagesize is used.

  Lacking a call to discover the system pagesize, we just set default bufrsize to 8192.

  The bufrsize is a property of a given open netcdf descriptor ncid, it is not a persistent property of the netcdf dataset.

`ncidp`
  Pointer to location where returned netCDF ID is to be stored.

### Errors

nc_create returns the value NC_NOERR if no errors occurred. Possible causes of errors include:

- Passing a dataset name that includes a directory that does not exist.
- Specifying a dataset name of a file that exists and also specifying NC_NOCLOBBER.
- Specifying a meaningless value for the creation mode.
- Attempting to create a netCDF dataset in a directory where you don't have permission to create files.

### Return Codes

`NC_NOERR`
  No error.
`NC_ENOMEM`
  System out of memory.
`NC_EHDFERR`
  HDF5 error (netCDF-4 files only).
`NC_EFILEMETA`
  Error writing netCDF-4 file-level metadata in HDF5 file. (netCDF-4 files only).

### Examples

In this example we create a netCDF dataset named foo.nc; we want the dataset to be created in the current directory only if a dataset with that name does not already exist:

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
         if (status != NC_NOERR) handle_error(status);

In this example we create a netCDF dataset named foo_large.nc; we want the dataset to be created in the current directory only if a dataset with that name does not already exist. We also specify that bufrsize and initial size for the file.

         #include <netcdf.h>
            ...
         int status;
         int ncid;
         int intialsz = 2048;
         int *bufrsize;
            ...
         *bufrsize = 1024;
         status = nc__create("foo.nc", NC_NOCLOBBER, initialsz, bufrsize, &ncid);
         if (status != NC_NOERR) handle_error(status);

Next: nc_open, Previous: nc__create, Up: Datasets

### 2.7 Create a NetCDF Dataset With Performance Options: nc_create_par

This function is a variant of nc_create, nc_create_par allows users to open a file on a MPI/IO or MPI/Posix parallel file system.

The parallel parameters are not written to the data file, they are only used for so long as the file remains open after an nc_create_par.

This function creates a new netCDF dataset, returning a netCDF ID that can subsequently be used to refer to the netCDF dataset in other netCDF function calls. The new netCDF dataset opened for write access and placed in define mode, ready for you to add dimensions, variables, and attributes.

If the NC_NETCDF4 flag is used, the HDF5 library is used for parallel I/O. If not, the parallel-netcdf library is used.

When a file is created for parallel access, collective operations are the default. To use independent access on a variable, See nc_var_par_access.

### Usage

         int nc_create_par(const char *path, int cmode, MPI_Comm comm,
                           MPI_Info info, int ncidp);

`path`
  The file name of the new netCDF dataset.
`cmode`
  Either the NC_MPIIO or NC_MPIPOSIX flags may be present if the NC_NETCDF4 flag is used.

  The NC_SHARE flag is ignored.

`comm`
  The MPI_Comm object returned by the MPI layer.
`info`
  The MPI_Info object returned by the MPI layer, if MPI/IO is being used, or 0 if MPI/Posix is being used.
`ncidp`
  Pointer to location where returned netCDF ID is to be stored.

### Return Codes

`NC_NOERR`
  No error.
`NC_EPARINIT`
  Could not initialize parallel access at the HDF5 layer.
`NC_EFILEMETA`
  HDF5 layer cannot handle create or root group open.
`NC_EEXIST`
  Specifying a dataset name of a file that exists and also specifying NC_NOCLOBBER.
`NC_EINVAL`
  Bad value for the creation mode.
`NC_EHDFERR`
  Unexpected error from the HDF5 layer.

### Examples

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         *bufrsize = 1024;
         status = nc__create("foo.nc", NC_NOCLOBBER, initialsz, bufrsize, &ncid);
         if (status != NC_NOERR) handle_error(status);

Next: nc__open, Previous: nc_create_par, Up: Datasets

### 2.8 Open a NetCDF Dataset for Access: nc_open

The function nc_open opens an existing netCDF dataset for access. It determines the underlying file format automatically. Use the same call to open a netCDF classic, 64-bit offset, or netCDF-4 file.

### Usage

         int nc_open (const char *path, int omode, int *ncidp);

`path`
  File name for netCDF dataset to be opened. When DAP support is enabled, then the path may be an OPeNDAP URL rather than a file path.
`omode`
  A zero value (or NC_NOWRITE) specifies the default behavior: open the dataset with read-only access, buffering and caching accesses for efficiency

  Otherwise, the open mode is NC_WRITE, NC_SHARE, or NC_WRITE|NC_SHARE. Setting the NC_WRITE flag opens the dataset with read-write access. ("Writing" means any kind of change to the dataset, including appending or changing data, adding or renaming dimensions, variables, and attributes, or deleting attributes.)

  The NC_SHARE flag is only used for netCDF classic and 64-bit offset files. It is appropriate when one process may be writing the dataset and one or more other processes reading the dataset concurrently; it means that dataset accesses are not buffered and caching is limited. Since the buffering scheme is optimized for sequential access, programs that do not access data sequentially may see some performance improvement by setting the NC_SHARE flag.

  It is not necessary to pass any information about the format of the file being opened. The file type will be detected automatically by the netCDF library.

  If a the path is a DAP URL, then the open mode is read-only. Setting NC_WRITE will be ignored.

`ncidp`
  Pointer to location where returned netCDF ID is to be stored.

### Errors

When opening a netCDF-4 file HDF5 error reporting is turned off, if it is on. This doesn't stop the HDF5 error stack from recording the errors, it simply stops their display to the user through stderr.

nc_open returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The specified netCDF dataset does not exist.
- A meaningless mode was specified.

### Return Codes

`NC_NOERR`
  No error.
`NC_NOMEM`
  Out of memory.
`NC_EHDFERR`
  HDF5 error. (NetCDF-4 files only.)
`NC_EDIMMETA`
  Error in netCDF-4 dimension metadata. (NetCDF-4 files only.)
`NC_ENOCOMPOIND`
  (NetCDF-4 files only.)

### Example

Here is an example using nc_open to open an existing netCDF dataset named foo.nc for read-only, non-shared access:

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_open("foo.nc", 0, &ncid);
         if (status != NC_NOERR) handle_error(status);

Next: nc_open_par, Previous: nc_open, Up: Datasets

### 2.9 Open a NetCDF Dataset for Access with Performance Tuning: nc__open

A function opens a netCDF dataset for access with an additional performance tuning parameter. When DAP support is enabled, it is possible to open a DAP data source through this interface, but it is deprecated because all of the performance tuning parameters are ignored. The standard nc_open interface should be used instead.

### Usage

         int nc__open(const char *path, int mode, size_t *bufrsizehintp, int *ncidp);

`path`
  File name for netCDF dataset to be opened.
`omode`
  A zero value (or NC_NOWRITE) specifies the default behavior: open the dataset with read-only access, buffering and caching accesses for efficiency

  Otherwise, the open mode is NC_WRITE, NC_SHARE, or NC_WRITE|NC_SHARE. Setting the NC_WRITE flag opens the dataset with read-write access. ("Writing" means any kind of change to the dataset, including appending or changing data, adding or renaming dimensions, variables, and attributes, or deleting attributes.) The NC_SHARE flag is appropriate when one process may be writing the dataset and one or more other processes reading the dataset concurrently; it means that dataset accesses are not buffered and caching is limited. Since the buffering scheme is optimized for sequential access, programs that do not access data sequentially may see some performance improvement by setting the NC_SHARE flag.

`bufrsizehintp`
  The argument referenced by bufrsizehintp controls a space versus time tradeoff, memory allocated in the netcdf library versus number of system calls.

  Because of internal requirements, the value may not be set to exactly the value requested. The actual value chosen is returned by reference.

  Using the value NC_SIZEHINT_DEFAULT causes the library to choose a default. How the system chooses the default depends on the system. On many systems, the "preferred I/O block size" is available from the stat() system call, struct stat member st_blksize. If this is available it is used. Lacking that, twice the system pagesize is used.

  Lacking a call to discover the system pagesize, we just set default bufrsize to 8192.

  The bufrsize is a property of a given open netcdf descriptor ncid, it is not a persistent property of the netcdf dataset.

`ncidp`
  Pointer to location where returned netCDF ID is to be stored.

### Errors

nc__open returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The specified netCDF dataset does not exist.
- A meaningless mode was specified.

### Example

Here is an example using nc__open to open an existing netCDF dataset named foo.nc for read-only, non-shared access:

         #include <netcdf.h>
            ...
         int status;
         int ncid;
         size_t bufrsize;
            ...
         *bufrsize = 1024;
         status = nc_open("foo.nc", 0, &bufrsize, &ncid);
         if (status != NC_NOERR) handle_error(status);

Next: nc_redef, Previous: nc__open, Up: Datasets

### 2.10 Open a NetCDF Dataset for Parallel Access

This function opens a netCDF-4 dataset for parallel access.

For netcdf-4/HDF5 files, the HDF5 library parallel I/O is used. This opens the file using either MPI-IO or MPI-POSIX.

DAP access is not allowed with parallel I/O.

When netCDF opens a file for parallel access, collective operations are the default. To use independent access on a variable, See nc_var_par_access.

### Usage

         int nc_open_par(const char *path, int mode, MPI_Comm comm,
                         MPI_Info info, int *ncidp);

`path`
  File name for netCDF dataset to be opened.
`omode`
  Either the NC_MPIIO or NC_MPIPOSIX flags may be present for a netCDF-4/HDF5 file.

  The flag NC_WRITE opens the dataset with read-write access. ("Writing" means any kind of change to the dataset, including appending or changing data, adding or renaming dimensions, variables, and attributes, or deleting attributes.)

  All other flags are ignored or not allowed. The NC_NETCDF4 flag is not required, as the file type is detected when the file is opened.

`comm`
  MPI_Comm object returned by the MPI layer.
`info`
  MPI_Info object returned by the MPI layer, or NULL if MPI-POSIX access is desired.
`ncidp`
  Pointer to location where returned netCDF ID is to be stored.

### Return Codes

`NC_NOERR`
  No error.
  The specified netCDF dataset does not exist.
  A meaningless mode was specified.

### Example

Here is an example (from nc_test4/tst_parallel2.c) using nc_open_par.

             /* Reopen the file and check it. */
             if (nc_open_par(file_name, NC_NOWRITE, comm, info, &ncid)) ERR;

             /* Read all the slabs this process is responsible for. */
             for (i = 0; i < NUM_SLABS / mpi_size; i++)
             {
                start[0] = NUM_SLABS / mpi_size * mpi_rank + i;
                /* Read one slab of data. */
                if (nc_get_vara_int(ncid, varid, start, count, data_in)) ERR;
             }

Next: nc_enddef, Previous: nc_open_par, Up: Datasets

### 2.11 Put Open NetCDF Dataset into Define Mode: nc_redef

The function nc_redef puts an open netCDF dataset into define mode, so dimensions, variables, and attributes can be added or renamed and attributes can be deleted.

### Usage

For netCDF-4 files (i.e. files created with NC_NETCDF4 in the cmode, see nc_create), it is not necessary to call nc_redef unless the file was also created with NC_STRICT_NC3. For straight-up netCDF-4 files, nc_redef is called automatically, as needed.

For all netCDF-4 files, the root ncid must be used. This is the ncid returned by nc_open and nc_create, and points to the root of the hierarchy tree for netCDF-4 files.

         int nc_redef(int ncid);

`ncid`
  netCDF ID, from a previous call to nc_open or nc_create.

### Errors

nc_redef returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The specified netCDF dataset is already in define mode. This error code will only be returned for classic and 64-bit offset format files.
- The specified netCDF dataset was opened for read-only.
- The specified netCDF ID does not refer to an open netCDF dataset.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad ncid.
`NC_EBADGRPID`
  The ncid must refer to the root group of the file, that is, the group returned by nc_open or nc_create. (see nc_open see nc_create).
`NC_EINDEFINE`
  Already in define mode.
`NC_EPERM`
  File is read-only.

### Example

Here is an example using nc_redef to open an existing netCDF dataset named foo.nc and put it into define mode:

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);  /* open dataset */
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_redef(ncid);                      /* put in define mode */
         if (status != NC_NOERR) handle_error(status);

Next: nc__enddef, Previous: nc_redef, Up: Datasets

### 2.12 Leave Define Mode: nc_enddef

The function nc_enddef takes an open netCDF dataset out of define mode. The changes made to the netCDF dataset while it was in define mode are checked and committed to disk if no problems occurred. Non-record variables may be initialized to a "fill value" as well. See nc_set_fill. The netCDF dataset is then placed in data mode, so variable data can be read or written.

It's not necessary to call nc_enddef for netCDF-4 files. With netCDF-4 files, nc_enddef is called when needed by the netcdf-4 library. User calls to nc_enddef for netCDF-4 files still flush the metadata to disk.

This call may involve copying data under some circumstances. For a more extensive discussion see File Structure and Performance.

For netCDF-4/HDF5 format files there are some variable settings (the compression, endianness, fletcher32 error correction, and fill value) which must be set (if they are going to be set at all) between the nc_def_var and the next nc_enddef. Once the nc_enddef is called, these settings can no longer be changed for a variable.

### Usage

         int nc_enddef(int ncid);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create. If you use a group id, the enddef will apply to the entire file. That all, the enddef will not just end define mode in one group, but in the entire file.

### Errors

nc_enddef returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The specified netCDF dataset is not in define mode.
- The specified netCDF ID does not refer to an open netCDF dataset.
- The size of one or more variables exceed the size constraints for whichever variant of the file format is in use). See Large File Support.

### Example

Here is an example using nc_enddef to finish the definitions of a new netCDF dataset named foo.nc and put it into data mode:

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
         if (status != NC_NOERR) handle_error(status);

            ...       /* create dimensions, variables, attributes */

         status = nc_enddef(ncid);  /*leave define mode*/
         if (status != NC_NOERR) handle_error(status);

Next: nc_close, Previous: nc_enddef, Up: Datasets

### 2.13 Leave Define Mode with Performance Tuning: nc__enddef

The function nc__enddef takes an open netCDF dataset out of define mode. The changes made to the netCDF dataset while it was in define mode are checked and committed to disk if no problems occurred. Non-record variables may be initialized to a "fill value" as well. See nc_set_fill. The netCDF dataset is then placed in data mode, so variable data can be read or written.

This call may involve copying data under some circumstances. For a more extensive discussion see File Structure and Performance.

Caution: this function exposes internals of the netcdf version 1 file format. Users should use nc_enddef in most circumstances. This function may not be available on future netcdf implementations.

The current netcdf file format has three sections, the "header" section, the data section for fixed size variables, and the data section for variables which have an unlimited dimension (record variables).

The header begins at the beginning of the file. The index (offset) of the beginning of the other two sections is contained in the header. Typically, there is no space between the sections. This causes copying overhead to accrue if one wishes to change the size of the sections, as may happen when changing names of things, text attribute values, adding attributes or adding variables. Also, for buffered i/o, there may be advantages to aligning sections in certain ways.

The minfree parameters allow one to control costs of future calls to nc_redef, nc_enddef by requesting that minfree bytes be available at the end of the section.

The align parameters allow one to set the alignment of the beginning of the corresponding sections. The beginning of the section is rounded up to an index which is a multiple of the align parameter. The flag value ALIGN_CHUNK tells the library to use the bufrsize (see above) as the align parameter. It has nothing to do with the chunking (multidimensional tiling) features of netCDF-4.

The file format requires mod 4 alignment, so the align parameters are silently rounded up to multiples of 4. The usual call,

         nc_enddef(ncid);

is equivalent to

         nc__enddef(ncid, 0, 4, 0, 4);

The file format does not contain a "record size" value, this is calculated from the sizes of the record variables. This unfortunate fact prevents us from providing minfree and alignment control of the "records" in a netcdf file. If you add a variable which has an unlimited dimension, the third section will always be copied with the new variable added.

### Usage

         int nc__enddef(int ncid, size_t h_minfree, size_t v_align,
                        size_t v_minfree, size_t r_align);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`h_minfree`
  Sets the pad at the end of the "header" section.
`v_align`
  Controls the alignment of the beginning of the data section for fixed size variables.
`v_minfree`
  Sets the pad at the end of the data section for fixed size variables.
`r_align`
  Controls the alignment of the beginning of the data section for variables which have an unlimited dimension (record variables).

### Errors

nc__enddef returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The specified netCDF dataset is not in define mode.
- The specified netCDF ID does not refer to an open netCDF dataset.
- The size of one or more variables exceed the size constraints for whichever variant of the file format is in use). See Large File Support.

### Example

Here is an example using nc_enddef to finish the definitions of a new netCDF dataset named foo.nc and put it into data mode:

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
         if (status != NC_NOERR) handle_error(status);

            ...       /* create dimensions, variables, attributes */

         status = nc_enddef(ncid);  /*leave define mode*/
         if (status != NC_NOERR) handle_error(status);

Next: nc_inq Family, Previous: nc__enddef, Up: Datasets

### 2.14 Close an Open NetCDF Dataset: nc_close

The function nc_close closes an open netCDF dataset.

If the dataset in define mode, nc_enddef will be called before closing. (In this case, if nc_enddef returns an error, nc_abort will automatically be called to restore the dataset to the consistent state before define mode was last entered.) After an open netCDF dataset is closed, its netCDF ID may be reassigned to the next netCDF dataset that is opened or created.

### Usage

For netCDF-4 files, the ncid of the root group must be passed into nc_close.

         int nc_close(int ncid);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.

### Errors

nc_close returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- Define mode was entered and the automatic call made to nc_enddef failed.
- The specified netCDF ID does not refer to an open netCDF dataset.

`NC_NOERR`
  No error.
`NC_EBADID`
  Invalid id passed.
`NC_EBADGRPID`
  ncid did not contain the root group id of this file. (NetCDF-4 only).

### Example

Here is an example using nc_close to finish the definitions of a new netCDF dataset named foo.nc and release its netCDF ID:

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
         if (status != NC_NOERR) handle_error(status);

            ...       /* create dimensions, variables, attributes */

         status = nc_close(ncid);       /* close netCDF dataset */
         if (status != NC_NOERR) handle_error(status);

Next: nc_sync, Previous: nc_close, Up: Datasets

### 2.15 Inquire about an Open NetCDF Dataset: nc_inq Family

Members of the nc_inq family of functions return information about an open netCDF dataset, given its netCDF ID. Dataset inquire functions may be called from either define mode or data mode. The first function, nc_inq, returns values for the number of dimensions, the number of variables, the number of global attributes, and the dimension ID of the dimension defined with unlimited length, if any. The other functions in the family each return just one of these items of information.

For C, these functions include nc_inq, nc_inq_ndims, nc_inq_nvars, nc_inq_natts, and nc_inq_unlimdim. An additional function, nc_inq_format, returns the (rarely needed) format version.

No I/O is performed when these functions are called, since the required information is available in memory for each open netCDF dataset.

### Usage

         int nc_inq          (int ncid, int *ndimsp, int *nvarsp, int *ngattsp,
                              int *unlimdimidp);
         int nc_inq_ndims    (int ncid, int *ndimsp);
         int nc_inq_nvars    (int ncid, int *nvarsp);
         int nc_inq_natts    (int ncid, int *ngattsp);
         int nc_inq_unlimdim (int ncid, int *unlimdimidp);
         int nc_inq_format   (int ncid, int *formatp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`ndimsp`
  Pointer to location for returned number of dimensions defined for this netCDF dataset.
`nvarsp`
  Pointer to location for returned number of variables defined for this netCDF dataset.
`ngattsp`
  Pointer to location for returned number of global attributes defined for this netCDF dataset.
`unlimdimidp`
  Pointer to location for returned ID of the unlimited dimension, if there is one for this netCDF dataset. If no unlimited length dimension has been defined, -1 is returned.
`formatp`
  Pointer to location for returned format version, one of NC_FORMAT_CLASSIC, NC_FORMAT_64BIT, NC_FORMAT_NETCDF4, NC_FORMAT_NETCDF4_CLASSIC.

### Errors

All members of the nc_inq family return the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_inq to find out about a netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int status, ncid, ndims, nvars, ngatts, unlimdimid;
            ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq(ncid, &ndims, &nvars, &ngatts, &unlimdimid);
         if (status != NC_NOERR) handle_error(status);

Next: nc_abort, Previous: nc_inq Family, Up: Datasets

### 2.16 Synchronize an Open NetCDF Dataset to Disk: nc_sync

The function nc_sync offers a way to synchronize the disk copy of a netCDF dataset with in-memory buffers. There are two reasons you might want to synchronize after writes:

- To minimize data loss in case of abnormal termination, or
- To make data available to other processes for reading immediately after it is written. But note that a process that already had the dataset open for reading would not see the number of records increase when the writing process calls nc_sync; to accomplish this, the reading process must call nc_sync.

This function is backward-compatible with previous versions of the netCDF library. The intent was to allow sharing of a netCDF dataset among multiple readers and one writer, by having the writer call nc_sync after writing and the readers call nc_sync before each read. For a writer, this flushes buffers to disk. For a reader, it makes sure that the next read will be from disk rather than from previously cached buffers, so that the reader will see changes made by the writing process (e.g., the number of records written) without having to close and reopen the dataset. If you are only accessing a small amount of data, it can be expensive in computer resources to always synchronize to disk after every write, since you are giving up the benefits of buffering.

An easier way to accomplish sharing (and what is now recommended) is to have the writer and readers open the dataset with the NC_SHARE flag, and then it will not be necessary to call nc_sync at all. However, the nc_sync function still provides finer granularity than the NC_SHARE flag, if only a few netCDF accesses need to be synchronized among processes.

It is important to note that changes to the ancillary data, such as attribute values, are not propagated automatically by use of the NC_SHARE flag. Use of the nc_sync function is still required for this purpose.

Sharing datasets when the writer enters define mode to change the data schema requires extra care. In previous releases, after the writer left define mode, the readers were left looking at an old copy of the dataset, since the changes were made to a new copy. The only way readers could see the changes was by closing and reopening the dataset. Now the changes are made in place, but readers have no knowledge that their internal tables are now inconsistent with the new dataset schema. If netCDF datasets are shared across redefinition, some mechanism external to the netCDF library must be provided that prevents access by readers during redefinition and causes the readers to call nc_sync before any subsequent access.

When calling nc_sync, the netCDF dataset must be in data mode. A netCDF dataset in define mode is synchronized to disk only when nc_enddef is called. A process that is reading a netCDF dataset that another process is writing may call nc_sync to get updated with the changes made to the data by the writing process (e.g., the number of records written), without having to close and reopen the dataset.

Data is automatically synchronized to disk when a netCDF dataset is closed, or whenever you leave define mode.

### Usage

         int nc_sync(int ncid);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.

### Errors

nc_sync returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The netCDF dataset is in define mode.
- The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_sync to synchronize the disk writes of a netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int status;
         int ncid;
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);  /* open for writing */
         if (status != NC_NOERR) handle_error(status);

            ...           /* write data or change attributes */

         status = nc_sync(ncid);      /* synchronize to disk */
         if (status != NC_NOERR) handle_error(status);

Next: nc_set_fill, Previous: nc_sync, Up: Datasets

### 2.17 Back Out of Recent Definitions: nc_abort

You no longer need to call this function, since it is called automatically by nc_close in case the dataset is in define mode and something goes wrong with committing the changes. The function nc_abort just closes the netCDF dataset, if not in define mode. If the dataset is being created and is still in define mode, the dataset is deleted. If define mode was entered by a call to nc_redef, the netCDF dataset is restored to its state before definition mode was entered and the dataset is closed.

### Usage

         int nc_abort(int ncid);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.

### Errors

nc_abort returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- When called from define mode while creating a netCDF dataset, deletion of the dataset failed.
- The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_abort to back out of redefinitions of a dataset named foo.nc:

         #include <netcdf.h>
            ...
         int ncid, status, latid;
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);/* open for writing */
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_redef(ncid);                    /* enter define mode */
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_def_dim(ncid, "lat", 18L, &latid);
         if (status != NC_NOERR) {
            handle_error(status);
            status = nc_abort(ncid);                 /* define failed, abort */
            if (status != NC_NOERR) handle_error(status);
         }

Next: nc_set_default_format, Previous: nc_abort, Up: Datasets

### 2.18 Set Fill Mode for Writes: nc_set_fill

This function is intended for advanced usage, to optimize writes under some circumstances described below. The function nc_set_fill sets the fill mode for a netCDF dataset open for writing and returns the current fill mode in a return parameter. The fill mode can be specified as either NC_FILL or NC_NOFILL. The default behavior corresponding to NC_FILL is that data is pre-filled with fill values, that is fill values are written when you create non-record variables or when you write a value beyond data that has not yet been written. This makes it possible to detect attempts to read data before it was written. For more information on the use of fill values see Fill Values. For information about how to define your own fill values see Attribute Conventions.

The behavior corresponding to NC_NOFILL overrides the default behavior of prefilling data with fill values. This can be used to enhance performance, because it avoids the duplicate writes that occur when the netCDF library writes fill values that are later overwritten with data.

A value indicating which mode the netCDF dataset was already in is returned. You can use this value to temporarily change the fill mode of an open netCDF dataset and then restore it to the previous mode.

After you turn on NC_NOFILL mode for an open netCDF dataset, you must be certain to write valid data in all the positions that will later be read. Note that nofill mode is only a transient property of a netCDF dataset open for writing: if you close and reopen the dataset, it will revert to the default behavior. You can also revert to the default behavior by calling nc_set_fill again to explicitly set the fill mode to NC_FILL.

There are three situations where it is advantageous to set nofill mode:

1. Creating and initializing a netCDF dataset. In this case, you should set nofill mode before calling nc_enddef and then write completely all non-record variables and the initial records of all the record variables you want to initialize.
2. Extending an existing record-oriented netCDF dataset. Set nofill mode after opening the dataset for writing, then append the additional records to the dataset completely, leaving no intervening unwritten records.
3. Adding new variables that you are going to initialize to an existing netCDF dataset. Set nofill mode before calling nc_enddef then write all the new variables completely.

If the netCDF dataset has an unlimited dimension and the last record was written while in nofill mode, then the dataset may be shorter than if nofill mode was not set, but this will be completely transparent if you access the data only through the netCDF interfaces.

The use of this feature may not be available (or even needed) in future releases. Programmers are cautioned against heavy reliance upon this feature.

### Usage

         int nc_set_fill (int ncid, int fillmode, int *old_modep);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`fillmode`
  Desired fill mode for the dataset, either NC_NOFILL or NC_FILL.
`old_modep`
  Pointer to location for returned current fill mode of the dataset before this call, either NC_NOFILL or NC_FILL.

### Return Codes

`NC_NOERR`
  No error.
`NC_EBADID`
  The specified netCDF ID does not refer to an open netCDF dataset.
`NC_EPERM`
  The specified netCDF ID refers to a dataset open for read-only access.
`NC_EINVAL`
  The fill mode argument is neither NC_NOFILL nor NC_FILL.

### Example

Here is an example using nc_set_fill to set nofill mode for subsequent writes of a netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int ncid, status, old_fill_mode;
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);  /* open for writing */
         if (status != NC_NOERR) handle_error(status);

            ...           /* write data with default prefilling behavior */

         status = nc_set_fill(ncid, NC_NOFILL, &old_fill_mode); /* set nofill */
         if (status != NC_NOERR) handle_error(status);

            ...           /* write data with no prefilling */

Next: nc_set_chunk_cache, Previous: nc_set_fill, Up: Datasets

### 2.19 Set Default Creation Format: nc_set_default_format

This function is intended for advanced users.

Starting in version 3.6, netCDF introduced a new data format, the first change in the underlying binary data format since the netCDF interface was released. The new format, 64-bit offset format, was introduced to greatly relax the limitations on creating very large files.

Users are warned that creating files in the 64-bit offset format makes them unreadable by the netCDF library prior to version 3.6.0. For reasons of compatibility, users should continue to create files in netCDF classic format.

Users who do want to use 64-bit offset format files can create them directory from nc_create, using the proper cmode flag. (see nc_create).

The function nc_set_default_format allows the user to change the format of the netCDF file to be created by future calls to nc_create (or nc__create) without changing the cmode flag.

This allows the user to convert a program to use 64-bit offset formation without changing all calls the nc_create. See Large File Support.

Once the default format is set, all future created files will be in the desired format.

Two constants are provided in the netcdf.h file to be used with this function, NC_FORMAT_64BIT and NC_FORMAT_CLASSIC.

If a non-NULL pointer is provided, it is assumed to point to an int, where the existing default format will be written.

Using nc_create with a cmode including NC_64BIT_OFFSET overrides the default format, and creates a 64-bit offset file.

### Usage

         int nc_set_default_format(int format, int *old_formatp);

`format`
  Valid formats include NC_FORMAT_CLASSIC (the default), NC_FORMAT_64BIT, and, if –enable-netcdf-4 was used during configure, NC_FORMAT_NETCDF4 and NC_FORMAT_NETCDF4_CLASSIC
`old_formatp`
  Either NULL (in which case it will be ignored), or a pointer to an int where the existing default format (i.e. before being changed to the new format) will be written. This allows you to get the existing default format while setting a new default format.

### Return Codes

`NC_NOERR`
  No error.
`NC_EINVAL`
  Invalid format. Valid formats include NC_FORMAT_CLASSIC, NC_FORMAT_64BIT, and, if –enable-netcdf-4 was used during configure, NC_FORMAT_NETCDF4 and NC_FORMAT_NETCDF4_CLASSIC. Trying to set the default format to something else will result in an invalid argument error.

### Example

Here is an example using nc_set_default_format to create the same file in four formats with the same nc_create call (from libsrc4/tst_utf8.c):

         #include <netcdf.h>
            ...
               int ncid, varid, dimids[NDIMS];
               int f;

               for (f = NC_FORMAT_CLASSIC; f < NC_FORMAT_NETCDF4_CLASSIC; f++)
               {
                  if (nc_set_default_format(f, NULL)) ERR;
                  if (nc_create(FILE_NAME, NC_CLOBBER, &ncid)) ERR;
            ...

Next: nc_get_chunk_cache, Previous: nc_set_default_format, Up: Datasets

### 2.20 Set HDF5 Chunk Cache for Future File Opens/Creates: nc_set_chunk_cache

This function changes the default chunk cache settings in the HDF5 library for all variables in the file. The settings apply for subsequent file opens/creates. This function does not change the chunk cache settings of already open files.

For more information, see the documentation for the H5Pset_cache() function in the HDF5 library at the HDF5 website: http://hdfgroup.org/HDF5/.

### Usage

         int nc_set_chunk_cache(size_t size, size_t nelems, float preemption);

`size`
  The total size of the raw data chunk cache, in bytes. This should be big enough to hold multiple chunks of data.
`nelems`
  The number of chunk slots in the raw data chunk cache hash table. This should be a prime number larger than the number of chunks that will be in the cache.
`preemption`
  The preemtion value must be between 0 and 1 inclusive and indicates how much chunks that have been fully read are favored for preemption. A value of zero means fully read chunks are treated no differently than other chunks (the preemption is strictly LRU) while a value of one means fully read chunks are always preempted before other chunks.

### Return Codes

`NC_NOERR`
  No error.
`NC_EINVAL`
  Preemption must be between zero and one (inclusive).

### Example

This example is from libsrc4/tst_files.c:

         #include <netcdf.h>
            ...
         #define NEW_CACHE_SIZE 32000000
         #define NEW_CACHE_NELEMS 2000
         #define NEW_CACHE_PREEMPTION .75

            /* Change chunk cache. */
            if (nc_set_chunk_cache(NEW_CACHE_SIZE, NEW_CACHE_NELEMS,
         			  NEW_CACHE_PREEMPTION)) ERR;

            /* Create a file with two dims, two vars, and two atts. */
            if (nc_create(FILE_NAME, cflags|NC_CLOBBER, &ncid)) ERR;

            ...

Previous: nc_set_chunk_cache, Up: Datasets

### 2.21 Get the HDF5 Chunk Cache Settings for Future File Opens/Creates: nc_get_chunk_cache

This function gets the chunk cache settings for the HDF5 library. The settings apply for subsequent file opens/creates.

This affects the per-file chunk cache which the HDF5 layer maintains. The chunk cache size can be tuned for better performance.

For more information, see the documentation for the H5Pget_cache() function in the HDF5 library at the HDF5 website: http://hdfgroup.org/HDF5/.

### Usage

         int nc_get_chunk_cache(size_t *sizep, size_t *nelemsp, float *preemptionp);

`sizep`
  The total size of the raw data chunk cache will be put here. If NULL, will be ignored.
`nelemsp`
  The number of chunk slots in the raw data chunk cache hash table will be put here. If NULL, will be ignored.
`preemptionp`
  The preemption will be put here. The preemtion value is between 0 and 1 inclusive and indicates how much chunks that have been fully read are favored for preemption. A value of zero means fully read chunks are treated no differently than other chunks (the preemption is strictly LRU) while a value of one means fully read chunks are always preempted before other chunks. If NULL, will be ignored.

### Return Codes

`NC_NOERR`
  No error.

### Example

This example is from libsrc4/tst_files.c:

         #include <netcdf.h>
            ...
            /* Retrieve the chunk cache settings, just for fun. */
            if (nc_get_chunk_cache(&cache_size_in, &cache_nelems_in,
         			  &cache_preemption_in)) ERR;
            if (cache_size_in != NEW_CACHE_SIZE || cache_nelems_in != NEW_CACHE_NELEMS ||
                cache_preemption_in != NEW_CACHE_PREEMPTION) ERR;

            ...

Next: Dimensions, Previous: Datasets, Up: Top

## 3 Groups

NetCDF-4 added support for hierarchical groups within netCDF datasets.

Groups are identified with a ncid, which identifies both the open file, and the group within that file. When a file is opened with nc_open or nc_create, the ncid for the root group of that file is provided. Using that as a starting point, users can add new groups, or list and navigate existing groups.

All netCDF calls take a ncid which determines where the call will take its action. For example, the nc_def_var function takes a ncid as its first parameter. It will create a variable in whichever group its ncid refers to. Use the root ncid provided by nc_create or nc_open to create a variable in the root group. Or use nc_def_grp to create a group and use its ncid to define a variable in the new group.

Variable are only visible in the group in which they are defined. The same applies to attributes. “Global” attributes are associated with the group whose ncid is used.

Dimensions are visible in their groups, and all child groups.

Group operations are only permitted on netCDF-4 files - that is, files created with the HDF5 flag in nc_create. (see nc_create). Groups are not compatible with the netCDF classic data model, so files created with the NC_CLASSIC_MODEL file cannot contain groups (except the root group).

Next: nc_inq_grps, Previous: Groups, Up: Groups

### 3.1 Find a Group ID: nc_inq_ncid

Given an ncid and group name (NULL or "" gets root group), return ncid of the named group.

### Usage

         int nc_inq_ncid(int ncid, const char *name, int *grp_ncid);

`ncid`
  The group id for this operation.
`name`
  A char array that holds the name of the desired group.
`grp_ncid`
  An int pointer that will receive the group id, if the group is found.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

            int root_ncid, child_ncid;
            char file[] = "nc4_test.nc";

            /* Open the file. */
            if ((res = nc_open(file, NC_NOWRITE, &root_ncid)))
               return res;

            /* Get the ncid of an existing group. */
            if ((res = nc_inq_ncid(root_ncid, "group1", &child_ncid)))
               return res;

Next: nc_inq_varids, Previous: nc_inq_ncid, Up: Groups

### 3.2 Get a List of Groups in a Group: nc_inq_grps

Given a location id, return the number of groups it contains, and an array of their ncids.

### Usage

         int nc_inq_grps(int ncid, int *numgrps, int *ncids);

`ncid`
  The group id for this operation.
`numgrps`
  Pointer to an int which will get number of groups in this group. If NULL, it's ignored.
`ncids`
  Pointer to a already allocated array of ints which will receive the ids of all the groups in this group. If NULL, it's ignored. Call this function with NULL for ncids parameter to find out how many groups there are.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

            int root_ncid, numgrps;
            int *ncids;
            char file[] = "nc4_test.nc";

            /* Open the file. */
            if ((res = nc_open(file, NC_NOWRITE, &root_ncid)))
               return res;

            /* Get a list of ncids for the root group. (That is, find out of
               there are any groups already defined. */
            if ((res = nc_inq_grps(root_ncid, &numgrps, NULL)))
               return res;
            ncids = malloc(sizeof(int) * numgrps);
            if ((res = nc_inq_grps(root_ncid, NULL, ncids)))
               return res;

Next: nc_inq_dimids, Previous: nc_inq_grps, Up: Groups

### 3.3 Find all the Variables in a Group: nc_inq_varids

Find all varids for a location.

### Usage

         nc_inq_varids(int ncid, int *nvars, int *varids);

`ncid`
  The group id for this operation.
`nvars`
  The integer pointed to by this parameter will get the number of variable IDs found.
`varids`
  An already allocated array to store the list of varids. Ignored if NULL.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from libsrc4/tst_vars.c.

               int nvars_in, varids_in[2];

               ...

               /* Open the file and make sure nc_inq_varids yeilds correct
                * result. */
               if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;
               if (nc_inq_varids(ncid, &nvars_in, varids_in)) ERR;

Next: nc_inq_grpname, Previous: nc_inq_varids, Up: Groups

### 3.4 Find all Dimensions Visible in a Group: nc_inq_dimids

Find all dimids for a location. This finds all dimensions in a group, or any of its parents.

### Usage

         int nc_inq_dimids(int ncid, int *ndims, int *dimids, int include_parents);

`ncid`
  The group id for this operation.
`dimids`
  An already allocated array of ints when the dimids of the visible dimensions will be stashed. Use nc_inq_ndims to find out how many dims are visible from this group. (see nc_inq Family).
`include_parents`
  If non-zero then all the dimensions in all parent groups will also be retrieved.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from libsrc4/tst_dims.c.

               int ncid, dimid;
               int ndims_in, dimids_in[MAX_DIMS];

               ...

               /* Open the file and make sure nc_inq_dimids yeilds correct
                * result. */
               if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;
               if (nc_inq_dimids(ncid, &ndims_in, dimids_in, 0)) ERR;
               if (ndims_in != 1 || dimids_in[0] != 0) ERR;

Next: nc_inq_grpname_full, Previous: nc_inq_dimids, Up: Groups

### 3.5 Find a Group's Name: nc_inq_grpname

Given a group ID find its name. (Root group is named "/"). See nc_inq_grpname_full.

### Usage

         int nc_inq_grpname(int ncid, char *name);

`ncid`
  The group id for this operation.
`name`
  Pointer to allocated space of correct length. The name of the group will be copied there. The name will be less than NC_MAX_NAME, not including a terminating NULL byte.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from libsrc4/tst_grps.c.

               int grpid_in[MAX_SIBLING_GROUPS];
               char name_in[NC_MAX_NAME + 1];

               ...

               if (nc_inq_grpname(grpid_in[0], name_in)) ERR;

Next: nc_inq_grpname_len, Previous: nc_inq_grpname, Up: Groups

### 3.6 Find a Group's Full Name: nc_inq_grpname_full

Given ncid, find complete name of group. (Root group is named "/", a full "path" for each group is provided in the name, with groups separated with a forward slash / as in Unix directory names. For example "/group1/subgrp1/subsubgrp1")

### Usage

         int nc_inq_grpname_full(int ncid, size_t *lenp, char *full_name);

`ncid`
  The group id for this operation.
`lenp`
  Pointer to a size_t which will get the length. (Note that this does not include the NULL terminator byte.)
`full_name`
  Pointer to allocated space of correct length. The name of the group will be copied there. To find the required length, call nc_inq_grpname_len call this function with NULL for the full_name parameter, or call (see nc_inq_grpname_len).

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from the test program libsrc4/tst_grps.c.

               int grpid_in[MAX_SIBLING_GROUPS];
               char full_name_in[NC_MAX_NAME * 10];
               size_t len;

               ...

               if (nc_inq_grpname_full(grpid_in[0], &len, full_name_in)) ERR;

Next: nc_inq_grp_parent, Previous: nc_inq_grpname_full, Up: Groups

### 3.7 Find the Length of a Group's Full Name: nc_inq_grpname_len

Given ncid, find len of the full name, as returned by nc_inq_grpname_full See nc_inq_grpname_full. (Root group is named "/", with length 1.)

### Usage

         int nc_inq_grpname_len(int ncid, size_t *lenp);

`ncid`
  The group id for this operation.
`lenp`
  Pointer to an int where the length will be placed. Length does not include NULL terminator.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from libsrc4/tst_grps.c.

               int ncid;
               size_t len;

               ...

               if (nc_inq_grpname_len(ncid, &len)) ERR;

Next: nc_inq_grp_ncid, Previous: nc_inq_grpname_len, Up: Groups

### 3.8 Find a Group's Parent: nc_inq_grp_parent

Given ncid, find the ncid of the parent group.

When used with the root group, this function returns the NC_ENOGRP error (since the root group has no parent.)

### Usage

         int nc_inq_grp_parent(int ncid, int *parent_ncid);

`ncid`
  The group id.
`parent_ncid`
  Pointer to an int. The ncid of the group will be copied there.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENOGRP`
  No parent group found (i.e. this is the root group).
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

            if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
            if (nc_def_grp(ncid, HENRY_VII, &henry_vii_id)) ERR;

            if (nc_inq_grp_parent(henry_vii_id, &parent_ncid)) ERR;
            if (parent_ncid != ncid) ERR;
            if (nc_close(ncid)) ERR;

Next: nc_inq_grp_full_ncid, Previous: nc_inq_grp_parent, Up: Groups

### 3.9 Find a Group by Name: nc_inq_grp_ncid

Given a group name an an ncid, find the ncid of the group id.

### Usage

         int nc_inq_grp_ncid(int ncid, const char *grp_name, int *grp_ncid);

`ncid`
  The group id to look in.
`grp_name`
  The name of the group that should be found.
`grp_ncid`
  A pointer to int which will get the group id, if it is found.

### Return Codes

The following return codes may be returned by this function.

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_EINVAL`
  No name provided or name longer than NC_MAX_NAME.
`NC_ENOGRP`
  Named group not found.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from test program libsrc4/tst_grps.c.

               /* Reopen and recheck. */
               if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;
               if (nc_inq_grp_ncid(ncid, SCI_FI, &g1id)) ERR;

Next: nc_def_grp, Previous: nc_inq_grp_ncid, Up: Groups

### 3.10 Find a Group by its Fully-qualified Name: nc_inq_grp_full_ncid

Given a fully qualified group name an an ncid, find the ncid of the group id.

### Usage

         int nc_inq_grp_full_ncid(int ncid, char *full_name, int *grp_ncid);

`ncid`
  The group id to look in.
`full_name`
  The fully-qualified group name.
`grp_ncid`
  A pointer to int which will get the group id, if it is found.

### Return Codes

The following return codes may be returned by this function.

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_EINVAL`
  No name provided or name longer than NC_MAX_NAME.
`NC_ENOGRP`
  Named group not found.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from test program libsrc4/tst_grps.c.

               /* Reopen and recheck. */
               if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;
               if (nc_inq_grp_ncid(ncid, SCI_FI, &g1id)) ERR;

Previous: nc_inq_grp_full_ncid, Up: Groups

### 3.11 Create a New Group: nc_def_grp

Create a group. Its location id is returned in the new_ncid pointer.

### Usage

         int nc_def_grp(int parent_ncid, const char *name, int *new_ncid);

`parent_ncid`
  The group id of the parent group.
`name`
  The name of the new group.
`new_ncid`
  A pointer to an int. The ncid of the new group will be placed there.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENAMEINUSE`
  That name is in use. Group names must be unique within a group, and must not be the same as any variable or type in the group.
`NC_EMAXNAME`
  Name exceed max length NC_MAX_NAME.
`NC_EBADNAME`
  Name contains illegal characters.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.
`NC_EPERM`
  Attempt to write to a read-only file.
`NC_ENOTINDEFINE`
  Not in define mode.

### Example

               int root_ncid, a1_ncid;
               char grpname[] = "assimilation1";

               /* Get the ncid of the root group. */
               if ((res = nc_inq_ncid(root_ncid, NULL, &root_ncid)))
                  return res;

               /* Create a group. */
               if ((res = nc_def_grp(root_ncid, grpname, &a1_ncid)))
                  return res;

Next: User Defined Data Types, Previous: Groups, Up: Top

## 4 Dimensions

Next: nc_def_dim, Previous: Dimensions, Up: Dimensions

### 4.1 Dimensions Introduction

Dimensions for a netCDF dataset are defined when it is created, while the netCDF dataset is in define mode. Additional dimensions may be added later by reentering define mode. A netCDF dimension has a name and a length. In a netCDF classic or 64-bit offset file, at most one dimension can have the unlimited length, which means variables using this dimension can grow along this dimension. In a netCDF-4 file multiple unlimited dimensions are supported.

There is a suggested limit (100) to the number of dimensions that can be defined in a single netCDF dataset. The limit is the value of the predefined macro NC_MAX_DIMS. The purpose of the limit is to make writing generic applications simpler. They need only provide an array of NC_MAX_DIMS dimensions to handle any netCDF dataset. The implementation of the netCDF library does not enforce this advisory maximum, so it is possible to use more dimensions, if necessary, but netCDF utilities that assume the advisory maximums may not be able to handle the resulting netCDF datasets.

Ordinarily, the name and length of a dimension are fixed when the dimension is first defined. The name may be changed later, but the length of a dimension (other than the unlimited dimension) cannot be changed without copying all the data to a new netCDF dataset with a redefined dimension length.

Dimension lengths in the C interface are type size_t rather than type int to make it possible to access all the data in a netCDF dataset on a platform that only supports a 16-bit int data type, for example MSDOS. If dimension lengths were type int instead, it would not be possible to access data from variables with a dimension length greater than a 16-bit int can accommodate.

A netCDF dimension in an open netCDF dataset is referred to by a small integer called a dimension ID. In the C interface, dimension IDs are 0, 1, 2, ..., in the order in which the dimensions were defined.

Operations supported on dimensions are:

- Create a dimension, given its name and length.
- Get a dimension ID from its name.
- Get a dimension's name and length from its ID.
- Rename a dimension.

Next: nc_inq_dimid, Previous: Dimensions Introduction, Up: Dimensions

### 4.2 Create a Dimension: nc_def_dim

The function nc_def_dim adds a new dimension to an open netCDF dataset in define mode. It returns (as an argument) a dimension ID, given the netCDF ID, the dimension name, and the dimension length. At most one unlimited length dimension, called the record dimension, may be defined for each classic or 64-bit offset netCDF dataset. NetCDF-4 datasets may have multiple unlimited dimensions.

### Usage

         int nc_def_dim (int ncid, const char *name, size_t len, int *dimidp);

`ncid`
  NetCDF group ID, from a previous call to nc_open, nc_create, nc_def_grp, etc.
`name`
  Dimension name.
`len`
  Length of dimension; that is, number of values for this dimension as an index to variables that use it. This should be either a positive integer (of type size_t) or the predefined constant NC_UNLIMITED.
`dimidp`
  Pointer to location for returned dimension ID.

### Errors

nc_def_dim returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The netCDF dataset is not in definition mode.
- The specified dimension name is the name of another existing dimension.
- The specified length is not greater than zero.
- The specified length is unlimited, but there is already an unlimited length dimension defined for this netCDF dataset.
- The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_def_dim to create a dimension named lat of length 18 and a unlimited dimension named rec in a new netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int status, ncid, latid, recid;
            ...
         status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_def_dim(ncid, "lat", 18L, &latid);
         if (status != NC_NOERR) handle_error(status);
         status = nc_def_dim(ncid, "rec", NC_UNLIMITED, &recid);
         if (status != NC_NOERR) handle_error(status);

Next: nc_inq_dim Family, Previous: nc_def_dim, Up: Dimensions

### 4.3 Get a Dimension ID from Its Name: nc_inq_dimid

The function nc_inq_dimid returns (as an argument) the ID of a netCDF dimension, given the name of the dimension. If ndims is the number of dimensions defined for a netCDF dataset, each dimension has an ID between 0 and ndims-1.

### Usage

When searching for a dimension, the specified group is searched, and then its parent group, and then its grandparent group, etc., up to the root group.

         int nc_inq_dimid (int ncid, const char *name, int *dimidp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`name`
  Dimension name.
`dimidp`
  Pointer to location for the returned dimension ID.

### Errors

nc_inq_dimid returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

The name that was specified is not the name of a dimension in the netCDF dataset. The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_inq_dimid to determine the dimension ID of a dimension named lat, assumed to have been defined previously in an existing netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int status, ncid, latid;
            ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);  /* open for reading */
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_dimid(ncid, "lat", &latid);
         if (status != NC_NOERR) handle_error(status);

Next: nc_rename_dim, Previous: nc_inq_dimid, Up: Dimensions

### 4.4 Inquire about a Dimension: nc_inq_dim Family

This family of functions returns information about a netCDF dimension. Information about a dimension includes its name and its length. The length for the unlimited dimension, if any, is the number of records written so far.

The functions in this family include nc_inq_dim, nc_inq_dimname, and nc_inq_dimlen. The function nc_inq_dim returns all the information about a dimension; the other functions each return just one item of information.

### Usage

         int nc_inq_dim     (int ncid, int dimid, char* name, size_t* lengthp);
         int nc_inq_dimname (int ncid, int dimid, char *name);
         int nc_inq_dimlen  (int ncid, int dimid, size_t *lengthp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`dimid`
  Dimension ID, from a previous call to nc_inq_dimid or nc_def_dim.
`name`
  Returned dimension name. The caller must allocate space for the returned name. The maximum possible length, in characters, of a dimension name is given by the predefined constant NC_MAX_NAME. (This doesn't include the null terminator, so declare your array to be size NC_MAX_NAME+1). The returned character array will be null-terminated.
`lengthp`
  Pointer to location for returned length of dimension. For the unlimited dimension, this is the number of records written so far.

### Errors

These functions return the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The dimension ID is invalid for the specified netCDF dataset.
- The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_inq_dim to determine the length of a dimension named lat, and the name and current maximum length of the unlimited dimension for an existing netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int status, ncid, latid, recid;
         size_t latlength, recs;
         char recname[NC_MAX_NAME+1];
            ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);  /* open for reading */
         if (status != NC_NOERR) handle_error(status);
         status = nc_inq_unlimdim(ncid, &recid); /* get ID of unlimited dimension */
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_dimid(ncid, "lat", &latid);  /* get ID for lat dimension */
         if (status != NC_NOERR) handle_error(status);
         status = nc_inq_dimlen(ncid, latid, &latlength); /* get lat length */
         if (status != NC_NOERR) handle_error(status);
         /* get unlimited dimension name and current length */
         status = nc_inq_dim(ncid, recid, recname, &recs);
         if (status != NC_NOERR) handle_error(status);

Next: nc_inq_unlimdims, Previous: nc_inq_dim Family, Up: Dimensions

### 4.5 Rename a Dimension: nc_rename_dim

The function nc_rename_dim renames an existing dimension in a netCDF dataset open for writing. You cannot rename a dimension to have the same name as another dimension.

For netCDF classic and 64-bit offset files, if the new name is longer than the old name, the netCDF dataset must be in define mode.

For netCDF-4 files the dataset is switched to define more for the rename, regardless of the name length.

### Usage

int nc_rename_dim(int ncid, int dimid, const char* name);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`dimid`
  Dimension ID, from a previous call to nc_inq_dimid or nc_def_dim.
`name`
  New dimension name.

### Errors

nc_rename_dim returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The new name is the name of another dimension.
- The dimension ID is invalid for the specified netCDF dataset.
- The specified netCDF ID does not refer to an open netCDF dataset.
- The new name is longer than the old name and the netCDF dataset is not in define mode.

### Example

Here is an example using nc_rename_dim to rename the dimension lat to latitude in an existing netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int status, ncid, latid;
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);  /* open for writing */
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_redef(ncid);  /* put in define mode to rename dimension */
         if (status != NC_NOERR) handle_error(status);
         status = nc_inq_dimid(ncid, "lat", &latid);
         if (status != NC_NOERR) handle_error(status);
         status = nc_rename_dim(ncid, latid, "latitude");
         if (status != NC_NOERR) handle_error(status);
         status = nc_enddef(ncid); /* leave define mode */
         if (status != NC_NOERR) handle_error(status);

Previous: nc_rename_dim, Up: Dimensions

### 4.6 Find All Unlimited Dimension IDs: nc_inq_unlimdims

In netCDF-4 files, it's possible to have multiple unlimited dimensions. This function returns a list of the unlimited dimension ids visible in a group.

Dimensions are visible in a group if they have been defined in that group, or any ancestor group.

### Usage

         int nc_inq_unlimdims(int ncid, int *nunlimdimsp, int *unlimdimidsp);

`ncid`
  NetCDF group ID, from a previous call to nc_open, nc_create, nc_def_grp, etc.
`nunlimdimsp`
  A pointer to an int which will get the number of visible unlimited dimensions. Ignored if NULL.
`unlimdimidsp`
  A pointer to an already allocated array of int which will get the ids of all visible unlimited dimensions. Ignored if NULL. To allocate the correct length for this array, call nc_inq_unlimdims with a NULL for this parameter and use the nunlimdimsp parameter to get the number of visible unlimited dimensions.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

            int root_ncid, num_unlimdims, unlimdims[NC_MAX_DIMS];
            char file[] = "nc4_test.nc";
            int res;

            /* Open the file. */
            if ((res = nc_open(file, NC_NOWRITE, &root_ncid)))
               return res;

            /* Find out if there are any unlimited dimensions in the root
               group. */
            if ((res = nc_inq_unlimdims(root_ncid, &num_unlimdims, unlimdims)))
               return res;

            printf("nc_inq_unlimdims reports %d unlimited dimensions\n", num_unlimdims);

Next: Variables, Previous: Dimensions, Up: Top

## 5 User Defined Data Types

Next: nc_inq_typeids, Previous: User Defined Data Types, Up: User Defined Data Types

### 5.1 User Defined Types Introduction

NetCDF-4 has added support for four different user defined data types. User defined type may only be used in files created with the NC_NETCDF4 and without NC_CLASSIC_MODEL.

`compound type`
  Like a C struct, a compound type is a collection of types, including other user defined types, in one package.
`variable length array type`
  The variable length array may be used to store ragged arrays.
`opaque type`
  This type has only a size per element, and no other type information.
`enum type`
  Like an enumeration in C, this type lets you assign text values to integer values, and store the integer values.

Users may construct user defined type with the various nc_def_* functions described in this section. They may learn about user defined types by using the nc_inq_ functions defined in this section.

Once types are constructed, define variables of the new type with nc_def_var (see nc_def_var). Write to them with nc_put_var1, nc_put_var, nc_put_vara, or nc_put_vars (see Variables). Read data of user-defined type with nc_get_var1, nc_get_var, nc_get_vara, or nc_get_vars (see Variables).

Create attributes of the new type with nc_put_att (see nc_put_att_ type). Read attributes of the new type with nc_get_att (see nc_get_att_ type).

Next: nc_inq_typeid, Previous: User Defined Types, Up: User Defined Data Types

### 5.2 Learn the IDs of All Types in Group: nc_inq_typeids

Learn the number of types defined in a group, and their IDs.

### Usage

         int nc_inq_typeids(int ncid, int *ntypes, int *typeids);

`ncid`
  The group id.
`ntypes`
  A pointer to int which will get the number of types defined in the group. If NULL, ignored.
`typeids`
  A pointer to an int array which will get the typeids. If NULL, ignored.

### Errors

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.

### Example

The following example is from the test program libsrc4/tst_enums.c.

               if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;

               /* Get type info. */
               if (nc_inq_typeids(ncid, &ntypes, typeids)) ERR;
               if (ntypes != 1 || !typeids[0]) ERR;

Next: nc_inq_type, Previous: nc_inq_typeids, Up: User Defined Data Types

### 5.3 Find a Typeid from Group and Name: nc_inq_typeid

Given a group ID and a type name, find the ID of the type. If the type is not found in the group, then the parents are searched. If still not found, the entire file is searched.

### Usage

         int nc_inq_typeid(int ncid, const char *name, nc_type *typeidp);

`ncid`
  The group id.
`name`
  The name of a type.
`typeidp`
  A pointer to an int which will get the typeid.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad ncid.
`NC_EBADTYPE`
  Can't find type.

### Example

The following example is from the test program libsrc4/tst_vars.c. It tests that the correct names are given for atomic types.

         	 /* Check inquire of atomic types */
         	 if (nc_inq_type(ncid, NC_BYTE, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "byte") || size_in != sizeof(char)) ERR;
         	 if (nc_inq_type(ncid, NC_CHAR, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "char") || size_in != sizeof(char)) ERR;
         	 if (nc_inq_type(ncid, NC_SHORT, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "short") || size_in != sizeof(short)) ERR;
         	 if (nc_inq_type(ncid, NC_INT, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "int") || size_in != sizeof(int)) ERR;
         	 if (nc_inq_type(ncid, NC_FLOAT, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "float") || size_in != sizeof(float)) ERR;
         	 if (nc_inq_type(ncid, NC_DOUBLE, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "double") || size_in != sizeof(double)) ERR;
         	 if (nc_inq_type(ncid, NC_UBYTE, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "ubyte") || size_in != sizeof(unsigned char)) ERR;
         	 if (nc_inq_type(ncid, NC_USHORT, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "ushort") || size_in != sizeof(unsigned short)) ERR;
         	 if (nc_inq_type(ncid, NC_UINT, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "uint") || size_in != sizeof(unsigned int)) ERR;
         	 if (nc_inq_type(ncid, NC_INT64, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "int64") || size_in != sizeof(long long)) ERR;
         	 if (nc_inq_type(ncid, NC_UINT64, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "uint64") || size_in != sizeof(unsigned long long)) ERR;
         	 if (nc_inq_type(ncid, NC_STRING, name_in, &size_in)) ERR;
         	 if (strcmp(name_in, "string") || size_in != 0) ERR;
         	 if (xtype_in != NC_SHORT) ERR;

Next: nc_inq_user_type, Previous: nc_inq_typeid, Up: User Defined Data Types

### 5.4 Learn About a User Defined Type: nc_inq_type

Given an ncid and a typeid, get the information about a type. This function will work on any type, including atomic and any user defined type, whether compound, opaque, enumeration, or variable length array.

For even more information about a user defined type nc_inq_user_type.

### Usage

         nc_inq_type(int ncid, nc_type xtype, char *name, size_t *sizep);

`ncid`
  The ncid for the group containing the type (ignored for atomic types).
`xtype`
  The typeid for this type, as returned by nc_def_compound, nc_def_opaque, nc_def_enum, nc_def_vlen, or nc_inq_var, or as found in netcdf.h in the list of atomic types (NC_CHAR, NC_INT, etc.).
`name`
  If non-NULL, the name of the user defined type will be copied here. It will be NC_MAX_NAME bytes or less. For atomic types, the type name from CDL will be given.
`sizep`
  If non-NULL, the (in-memory) size of the type in bytes will be copied here. VLEN type size is the size of nc_vlen_t. String size is returned as the size of a character pointer. The size may be used to malloc space for the data, no matter what the type.

### Return Codes

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad typeid.
`NC_ENOTNC4`
  Seeking a user-defined type in a netCDF-3 file.
`NC_ESTRICTNC3`
  Seeking a user-defined type in a netCDF-4 file for which classic model has been turned on.
`NC_EBADGRPID`
  Bad group ID in ncid.
`NC_EBADID`
  Type ID not found.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from the test program tst_enums.c, and it uses all the possible inquiry functions on an enum type.

               /* Check it out. */
               if (nc_inq_user_type(ncid, typeids[0], name_in, &base_size_in, &base_nc_type_in,
                                    &nfields_in, &class_in)) ERR;
               if (strcmp(name_in, TYPE_NAME) || base_size_in != sizeof(int) ||
                   base_nc_type_in != NC_INT || nfields_in != NUM_MEMBERS || class_in != NC_ENUM) ERR;
               if (nc_inq_type(ncid, typeids[0], name_in, &base_size_in)) ERR;
               if (strcmp(name_in, TYPE_NAME) || base_size_in != sizeof(int)) ERR;
               if (nc_inq_enum(ncid, typeids[0], name_in, &base_nc_type, &base_size_in, &num_members)) ERR;
               if (strcmp(name_in, TYPE_NAME) || base_nc_type != NC_INT || num_members != NUM_MEMBERS) ERR;
               for (i = 0; i < NUM_MEMBERS; i++)
               {
                  if (nc_inq_enum_member(ncid, typeid, i, name_in, &value_in)) ERR;
                  if (strcmp(name_in, member_name[i]) || value_in != member_value[i]) ERR;
                  if (nc_inq_enum_ident(ncid, typeid, member_value[i], name_in)) ERR;
                  if (strcmp(name_in, member_name[i])) ERR;
               }

               if (nc_close(ncid)) ERR;

Next: Compound Types, Previous: nc_inq_type, Up: User Defined Data Types

### 5.5 Learn About a User Defined Type: nc_inq_user_type

Given an ncid and a typeid, get the information about a user defined type. This function will work on any user defined type, whether compound, opaque, enumeration, or variable length array.

### Usage

         nc_inq_user_type(int ncid, nc_type xtype, char *name, size_t *sizep,
                          nc_type *base_nc_typep, size_t *nfieldsp, int *classp);

`ncid`
  The ncid for the group containing the user defined type.
`xtype`
  The typeid for this type, as returned by nc_def_compound, nc_def_opaque, nc_def_enum, nc_def_vlen, or nc_inq_var.
`name`
  If non-NULL, the name of the user defined type will be copied here. It will be NC_MAX_NAME bytes or less.
`sizep`
  If non-NULL, the (in-memory) size of the type in bytes will be copied here. VLEN type size is the size of nc_vlen_t. String size is returned as the size of a character pointer. The size may be used to malloc space for the data, no matter what the type.
`nfieldsp`
  If non-NULL, the number of fields will be copied here for enum and compound types.
`classp`
  Return the class of the user defined type, NC_VLEN, NC_OPAQUE, NC_ENUM, or NC_COMPOUND.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad typeid.
`NC_EBADFIELDID`
  Bad fieldid.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

               /* Create a file. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;

               /* Create an enum type. */
               if (nc_def_enum(ncid, NC_INT, TYPE_NAME, &typeid)) ERR;
               for (i = 0; i < NUM_MEMBERS; i++)
                  if (nc_insert_enum(ncid, typeid, member_name[i],
                                     &member_value[i])) ERR;

               /* Check it out. */
               if (nc_inq_user_type(ncid, typeid, name_in, &base_size_in, &base_nc_type_in,
                                    &nfields_in, &class_in)) ERR;
               if (strcmp(name_in, TYPE_NAME) || base_size_in != sizeof(int) ||
                   base_nc_type_in != NC_INT || nfields_in != NUM_MEMBERS || class_in != NC_ENUM) ERR;

Next: nc_def_compound, Previous: nc_inq_user_type, Up: User Defined Data Types

### 5.6 Compound Types Introduction

Compound data types can be defined for netCDF-4/HDF5 format files. A compound datatype is similar to a struct in C and contains a collection of one or more atomic or user-defined types. The netCDF-4 compound data must comply with the properties and constraints of the HDF5 compound data type in terms of which it is implemented.

In summary these are:

- It has a fixed total size.
- It consists of zero or more named members that do not overlap with other members.
- Each member has a name distinct from other members.
- Each member has its own datatype.
- Each member is referenced by an index number between zero and N-1, where N is the number of members in the compound datatype.
- Each member has a fixed byte offset, which is the first byte (smallest byte address) of that member in the compound datatype.
- In addition to other other user-defined data types or atomic datatypes, a member can be a small fixed-size array of any type with up to four fixed-size “dimensions” (not associated with named netCDF dimensions).

Currently there is an HDF5 restriction on total size of a compound type to not larger than 2^16 = 65536 bytes. Attempts to exceed this limit result in an NC_EHDFERR error.

Compound types are not supported in classic or 64-bit offset format files.

To write data in a compound type, first use nc_def_compound to create the type, multiple calls to nc_insert_compound to add to the compound type, and then write data with the appropriate nc_put_var1, nc_put_vara, nc_put_vars, or nc_put_varm call.

To read data written in a compound type, you must know its structure. Use the nc_inq_compound functions to learn about the compound type.

Next: nc_insert_compound, Previous: Compound Types, Up: User Defined Data Types

### 5.7 Creating a Compound Type: nc_def_compound

Create a compound type. Provide an ncid, a name, and a total size (in bytes) of one element of the completed compound type.

After calling this function, fill out the type with repeated calls to nc_insert_compound (see nc_insert_compound). Call nc_insert_compound once for each field you wish to insert into the compound type.

Note that there does not seem to be a way to read such types into structures in Fortran 90 (and there are no structures in Fortran 77).

### Usage

         int nc_def_compound(int ncid, size_t size, const char *name, nc_type *typeidp);

`ncid`
  The groupid where this compound type will be created.
`size`
  The size, in bytes, of the compound type.
`name`
  The name of the new compound type.
`typeidp`
  A pointer to an nc_type. The typeid of the new type will be placed there.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENAMEINUSE`
  That name is in use.
`NC_EMAXNAME`
  Name exceeds max length NC_MAX_NAME.
`NC_EBADNAME`
  Name contains illegal characters.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag NC_NETCDF4. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.
`NC_EPERM`
  Attempt to write to a read-only file.
`NC_ENOTINDEFINE`
  Not in define mode.

### Example

               struct s1
               {
                     int i1;
                     int i2;
               };
               struct s1 data[DIM_LEN], data_in[DIM_LEN];

               /* Create a file with a compound type. Write a little data. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_def_compound(ncid, sizeof(struct s1), SVC_REC, &typeid)) ERR;
               if (nc_insert_compound(ncid, typeid, BATTLES_WITH_KLINGONS,
                                      HOFFSET(struct s1, i1), NC_INT)) ERR;
               if (nc_insert_compound(ncid, typeid, DATES_WITH_ALIENS,
                                      HOFFSET(struct s1, i2), NC_INT)) ERR;
               if (nc_def_dim(ncid, STARDATE, DIM_LEN, &dimid)) ERR;
               if (nc_def_var(ncid, SERVICE_RECORD, typeid, 1, dimids, &varid)) ERR;
               if (nc_put_var(ncid, varid, data)) ERR;
               if (nc_close(ncid)) ERR;

Next: nc_insert_array_compound, Previous: nc_def_compound, Up: User Defined Data Types

### 5.8 Inserting a Field into a Compound Type: nc_insert_compound

Insert a named field into a compound type.

### Usage

         int nc_insert_compound(int ncid, nc_type typeid, const char *name, size_t offset,
                                nc_type field_typeid);

`ncid`
  The groupid where a field for this compound type will be inserted.
`typeid`
  The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var.
`name`
  The name of the new field.
`offset`
  Offset in byte from the beginning of the compound type for this field.
`field_typeid`
  The type of the field to be inserted.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENAMEINUSE`
  That name is in use. Field names must be unique within a compound type.
`NC_EMAXNAME`
  Name exceed max length NC_MAX_NAME.
`NC_EBADNAME`
  Name contains illegal characters.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag NC_NETCDF4. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.
`NC_ENOTINDEFINE`
  Not in define mode.

### Example

Next: nc_inq_compound, Previous: nc_insert_compound, Up: User Defined Data Types

### 5.9 Inserting an Array Field into a Compound Type: nc_insert_array_compound

Insert a named field into a compound type.

### Usage

         int nc_insert_array_compound(int ncid, nc_type xtype, const char *name,
                                  size_t offset, nc_type field_typeid,
                                  int ndims, const int *dim_sizes);

`ncid`
  The ID of the file that contains the array type and the compound type.
`xtype`
  The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var.
`name`
  The name of the new field.
`offset`
  Offset in byte from the beginning of the compound type for this field.
`field_typeid`
  The base type of the array to be inserted.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENAMEINUSE`
  That name is in use. Field names must be unique within a compound type.
`NC_EMAXNAME`
  Name exceed max length NC_MAX_NAME.
`NC_EBADNAME`
  Name contains illegal characters.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag NC_NETCDF4. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.
`NC_ENOTINDEFINE`
  Not in define mode.
`NC_ETYPEDEFINED`
  Attempt to change type that has already been committed. The first time the file leaves define mode, all defined types are committed, and can't be changed. If you wish to add an array to a compound type, you must do so before the compound type is committed.

### Example

This example comes from the test file libsrc4/tst_compounds.c, which writes data about some Star Fleet officers who are known to use netCDF data.

            /* Since some aliens exists in different, or more than one,
             * dimensions, StarFleet keeps track of the dimensional abilities
             * of everyone on 7 dimensions. */
         #define NUM_DIMENSIONS 7
            struct dim_rec
            {
                  int starfleet_id;
                  int abilities[NUM_DIMENSIONS];
            };
            struct dim_rec dim_data_out[DIM_LEN], dim_data_in[DIM_LEN];

            /* Create some phoney data. */
            for (i=0; i<DIM_LEN; i++)
            {
               /* snip */
               /* Dimensional data. */
               dim_data_out[i].starfleet_id = i;
               for (j = 0; j < NUM_DIMENSIONS; j++)
                  dim_data_out[i].abilities[j] = j;
               /* snip */
            }

            printf("*** testing compound variable containing an array of ints...");
            {
               nc_type field_typeid;
               int dim_sizes[] = {NUM_DIMENSIONS};

               /* Create a file with a compound type which contains an array of
                * int. Write a little data. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_def_compound(ncid, sizeof(struct dim_rec), "SFDimRec", &typeid)) ERR;
               if (nc_insert_compound(ncid, typeid, "starfleet_id",
                                      HOFFSET(struct dim_rec, starfleet_id), NC_INT)) ERR;
               if (nc_insert_array_compound(ncid, typeid, "abilities",
                                      HOFFSET(struct dim_rec, abilities), NC_INT, 1, dim_sizes)) ERR;
               if (nc_inq_compound_field(ncid, xtype, 1, name, &offset, &field_typeid,
                                         &field_ndims, field_sizes)) ERR;
               if (strcmp(name, "abilities") || offset != 4 || field_typeid != NC_INT ||
                   field_ndims != 1 || field_sizes[0] != dim_sizes[0]) ERR;
               if (nc_def_dim(ncid, STARDATE, DIM_LEN, &dimid)) ERR;
               if (nc_def_var(ncid, "dimension_data", typeid, 1, dimids, &varid)) ERR;
               if (nc_put_var(ncid, varid, dim_data_out)) ERR;
               if (nc_close(ncid)) ERR;

               /* Open the file and take a look. */
               if (nc_open(FILE_NAME, NC_WRITE, &ncid)) ERR;
               if (nc_inq_var(ncid, 0, name, &xtype, &ndims, dimids, &natts)) ERR;
               if (strcmp(name, "dimension_data") || ndims != 1 || natts != 0 || dimids[0] != 0) ERR;
               if (nc_inq_compound(ncid, xtype, name, &size, &nfields)) ERR;
               if (nfields != 2 || size != sizeof(struct dim_rec) || strcmp(name, "SFDimRec")) ERR;
               if (nc_inq_compound_field(ncid, xtype, 1, name, &offset, &field_typeid,
                                         &field_ndims, field_sizes)) ERR;
               if (strcmp(name, "abilities") || offset != 4 || field_typeid != NC_INT ||
                   field_ndims != 1 || field_sizes[0] != NUM_DIMENSIONS) ERR;
               if (nc_get_var(ncid, varid, dim_data_in)) ERR;
               for (i=0; i<DIM_LEN; i++)
               {
                  if (dim_data_in[i].starfleet_id != dim_data_out[i].starfleet_id) ERR;
                  for (j = 0; j < NUM_DIMENSIONS; j++)
                     if (dim_data_in[i].abilities[j] != dim_data_out[i].abilities[j]) ERR;
               }
               if (nc_close(ncid)) ERR;
            }

Next: nc_inq_compound_name, Previous: nc_insert_array_compound, Up: User Defined Data Types

### 5.10 Learn About a Compound Type: nc_inq_compound

Get the number of fields, len, and name of a compound type.

### Usage

         int nc_inq_compound(int ncid, nc_type xtype, char *name, size_t *sizep,
                             size_t *nfieldsp);

`ncid`
  The ID of any group in the file that contains the compound type.
`xtype`
  The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var.
`name`
  Pointer to an already allocated char array which will get the name, as a null terminated string. It will have a maximum length of NC_MAX_NAME + 1. Ignored if NULL.
`sizep`
  A pointer to a size_t. The size of the compound type will be put here. Ignored if NULL.
`nfieldsp`
  A pointer to a size_t. The number of fields in the compound type will be placed here. Ignored if NULL.

### Return Codes

`NC_NOERR`
  No error.
`NC_EBADID`
  Couldn't find this ncid.
`NC_ENOTNC4`
  Not a netCDF-4/HDF5 file.
`NC_ESTRICTNC3`
  A netCDF-4/HDF5 file, but with CLASSIC_MODEL. No user defined types are allowed in the classic model.
`NC_EBADTYPE`
  This type not a compound type.
`NC_EBADTYPEID`
  Bad type id.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

The following example is from the test program libsrc4/tst_compounds.c. See also the example for See nc_insert_array_compound.

         #define BATTLES_WITH_KLINGONS "Number_of_Battles_with_Klingons"
         #define DATES_WITH_ALIENS "Dates_with_Alien_Hotties"

            struct s1
            {
                  int i1;
                  int i2;
            };

            /* Create a file with a compound type. */
            if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
            if (nc_def_compound(ncid, sizeof(struct s1), SVC_REC, &typeid)) ERR;
            if (nc_inq_compound(ncid, typeid, name, &size, &nfields)) ERR;
            if (nfields) ERR;
            if (nc_insert_compound(ncid, typeid, BATTLES_WITH_KLINGONS,
                              HOFFSET(struct s1, i1), NC_INT)) ERR;
            if (nc_insert_compound(ncid, typeid, DATES_WITH_ALIENS,
                              HOFFSET(struct s1, i2), NC_INT)) ERR;

            /* Check the compound type. */
            if (nc_inq_compound(ncid, xtype, name, &size, &nfields)) ERR;
            if (nfields != 2 || size != 8 || strcmp(name, SVC_REC)) ERR;
            if (nc_inq_compound_name(ncid, xtype, name)) ERR;
            if (strcmp(name, SVC_REC)) ERR;
            if (nc_inq_compound_size(ncid, xtype, &size)) ERR;
            if (size != 8) ERR;
            if (nc_inq_compound_nfields(ncid, xtype, &nfields)) ERR;
            if (nfields != 2) ERR;
            if (nc_inq_compound_field(ncid, xtype, 0, name, &offset, &field_xtype, &field_ndims, field_sizes)) ERR;
            if (strcmp(name, BATTLES_WITH_KLINGONS) || offset != 0 || (field_xtype != NC_INT || field_ndims != 0)) ERR;
            if (nc_inq_compound_field(ncid, xtype, 1, name, &offset, &field_xtype, &field_ndims, field_sizes)) ERR;
            if (strcmp(name, DATES_WITH_ALIENS) || offset != 4 || field_xtype != NC_INT) ERR;
            if (nc_inq_compound_fieldname(ncid, xtype, 1, name)) ERR;
            if (strcmp(name, DATES_WITH_ALIENS)) ERR;
            if (nc_inq_compound_fieldindex(ncid, xtype, BATTLES_WITH_KLINGONS, &fieldid)) ERR;
            if (fieldid != 0) ERR;
            if (nc_inq_compound_fieldoffset(ncid, xtype, 1, &offset)) ERR;
            if (offset != 4) ERR;
            if (nc_inq_compound_fieldtype(ncid, xtype, 1, &field_xtype)) ERR;
            if (field_xtype != NC_INT) ERR;

Next: nc_inq_compound_size, Previous: nc_inq_compound, Up: User Defined Data Types

### 5.11 Learn the Name of a Compound Type: nc_inq_compound_name

Get the name of a compound type.

### Usage

         int nc_inq_compound_name(int ncid, nc_type xtype, char *name);

`ncid`
  The groupid where this compound type exists.
`xtype`
  The typeid for this compound type.
`name`
  Pointer to an already allocated char array which will get the name, as a null terminated string. It will have a maximum length of NC_MAX_NAME+1.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad type id.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

See the example section for nc_inq_compound.

Next: nc_inq_compound_nfields, Previous: nc_inq_compound_name, Up: User Defined Data Types

### 5.12 Learn the Size of a Compound Type: nc_inq_compound_size

Get the len of a compound type.

### Usage

         int nc_inq_compound_size(int ncid, nc_type xtype, size_t *sizep);

`ncid`
  The groupid where this compound type exists.
`xtype`
  The typeid for this compound type.
`size`
  A pointer, which, if not NULL, get the size of the compound type.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad type id.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

See the example section for nc_inq_compound.

Next: nc_inq_compound_field, Previous: nc_inq_compound_size, Up: User Defined Data Types

### 5.13 Learn the Number of Fields in a Compound Type: nc_inq_compound_nfields

Get the number of fields of a compound type.

### Usage

         nc_inq_compound_nfields(int ncid, nc_type xtype, size_t *nfieldsp);

`ncid`
  The groupid where this compound type exists.
`xtype`
  The typeid for this compound type.
`nfieldsp`
  A pointer, which, if not NULL, get the number of fields of the compound type.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad type id.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

See the example section for nc_inq_compound.

Next: nc_inq_compound_fieldname, Previous: nc_inq_compound_nfields, Up: User Defined Data Types

### 5.14 Learn About a Field of a Compound Type: nc_inq_compound_field

Get information about one of the fields of a compound type.

### Usage

         int nc_inq_compound_field(int ncid, nc_type xtype, int fieldid, char *name,
                               size_t *offsetp, nc_type *field_typeidp, int *ndimsp,
                               int *dim_sizesp);

`ncid`
  The groupid where this compound type exists.
`xtype`
  The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var.
`fieldid`
  A zero-based index number specifying a field in the compound type.
`name`
  A pointer which, if non-NULL, will get the name of the field.
`offsetp`
  A pointer which, if non-NULL, will get the offset of the field.
`field_typeid`
  A pointer which, if non-NULL, will get the typeid of the field.
`ndimsp`
  A pointer which, if non-NULL, will get the number of dimensions of the field.
`dim_sizesp`
  A pointer which, if non-NULL, will get the dimension sizes of the field.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad type id.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

See the example section for nc_inq_compound.

Next: nc_inq_compound_fieldindex, Previous: nc_inq_compound_field, Up: User Defined Data Types

### 5.15 Find the Name of a Field in a Compound Type: nc_inq_compound_fieldname

Given the typeid and the fieldid, get the name.

### Usage

         int nc_inq_compound_fieldname(nc_type typeid, int fieldid, char *name);

`typeid`
  The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var.
`fieldid`
  The id of the field in the compound type. Fields are numbered starting with 0 for the first inserted field.
`name`
  Pointer to an already allocated char array which will get the name, as a null terminated string. It will have a maximum length of NC_MAX_NAME+1.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad type id.
`NC_EBADFIELDID`
  Bad field id.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

See the example section for nc_inq_compound.

Next: nc_inq_compound_fieldoffset, Previous: nc_inq_compound_fieldname, Up: User Defined Data Types

### 5.16 Get the FieldID of a Compound Type Field: nc_inq_compound_fieldindex

Given the typeid and the name, get the fieldid.

### Usage

         int nc_inq_compound_fieldindex(nc_type typeid, const char *name, int *fieldidp);

`typeid`
  The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var.
`name`
  The name of the field.
`fieldidp`
  A pointer to an int which will get the field id of the named field.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad type id.
`NC_EUNKNAME`
  Can't find field of this name.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

See the example section for nc_inq_compound.

Next: nc_inq_compound_fieldtype, Previous: nc_inq_compound_fieldindex, Up: User Defined Data Types

### 5.17 Get the Offset of a Field: nc_inq_compound_fieldoffset

Given the typeid and fieldid, get the offset.

### Usage

         int nc_inq_compound_fieldoffset(nc_type typeid, int fieldid,
                                         size_t *offsetp);

`typeid`
  The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var.
`fieldid`
  The id of the field in the compound type. Fields are numbered starting with 0 for the first inserted field.
`offsetp`
  A pointer to a size_t. The offset of the field will be placed there.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad typeid.
`NC_EBADFIELDID`
  Bad fieldid.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

See the example section for nc_inq_compound.

Next: nc_inq_compound_fieldndims, Previous: nc_inq_compound_fieldoffset, Up: User Defined Data Types

### 5.18 Find the Type of a Field: nc_inq_compound_fieldtype

Given the typeid and the fieldid, get the type of that field.

### Usage

         nc_inq_compound_fieldtype(nc_type typeid, int fieldid, nc_type *field_typeidp);

`typeid`
  The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var.
`fieldid`
  The id of the field in the compound type. Fields are numbered starting with 0 for the first inserted field.
`field_typeidp`
  Pointer to a nc_type which will get the typeid of the field.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad typeid.
`NC_EBADFIELDID`
  Bad fieldid.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

See the example section for nc_inq_compound.

Next: nc_inq_compound_fielddim_sizes, Previous: nc_inq_compound_fieldtype, Up: User Defined Data Types

### 5.19 Find the Number of Dimensions in an Array Field: nc_inq_compound_fieldndims

Given the typeid and the fieldid, get the number of dimensions of that field.

### Usage

         int nc_inq_compound_fieldndims(int ncid, nc_type xtype, int fieldid,
                                        int *ndimsp);

`ncid`
  The file or group ID.
`xtype`
  The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var.
`fieldid`
  The id of the field in the compound type. Fields are numbered starting with 0 for the first inserted field.
`ndimsp`
  Pointer to an int which will get the number of dimensions of the field. Non-array fields have 0 dimensions.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad typeid.
`NC_EBADFIELDID`
  Bad fieldid.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

See the example section for nc_inq_compound.

Next: Variable Length Array, Previous: nc_inq_compound_fieldndims, Up: User Defined Data Types

### 5.20 Find the Sizes of Dimensions in an Array Field: nc_inq_compound_fielddim_sizes

Given the xtype and the fieldid, get the sizes of dimensions for that field. User must have allocated storage for the dim_sizes.

### Usage

         int nc_inq_compound_fielddim_sizes(int ncid, nc_type xtype, int fieldid,
                                            int *dim_sizes);

`ncid`
  The file or group ID.
`xtype`
  The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var.
`fieldid`
  The id of the field in the compound type. Fields are numbered starting with 0 for the first inserted field.
`dim_sizesp`
  Pointer to an array of int which will get the sizes of the dimensions of the field. Non-array fields have 0 dimensions.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad typeid.
`NC_EBADFIELDID`
  Bad fieldid.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

See the example section for nc_inq_compound.

Next: nc_def_vlen, Previous: nc_inq_compound_fielddim_sizes, Up: User Defined Data Types

### 5.21 Variable Length Array Introduction

NetCDF-4 added support for a variable length array type. This is not supported in classic or 64-bit offset files, or in netCDF-4 files which were created with the NC_CLASSIC_MODEL flag.

A variable length array is represented in C as a structure from HDF5, the nc_vlen_t structure. It contains a len member, which contains the length of that array, and a pointer to the array.

So an array of VLEN in C is an array of nc_vlen_t structures.

VLEN arrays are handled differently with respect to allocation of memory. Generally, when reading data, it is up to the user to malloc (and subsequently free) the memory needed to hold the data. It is up to the user to ensure that enough memory is allocated.

With VLENs, this is impossible. The user cannot know the size of an array of VLEN until after reading the array. Therefore when reading VLEN arrays, the netCDF library will allocate the memory for the data within each VLEN.

It is up to the user, however, to eventually free this memory. This is not just a matter of one call to free, with the pointer to the array of VLENs; each VLEN contains a pointer which must be freed.

When dynamically allocating space to hold an array of VLEN, allocate storage for an array of nc_vlen_t.

Compression is permitted but may not be effective for VLEN data, because the compression is applied to the nc_vlen_t structs, rather than the actual data.

Next: nc_inq_vlen, Previous: Variable Length Array, Up: User Defined Data Types

### 5.22 Define a Variable Length Array (VLEN): nc_def_vlen

Use this function to define a variable length array type.

### Usage

         nc_def_vlen(int ncid, const char *name, nc_type base_typeid, nc_type *xtypep);

`ncid`
  The ncid of the file to create the VLEN type in.
`name`
  A name for the VLEN type.
`base_typeid`
  The typeid of the base type of the VLEN. For example, for a VLEN of shorts, the base type is NC_SHORT. This can be a user defined type.
`xtypep`
  A pointer to an nc_type variable. The typeid of the new VLEN type will be set here.

### Errors

`NC_NOERR`
  No error.
`NC_EMAXNAME`
  NC_MAX_NAME exceeded.
`NC_ENAMEINUSE`
  Name is already in use.
`NC_EBADNAME`
  Attribute or variable name contains illegal characters.
`NC_EBADID`
  ncid invalid.
`NC_EBADGRPID`
  Group ID part of ncid was invalid.
`NC_EINVAL`
  Size is invalid.
`NC_ENOMEM`
  Out of memory.

### Example

         #define DIM_LEN 3
         #define ATT_NAME "att_name"

            nc_vlen_t data[DIM_LEN];
            int *phony;

            /* Create phony data. */
            for (i=0; i<DIM_LEN; i++)
            {
               if (!(phony = malloc(sizeof(int) * i+1)))
                  return NC_ENOMEM;
               for (j=0; j<i+1; j++)
                  phony[j] = -99;
               data[i].p = phony;
               data[i].len = i+1;
            }

               /* Define a VLEN of NC_INT, and write an attribute of that
               type. */
               if (nc_def_vlen(ncid, "name1", NC_INT, &typeid)) ERR;
               if (nc_put_att(ncid, NC_GLOBAL, ATT_NAME, typeid, DIM_LEN, data)) ERR;

Next: nc_free_vlen, Previous: nc_def_vlen, Up: User Defined Data Types

### 5.23 Learning about a Variable Length Array (VLEN) Type: nc_inq_vlen

Use this type to learn about a vlen.

### Usage

         nc_inq_vlen(int ncid, nc_type xtype, char *name, size_t *datum_sizep,
                     nc_type *base_nc_typep);

`ncid`
  The ncid of the file that contains the VLEN type.
`xtype`
  The type of the VLEN to inquire about.
`name`
  A pointer for storage for the types name. The name will be NC_MAX_NAME characters or less.
`datum_sizep`
  A pointer to a size_t, this will get the size of one element of this vlen.
`base_nc_typep`
  A pointer to an nc_type, this will get the type of the VLEN base type. (In other words, what type is this a VLEN of?)

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPE`
  Can't find the typeid.
`NC_EBADID`
  ncid invalid.
`NC_EBADGRPID`
  Group ID part of ncid was invalid.

### Example

               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_def_vlen(ncid, "name1", NC_INT, &typeid)) ERR;
               if (nc_inq_vlen(ncid, typeid, name_in, &size_in, &base_nc_type_in)) ERR;
               if (base_nc_type_in != NC_INT || (size_in != sizeof(int) || strcmp(name_in, VLEN_NAME))) ERR;
               if (nc_inq_user_type(ncid, typeid, name_in, &size_in, &base_nc_type_in, NULL, &class_in)) ERR;
               if (base_nc_type_in != NC_INT || (size_in != sizeof(int) || strcmp(name_in, VLEN_NAME))) ERR;
               if (nc_inq_compound(ncid, typeid, name_in, &size_in, NULL) != NC_EBADTYPE) ERR;
               if (nc_put_att(ncid, NC_GLOBAL, ATT_NAME, typeid, DIM_LEN, data)) ERR;
               if (nc_close(ncid)) ERR;

Next: nc_free_vlens, Previous: nc_inq_vlen, Up: User Defined Data Types

### 5.24 Releasing Memory for a Variable Length Array (VLEN) Type: nc_free_vlen

When a VLEN is read into user memory from the file, the HDF5 library performs memory allocations for each of the variable length arrays contained within the VLEN structure. This memory must be freed by the user to avoid memory leaks.

This violates the normal netCDF expectation that the user is responsible for all memory allocation. But, with VLEN arrays, the underlying HDF5 library allocates the memory for the user, and the user is responsible for deallocating that memory.

To save the user the trouble calling free() on each element of the VLEN array (i.e. the array of arrays), the nc_free_vlen function is provided.

### Usage

         int nc_free_vlen(nc_vlen_t *vl);

`vl`
  A pointer to the variable length array structure which is to be freed.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPE`
  Can't find the typeid.

### Example

This example is from test program libsrc4/tst_vl.c.

            /* Free the memory used in our phony data. */
            for (i=0; i<DIM_LEN; i++)
               if (nc_free_vlen(&data[i])) ERR;

Next: Opaque Type, Previous: nc_free_vlen, Up: User Defined Data Types

### 5.25 Releasing Memory for an Array of Variable Length Array (VLEN) Type: nc_free_vlen

When a VLEN is read into user memory from the file, the HDF5 library performs memory allocations for each of the variable length arrays contained within the VLEN structure. This memory must be freed by the user to avoid memory leaks.

This violates the normal netCDF expectation that the user is responsible for all memory allocation. But, with VLEN arrays, the underlying HDF5 library allocates the memory for the user, and the user is responsible for deallocating that memory.

To save the user the trouble calling free() on each element of the VLEN array (i.e. the array of arrays), the nc_free_vlens function is provided. It frees all the vlens in an array.

### Usage

         int nc_free_vlens(size_t len, nc_vlen_t vlens[])

`len`
  Length of the VLEN array to be freed.
`vlens`
  Array of VLENs to be freed.

### Return Codes

`NC_NOERR`
  No error.

Next: nc_def_opaque, Previous: nc_free_vlens, Up: User Defined Data Types

### 5.26 Opaque Type Introduction

NetCDF-4 added support for the opaque type. This is not supported in classic or 64-bit offset files.

The opaque type is a type which is a collection of objects of a known size. (And each object is the same size). Nothing is known to netCDF about the contents of these blobs of data, except their size in bytes, and the name of the type.

To use an opaque type, first define it with nc_def_opaque. If encountering an enum type in a new data file, use nc_inq_opaque to learn its name and size.

Next: nc_inq_opaque, Previous: Opaque Type, Up: User Defined Data Types

### 5.27 Creating Opaque Types: nc_def_opaque

Create an opaque type. Provide a size and a name.

### Usage

         nc_def_opaque(int ncid, const char *name, size_t size, nc_type *typeidp);

`ncid`
  The groupid where the type will be created. The type may be used anywhere in the file, no matter what group it is in.
`name`
  The name for this type. Must be shorter than NC_MAX_NAME.
`size`
  The size of each opaque object.
`typeidp`
  Pointer where the new typeid for this type is returned. Use this typeid when defining variables of this type with nc_def_var.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad typeid.
`NC_EBADFIELDID`
  Bad fieldid.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from the test program libsrc4/tst_opaques.c.

               /* Create a file that has an opaque attribute. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_def_opaque(ncid, BASE_SIZE, TYPE_NAME, &xtype)) ERR;

Next: Enum Type, Previous: nc_def_opaque, Up: User Defined Data Types

### 5.28 Learn About an Opaque Type: nc_inq_opaque

Given a typeid, get the information about an opaque type.

### Usage

         int nc_inq_opaque(int ncid, nc_type xtype, char *name, size_t *sizep);

`ncid`
  The ncid for the group containing the opaque type.
`xtype`
  The typeid for this opaque type, as returned by nc_def_compound, or nc_inq_var.
`name`
  If non-NULL, the name of the opaque type will be copied here. It will be NC_MAX_NAME bytes or less.
`sizep`
  If non-NULL, the size of the opaque type will be copied here.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad typeid.
`NC_EBADFIELDID`
  Bad fieldid.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from test program libsrc4/tst_opaques.c:

               if (nc_def_opaque(ncid, BASE_SIZE, TYPE_NAME, &xtype)) ERR;

               if (nc_inq_opaque(ncid, xtype, name_in, &base_size_in)) ERR;
               if (strcmp(name_in, TYPE_NAME) || base_size_in != BASE_SIZE) ERR;

Next: nc_def_enum, Previous: nc_inq_opaque, Up: User Defined Data Types

### 5.29 Enum Type Introduction

NetCDF-4 added support for the enum type. This is not supported in classic or 64-bit offset files.

Next: nc_insert_enum, Previous: Enum Type, Up: User Defined Data Types

### 5.30 Creating a Enum Type: nc_def_enum

Create an enum type. Provide an ncid, a name, and a base integer type.

After calling this function, fill out the type with repeated calls to nc_insert_enum (see nc_insert_enum). Call nc_insert_enum once for each value you wish to make part of the enumeration.

### Usage

         int nc_def_enum(int ncid, nc_type base_typeid, const char *name,
                         nc_type *typeidp);

`ncid`
  The groupid where this compound type will be created.
`base_typeid`
  The base integer type for this enum. Must be one of: NC_BYTE, NC_UBYTE, NC_SHORT, NC_USHORT, NC_INT, NC_UINT, NC_INT64, NC_UINT64.
`name`
  The name of the new enum type.
`typeidp`
  A pointer to an nc_type. The typeid of the new type will be placed there.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENAMEINUSE`
  That name is in use.
`NC_EMAXNAME`
  Name exceeds max length NC_MAX_NAME.
`NC_EBADNAME`
  Name contains illegal characters.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag NC_NETCDF4. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.
`NC_EPERM`
  Attempt to write to a read-only file.
`NC_ENOTINDEFINE`
  Not in define mode.

The following example, from libsrc4/tst_enums.c, shows the creation and use of an enum type, including the use of a fill value.

                int dimid, varid;
                size_t num_members_in;
                int class_in;
                unsigned char value_in;

                enum clouds {           /* a C enumeration */
                    CLEAR=0,
                    CUMULONIMBUS=1,
                    STRATUS=2,
                    STRATOCUMULUS=3,
                    CUMULUS=4,
                    ALTOSTRATUS=5,
                    NIMBOSTRATUS=6,
                    ALTOCUMULUS=7,
                    CIRROSTRATUS=8,
                    CIRROCUMULUS=9,
                    CIRRUS=10,
                    MISSING=255};

                struct {
                    char *name;
                    unsigned char value;
                } cloud_types[] = {
                    {"Clear", CLEAR},
                    {"Cumulonimbus", CUMULONIMBUS},
                    {"Stratus", STRATUS},
                    {"Stratocumulus", STRATOCUMULUS},
                    {"Cumulus", CUMULUS},
                    {"Altostratus", ALTOSTRATUS},
                    {"Nimbostratus", NIMBOSTRATUS},
                    {"Altocumulus", ALTOCUMULUS},
                    {"Cirrostratus", CIRROSTRATUS},
                    {"Cirrocumulus", CIRROCUMULUS},
                    {"Cirrus", CIRRUS},
                    {"Missing", MISSING}
                };
                int var_dims[VAR2_RANK];
                unsigned char att_val;
                unsigned char cloud_data[DIM2_LEN] = {
                    CLEAR, STRATUS, CLEAR, CUMULONIMBUS, MISSING};
                unsigned char cloud_data_in[DIM2_LEN];

                if (nc_create(FILE_NAME, NC_CLOBBER | NC_NETCDF4, &ncid)) ERR;

                /* Create an enum type. */
                if (nc_def_enum(ncid, NC_UBYTE, TYPE2_NAME, &typeid)) ERR;
                num_members = (sizeof cloud_types) / (sizeof cloud_types[0]);
                for (i = 0; i < num_members; i++)
                    if (nc_insert_enum(ncid, typeid, cloud_types[i].name,
                                       &cloud_types[i].value)) ERR;

                /* Declare a station dimension */
                if (nc_def_dim(ncid, DIM2_NAME, DIM2_LEN, &dimid)) ERR;
                /* Declare a variable of the enum type */
                var_dims[0] = dimid;
                if (nc_def_var(ncid, VAR2_NAME, typeid, VAR2_RANK, var_dims, &varid)) ERR;
                /* Create and write a variable attribute of the enum type */
                att_val = MISSING;
                if (nc_put_att(ncid, varid, ATT2_NAME, typeid, ATT2_LEN, &att_val)) ERR;
                if (nc_enddef(ncid)) ERR;
                /* Store some data of the enum type */
                if(nc_put_var(ncid, varid, cloud_data)) ERR;
                /* Write the file. */
                if (nc_close(ncid)) ERR;

Next: nc_inq_enum, Previous: nc_def_enum, Up: User Defined Data Types

### 5.31 Inserting a Field into a Enum Type: nc_insert_enum

Insert a named member into a enum type.

### Usage

         int nc_insert_enum(int ncid, nc_type xtype, const char *identifier,
                            const void *value);

`ncid`
  The ncid of the group which contains the type.
`typeid`
  The typeid for this enum type, as returned by nc_def_enum, or nc_inq_var.
`identifier`
  The identifier of the new member.
`value`
  The value that is to be associated with this member.

### Errors

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad group id.
`NC_ENAMEINUSE`
  That name is in use. Field names must be unique within a enum type.
`NC_EMAXNAME`
  Name exceed max length NC_MAX_NAME.
`NC_EBADNAME`
  Name contains illegal characters.
`NC_ENOTNC4`
  Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag NC_NETCDF4. (see nc_open).
`NC_ESTRICTNC3`
  This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see nc_open).
`NC_EHDFERR`
  An error was reported by the HDF5 layer.
`NC_ENOTINDEFINE`
  Not in define mode.

### Example

This example is from libsrc4/tst_enums.c; also see the example in See nc_def_enum.

               char brady_name[NUM_BRADYS][NC_MAX_NAME + 1] = {"Mike", "Carol", "Greg", "Marsha",
                                                                "Peter", "Jan", "Bobby", "Whats-her-face",
                                                                "Alice"};
               unsigned char brady_value[NUM_BRADYS] = {0, 1,2,3,4,5,6,7,8};
               unsigned char data[BRADY_DIM_LEN] = {0, 4, 8};
               unsigned char value_in;

               /* Create a file. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;

               /* Create an enum type based on unsigned bytes. */
               if (nc_def_enum(ncid, NC_UBYTE, BRADYS, &typeid)) ERR;
               for (i = 0; i < NUM_BRADYS; i++)
                  if (nc_insert_enum(ncid, typeid, brady_name[i],
                                     &brady_value[i])) ERR;

Next: nc_inq_enum_member, Previous: nc_insert_enum, Up: User Defined Data Types

### 5.32 Learn About a Enum Type: nc_inq_enum

Get information about a user-define enumeration type.

### Usage

         nc_inq_enum(int ncid, nc_type xtype, char *name, nc_type *base_nc_typep,
                     size_t *base_sizep, size_t *num_membersp);

`ncid`
  The group ID of the group which holds the enum type.
`xtype`
  The typeid for this enum type, as returned by nc_def_enum, or nc_inq_var.
`name`
  Pointer to an already allocated char array which will get the name, as a null terminated string. It will have a maximum length of NC_MAX_NAME+1.
`base_nc_typep`
  If non-NULL, a pointer to a nc_type, which will get the base integer type of this enum.
`base_sizep`
  If non-NULL, a size_t pointer, which will get the size (in bytes) of the base integer type of this enum.
`num_membersp`
  If non-NULL, a size_t pointer which will get the number of members defined for this enumeration type.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad type id.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This example is from libsrc4/tst_enums.c, and is a continuation of the example above for nc_insert_enum. First an enum type is created, with one element for each of the nine members of the Brady family on a popular American television show which occupies far too much memory space in my brain!

In the example, the enum type is created, then checked using the nc_inq_enum and nc_inq_enum_member functions. See nc_inq_enum_member.

               char brady_name[NUM_BRADYS][NC_MAX_NAME + 1] = {"Mike", "Carol", "Greg", "Marsha",
                                                                "Peter", "Jan", "Bobby", "Whats-her-face",
                                                                "Alice"};
               unsigned char brady_value[NUM_BRADYS] = {0, 1,2,3,4,5,6,7,8};
               unsigned char data[BRADY_DIM_LEN] = {0, 4, 8};
               unsigned char value_in;

               /* Create a file. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;

               /* Create an enum type based on unsigned bytes. */
               if (nc_def_enum(ncid, NC_UBYTE, BRADYS, &typeid)) ERR;
               for (i = 0; i < NUM_BRADYS; i++)
                  if (nc_insert_enum(ncid, typeid, brady_name[i],
                                     &brady_value[i])) ERR;

               /* Check it out. */
               if (nc_inq_enum(ncid, typeid, name_in, &base_nc_type, &base_size_in, &num_members)) ERR;
               if (strcmp(name_in, BRADYS) || base_nc_type != NC_UBYTE || base_size_in != 1 ||
                   num_members != NUM_BRADYS) ERR;
               for (i = 0; i < NUM_BRADYS; i++)
               {
                  if (nc_inq_enum_member(ncid, typeid, i, name_in, &value_in)) ERR;
                  if (strcmp(name_in, brady_name[i]) || value_in != brady_value[i]) ERR;
                  if (nc_inq_enum_ident(ncid, typeid, brady_value[i], name_in)) ERR;
                  if (strcmp(name_in, brady_name[i])) ERR;
               }

Next: nc_inq_enum_ident, Previous: nc_inq_enum, Up: User Defined Data Types

### 5.33 Learn the Name of a Enum Type: nc_inq_enum_member

Get information about a member of an enum type.

### Usage

         int nc_inq_enum_member(int ncid, nc_type xtype, int idx, char *name,
                                void *value);

`ncid`
  The groupid where this enum type exists.
`xtype`
  The typeid for this enum type.
`idx`
  The zero-based index number for the member of interest.
`name`
  If non-NULL, a pointer to an already allocated char array which will get the name, as a null terminated string. It will have a maximum length of NC_MAX_NAME+1.
`value`
  If non-NULL, a pointer to storage of the correct integer type (i.e. the base type of this enum type). It will get the value associated with this member.

### Errors

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad type id.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.

### Example

This is the continuation of the example in nc_def_enum. The file is reopened and the cloud enum type is examined.

                /* Reopen the file. */
                if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;

                if (nc_inq_user_type(ncid, typeid, name_in, &base_size_in, &base_nc_type_in,
                                     &nfields_in, &class_in)) ERR;
                if (strcmp(name_in, TYPE2_NAME) ||
                    base_size_in != sizeof(unsigned char) ||
                    base_nc_type_in != NC_UBYTE ||
                    nfields_in != num_members ||
                    class_in != NC_ENUM) ERR;
                if (nc_inq_enum(ncid, typeid, name_in,
                                &base_nc_type_in, &base_size_in, &num_members_in)) ERR;
                if (strcmp(name_in, TYPE2_NAME) ||
                    base_nc_type_in !=  NC_UBYTE ||
                    num_members_in != num_members) ERR;
                for (i = 0; i < num_members; i++)
                {
                    if (nc_inq_enum_member(ncid, typeid, i, name_in, &value_in)) ERR;
                    if (strcmp(name_in, cloud_types[i].name) ||
                        value_in != cloud_types[i].value) ERR;
                    if (nc_inq_enum_ident(ncid, typeid, cloud_types[i].value,
                                          name_in)) ERR;
                    if (strcmp(name_in, cloud_types[i].name)) ERR;
                }
                if (nc_inq_varid(ncid, VAR2_NAME, &varid)) ERR;

                if (nc_get_att(ncid, varid, ATT2_NAME, &value_in)) ERR;
                if (value_in != MISSING) ERR;

                if(nc_get_var(ncid, varid, cloud_data_in)) ERR;
                for (i = 0; i < DIM2_LEN; i++) {
                    if (cloud_data_in[i] != cloud_data[i]) ERR;
                }

                if (nc_close(ncid)) ERR;

Previous: nc_inq_enum_member, Up: User Defined Data Types

### 5.34 Learn the Name of a Enum Type: nc_inq_enum_ident

Get the name which is associated with an enum member value.

### Usage

         int nc_inq_enum_ident(int ncid, nc_type xtype, long long value, char *identifier);

`ncid`
  The groupid where this enum type exists.
`xtype`
  The typeid for this enum type.
`value`
  The value for which an identifier is sought.
`identifier`
  If non-NULL, a pointer to an already allocated char array which will get the identifier, as a null terminated string. It will have a maximum length of NC_MAX_NAME+1.

### Return Code

`NC_NOERR`
  No error.
`NC_EBADTYPEID`
  Bad type id, or not an enum type.
`NC_EHDFERR`
  An error was reported by the HDF5 layer.
`NC_EINVAL`
  The value was not found in the enum.

### Example

See the example section for nc_inq_enum for a full example.

Next: Attributes, Previous: User Defined Data Types, Up: Top

## 6 Variables

Next: Variable Types, Previous: Variables, Up: Variables

### 6.1 Introduction

Variables for a netCDF dataset are defined when the dataset is created, while the netCDF dataset is in define mode. Other variables may be added later by reentering define mode. A netCDF variable has a name, a type, and a shape, which are specified when it is defined. A variable may also have values, which are established later in data mode.

Ordinarily, the name, type, and shape are fixed when the variable is first defined. The name may be changed, but the type and shape of a variable cannot be changed. However, a variable defined in terms of the unlimited dimension can grow without bound in that dimension.

A netCDF variable in an open netCDF dataset is referred to by a small integer called a variable ID.

Variable IDs reflect the order in which variables were defined within a netCDF dataset. Variable IDs are 0, 1, 2,..., in the order in which the variables were defined. A function is available for getting the variable ID from the variable name and vice-versa.

Attributes (see Attributes) may be associated with a variable to specify such properties as units.

Operations supported on variables are:

- Create a variable, given its name, data type, and shape.
- Get a variable ID from its name.
- Get a variable's name, data type, shape, and number of attributes from its ID.
- Put a data value into a variable, given variable ID, indices, and value.
- Put an array of values into a variable, given variable ID, corner indices, edge lengths, and a block of values.
- Put a subsampled or mapped array-section of values into a variable, given variable ID, corner indices, edge lengths, stride vector, index mapping vector, and a block of values.
- Get a data value from a variable, given variable ID and indices.
- Get an array of values from a variable, given variable ID, corner indices, and edge lengths.
- Get a subsampled or mapped array-section of values from a variable, given variable ID, corner indices, edge lengths, stride vector, and index mapping vector.
- Rename a variable.

Next: NetCDF-3 Variable Types, Previous: Variable Introduction, Up: Variables

### 6.2 Language Types Corresponding to netCDF external data types

NetCDF supported six atomic data types through version 3.6.0 (char, byte, short, int, float, and double). Starting with version 4.0, many new atomic and user defined data types are supported (unsigned int types, strings, compound types, variable length arrays, enums, opaque).

The additional data types are only supported in netCDF-4/HDF5 files. To create netCDF-4/HDF5 files, use the HDF5 flag in nc_create. (see nc_create).

Next: NetCDF-4 Atomic Types, Previous: Variable Types, Up: Variables

### 6.3 NetCDF-3 Classic and 64-Bit Offset Data Types

NetCDF-3 classic and 64-bit offset files support 6 atomic data types, and none of the user defined datatype introduced in NetCDF-4.

The following table gives the netCDF-3 external data types and the corresponding type constants for defining variables in the C interface:

Type | C #define | Bits
byte | NC_BYTE | 8
char | NC_CHAR | 8
short | NC_SHORT | 16
int | NC_INT | 32
float | NC_FLOAT | 32
double | NC_DOUBLE | 64

The first column gives the netCDF external data type, which is the same as the CDL data type. The next column gives the corresponding C pre-processor macro for use in netCDF functions (the pre-processor macros are defined in the netCDF C header-file netcdf.h). The last column gives the number of bits used in the external representation of values of the corresponding type.

Next: nc_def_var, Previous: NetCDF-3 Variable Types, Up: Variables

### 6.4 NetCDF-4 Atomic Types

NetCDF-4 files support all of the atomic data types from netCDF-3, plus additional unsigned integer types, 64-bit integer types, and a string type.

Type | C #define | Bits
byte | NC_BYTE | 8
unsigned byte | NC_UBYTE^ | 8
char | NC_CHAR | 8
short | NC_SHORT | 16
unsigned short | NC_USHORT^ | 16
int | NC_INT | 32
unsigned int | NC_UINT^ | 32
unsigned long long | NC_UINT64^ | 64
long long | NC_INT64^ | 64
float | NC_FLOAT | 32
double | NC_DOUBLE | 64
char ** | NC_STRING^ | string length + 1

^This type was introduced in netCDF-4, and is not supported in netCDF classic or 64-bit offset format files, or in netCDF-4 files if they are created with the NC_CLASSIC_MODEL flags.

Next: nc_def_var_chunking, Previous: NetCDF-4 Atomic Types, Up: Variables

### 6.5 Create a Variable: `nc_def_var`

The function nc_def_var adds a new variable to an open netCDF dataset in define mode. It returns (as an argument) a variable ID, given the netCDF ID, the variable name, the variable type, the number of dimensions, and a list of the dimension IDs.

### Usage

         int nc_def_var (int ncid, const char *name, nc_type xtype,
                         int ndims, const int dimids[], int *varidp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`name`
  Variable name.
`xtype`
  One of the set of predefined netCDF external data types. The type of this parameter, nc_type, is defined in the netCDF header file. The valid netCDF external data types are NC_BYTE, NC_CHAR, NC_SHORT, NC_INT, NC_FLOAT, and NC_DOUBLE. If the file is a NetCDF-4/HDF5 file, the additional types NC_UBYTE, NC_USHORT, NC_UINT, NC_INT64, NC_UINT64, and NC_STRING may be used, as well as a user defined type ID.
`ndims`
  Number of dimensions for the variable. For example, 2 specifies a matrix, 1 specifies a vector, and 0 means the variable is a scalar with no dimensions. Must not be negative or greater than the predefined constant NC_MAX_VAR_DIMS.
`dimids`
  Vector of ndims dimension IDs corresponding to the variable dimensions. For classic model netCDF files, if the ID of the unlimited dimension is included, it must be first. This argument is ignored if ndims is 0. For expanded model netCDF4/HDF5 files, there may be any number of unlimited dimensions, and they may be used in any element of the dimids array.
`varidp`
  Pointer to location for the returned variable ID.

### Errors

nc_def_var returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTINDEFINE`
  Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag. (see nc_create).
`NC_ESTRICTNC3`
  Trying to create a var some place other than the root group in a netCDF file with NC_STRICT_NC3 turned on.
`NC_MAX_VARS`
  Max number of variables exceeded in a classic or 64-bit offset file, or an netCDF-4 file with NC_STRICT_NC3 on.
`NC_EBADTYPE`
  Bad type.
`NC_EINVAL`
  Number of dimensions to large.
`NC_ENAMEINUSE`
  Name already in use.
`NC_EPERM`
  Attempt to create object in read-only file.

### Example

Here is an example using nc_def_var to create a variable named rh of type double with three dimensions, time, lat, and lon in a new netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int  status;                       /* error status */
         int  ncid;                         /* netCDF ID */
         int  lat_dim, lon_dim, time_dim;   /* dimension IDs */
         int  rh_id;                        /* variable ID */
         int  rh_dimids[3];                 /* variable shape */
            ...
         status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
                                            /* define dimensions */
         status = nc_def_dim(ncid, "lat", 5L, &lat_dim);
         if (status != NC_NOERR) handle_error(status);
         status = nc_def_dim(ncid, "lon", 10L, &lon_dim);
         if (status != NC_NOERR) handle_error(status);
         status = nc_def_dim(ncid, "time", NC_UNLIMITED, &time_dim);
         if (status != NC_NOERR) handle_error(status);
            ...
                                            /* define variable */
         rh_dimids[0] = time_dim;
         rh_dimids[1] = lat_dim;
         rh_dimids[2] = lon_dim;
         status = nc_def_var (ncid, "rh", NC_DOUBLE, 3, rh_dimids, &rh_id);
         if (status != NC_NOERR) handle_error(status);

Next: nc_inq_var_chunking, Previous: nc_def_var, Up: Variables

### 6.6 Define Chunking Parameters for a Variable: `nc_def_var_chunking`

The function nc_def_var_chunking sets the chunking parameters for a variable in a netCDF-4 file. It can set the chunk sizes to get chunked storage, or it can set the contiguous flag to get contiguous storage.

Variables that make use of one or more unlimited dimensions, compression, or checksums must use chunking. Such variables are created with default chunk sizes of 1 for each unlimited dimension and the dimension length for other dimensions, except that if the resulting chunks are too large, the default chunk sizes for non-record dimensions are reduced.

The total size of a chunk must be less than 4 GiB. That is, the product of all chunksizes and the size of the data (or the size of nc_vlen_t for VLEN types) must be less than 4 GiB.

This function may only be called after the variable is defined, but before nc_enddef is called. Once the chunking parameters are set for a variable, they cannot be changed. This function can be used to change the default chunking for record, compressed, or checksummed variables before nc_enddef is called.

Note that you cannot set chunking for scalar variables. Only non-scalar variables can have chunking.

### Usage

         int nc_def_var_chunking(int ncid, int varid, int storage, size_t *chunksizesp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`storage`
  If NC_CONTIGUOUS, then contiguous storage is used for this variable. Variables with chunking, compression, checksums, or one or more unlimited dimensions cannot use contiguous storage.

  If NC_CHUNKED, then chunked storage is used for this variable. Chunk sizes may be specified with the chunksizes parameter or default sizes will be used if that parameter is NULL.

  By default contiguous storage is used for fix-sized variables when conpression, chunking, and checksums are not used.

`*chunksizes`
  A pointer to an array list of chunk sizes. The array must have one chunksize for each dimension of the variable.

### Errors

nc_def_var_chunking returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error.

Possible return codes include:

`NC_NOERR`
  No error.
`NC_EBADID`
  Bad ncid.
`NC_EINVAL`
  Invalid input. This can occur if contiguous storage is set on a variable which uses compression, checksums, or one or more unlimited dimensions.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.
`NC_ELATEDEF`
  This variable has already been the subject of a nc_enddef call. In netCDF-4 files nc_enddef will be called automatically for any data read or write. Once nc_enddef has been called after the nc_def_var call for a variable, it is impossible to set the chunking for that variable.
`NC_ENOTINDEFINE`
  Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag. (see nc_create).
`NC_ESTRICTNC3`
  Trying to create a var some place other than the root group in a netCDF file with NC_STRICT_NC3 turned on.
`NC_EPERM`
  Attempt to create object in read-only file.

### Example

In this example from libsrc4/tst_vars2.c, chunksizes are set with nc_var_def_chunking, and checked with nc_var_inq_chunking.

            printf("**** testing chunking...");
            {
         #define NDIMS5 1
         #define DIM5_NAME "D5"
         #define VAR_NAME5 "V5"
         #define DIM5_LEN 1000

               int dimids[NDIMS5], dimids_in[NDIMS5];
               int varid;
               int ndims, nvars, natts, unlimdimid;
               nc_type xtype_in;
               char name_in[NC_MAX_NAME + 1];
               int data[DIM5_LEN], data_in[DIM5_LEN];
               size_t chunksize[NDIMS5] = {5};
               size_t chunksize_in[NDIMS5];
               int storage_in;
               int i, d;

               for (i = 0; i < DIM5_LEN; i++)
                  data[i] = i;

               /* Create a netcdf-4 file with one dim and one var. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_def_dim(ncid, DIM5_NAME, DIM5_LEN, &dimids[0])) ERR;
               if (nc_def_var(ncid, VAR_NAME5, NC_INT, NDIMS5, dimids, &varid)) ERR;
               if (nc_def_var_chunking(ncid, varid, NC_CHUNKED, chunksize)) ERR;
               if (nc_put_var_int(ncid, varid, data)) ERR;

               /* Check stuff. */
               if (nc_inq_var_chunking(ncid, varid, &storage_in, chunksize_in)) ERR;
               for (d = 0; d < NDIMS5; d++)
                  if (chunksize[d] != chunksize_in[d]) ERR;
               if (storage_in != NC_CHUNKED) ERR;

Next: nc_set_var_chunk_cache, Previous: nc_def_var_chunking, Up: Variables

### 6.7 Learn About Chunking Parameters for a Variable: `nc_inq_var_chunking`

The function nc_inq_var_chunking returns the chunking settings for a variable in a netCDF-4 file.

### Usage

         int nc_inq_var_chunking(int ncid, int varid, int *storagep, size_t *chunksizesp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`storagep`
  Address of returned storage property, returned as NC_CONTIGUOUS if this variable uses contiguous storage, or NC_CHUNKEDif it uses chunked storage.
`*chunksizesp`
  A pointer to an array list of chunk sizes. The array must have one chunksize for each dimension in the variable.

### Errors

nc_inq_var_chunking returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error.

Possible return codes include:

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.

### Example

This example is from libsrc4/tst_vars2.c in which a variable with contiguous storage is created, and then checked with nc_inq_var_chunking:

            printf("**** testing contiguous storage...");
            {
         #define NDIMS6 1
         #define DIM6_NAME "D5"
         #define VAR_NAME6 "V5"
         #define DIM6_LEN 100

               int dimids[NDIMS6], dimids_in[NDIMS6];
               int varid;
               int ndims, nvars, natts, unlimdimid;
               nc_type xtype_in;
               char name_in[NC_MAX_NAME + 1];
               int data[DIM6_LEN], data_in[DIM6_LEN];
               size_t chunksize_in[NDIMS6];
               int storage_in;
               int i, d;

               for (i = 0; i < DIM6_LEN; i++)
                  data[i] = i;

               /* Create a netcdf-4 file with one dim and one var. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_def_dim(ncid, DIM6_NAME, DIM6_LEN, &dimids[0])) ERR;
               if (dimids[0] != 0) ERR;
               if (nc_def_var(ncid, VAR_NAME6, NC_INT, NDIMS6, dimids, &varid)) ERR;
               if (nc_def_var_chunking(ncid, varid, NC_CONTIGUOUS, NULL)) ERR;
               if (nc_put_var_int(ncid, varid, data)) ERR;

               /* Check stuff. */
               if (nc_inq_var_chunking(ncid, 0, &storage_in, chunksize_in)) ERR;
               if (storage_in != NC_CONTIGUOUS) ERR;

Next: nc_get_var_chunk_cache, Previous: nc_inq_var_chunking, Up: Variables

### 6.8 Set HDF5 Chunk Cache for a Variable: nc_set_var_chunk_cache

This function changes the chunk cache settings for a variable. The change in cache size happens immediately. This is a property of the open file - it does not persist the next time you open the file.

For more information, see the documentation for the H5Pset_cache() function in the HDF5 library at the HDF5 website: http://hdfgroup.org/HDF5/.

### Usage

         nc_set_var_chunk_cache(int ncid, int varid, size_t size, size_t nelems,
         		       float preemption);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`size`
  The total size of the raw data chunk cache, in bytes. This should be big enough to hold multiple chunks of data.
`nelems`
  The number of chunk slots in the raw data chunk cache hash table. This should be a prime number larger than the number of chunks that will be in the cache.
`preemption`
  The preemtion value must be between 0 and 1 inclusive and indicates how much chunks that have been fully read are favored for preemption. A value of zero means fully read chunks are treated no differently than other chunks (the preemption is strictly LRU) while a value of one means fully read chunks are always preempted before other chunks.

### Return Codes

`NC_NOERR`
  No error.
`NC_EINVAL`
  Preemption must be between zero and one (inclusive).

### Example

This example is from libsrc4/tst_vars2.c:

         #include <netcdf.h>
            ...
         #define CACHE_SIZE 32000000
         #define CACHE_NELEMS 1009
         #define CACHE_PREEMPTION .75
            ...

               /* Create a netcdf-4 file with one dim and one var. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_def_dim(ncid, DIM5_NAME, DIM5_LEN, &dimids[0])) ERR;
               if (dimids[0] != 0) ERR;
               if (nc_def_var(ncid, VAR_NAME5, NC_INT, NDIMS5, dimids, &varid)) ERR;
               if (nc_def_var_chunking(ncid, varid, NC_CHUNKED, chunksize)) ERR;
               if (nc_set_var_chunk_cache(ncid, varid, CACHE_SIZE, CACHE_NELEMS, CACHE_PREEMPTION)) ERR;

Next: nc_def_var_fill, Previous: nc_set_var_chunk_cache, Up: Variables

### 6.9 Get the HDF5 Chunk Cache Settings for a Variable: nc_get_var_chunk_cache

This function gets the current chunk cache settings for a variable in a netCDF-4/HDF5 file.

For more information, see the documentation for the H5Pget_cache() function in the HDF5 library at the HDF5 website: http://hdfgroup.org/HDF5/.

### Usage

         int nc_get_var_chunk_cache(int ncid, int varid, size_t *sizep, size_t *nelemsp,
                                    float *preemptionp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`sizep`
  The total size of the raw data chunk cache, in bytes, will be put here. If NULL, will be ignored.
`nelemsp`
  The number of chunk slots in the raw data chunk cache hash table will be put here. If NULL, will be ignored.
`preemptionp`
  The preemption will be put here. The preemtion value is between 0 and 1 inclusive and indicates how much chunks that have been fully read are favored for preemption. A value of zero means fully read chunks are treated no differently than other chunks (the preemption is strictly LRU) while a value of one means fully read chunks are always preempted before other chunks. If NULL, will be ignored.

### Return Codes

`NC_NOERR`
  No error.

### Example

This example is from libsrc4/tst_vars2.c:

         #include <netcdf.h>
            ...
               /* Create a netcdf-4 file with one dim and one var. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_def_dim(ncid, DIM5_NAME, DIM5_LEN, &dimids[0])) ERR;
               if (nc_def_var(ncid, VAR_NAME5, NC_INT, NDIMS5, dimids, &varid)) ERR;
               if (nc_def_var_chunking(ncid, varid, NC_CHUNKED, chunksize)) ERR;
               if (nc_set_var_chunk_cache(ncid, varid, CACHE_SIZE, CACHE_NELEMS,
                                          CACHE_PREEMPTION)) ERR;
            ...
               if (nc_get_var_chunk_cache(ncid, varid, &cache_size_in, &cache_nelems_in,
         				 &cache_preemption_in)) ERR;
               if (cache_size_in != CACHE_SIZE || cache_nelems_in != CACHE_NELEMS ||
         	  cache_preemption_in != CACHE_PREEMPTION) ERR;

            ...

Next: nc_inq_var_fill, Previous: nc_get_var_chunk_cache, Up: Variables

### 6.10 Define Fill Parameters for a Variable: `nc_def_var_fill`

The function nc_def_var_fill sets the fill parameters for a variable in a netCDF-4 file.

This function must be called after the variable is defined, but before nc_enddef is called.

### Usage

         int nc_def_var_fill(int ncid, int varid, int no_fill, void *fill_value);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`no_fill`
  Set no_fill mode on a variable. When this mode is on, fill values will not be written for the variable. This is helpful in high performance applications. For netCDF-4/HDF5 files (whether classic model or not), this may only be changed after the variable is defined, but before it is committed to disk (i.e. before the first nc_enddef after the nc_def_var.) For classic and 64-bit offset file, the no_fill mode may be turned on and off at any time.
`*fill_value`
  A pointer to a value which will be used as the fill value for the variable. Must be the same type as the variable. This will be written to a _FillValue attribute, created for this purpose. If NULL, this argument will be ignored.

### Return Codes

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.
`NC_ELATEDEF`
  This variable has already been the subject of a nc_enddef call. In netCDF-4 files nc_enddef will be called automatically for any data read or write. Once enddef has been called, it is impossible to set the fill for a variable.
`NC_ENOTINDEFINE`
  Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag. (see nc_create).
`NC_EPERM`
  Attempt to create object in read-only file.

### Example

This example is from libsrc4/tst_vars.c

               int dimids[NDIMS];
               size_t index[NDIMS];
               int varid;
               int no_fill;
               unsigned short ushort_data = 42, ushort_data_in, fill_value_in;

               /* Create a netcdf-4 file with one dim and 1 NC_USHORT var. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_def_dim(ncid, DIM7_NAME, DIM7_LEN, &dimids[0])) ERR;
               if (nc_def_var(ncid, VAR7_NAME, NC_USHORT, NDIMS, dimids,
         		     &varid)) ERR;
               if (nc_def_var_fill(ncid, varid, 1, NULL)) ERR;

Next: nc_def_var_deflate, Previous: nc_def_var_fill, Up: Variables

### 6.11 Learn About Fill Parameters for a Variable: `nc_inq_var_fill`

The function nc_inq_var_fill returns the fill settings for a variable in a netCDF-4 file.

### Usage

         int nc_inq_var_fill(int ncid, int varid, int *no_fill, void *fill_value);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`*no_fill`
  Pointer to an integer which will get a 1 if no_fill mode is set for this variable. See nc_def_var_fill. This parameter will be ignored if it is NULL.
`*fill_value`
  A pointer which will get the fill value for this variable. This parameter will be ignored if it is NULL.

### Return Codes

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.

### Example

This example is from libsrc4/tst_vars.c

               int dimids[NDIMS];
               size_t index[NDIMS];
               int varid;
               int no_fill;
               unsigned short ushort_data = 42, ushort_data_in, fill_value_in;

               /* Create a netcdf-4 file with one dim and 1 NC_USHORT var. */
               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_def_dim(ncid, DIM7_NAME, DIM7_LEN, &dimids[0])) ERR;
               if (nc_def_var(ncid, VAR7_NAME, NC_USHORT, NDIMS, dimids,
         		     &varid)) ERR;
               if (nc_def_var_fill(ncid, varid, 1, NULL)) ERR;

               /* Check stuff. */
               if (nc_inq_var_fill(ncid, varid, &no_fill, &fill_value_in)) ERR;
               if (!no_fill) ERR;

Next: nc_inq_var_deflate, Previous: nc_inq_var_fill, Up: Variables

### 6.12 Define Compression Parameters for a Variable: `nc_def_var_deflate`

The function nc_def_var_deflate sets the deflate parameters for a variable in a netCDF-4 file.

This function must be called after the variable is defined, but before nc_enddef is called.

This does not work with scalar variables.

### Usage

         nc_def_var_deflate(int ncid, int varid, int shuffle, int deflate,
                            int deflate_level);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`shuffle`
  If non-zero, turn on the shuffle filter.
`deflate`
  If non-zero, turn on the deflate filter at the level specified by the deflate_level parameter.
`deflate_level`
  If the deflate parameter is non-zero, set the deflate level to this value. Must be between 0 and 9.

### Errors

nc_def_var_deflate returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error.

Possible return codes include:

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.
`NC_ELATEDEF`
  This variable has already been the subject of a nc_enddef call. In netCDF-4 files nc_enddef will be called automatically for any data read or write. Once enddef has been called, it is impossible to set the deflate for a variable.
`NC_ENOTINDEFINE`
  Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag. (see nc_create).
`NC_EPERM`
  Attempt to create object in read-only file.
`NC_EINVAL`
  Invalid deflate_level. The deflate level must be between 0 and 9, inclusive.

### Example

Next: nc_inq_var_szip, Previous: nc_def_var_deflate, Up: Variables

### 6.13 Learn About Deflate Parameters for a Variable: `nc_inq_var_deflate`

The function nc_inq_var_deflate returns the deflate settings for a variable in a netCDF-4 file.

### Usage

         nc_inq_var_deflate(int ncid, int varid, int *shufflep,
                            int *deflatep, int *deflate_levelp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`*shufflep`
  If this pointer is non-NULL, the nc_inq_var_deflate function will write a 1 if the shuffle filter is turned on for this variable, and a 0 otherwise.
`*deflatep`
  If this pointer is non-NULL, the nc_inq_var_deflate function will write a 1 if the deflate filter is turned on for this variable, and a 0 otherwise.
`*deflate_levelp`
  If this pointer is non-NULL, and the deflate filter is in use for this variable, the nc_inq_var_deflate function will write the deflate_level here.

### Errors

nc_inq_var_deflate returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error.

Possible return codes include:

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.

### Example

Next: nc_def_var_fletcher32, Previous: nc_inq_var_deflate, Up: Variables

### 6.14 Learn About Szip Parameters for a Variable: `nc_inq_var_szip`

The function nc_inq_var_szip returns the szip settings for a variable in a netCDF-4 file.

### Usage

         int nc_inq_var_szip(int ncid, int varid, int *options_maskp, int *pixels_per_blockp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`*options_maskp`
  If this pointer is non-NULL, the nc_inq_var_szip function will put the options_mask here.
`*pixels_per_blockp`
  If this pointer is non-NULL, the nc_inq_var_szip function will write the bits per pixel here.

### Errors

nc_inq_var_szip returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error.

Possible return codes include:

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.

### Example

This example is from libsrc4/tst_vars3.c.

               /* Make sure we have the szip settings we expect. */
               if (nc_inq_var_szip(ncid, small_varid, &options_mask_in, &pixels_per_block_in)) ERR;
               if (options_mask_in != 0 || pixels_per_block_in !=0) ERR;
               if (nc_inq_var_szip(ncid, medium_varid, &options_mask_in, &pixels_per_block_in)) ERR;
               if (!(options_mask_in & NC_SZIP_EC_OPTION_MASK) || pixels_per_block_in != 32) ERR;
               if (nc_inq_var_szip(ncid, large_varid, &options_mask_in, &pixels_per_block_in)) ERR;
               if (!(options_mask_in & NC_SZIP_NN_OPTION_MASK) || pixels_per_block_in != 16) ERR;

Next: nc_inq_var_fletcher32, Previous: nc_inq_var_szip, Up: Variables

### 6.15 Define Checksum Parameters for a Variable: `nc_def_var_fletcher32`

The function nc_def_var_fletcher32 sets the checksum parameters for a variable in a netCDF-4 file.

This function may only be called after the variable is defined, but before nc_enddef is called.

### Usage

         nc_def_var_fletcher32(int ncid, int varid, int checksum);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`checksum`
  If this is NC_FLETCHER32, fletcher32 checksums will be turned on for this variable.

### Errors

nc_def_var_fletcher32 returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error.

Possible return codes include:

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.
`NC_ELATEDEF`
  This variable has already been the subject of a nc_enddef call. In netCDF-4 files nc_enddef will be called automatically for any data read or write. Once enddef has been called, it is impossible to set the checksum property for a variable.
`NC_ENOTINDEFINE`
  Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag. (see nc_create).
`NC_EPERM`
  Attempt to create object in read-only file.

### Example

Next: nc_def_var_endian, Previous: nc_def_var_fletcher32, Up: Variables

### 6.16 Learn About Checksum Parameters for a Variable: `nc_inq_var_fletcher32`

The function nc_inq_var_fletcher32 returns the checksum settings for a variable in a netCDF-4 file.

### Usage

         nc_inq_var_fletcher32(int ncid, int varid, int *checksump);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`*checksump`
  If not-NULL, the nc_inq_var_fletcher32 function will set the int pointed at to NC_FLETCHER32 if the fletcher32 checksum filter is turned on for this variable, and NC_NOCHECKSUM if it is not.

### Errors

nc_inq_var_fletcher32 returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error.

Possible return codes include:

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.

### Example

Next: nc_inq_var_endian, Previous: nc_inq_var_fletcher32, Up: Variables

### 6.17 Define Endianness of a Variable: `nc_def_var_endian`

The function nc_def_var_endian sets the endianness for a variable in a netCDF-4 file.

This function must be called after the variable is defined, but before nc_enddef is called.

By default, netCDF-4 variables are in native endianness. That is, they are big-endian on a big-endian machine, and little-endian on a little endian machine.

In some cases a user might wish to change from native endianness to either big or little-endianness. This function allows them to do that.

### Usage

         nc_def_var_endian(int ncid, int varid, int endian);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`endian`
  Set to NC_ENDIAN_NATIVE for native endianness. (This is the default). Set to NC_ENDIAN_LITTLE for little endian, or NC_ENDIAN_BIG for big endian.

### Errors

nc_def_var_endian returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error.

Possible return codes include:

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.
`NC_ELATEDEF`
  This variable has already been the subject of a nc_enddef call. In netCDF-4 files nc_enddef will be called automatically for any data read or write. Once enddef has been called, it is impossible to set the endianness of a variable.
`NC_ENOTINDEFINE`
  Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag, and the file is not in define mode. (see nc_create).
`NC_EPERM`
  Attempt to create object in read-only file.

### Example

Next: nc_inq_varid, Previous: nc_def_var_endian, Up: Variables

### 6.18 Learn About Endian Parameters for a Variable: `nc_inq_var_endian`

The function nc_inq_var_endian returns the endianness settings for a variable in a netCDF-4 file.

### Usage

         nc_inq_var_endian(int ncid, int varid, int *endianp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`*endianp`
  If not-NULL, the nc_inq_var_endian function will set the int pointed to this to NC_ENDIAN_LITTLE if this variable is stored in little-endian format, NC_ENDIAN_BIG if it is stored in big-endian format, and NC_ENDIAN_NATIVE if the endianness is not set, and the variable is not created yet.

### Errors

nc_inq_var_endian returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error.

Possible return codes include:

`NC_NOERR`
  No error.
`NC_BADID`
  Bad ncid.
`NC_ENOTNC4`
  Not a netCDF-4 file.
`NC_ENOTVAR`
  Can't find this variable.

### Example

Next: nc_inq_var, Previous: nc_inq_var_endian, Up: Variables

### 6.19 Get a Variable ID from Its Name: nc_inq_varid

The function nc_inq_varid returns the ID of a netCDF variable, given its name.

### Usage

         int nc_inq_varid (int ncid, const char *name, int *varidp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`name`
  Variable name for which ID is desired.
`varidp`
  Pointer to location for returned variable ID.

### Errors

nc_inq_varid returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The specified variable name is not a valid name for a variable in the specified netCDF dataset.
- The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_inq_varid to find out the ID of a variable named rh in an existing netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int  status, ncid, rh_id;
            ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);

Next: nc_put_var1_ type, Previous: nc_inq_varid, Up: Variables

### 6.20 Get Information about a Variable from Its ID: nc_inq_var

family &findex nc_inq_vardimid A family of functions that returns information about a netCDF variable, given its ID. Information about a variable includes its name, type, number of dimensions, a list of dimension IDs describing the shape of the variable, and the number of variable attributes that have been assigned to the variable.

The function nc_inq_var returns all the information about a netCDF variable, given its ID. The other functions each return just one item of information about a variable.

These other functions include nc_inq_varname, nc_inq_vartype, nc_inq_varndims, nc_inq_vardimid, and nc_inq_varnatts.

### Usage

         int nc_inq_var      (int ncid, int varid, char *name, nc_type *xtypep,
                              int *ndimsp, int dimids[], int *nattsp);
         int nc_inq_varname  (int ncid, int varid, char *name);
         int nc_inq_vartype  (int ncid, int varid, nc_type *xtypep);
         int nc_inq_varndims (int ncid, int varid, int *ndimsp);
         int nc_inq_vardimid (int ncid, int varid, int dimids[]);
         int nc_inq_varnatts (int ncid, int varid, int *nattsp);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`name`
  Returned variable name. The caller must allocate space for the returned name. The maximum possible length, in characters, of a variable name is given by the predefined constant NC_MAX_NAME. (This doesn't include the null terminator, so declare your array to be size NC_MAX_NAME+1). The returned character array will be null-terminated.
`xtypep`
  Pointer to location for returned variable type, one of the set of predefined netCDF external data types. The type of this parameter, nc_type, is defined in the netCDF header file. The valid netCDF external data types are NC_BYTE, NC_CHAR, NC_SHORT, NC_INT, NC_FLOAT, and NC_DOUBLE.
`ndimsp`
  Pointer to location for returned number of dimensions the variable was defined as using. For example, 2 indicates a matrix, 1 indicates a vector, and 0 means the variable is a scalar with no dimensions.
`dimids`
  Returned vector of *ndimsp dimension IDs corresponding to the variable dimensions. The caller must allocate enough space for a vector of at least *ndimsp integers to be returned. The maximum possible number of dimensions for a variable is given by the predefined constant NC_MAX_VAR_DIMS.
`nattsp`
  Pointer to location for returned number of variable attributes assigned to this variable.

These functions return the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

The variable ID is invalid for the specified netCDF dataset. The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_inq_var to find out about a variable named rh in an existing netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int  status                        /* error status */
         int  ncid;                         /* netCDF ID */
         int  rh_id;                        /* variable ID */
         nc_type rh_type;                   /* variable type */
         int rh_ndims;                      /* number of dims */
         int  rh_dimids[NC_MAX_VAR_DIMS];   /* dimension IDs */
         int rh_natts                       /* number of attributes */
            ...
         status = nc_open ("foo.nc", NC_NOWRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
         /* we don't need name, since we already know it */
         status = nc_inq_var (ncid, rh_id, 0, &rh_type, &rh_ndims, rh_dimids,
                              &rh_natts);
         if (status != NC_NOERR) handle_error(status);

Next: nc_put_var_ type, Previous: nc_inq_var, Up: Variables

### 6.21 Write a Single Data Value: nc_put_var1_ type

The functions nc_put_var1_ type put a single data value of the specified type into a variable of an open netCDF dataset that is in data mode. Inputs are the netCDF ID, the variable ID, an index that specifies which value to add or alter, and the data value. The value is converted to the external data type of the variable, if necessary.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_put_var1() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

### Usage

         int nc_put_var1_text  (int ncid, int varid, const size_t index[],
                                const char *tp);
         int nc_put_var1_uchar (int ncid, int varid, const size_t index[],
                                const unsigned char *up);
         int nc_put_var1_schar (int ncid, int varid, const size_t index[],
                                const signed char *cp);
         int nc_put_var1_short (int ncid, int varid, const size_t index[],
                                const short *sp);
         int nc_put_var1_int   (int ncid, int varid, const size_t index[],
                                const int *ip);
         int nc_put_var1_long  (int ncid, int varid, const size_t index[],
                                const long *lp);
         int nc_put_var1_float (int ncid, int varid, const size_t index[],
                                const float *fp);
         int nc_put_var1_double(int ncid, int varid, const size_t index[],
                                const double *dp);
         int nc_put_var1_ubyte (int ncid, int varid, const size_t index[],
                                const unsigned char *up);
         int nc_put_var1_ushort(int ncid, int varid, const size_t index[],
                                const unsigned short *sp);
         int nc_put_var1_uint  (int ncid, int varid, const size_t index[],
                                const unsigned int *ip);
         int nc_put_var1_longlong(int ncid, int varid, const size_t index[],
                                  const long long *ip);
         int nc_put_var1_ulonglong(int ncid, int varid, const size_t index[],
                                  const unsigned long long *ip);
         int nc_put_var1_string(int ncid, int varid, const size_t index[],
                                const char **ip);
         int nc_put_var1(int ncid, int varid, const size_t *indexp,
                         const void *op);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`index[]`
  The index of the data value to be written. The indices are relative to 0, so for example, the first data value of a two-dimensional variable would have index (0,0). The elements of index must correspond to the variable's dimensions. Hence, if the variable uses the unlimited dimension, the first index would correspond to the unlimited dimension.
`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to the data value to be written. If the type of data values differs from the netCDF variable type, type conversion will occur. See Type Conversion.

### Return Codes

- NC_NOERR No error.
- NC_EHDFERR Error reported by HDF5 layer.
- NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset.
- NC_EINVALCOORDS The specified indices were out of range for the rank of the specified variable. For example, a negative index or an index that is larger than the corresponding dimension length will cause an error.
- NC_ERANGE The specified value is out of the range of values representable by the external data type of the variable. (Does not apply to nc_put_var1() function).
- NC_EINDEFINE The specified netCDF is in define mode rather than data mode.
- NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_put_var1_double to set the (1,2,3) element of the variable named rh to 0.5 in an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, so we want to set the value of rh that corresponds to the second time value, the third lat value, and the fourth lon value:

         #include <netcdf.h>
            ...
         int  status;                          /* error status */
         int  ncid;                            /* netCDF ID */
         int  rh_id;                           /* variable ID */
         static size_t rh_index[] = {1, 2, 3}; /* where to put value */
         static double rh_val = 0.5;           /* value to put */
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_put_var1_double(ncid, rh_id, rh_index, &rh_val);
         if (status != NC_NOERR) handle_error(status);

Next: nc_put_vara_ type, Previous: nc_put_var1_ type, Up: Variables

### 6.22 Write an Entire Variable: nc_put_var_ type

The nc_put_var_ type family of functions write all the values of a variable into a netCDF variable of an open netCDF dataset. This is the simplest interface to use for writing a value in a scalar variable or whenever all the values of a multidimensional variable can all be written at once. The values to be written are associated with the netCDF variable by assuming that the last dimension of the netCDF variable varies fastest in the C interface. The values are converted to the external data type of the variable, if necessary.

Take care when using the simplest forms of this interface with record variables when you don't specify how many records are to be written. If you try to write all the values of a record variable into a netCDF file that has no record data yet (hence has 0 records), nothing will be written. Similarly, if you try to write all of a record variable but there are more records in the file than you assume, more data may be written to the file than you supply, which may result in a segmentation violation.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_put_var() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

### Usage

         int nc_put_var_text  (int ncid, int varid, const char *tp);
         int nc_put_var_uchar (int ncid, int varid, const unsigned char *up);
         int nc_put_var_schar (int ncid, int varid, const signed char *cp);
         int nc_put_var_short (int ncid, int varid, const short *sp);
         int nc_put_var_int   (int ncid, int varid, const int *ip);
         int nc_put_var_long  (int ncid, int varid, const long *lp);
         int nc_put_var_float (int ncid, int varid, const float *fp);
         int nc_put_var_double(int ncid, int varid, const double *dp);
         int nc_put_var_ubyte (int ncid, int varid, const unsigned char *op);
         int nc_put_var_ushort(int ncid, int varid, const unsigned short *op);
         int nc_put_var_uint  (int ncid, int varid, const unsigned int *op);
         int nc_put_var_longlong (int ncid, int varid, const long long *op);
         int nc_put_var_ulonglong(int ncid, int varid, const unsigned long long *op);
         int nc_put_var_string(int ncid, int varid, const char **op);
         int nc_put_var       (int ncid, int varid,  const void *op);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to a block of data values to be written. The order in which the data will be written to the netCDF variable is with the last dimension of the specified variable varying fastest. If the type of data values differs from the netCDF variable type, type conversion will occur. See Type Conversion.

### Return Codes

- NC_NOERR The variable ID is invalid for the specified netCDF dataset.
- NC_EHDFERR Error reported by HDF5 layer.
- NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to nc_put_var() function).
- NC_EINDEFINE The specified netCDF dataset is in define mode rather than data mode.
- NC_BADID The specified netCDF ID does not refer to an open netCDF dataset.
- NC_ENOTVAR Bad variable ID.

### Example

Here is an example using nc_put_var_double to add or change all the values of the variable named rh to 0.5 in an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, and that there are three time values, five lat values, and ten lon values.

         #include <netcdf.h>
            ...
         #define TIMES 3
         #define LATS  5
         #define LONS  10
         int  status;                       /* error status */
         int  ncid;                         /* netCDF ID */
         int  rh_id;                        /* variable ID */
         double rh_vals[TIMES*LATS*LONS];   /* array to hold values */
         int i;
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         for (i = 0; i < TIMES*LATS*LONS; i++)
             rh_vals[i] = 0.5;
         /* write values into netCDF variable */
         status = nc_put_var_double(ncid, rh_id, rh_vals);
         if (status != NC_NOERR) handle_error(status);

Next: nc_put_vars_ type, Previous: nc_put_var_ type, Up: Variables

### 6.23 Write an Array of Values: nc_put_vara_ type

The function nc_put_vara_ type writes values into a netCDF variable of an open netCDF dataset. The part of the netCDF variable to write is specified by giving a corner and a vector of edge lengths that refer to an array section of the netCDF variable. The values to be written are associated with the netCDF variable by assuming that the last dimension of the netCDF variable varies fastest in the C interface. The netCDF dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_put_var() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

### Usage

         int nc_put_vara_ type (int ncid, int varid, const size_t start[],
                                const size_t count[], const type *valuesp);
         int nc_put_vara_text  (int ncid, int varid, const size_t start[],
                                const size_t count[], const char *tp);
         int nc_put_vara_uchar (int ncid, int varid, const size_t start[],
                                const size_t count[], const unsigned char *up);
         int nc_put_vara_schar (int ncid, int varid, const size_t start[],
                                const size_t count[], const signed char *cp);
         int nc_put_vara_short (int ncid, int varid, const size_t start[],
                                const size_t count[], const short *sp);
         int nc_put_vara_int   (int ncid, int varid, const size_t start[],
                                const size_t count[], const int *ip);
         int nc_put_vara_long  (int ncid, int varid, const size_t start[],
                                const size_t count[], const long *lp);
         int nc_put_vara_float (int ncid, int varid, const size_t start[],
                                const size_t count[], const float *fp);
         int nc_put_vara_double(int ncid, int varid, const size_t start[],
                                const size_t count[], const double *dp);
         int nc_put_vara_ubyte (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const unsigned char *op);
         int nc_put_vara_ushort(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const unsigned short *op);
         int nc_put_vara_uint  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const unsigned int *op);
         int nc_put_vara_longlong (int ncid, int varid, const size_t *startp,
                                   const size_t *countp, const long long *op);
         int nc_put_vara_ulonglong(int ncid, int varid, const size_t *startp,
                                   const size_t *countp, const unsigned long long *op);
         int nc_put_vara_string(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const char **op);
         int nc_put_vara       (int ncid, int varid,  const size_t *startp,
                                const size_t *countp, const void *op);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`start`
  A vector of size_t integers specifying the index in the variable where the first of the data values will be written. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The size of start must be the same as the number of dimensions of the specified variable. The elements of start must correspond to the variable's dimensions in order. Hence, if the variable is a record variable, the first index would correspond to the starting record number for writing the data values.
`count`
  A vector of size_t integers specifying the edge lengths along each dimension of the block of data values to be written. To write a single value, for example, specify count as (1, 1, ... , 1). The length of count is the number of dimensions of the specified variable. The elements of count correspond to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to write.

  Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything.

`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to a block of data values to be written. The order in which the data will be written to the netCDF variable is with the last dimension of the specified variable varying fastest. If the type of data values differs from the netCDF variable type, type conversion will occur. See Type Conversion.

### Return Codes

- NC_NOERR No error.
- NC_EHDFERR Error reported by HDF5 layer.
- NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset.
- NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error.
- NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error.
- NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_put_vara() function).
- NC_EINDEFINE The specified netCDF dataset is in define mode rather than data mode.
- NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset.
- NC_ECHAR Attempt to convert to or from char.
- NC_ENOMEM Out of memory.
- NC_EBADTYPE Bad type.

### Example

Here is an example using nc_put_vara_double to add or change all the values of the variable named rh to 0.5 in an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, and that there are three time values, five lat values, and ten lon values.

         #include <netcdf.h>
            ...
         #define TIMES 3
         #define LATS  5
         #define LONS  10
         int  status;                       /* error status */
         int  ncid;                         /* netCDF ID */
         int  rh_id;                        /* variable ID */
         static size_t start[] = {0, 0, 0}; /* start at first value */
         static size_t count[] = {TIMES, LATS, LONS};
         double rh_vals[TIMES*LATS*LONS];   /* array to hold values */
         int i;
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         for (i = 0; i < TIMES*LATS*LONS; i++)
             rh_vals[i] = 0.5;
         /* write values into netCDF variable */
         status = nc_put_vara_double(ncid, rh_id, start, count, rh_vals);
         if (status != NC_NOERR) handle_error(status);

Next: nc_put_varm_ type, Previous: nc_put_vara_ type, Up: Variables

### 6.24 Write a Subsampled Array of Values: nc_put_vars_ type

Each member of the family of functions nc_put_vars_ type writes a subsampled (strided) array section of values into a netCDF variable of an open netCDF dataset. The subsampled array section is specified by giving a corner, a vector of counts, and a stride vector. The netCDF dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_put_vars() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

### Usage

         int nc_put_vars_text  (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const char *tp);
         int nc_put_vars_uchar (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const unsigned char *up);
         int nc_put_vars_schar (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const signed char *cp);
         int nc_put_vars_short (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const short *sp);
         int nc_put_vars_int   (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const int *ip);
         int nc_put_vars_long  (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const long *lp);
         int nc_put_vars_float (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const float *fp);
         int nc_put_vars_double(int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const double *dp);
         int nc_put_vars_ubyte (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const unsigned char *op);
         int nc_put_vars_ushort(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const unsigned short *op);
         int nc_put_vars_uint  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const unsigned int *op);
         int nc_put_vars_longlong (int ncid, int varid, const size_t *startp,
                                   const size_t *countp, const ptrdiff_t *stridep,
                                   const long long *op);
         int nc_put_vars_ulonglong(int ncid, int varid, const size_t *startp,
                                   const size_t *countp, const ptrdiff_t *stridep,
                                   const unsigned long long *op);
         int nc_put_vars_string(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const char **op);
         int nc_put_vars       (int ncid, int varid,  const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const void *op);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`start`
  A vector of size_t integers specifying the index in the variable where the first of the data values will be written. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The elements of start correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first index corresponds to the starting record number for writing the data values.
`count`
  A vector of size_t integers specifying the number of indices selected along each dimension. To write a single value, for example, specify count as (1, 1, ... , 1). The elements of count correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to write.

  Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything.

`stride`
  A vector of ptrdiff_t integers that specifies the sampling interval along each dimension of the netCDF variable. The elements of the stride vector correspond, in order, to the netCDF variable's dimensions (stride[0] gives the sampling interval along the most slowly varying dimension of the netCDF variable). Sampling intervals are specified in type-independent units of elements (a value of 1 selects consecutive elements of the netCDF variable along the corresponding dimension, a value of 2 selects every other element, etc.). A NULL stride argument is treated as (1, 1, ... , 1).
`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to a block of data values to be written. The order in which the data will be written to the netCDF variable is with the last dimension of the specified variable varying fastest. If the type of data values differs from the netCDF variable type, type conversion will occur. See Type Conversion.

### Return Codes

- NC_NOERR No error.
- NC_EHDFERR Error reported by HDF5 layer.
- NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset.
- NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error.
- NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error.
- NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_put_vars() function).
- NC_EINDEFINE The specified netCDF dataset is in define mode rather than data mode.
- NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset.
- NC_ECHAR Attempt to convert to or from char.
- NC_ENOMEM Out of memory.
- NC_EBADTYPE Bad type.

### Example

Here is an example of using nc_put_vars_float to write – from an internal array – every other point of a netCDF variable named rh which is described by the C declaration float rh[4][6] (note the size of the dimensions):

         #include <netcdf.h>
            ...
         #define NDIM 2                /* rank of netCDF variable */
         int ncid;                     /* netCDF ID */
         int status;                   /* error status */
         int rhid;                     /* variable ID */
         static size_t start[NDIM]     /* netCDF variable start point: */
                          = {0, 0};    /* first element */
         static size_t count[NDIM]     /* size of internal array: entire */
                            = {2, 3};  /* (subsampled) netCDF variable */
         static ptrdiff_t stride[NDIM] /* variable subsampling intervals: */
                          = {2, 2};    /* access every other netCDF element */
         float rh[2][3];               /* note subsampled sizes for */
                                       /* netCDF variable dimensions */
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid(ncid, "rh", &rhid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_put_vars_float(ncid, rhid, start, count, stride, rh);
         if (status != NC_NOERR) handle_error(status);

Next: nc_get_var1_ type, Previous: nc_put_vars_ type, Up: Variables

### 6.25 Write a Mapped Array of Values: nc_put_varm_ type

The nc_put_varm_ type family of functions writes a mapped array section of values into a netCDF variable of an open netCDF dataset. The mapped array section is specified by giving a corner, a vector of counts, a stride vector, and an index mapping vector. The index mapping vector is a vector of integers that specifies the mapping between the dimensions of a netCDF variable and the in-memory structure of the internal data array. No assumptions are made about the ordering or length of the dimensions of the data array. The netCDF dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_put_varm() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

### Usage

         int nc_put_varm_text  (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], const char *tp);
         int nc_put_varm_uchar (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], const unsigned char *up);
         int nc_put_varm_schar (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], const signed char *cp);
         int nc_put_varm_short (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], const short *sp);
         int nc_put_varm_int   (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], const int *ip);
         int nc_put_varm_long  (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], const long *lp);
         int nc_put_varm_float (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], const float *fp);
         int nc_put_varm_double(int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], const double *dp);
         int nc_put_varm_ubyte (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t * imapp, const unsigned char *op);
         int nc_put_varm_ushort(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t * imapp, const unsigned short *op);
         int nc_put_varm_uint  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t * imapp, const unsigned int *op);
         int nc_put_varm_longlong (int ncid, int varid, const size_t *startp,
                                   const size_t *countp, const ptrdiff_t *stridep,
                                   const ptrdiff_t * imapp, const long long *op);
         int nc_put_varm_ulonglong(int ncid, int varid, const size_t *startp,
                                   const size_t *countp, const ptrdiff_t *stridep,
                                   const ptrdiff_t * imapp, const unsigned long long *op);
         int nc_put_varm_string(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t * imapp, const char **op);
         int nc_put_varm       (int ncid, int varid,  const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, const void *op);
         n

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`start`
  A vector of size_t integers specifying the index in the variable where the first of the data values will be written. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The elements of start correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first index corresponds to the starting record number for writing the data values.
`count`
  A vector of size_t integers specifying the number of indices selected along each dimension. To write a single value, for example, specify count as (1, 1, ... , 1). The elements of count correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to write.

  Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything.

`stride`
  A vector of ptrdiff_t integers that specifies the sampling interval along each dimension of the netCDF variable. The elements of the stride vector correspond, in order, to the netCDF variable's dimensions (stride[0] gives the sampling interval along the most slowly varying dimension of the netCDF variable). Sampling intervals are specified in type-independent units of elements (a value of 1 selects consecutive elements of the netCDF variable along the corresponding dimension, a value of 2 selects every other element, etc.). A NULL stride argument is treated as (1, 1, ... , 1).
`imap`
  A vector of ptrdiff_t integers that specifies the mapping between the dimensions of a netCDF variable and the in-memory structure of the internal data array. The elements of the index mapping vector correspond, in order, to the netCDF variable's dimensions (imap[0] gives the distance between elements of the internal array corresponding to the most slowly varying dimension of the netCDF variable). Distances between elements are specified in type-independent units of elements (the distance between internal elements that occupy adjacent memory locations is 1 and not the element's byte-length as in netCDF 2). A NULL argument means the memory-resident values have the same structure as the associated netCDF variable.
`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to the location used for computing where the data values will be found; the data should be of the type appropriate for the function called. If the type of data values differs from the netCDF variable type, type conversion will occur. See Type Conversion.

### Return Codes

- NC_NOERR No error.
- NC_EHDFERR Error reported by HDF5 layer.
- NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset.
- NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error.
- NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error.
- NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_put_vars() function).
- NC_EINDEFINE The specified netCDF dataset is in define mode rather than data mode.
- NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset.
- NC_ECHAR Attempt to convert to or from char.
- NC_ENOMEM Out of memory.

### Example

The following imap vector maps in the trivial way a 4x3x2 netCDF variable and an internal array of the same shape:

         float a[4][3][2];       /* same shape as netCDF variable */
         int   imap[3] = {6, 2, 1};
                                 /* netCDF dimension       inter-element distance */
                                 /* ----------------       ---------------------- */
                                 /* most rapidly varying       1                  */
                                 /* intermediate               2 (=imap[2]*2)     */
                                 /* most slowly varying        6 (=imap[1]*3)     */

Using the imap vector above with nc_put_varm_float obtains the same result as simply using nc_put_var_float.

Here is an example of using nc_put_varm_float to write – from a transposed, internal array – a netCDF variable named rh which is described by the C declaration float rh[6][4] (note the size and order of the dimensions):

         #include <netcdf.h>
            ...
         #define NDIM 2               /* rank of netCDF variable */
         int ncid;                    /* netCDF ID */
         int status;                  /* error status */
         int rhid;                    /* variable ID */
         static size_t start[NDIM]    /* netCDF variable start point: */
                          = {0, 0};   /* first element */
         static size_t count[NDIM]    /* size of internal array: entire netCDF */
                          = {6, 4};   /* variable; order corresponds to netCDF */
                                      /* variable -- not internal array */
         static ptrdiff_t stride[NDIM]/* variable subsampling intervals: */
                          = {1, 1};   /* sample every netCDF element */
         static ptrdiff_t imap[NDIM]  /* internal array inter-element distances; */
                          = {1, 6};   /* would be {4, 1} if not transposing */
         float rh[4][6];              /* note transposition of netCDF variable */
                                      /* dimensions */
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid(ncid, "rh", &rhid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_put_varm_float(ncid, rhid, start, count, stride, imap, rh);
         if (status != NC_NOERR) handle_error(status);

Here is another example of using nc_put_varm_float to write – from a transposed, internal array – a subsample of the same netCDF variable, by writing every other point of the netCDF variable:

         #include <netcdf.h>
            ...
         #define NDIM 2                /* rank of netCDF variable */
         int ncid;                     /* netCDF ID */
         int status;                   /* error status */
         int rhid;                     /* variable ID */
         static size_t start[NDIM]     /* netCDF variable start point: */
                          = {0, 0};    /* first element */
         static size_t count[NDIM]     /* size of internal array: entire */
                            = {3, 2};  /* (subsampled) netCDF variable; order of */
                                       /* dimensions corresponds to netCDF */
                                       /* variable -- not internal array */
         static ptrdiff_t stride[NDIM] /* variable subsampling intervals: */
                          = {2, 2};    /* sample every other netCDF element */
         static ptrdiff_t imap[NDIM]   /* internal array inter-element distances; */
                          = {1, 3};    /* would be {2, 1} if not transposing */
         float rh[2][3];               /* note transposition of (subsampled) */
                                       /* netCDF variable dimensions */
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid(ncid, "rh", &rhid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_put_varm_float(ncid, rhid, start, count, stride, imap, rh);
         if (status != NC_NOERR) handle_error(status);

Next: nc_get_var_ type, Previous: nc_put_varm_ type, Up: Variables

### 6.26 Read a Single Data Value: nc_get_var1_ type

The functions nc_get_var1_ type get a single data value from a variable of an open netCDF dataset that is in data mode. Inputs are the netCDF ID, the variable ID, a multidimensional index that specifies which value to get, and the address of a location into which the data value will be read. The value is converted from the external data type of the variable, if necessary.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_get_var1() function will read a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

### Usage

         int nc_get_var1_text  (int ncid, int varid, const size_t index[],
                                char *tp);
         int nc_get_var1_uchar (int ncid, int varid, const size_t index[],
                                unsigned char *up);
         int nc_get_var1_schar (int ncid, int varid, const size_t index[],
                                signed char *cp);
         int nc_get_var1_short (int ncid, int varid, const size_t index[],
                                short *sp);
         int nc_get_var1_int   (int ncid, int varid, const size_t index[],
                                int *ip);
         int nc_get_var1_long  (int ncid, int varid, const size_t index[],
                                long *lp);
         int nc_get_var1_float (int ncid, int varid, const size_t index[],
                                float *fp);
         int nc_get_var1_double(int ncid, int varid, const size_t index[],
                                double *dp);
         int nc_get_var1_ubyte (int ncid, int varid, const size_t *indexp,
                                unsigned char *ip);
         int nc_get_var1_ushort(int ncid, int varid, const size_t *indexp,
                                unsigned short *ip);
         int nc_get_var1_uint  (int ncid, int varid, const size_t *indexp,
                                unsigned int *ip);
         int nc_get_var1_longlong (int ncid, int varid, const size_t *indexp,
                                   long long *ip);
         int nc_get_var1_ulonglong(int ncid, int varid, const size_t *indexp,
                                   unsigned long long *ip);
         int nc_get_var1_string(int ncid, int varid, const size_t *indexp,
                                char **ip);
         int nc_get_var1       (int ncid, int varid,  const size_t *indexp,
                                void *ip);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`index[]`
  The index of the data value to be read. The indices are relative to 0, so for example, the first data value of a two-dimensional variable would have index (0,0). The elements of index must correspond to the variable's dimensions. Hence, if the variable is a record variable, the first index is the record number.
`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to the location into which the data value is read. If the type of data value differs from the netCDF variable type, type conversion will occur. See Type Conversion.

### Return Codes

- NC_NOERR No error.
- NC_EHDFERR Error reported by HDF5 layer.
- NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset.
- NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error.
- NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error.
- NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_put_vars() function).
- NC_EINDEFINE The specified netCDF is in define mode rather than data mode.
- NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset.
- NC_ECHAR Attempt to convert to or from char.
- NC_ENOMEM Out of memory.

### Example

Here is an example using nc_get_var1_double to get the (1,2,3) element of the variable named rh in an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, so we want to get the value of rh that corresponds to the second time value, the third lat value, and the fourth lon value:

         #include <netcdf.h>
            ...
         int  status;                           /* error status */
         int ncid;                              /* netCDF ID */
         int rh_id;                             /* variable ID */
         static size_t rh_index[] = {1, 2, 3};  /* where to get value from */
         double rh_val;                         /* where to put it */
            ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_get_var1_double(ncid, rh_id, rh_index, &rh_val);
         if (status != NC_NOERR) handle_error(status);

Next: nc_get_vara_ type, Previous: nc_get_var1_ type, Up: Variables

### 6.27 Read an Entire Variable nc_get_var_ type

The members of the nc_get_var_ type family of functions read all the values from a netCDF variable of an open netCDF dataset. This is the simplest interface to use for reading the value of a scalar variable or when all the values of a multidimensional variable can be read at once. The values are read into consecutive locations with the last dimension varying fastest. The netCDF dataset must be in data mode.

Take care when using the simplest forms of this interface with record variables when you don't specify how many records are to be read. If you try to read all the values of a record variable into an array but there are more records in the file than you assume, more data will be read than you expect, which may cause a segmentation violation.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_get_var() function will read a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

### Usage

         int nc_get_var_text  (int ncid, int varid, char *tp);
         int nc_get_var_uchar (int ncid, int varid, unsigned char *up);
         int nc_get_var_schar (int ncid, int varid, signed char *cp);
         int nc_get_var_short (int ncid, int varid, short *sp);
         int nc_get_var_int   (int ncid, int varid, int *ip);
         int nc_get_var_long  (int ncid, int varid, long *lp);
         int nc_get_var_float (int ncid, int varid, float *fp);
         int nc_get_var_double(int ncid, int varid, double *dp);
         int nc_get_var_ubyte (int ncid, int varid, unsigned char *ip);
         int nc_get_var_ushort(int ncid, int varid, unsigned short *ip);
         int nc_get_var_uint  (int ncid, int varid, unsigned int *ip);
         int nc_get_var_longlong (int ncid, int varid, long long *ip);
         int nc_get_var_ulonglong(int ncid, int varid, unsigned long long *ip);
         int nc_get_var_string(int ncid, int varid, char **ip);
         int nc_get_var       (int ncid, int varid,  void *ip);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to the location into which the data value is read. If the type of data value differs from the netCDF variable type, type conversion will occur. See Type Conversion.

### Return Codes

- NC_NOERR No error.
- NC_EHDFERR Error reported by HDF5 layer.
- NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset.
- NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error.
- NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error.
- NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_put_vars() function).
- NC_EINDEFINE The specified netCDF is in define mode rather than data mode.
- NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset.
- NC_ECHAR Attempt to convert to or from char.
- NC_ENOMEM Out of memory.

### Example

Here is an example using nc_get_var_double to read all the values of the variable named rh from an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, and that there are three time values, five lat values, and ten lon values.

         #include <netcdf.h>
            ...
         #define TIMES 3
         #define LATS 5
         #define LONS 10
         int  status;                       /* error status */
         int ncid;                          /* netCDF ID */
         int rh_id;                         /* variable ID */
         double rh_vals[TIMES*LATS*LONS];   /* array to hold values */
            ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         /* read values from netCDF variable */
         status = nc_get_var_double(ncid, rh_id, rh_vals);
         if (status != NC_NOERR) handle_error(status);

Next: nc_get_vars_ type, Previous: nc_get_var_ type, Up: Variables

### 6.28 Read an Array of Values: nc_get_vara_ type

The members of the nc_get_vara_ type family of functions read an array of values from a netCDF variable of an open netCDF dataset. The array is specified by giving a corner and a vector of edge lengths. The values are read into consecutive locations with the last dimension varying fastest. The netCDF dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_get_vara() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

### Usage

         int nc_get_vara_text  (int ncid, int varid, const size_t start[],
                                const size_t count[], char *tp);
         int nc_get_vara_uchar (int ncid, int varid, const size_t start[],
                                const size_t count[], unsigned char *up);
         int nc_get_vara_schar (int ncid, int varid, const size_t start[],
                                const size_t count[], signed char *cp);
         int nc_get_vara_short (int ncid, int varid, const size_t start[],
                                const size_t count[], short *sp);
         int nc_get_vara_int   (int ncid, int varid, const size_t start[],
                                const size_t count[], int *ip);
         int nc_get_vara_long  (int ncid, int varid, const size_t start[],
                                const size_t count[], long *lp);
         int nc_get_vara_float (int ncid, int varid, const size_t start[],
                                const size_t count[], float *fp);
         int nc_get_vara_double(int ncid, int varid, const size_t start[],
                                const size_t count[], double *dp);
         int nc_get_vara_ubyte (int ncid, int varid, const size_t *startp,
                                const size_t *countp, unsigned char *ip);
         int nc_get_vara_ushort(int ncid, int varid, const size_t *startp,
                                const size_t *countp, unsigned short *ip);
         int nc_get_vara_uint  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, unsigned int *ip);
         int nc_get_vara_longlong(int ncid, int varid, const size_t *startp,
                                  const size_t *countp, long long *ip);
         int nc_get_vara_ulonglong(int ncid, int varid, const size_t *startp,
                                   const size_t *countp, unsigned long long *ip);
         int nc_get_vara_string(int ncid, int varid, const size_t *startp,
                                const size_t *countp, char **ip);
         int nc_get_vara       (int ncid, int varid, const size_t start[],
                                const size_t count[], void *ip);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`start`
  A vector of size_t integers specifying the index in the variable where the first of the data values will be read. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The length of start must be the same as the number of dimensions of the specified variable. The elements of start correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first index would correspond to the starting record number for reading the data values.
`count`
  A vector of size_t integers specifying the edge lengths along each dimension of the block of data values to be read. To read a single value, for example, specify count as (1, 1, ... , 1). The length of count is the number of dimensions of the specified variable. The elements of count correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to read.

  Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything.

`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to the location into which the data value is read. If the type of data value differs from the netCDF variable type, type conversion will occur. See Type Conversion.

### Return Codes

- NC_NOERR No error.
- NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset.
- NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index or an index that is larger than the corresponding dimension length will cause an error.
- NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error.
- NC_ERANGE One or more of the values are out of the range of values representable by the desired type. (Does not apply to nc_get_vara() function).
- NC_EINDEFINE The specified netCDF is in define mode rather than data mode.
- NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_get_vara_double to read all the values of the variable named rh from an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, and that there are three time values, five lat values, and ten lon values.

         #include <netcdf.h>
            ...
         #define TIMES 3
          #define LATS 5
         #define LONS 10
         int  status;                       /* error status */
         int ncid;                          /* netCDF ID */
         int rh_id;                         /* variable ID */
         static size_t start[] = {0, 0, 0}; /* start at first value */
         static size_t count[] = {TIMES, LATS, LONS};
         double rh_vals[TIMES*LATS*LONS];   /* array to hold values */
            ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         /* read values from netCDF variable */
         status = nc_get_vara_double(ncid, rh_id, start, count, rh_vals);
         if (status != NC_NOERR) handle_error(status);

Next: nc_get_varm_ type, Previous: nc_get_vara_ type, Up: Variables

### 6.29 Read a Subsampled Array of Values: nc_get_vars_ type

The nc_get_vars_ type family of functions read a subsampled (strided) array section of values from a netCDF variable of an open netCDF dataset. The subsampled array section is specified by giving a corner, a vector of edge lengths, and a stride vector. The values are read with the last dimension of the netCDF variable varying fastest. The netCDF dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_get_vars() function will read a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

### Usage

         int nc_get_vars_text  (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                char *tp);
         int nc_get_vars_uchar (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                unsigned char *up);
         int nc_get_vars_schar (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                signed char *cp);
         int nc_get_vars_short (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                short *sp);
         int nc_get_vars_int   (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                int *ip);
         int nc_get_vars_long  (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                long *lp);
         int nc_get_vars_float (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                float *fp);
         int nc_get_vars_double(int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                double *dp)
         int nc_get_vars_ubyte (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                unsigned char *ip);
         int nc_get_vars_ushort(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                unsigned short *ip);
         int nc_get_vars_uint  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                unsigned int *ip);
         int nc_get_vars_longlong (int ncid, int varid, const size_t *startp,
                                   const size_t *countp, const ptrdiff_t *stridep,
                                   long long *ip);
         int nc_get_vars_ulonglong(int ncid, int varid, const size_t *startp,
                                   const size_t *countp, const ptrdiff_t *stridep,
                                   unsigned long long *ip);
         int nc_get_vars_string(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                char **ip);
         int nc_get_vars       (int ncid, int varid,  const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                void *ip);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`start`
  A vector of size_t integers specifying the index in the variable where the first of the data values will be read. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The elements of start correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first index corresponds to the starting record number for reading the data values.
`count`
  A vector of size_t integers specifying the number of indices selected along each dimension. To read a single value, for example, specify count as (1, 1, ... , 1). The elements of count correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to read.

  Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything.

`stride`
  A vector of ptrdiff_t integers specifying, for each dimension, the interval between selected indices. The elements of the stride vector correspond, in order, to the variable's dimensions. A value of 1 accesses adjacent values of the netCDF variable in the corresponding dimension; a value of 2 accesses every other value of the netCDF variable in the corresponding dimension; and so on. A NULL stride argument is treated as (1, 1, ... , 1).
`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to the location into which the data value is read. If the type of data value differs from the netCDF variable type, type conversion will occur. See Type Conversion.

### Return Codes

- NC_NOERR No error.
- NC_EHDFERR Error reported by HDF5 layer.
- NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset.
- NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error.
- NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error.
- NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_get_vars() function).
- NC_EINDEFINE The specified netCDF is in define mode rather than data mode.
- NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset.
- NC_ECHAR Attempt to convert to or from char.
- NC_ENOMEM Out of memory.

### Example

Here is an example that uses nc_get_vars_double to read every other value in each dimension of the variable named rh from an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, and that there are three time values, five lat values, and ten lon values.

         #include <netcdf.h>
            ...
         #define TIMES 3
         #define LATS  5
         #define LONS 10
         int  status;                          /* error status */
         int ncid;                             /* netCDF ID */
         int rh_id;                            /* variable ID */
         static size_t start[] = {0, 0, 0};    /* start at first value */
         static size_t count[] = {TIMES, LATS, LONS};
         static ptrdiff_t stride[] = {2, 2, 2};/* every other value */
         double data[TIMES][LATS][LONS];       /* array to hold values */
          ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
          ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
          ...
         /* read subsampled values from netCDF variable into array */
         status = nc_get_vars_double(ncid, rh_id, start, count, stride,
                                     &data[0][0][0]);
         if (status != NC_NOERR) handle_error(status);
          ...

Next: Strings, Previous: nc_get_vars_ type, Up: Variables

### 6.30 Read a Mapped Array of Values: nc_get_varm_ type

The nc_get_varm_ type family of functions reads a mapped array section of values from a netCDF variable of an open netCDF dataset. The mapped array section is specified by giving a corner, a vector of edge lengths, a stride vector, and an index mapping vector. The index mapping vector is a vector of integers that specifies the mapping between the dimensions of a netCDF variable and the in-memory structure of the internal data array. No assumptions are made about the ordering or length of the dimensions of the data array. The netCDF dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_get_varm() function will read a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

### Usage

         int nc_get_varm_text  (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], char *tp);
         int nc_get_varm_uchar (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], unsigned char *up);
         int nc_get_varm_schar (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], signed char *cp);
         int nc_get_varm_short (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], short *sp);
         int nc_get_varm_int   (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], int *ip);
         int nc_get_varm_long  (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], long *lp);
         int nc_get_varm_float (int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], float *fp);
         int nc_get_varm_double(int ncid, int varid, const size_t start[],
                                const size_t count[], const ptrdiff_t stride[],
                                const ptrdiff_t imap[], double *dp);
         int nc_get_varm_ubyte (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t * imapp, unsigned char *ip);
         int nc_get_varm_ushort(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t * imapp, unsigned short *ip);
         int nc_get_varm_uint  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t * imapp, unsigned int *ip);
         int nc_get_varm_longlong (int ncid, int varid, const size_t *startp,
                                   const size_t *countp, const ptrdiff_t *stridep,
                                   const ptrdiff_t * imapp, long long *ip);
         int nc_get_varm_ulonglong(int ncid, int varid, const size_t *startp,
                                   const size_t *countp, const ptrdiff_t *stridep,
                                   const ptrdiff_t * imapp, unsigned long long *ip);
         int nc_get_varm_string(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t * imapp, char **ip);
         int nc_get_varm       (int ncid, int varid,  const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, void *ip);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID.
`start`
  A vector of size_t integers specifying the index in the variable where the first of the data values will be read. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The elements of start correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first index corresponds to the starting record number for reading the data values.
`count`
  A vector of size_t integers specifying the number of indices selected along each dimension. To read a single value, for example, specify count as (1, 1, ... , 1). The elements of count correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to read.

  Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything.

`stride`
  A vector of ptrdiff_t integers specifying, for each dimension, the interval between selected indices. The elements of the stride vector correspond, in order, to the variable's dimensions. A value of 1 accesses adjacent values of the netCDF variable in the corresponding dimension; a value of 2 accesses every other value of the netCDF variable in the corresponding dimension; and so on. A NULL stride argument is treated as (1, 1, ... , 1).
`imap`
  A vector of integers that specifies the mapping between the dimensions of a netCDF variable and the in-memory structure of the internal data array. imap[0] gives the distance between elements of the internal array corresponding to the most slowly varying dimension of the netCDF variable. imap[n-1] (where n is the rank of the netCDF variable) gives the distance between elements of the internal array corresponding to the most rapidly varying dimension of the netCDF variable. Intervening imap elements correspond to other dimensions of the netCDF variable in the obvious way. Distances between elements are specified in type-independent units of elements (the distance between internal elements that occupy adjacent memory locations is 1 and not the element's byte-length as in netCDF 2).
`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to the location used for computing where the data values are read; the data should be of the type appropriate for the function called. If the type of data value differs from the netCDF variable type, type conversion will occur. See Type Conversion.

### Return Codes

- NC_NOERR No error.
- NC_EHDFERR Error reported by HDF5 layer.
- NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset.
- NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error.
- NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error.
- NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_get_vars() function).
- NC_EINDEFINE The specified netCDF is in define mode rather than data mode.
- NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset.
- NC_ECHAR Attempt to convert to or from char.
- NC_ENOMEM Out of memory.

### Example

The following imap vector maps in the trivial way a 4x3x2 netCDF variable and an internal array of the same shape:

         float a[4][3][2];       /* same shape as netCDF variable */
         size_t imap[3] = {6, 2, 1};
                                 /* netCDF dimension       inter-element distance */
                                 /* ----------------       ---------------------- */
                                 /* most rapidly varying       1                  */
                                 /* intermediate               2 (=imap[2]*2)     */
                                 /* most slowly varying        6 (=imap[1]*3)     */

Using the imap vector above with nc_get_varm_float obtains the same result as simply using nc_get_var_float.

Here is an example of using nc_get_varm_float to transpose a netCDF variable named rh which is described by the C declaration float rh[6][4] (note the size and order of the dimensions):

         #include <netcdf.h>
            ...
         #define NDIM 2                /* rank of netCDF variable */
         int ncid;                     /* netCDF ID */
         int status;                   /* error status */
         int rhid;                     /* variable ID */
         static size_t start[NDIM]     /* netCDF variable start point: */
                          = {0, 0};    /* first element */
         static size_t count[NDIM]     /* size of internal array: entire netCDF */
                          = {6, 4};    /* variable; order corresponds to netCDF */
                                       /* variable -- not internal array */
         static ptrdiff_t stride[NDIM] /* variable subsampling intervals: */
                          = {1, 1};    /* sample every netCDF element */
         static ptrdiff_t imap[NDIM]   /* internal array inter-element distances; */
                          = {1, 6};    /* would be {4, 1} if not transposing */
         float rh[4][6];               /* note transposition of netCDF variable */
                                       /* dimensions */
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid(ncid, "rh", &rhid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_get_varm_float(ncid, rhid, start, count, stride, imap, rh);
         if (status != NC_NOERR) handle_error(status);

Here is another example of using nc_get_varm_float to simultaneously transpose and subsample the same netCDF variable, by accessing every other point of the netCDF variable:

         #include <netcdf.h>
            ...
         #define NDIM 2               /* rank of netCDF variable */
         int ncid;                    /* netCDF ID */
         int status;                  /* error status */
         int rhid;                    /* variable ID */
         static size_t start[NDIM]    /* netCDF variable start point: */
                          = {0, 0};   /* first element */
         static size_t count[NDIM]    /* size of internal array: entire */
                            = {3, 2}; /* (subsampled) netCDF variable; order of */
                                      /* dimensions corresponds to netCDF */
                                      /* variable -- not internal array */
         static ptrdiff_t stride[NDIM]/* variable subsampling intervals: */
                          = {2, 2};   /* sample every other netCDF element */
         static ptrdiff_t imap[NDIM]  /* internal array inter-element distances; */
                          = {1, 3};   /* would be {2, 1} if not transposing */
         float rh[2][3];              /* note transposition of (subsampled) */
                                      /* netCDF variable dimensions */
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid(ncid, "rh", &rhid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_get_varm_float(ncid, rhid, start, count, stride, imap, rh);
         if (status != NC_NOERR) handle_error(status);

Next: nc_free_string, Previous: nc_get_varm_ type, Up: Variables

### 6.31 Reading and Writing Character String Values

Prior to version 4.0, strings could only be stored as simple arrays of characters. Users may still wish to store strings this way, as it ensures maximum compatibility with other software.

Starting in netCDF-4.0, the atomic string type allows a new way to store strings, as a variable length array in the underlying HDF5 layer. This allows arrays of strings to be stored compactly.

For more information of classic models strings Classic Strings. For more information on the netCDF-4.0 string type Arrays of Strings.

Next: Arrays of Strings, Previous: Strings, Up: Strings

#### 6.31.1 Reading and Writing Character String Values in the Classic Model

Character strings are not a primitive netCDF external data type, in part because FORTRAN does not support the abstraction of variable-length character strings (the FORTRAN LEN function returns the static length of a character string, not its dynamic length). As a result, a character string cannot be written or read as a single object in the netCDF interface. Instead, a character string must be treated as an array of characters, and array access must be used to read and write character strings as variable data in netCDF datasets. Furthermore, variable-length strings are not supported by the netCDF interface except by convention; for example, you may treat a zero byte as terminating a character string, but you must explicitly specify the length of strings to be read from and written to netCDF variables.

Character strings as attribute values are easier to use, since the strings are treated as a single unit for access. However, the value of a character-string attribute is still an array of characters with an explicit length that must be specified when the attribute is defined.

When you define a variable that will have character-string values, use a character-position dimension as the most quickly varying dimension for the variable (the last dimension for the variable in C). The length of the character-position dimension will be the maximum string length of any value to be stored in the character-string variable. Space for maximum-length strings will be allocated in the disk representation of character-string variables whether you use the space or not. If two or more variables have the same maximum length, the same character-position dimension may be used in defining the variable shapes.

To write a character-string value into a character-string variable, use either entire variable access or array access. The latter requires that you specify both a corner and a vector of edge lengths. The character-position dimension at the corner should be zero for C. If the length of the string to be written is n, then the vector of edge lengths will specify n in the character-position dimension, and one for all the other dimensions:(1, 1, ... , 1, n).

In C, fixed-length strings may be written to a netCDF dataset without the terminating zero byte, to save space. Variable-length strings should be written with a terminating zero byte so that the intended length of the string can be determined when it is later read.

Here is an example that defines a record variable, tx, for character strings and stores a character-string value into the third record using nc_put_vara_text. In this example, we assume the string variable and data are to be added to an existing netCDF dataset named foo.nc that already has an unlimited record dimension time.

         #include <netcdf.h>
            ...
         int  ncid;            /* netCDF ID */
         int  chid;            /* dimension ID for char positions */
         int  timeid;          /* dimension ID for record dimension */
         int  tx_id;           /* variable ID */
         #define TDIMS 2       /* rank of tx variable */
         int tx_dims[TDIMS];   /* variable shape */
         size_t tx_start[TDIMS];
         size_t tx_count[TDIMS];
         static char tx_val[] =
                 "example string"; /* string to be put */
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
         status = nc_redef(ncid);       /* enter define mode */
         if (status != NC_NOERR) handle_error(status);
            ...
         /* define character-position dimension for strings of max length 40 */
         status = nc_def_dim(ncid, "chid", 40L, &chid);
         if (status != NC_NOERR) handle_error(status);
            ...
         /* define a character-string variable */
         tx_dims[0] = timeid;
         tx_dims[1] = chid;    /* character-position dimension last */
         status = nc_def_var (ncid, "tx", NC_CHAR, TDIMS, tx_dims, &tx_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_enddef(ncid);       /* leave define mode */
         if (status != NC_NOERR) handle_error(status);
            ...
         /* write tx_val into tx netCDF variable in record 3 */
         tx_start[0] = 3;      /* record number to write */
         tx_start[1] = 0;      /* start at beginning of variable */
         tx_count[0] = 1;      /* only write one record */
         tx_count[1] = strlen(tx_val) + 1;  /* number of chars to write */
         status = nc_put_vara_text(ncid, tx_id, tx_start, tx_count, tx_val);
         if (status != NC_NOERR) handle_error(status);

Previous: Classic Strings, Up: Strings

#### 6.31.2 Reading and Writing Arrays of Strings

In netCDF-4, the NC_STRING type is introduced. It can store arrays of strings compactly.

By using the NC_STRING type, arrays of strings (char **) can be read and written to the file.

This allows attributes to hold more than one string. Since attributes are one-dimensional, using the classic model, an attribute could only hold one string, as an array of char. With the NC_STRING type, an array of strings can be stored in one attribute.

When reading data of type NC_STRING, the HDF5 layer will allocate memory to hold the data. It is up to the user to free this memory with the nc_free_string function. See nc_free_string.

            int ncid, varid, i, dimids[NDIMS];
            char *data[DIM_LEN] = {"Let but your honour know",
                               "Whom I believe to be most strait in virtue",
                               "That, in the working of your own affections",
                               "Had time cohered with place or place with wishing",
                               "Or that the resolute acting of your blood",
                               "Could have attain'd the effect of your own purpose",
                               "Whether you had not sometime in your life",
                               "Err'd in this point which now you censure him",
                               "And pull'd the law upon you."};
            char *data_in[DIM_LEN];

            printf("*** testing string attribute...");
            {
               size_t att_len;
               int ndims, nvars, natts, unlimdimid;
               nc_type att_type;

               if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
               if (nc_put_att(ncid, NC_GLOBAL, ATT_NAME, NC_STRING, DIM_LEN, data)) ERR;
               if (nc_inq(ncid, &ndims, &nvars, &natts, &unlimdimid)) ERR;
               if (ndims != 0 || nvars != 0 || natts != 1 || unlimdimid != -1) ERR;
               if (nc_inq_att(ncid, NC_GLOBAL, ATT_NAME, &att_type, &att_len)) ERR;
               if (att_type != NC_STRING || att_len != DIM_LEN) ERR;
               if (nc_close(ncid)) ERR;
               nc_exit();

               /* Check it out. */
               if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;
               if (nc_inq(ncid, &ndims, &nvars, &natts, &unlimdimid)) ERR;
               if (ndims != 0 || nvars != 0 || natts != 1 || unlimdimid != -1) ERR;
               if (nc_inq_att(ncid, NC_GLOBAL, ATT_NAME, &att_type, &att_len)) ERR;
               if (att_type != NC_STRING || att_len != DIM_LEN) ERR;
               if (nc_get_att(ncid, NC_GLOBAL, ATT_NAME, data_in)) ERR;
               for (i=0; i<att_len; i++)
                  if (strcmp(data_in[i], data[i])) ERR;
               if (nc_free_string(att_len, (char **)data_in)) ERR;
               if (nc_close(ncid)) ERR;
               nc_exit();
            }

Next: Fill Values, Previous: Strings, Up: Variables

### 6.32 Releasing Memory for a NC_STRING: nc_free_string

When a STRING is read into user memory from the file, the HDF5 library performs memory allocations for each of the variable length character arrays contained within the STRING structure. This memory must be freed by the user to avoid memory leaks.

This violates the normal netCDF expectation that the user is responsible for all memory allocation. But, with NC_STRING arrays, the underlying HDF5 library allocates the memory for the user, and the user is responsible for deallocating that memory.

To save the user the trouble calling free() on each element of the NC_STRING array (i.e. the array of arrays), the nc_free_string function is provided.

### Usage

         int nc_free_string(size_t len, char **data);

`len`
  The number of character arrays in the array.
`**data`
  The pointer to the data array.

### Return Codes

`NC_NOERR`
  No error.

### Example

               if (nc_get_att(ncid, NC_GLOBAL, ATT_NAME, data_in)) ERR;
               ...
               if (nc_free_string(att_len, (char **)data_in)) ERR;

Next: nc_rename_var, Previous: nc_free_string, Up: Variables

### 6.33 Fill Values

What happens when you try to read a value that was never written in an open netCDF dataset? You might expect that this should always be an error, and that you should get an error message or an error status returned. You do get an error if you try to read data from a netCDF dataset that is not open for reading, if the variable ID is invalid for the specified netCDF dataset, or if the specified indices are not properly within the range defined by the dimension lengths of the specified variable. Otherwise, reading a value that was not written returns a special fill value used to fill in any undefined values when a netCDF variable is first written.

You may ignore fill values and use the entire range of a netCDF external data type, but in this case you should make sure you write all data values before reading them. If you know you will be writing all the data before reading it, you can specify that no prefilling of variables with fill values will occur by calling nc_set_fill before writing. This may provide a significant performance gain for netCDF writes.

The variable attribute _FillValue may be used to specify the fill value for a variable. Their are default fill values for each type, defined in the include file netcdf.h: NC_FILL_CHAR, NC_FILL_BYTE, NC_FILL_SHORT, NC_FILL_INT, NC_FILL_FLOAT, and NC_FILL_DOUBLE.

The netCDF byte and character types have different default fill values. The default fill value for characters is the zero byte, a useful value for detecting the end of variable-length C character strings. If you need a fill value for a byte variable, it is recommended that you explicitly define an appropriate _FillValue attribute, as generic utilities such as ncdump will not assume a default fill value for byte variables.

Type conversion for fill values is identical to type conversion for other values: attempting to convert a value from one type to another type that can't represent the value results in a range error. Such errors may occur on writing or reading values from a larger type (such as double) to a smaller type (such as float), if the fill value for the larger type cannot be represented in the smaller type.

Next: nc_copy_var, Previous: Fill Values, Up: Variables

### 6.34 Rename a Variable: nc_rename_var

The function nc_rename_var changes the name of a netCDF variable in an open netCDF dataset. If the new name is longer than the old name, the netCDF dataset must be in define mode. You cannot rename a variable to have the name of any existing variable.

### Usage

int nc_rename_var(int ncid, int varid, const char* name);

ncid NetCDF ID, from a previous call to nc_open or nc_create.

varid Variable ID.

name New name for the specified variable.

### Errors

nc_rename_var returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

The new name is in use as the name of another variable. The variable ID is invalid for the specified netCDF dataset. The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_rename_var to rename the variable rh to rel_hum in an existing netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int  status;              /* error status */
         int  ncid;                /* netCDF ID */
         int  rh_id;               /* variable ID */
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_redef(ncid);  /* put in define mode to rename variable */
         if (status != NC_NOERR) handle_error(status);
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
         status = nc_rename_var (ncid, rh_id, "rel_hum");
         if (status != NC_NOERR) handle_error(status);
         status = nc_enddef(ncid); /* leave define mode */
         if (status != NC_NOERR) handle_error(status);

Next: nc_var_par_access, Previous: nc_rename_var, Up: Variables

### 6.35 Copy a Variable from One File to Another: nc_copy_var

This function will copy a variable from one file to another.

It works even if the files are different formats, (i.e. classic vs. netCDF-4/HDF5.)

If you're copying into a netcdf-3 file, from a netcdf-4 file, you must be copying a var of one of the six netcdf-3 types. Similarly for the attributes.

### Usage

         nc_copy_var(int ncid_in, int varid_in, int ncid_out)

- ncid_in The file ID for the file that contains the variable to be copied.
- varid_in The variable ID for the variable to be copied.
- ncid_out The file ID for the file where the variable should be copied to.

### Return Codes

- NC_NOERR No error.
- NC_EBADID Bad ncid.
- NC_EBADVAR Bad varid.
- NC_EHDFERR HDF5 layer error.
- NC_ENOMEM Out of memory.
- NC_ERANGE One or more values out of range.

### Example

Previous: nc_copy_var, Up: Variables

### 6.36 Change between Collective and Independent Parallel Access: nc_var_par_access

The function nc_var_par_access changes whether read/write operations on a parallel file system are performed collectively (the default) or independently on the variable. This function can only be called if the file was created with nc_create_par (see nc_create_par) or opened with nc_open_par (see nc_open_par).

Calling this function affects only the open file - information about whether a variable is to be accessed collectively or independently is not written to the data file. Every time you open a file on a parallel file system, all variables default to collective operations. The change a variable to independent lasts only as long as that file is open.

The variable can be changed from collective to independent, and back, as often as desired.

Note that classic and 64-bit offset files are access using the parallel-netcdf library, which does not allow per-variable setting of the parallel access mode. For these files, calling nc_var_par_access sets the access for all of the variables in the file.

### Usage

int nc_var_par_access(int ncid, int varid, int access);

`ncid`
  NetCDF ID, from a previous call to nc_open_par (see nc_open_par) or nc_create_par (see nc_create_par).
`varid`
  Variable ID.
`access`
  NC_INDEPENDENT to set this variable to independent operations.NC_COLLECTIVE to set it to collective operations.

### Return Values

`NC_NOERR`
  No error.

### Example

Here is an example using nc_var_par_access:

         #include <netcdf.h>

             ...
             int ncid, v1id, dimids[NDIMS];
             int data[DIMSIZE*DIMSIZE], j, i, res;
             ...

             /* Create a parallel netcdf-4 file. */
             if ((res = nc_create_par(FILE, NC_NETCDF4|NC_MPIIO, comm, info, &ncid)))
                 BAIL(res);

             /* Create two dimensions. */
             if ((res = nc_def_dim(ncid, "d1", DIMSIZE, dimids)))
                BAIL(res);
             if ((res = nc_def_dim(ncid, "d2", DIMSIZE, &dimids[1])))
                BAIL(res);

             /* Create one var. */
             if ((res = nc_def_var(ncid, "v1", NC_INT, NDIMS, dimids, &v1id)))
                BAIL(res);

             if ((res = nc_enddef(ncid)))
                BAIL(res);

             /* Tell HDF5 to use independent parallel access for this var. */
             if ((res = nc_var_par_access(ncid, v1id, NC_INDEPENDENT)))
                BAIL(res);

             /* Write slabs of phony data. */
             if ((res = nc_put_vara_int(ncid, v1id, start, count,
                                        &data[mpi_rank*QTR_DATA])))
                BAIL(res);

Next: Summary of C Interface, Previous: Variables, Up: Top

## 7 Attributes

Next: nc_put_att_ type, Previous: Attributes, Up: Attributes

### 7.1 Introduction

Attributes may be associated with each netCDF variable to specify such properties as units, special values, maximum and minimum valid values, scaling factors, and offsets. Attributes for a netCDF dataset are defined when the dataset is first created, while the netCDF dataset is in define mode. Additional attributes may be added later by reentering define mode. A netCDF attribute has a netCDF variable to which it is assigned, a name, a type, a length, and a sequence of one or more values. An attribute is designated by its variable ID and name. When an attribute name is not known, it may be designated by its variable ID and number in order to determine its name, using the function nc_inq_attname.

The attributes associated with a variable are typically defined immediately after the variable is created, while still in define mode. The data type, length, and value of an attribute may be changed even when in data mode, as long as the changed attribute requires no more space than the attribute as originally defined.

It is also possible to have attributes that are not associated with any variable. These are called global attributes and are identified by using NC_GLOBAL as a variable pseudo-ID. Global attributes are usually related to the netCDF dataset as a whole and may be used for purposes such as providing a title or processing history for a netCDF dataset.

Operations supported on attributes are:

- Create an attribute, given its variable ID, name, data type, length, and value.
- Get attribute's data type and length from its variable ID and name.
- Get attribute's value from its variable ID and name.
- Copy attribute from one netCDF variable to another.
- Get name of attribute from its number.
- Rename an attribute.
- Delete an attribute.

Next: nc_inq_att Family, Previous: Attributes Introduction, Up: Attributes

### 7.2 Create an Attribute: nc_put_att_ type

The function nc_put_att_ type adds or changes a variable attribute or global attribute of an open netCDF dataset. If this attribute is new, or if the space required to store the attribute is greater than before, the netCDF dataset must be in define mode.

### Usage

With netCDF-4 files, nc_put_att will notice if you are writing a _Fill_Value_ attribute, and will tell the HDF5 layer to use the specified fill value for that variable.

Although it's possible to create attributes of all types, text and double attributes are adequate for most purposes.

Use the nc_put_att function to create attributes of any type, including user-defined types. We recommend using the type safe versions of this function whenever possible.

         int nc_put_att_text      (int ncid, int varid, const char *name,
                                   size_t len, const char *tp);
         int nc_put_att_uchar     (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const unsigned char *up);
         int nc_put_att_schar     (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const signed char *cp);
         int nc_put_att_short     (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const short *sp);
         int nc_put_att_int       (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const int *ip);
         int nc_put_att_long      (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const long *lp);
         int nc_put_att_float     (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const float *fp);
         int nc_put_att_double    (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const double *dp);
         int nc_put_att_ubyte     (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const unsigned char *op);
         int nc_put_att_ushort    (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const unsigned short *op);
         int nc_put_att_uint      (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const unsigned int *op);
         int nc_put_att_longlong  (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const long long *op);
         int nc_put_att_ulonglong (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len,
                                   const unsigned long long *op);
         int nc_put_att_string    (int ncid, int varid, const char *name, size_t len,
                                   const char **op);
         int nc_put_att           (int ncid, int varid, const char *name, nc_type xtype,
                                   size_t len, const void *op);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID of the variable to which the attribute will be assigned or NC_GLOBAL for a global attribute.
`name`
  Attribute name. Attribute name conventions are assumed by some netCDF generic applications, e.g., ‘`units`’ as the name for a string attribute that gives the units for a netCDF variable. For examples of attribute conventions see Attribute Conventions.
`xtype`
  One of the set of predefined netCDF external data types. The type of this parameter, nc_type, is defined in the netCDF header file. The valid netCDF external data types are NC_BYTE, NC_CHAR, NC_SHORT, NC_INT, NC_FLOAT, and NC_DOUBLE. Although it's possible to create attributes of all types, NC_CHAR and NC_DOUBLE attributes are adequate for most purposes.
`len`
  Number of values provided for the attribute.
`tp, up, cp, sp, ip, lp, fp, or dp`
  Pointer to one or more values. If the type of values differs from the netCDF attribute type specified as xtype, type conversion will occur. See Type Conversion.

### Errors

nc_put_att_ type returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The variable ID is invalid for the specified netCDF dataset.
- The specified netCDF type is invalid.
- The specified length is negative.
- The specified open netCDF dataset is in data mode and the specified attribute would expand.
- The specified open netCDF dataset is in data mode and the specified attribute does not already exist.
- The specified netCDF ID does not refer to an open netCDF dataset.
- The number of attributes for this variable exceeds NC_MAX_ATTRS.

### Return Codes

`NC_NOERR`
  No error.
`NC_EINVAL`
  Trying to set global _FillValue. (NetCDF-4 files only).
`NC_ENOTVAR`
  Couldn't find varid.
`NC_EBADTYPE`
  Fill value must be same type as variable. (NetCDF-4 files only).
`NC_ENOMEM`
  Out of memory
`NC_EFILLVALUE`
  Fill values must be written while the file is still in initial define mode, that is, after the file is created, but before it leaves define mode for the first time. NC_EFILLVALUE is returned when the user attempts to set the fill value after it's too late.

### Example

Here is an example using nc_put_att_double to add a variable attribute named valid_range for a netCDF variable named rh and a global attribute named title to an existing netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int  status;                            /* error status */
         int  ncid;                              /* netCDF ID */
         int  rh_id;                             /* variable ID */
         static double rh_range[] = {0.0, 100.0};/* attribute vals */
         static char title[] = "example netCDF dataset";
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_redef(ncid);                /* enter define mode */
         if (status != NC_NOERR) handle_error(status);
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_put_att_double (ncid, rh_id, "valid_range",
                                     NC_DOUBLE, 2, rh_range);
         if (status != NC_NOERR) handle_error(status);
         status = nc_put_att_text (ncid, NC_GLOBAL, "title",
                                   strlen(title), title)
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_enddef(ncid);               /* leave define mode */
         if (status != NC_NOERR) handle_error(status);

Next: nc_get_att_ type, Previous: nc_put_att_ type, Up: Attributes

### 7.3 Get Information about an Attribute: nc_inq_att Family

This family of functions returns information about a netCDF attribute. All but one of these functions require the variable ID and attribute name; the exception is nc_inq_attname. Information about an attribute includes its type, length, name, and number. See the nc_get_att family for getting attribute values.

The function nc_inq_attname gets the name of an attribute, given its variable ID and number. This function is useful in generic applications that need to get the names of all the attributes associated with a variable, since attributes are accessed by name rather than number in all other attribute functions. The number of an attribute is more volatile than the name, since it can change when other attributes of the same variable are deleted. This is why an attribute number is not called an attribute ID.

The function nc_inq_att returns the attribute's type and length. The other functions each return just one item of information about an attribute.

### Usage

         int nc_inq_att    (int ncid, int varid, const char *name,
                            nc_type *xtypep, size_t *lenp);
         int nc_inq_atttype(int ncid, int varid, const char *name,
                            nc_type *xtypep);
         int nc_inq_attlen  (int ncid, int varid, const char *name, size_t *lenp);
         int nc_inq_attname(int ncid, int varid, int attnum, char *name);
         int nc_inq_attid   (int ncid, int varid, const char *name, int *attnump);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID of the attribute's variable, or NC_GLOBAL for a global attribute.
`name`
  Attribute name. For nc_inq_attname, this is a pointer to the location for the returned attribute name.
`xtypep`
  Pointer to location for returned attribute type, one of the set of predefined netCDF external data types. The type of this parameter, nc_type, is defined in the netCDF header file. The valid netCDF external data types are NC_BYTE, NC_CHAR, NC_SHORT, NC_INT, NC_FLOAT, and NC_DOUBLE. If this parameter is given as '0' (a null pointer), no type will be returned so no variable to hold the type needs to be declared.
`lenp`
  Pointer to location for returned number of values currently stored in the attribute. For attributes of type NC_CHAR, you should not assume that this includes a trailing zero byte; it doesn't if the attribute was stored without a trailing zero byte, for example from a FORTRAN program. Before using the value as a C string, make sure it is null-terminated. If this parameter is given as '0' (a null pointer), no length will be returned so no variable to hold this information needs to be declared.
`attnum`
  For nc_inq_attname, attribute number. The attributes for each variable are numbered from 0 (the first attribute) to natts-1, where natts is the number of attributes for the variable, as returned from a call to nc_inq_varnatts.
`attnump`
  For nc_inq_attid, pointer to location for returned attribute number that specifies which attribute this is for this variable (or which global attribute). If you already know the attribute name, knowing its number is not very useful, because accessing information about an attribute requires its name.

### Errors

Each function returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The variable ID is invalid for the specified netCDF dataset.
- The specified attribute does not exist.
- The specified netCDF ID does not refer to an open netCDF dataset.
- For nc_inq_attname, the specified attribute number is negative or more than the number of attributes defined for the specified variable.

### Example

Here is an example using nc_inq_att to find out the type and length of a variable attribute named valid_range for a netCDF variable named rh and a global attribute named title in an existing netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int  status;               /* error status */
         int  ncid;                 /* netCDF ID */
         int  rh_id;                /* variable ID */
         nc_type vr_type, t_type;   /* attribute types */
         size_t  vr_len, t_len;     /* attribute lengths */

            ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_att (ncid, rh_id, "valid_range", &vr_type, &vr_len);
         if (status != NC_NOERR) handle_error(status);
         status = nc_inq_att (ncid, NC_GLOBAL, "title", &t_type, &t_len);
         if (status != NC_NOERR) handle_error(status);

Next: nc_copy_att, Previous: nc_inq_att Family, Up: Attributes

### 7.4 Get Attribute's Values:nc_get_att_ type

Members of the nc_get_att_ type family of functions get the value(s) of a netCDF attribute, given its variable ID and name.

The nc_get_att() functions works for any type of attribute, and must be used to get attributes of user-defined type. We recommend that they type safe versions of this function be used where possible.

### Usage

         int nc_get_att_text      (int ncid, int varid, const char *name, char *tp);
         int nc_get_att_uchar     (int ncid, int varid, const char *name, unsigned char *up);
         int nc_get_att_schar     (int ncid, int varid, const char *name, signed char *cp);
         int nc_get_att_short     (int ncid, int varid, const char *name, short *sp);
         int nc_get_att_int       (int ncid, int varid, const char *name, int *ip);
         int nc_get_att_long      (int ncid, int varid, const char *name, long *lp);
         int nc_get_att_float     (int ncid, int varid, const char *name, float *fp);
         int nc_get_att_double    (int ncid, int varid, const char *name, double *dp);
         int nc_get_att_ubyte     (int ncid, int varid, const char *name, unsigned char *ip);
         int nc_get_att_ushort    (int ncid, int varid, const char *name, unsigned short *ip);
         int nc_get_att_uint      (int ncid, int varid, const char *name, unsigned int *ip);
         int nc_get_att_longlong  (int ncid, int varid, const char *name, long long *ip);
         int nc_get_att_ulonglong (int ncid, int varid, const char *name, unsigned long long *ip);
         int nc_get_att_string    (int ncid, int varid, const char *name, char **ip);
         int nc_get_att           (int ncid, int varid, const char *name, void *ip);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  Variable ID of the attribute's variable, or NC_GLOBAL for a global attribute.
`name`
  Attribute name.
`tp`
`up`
`cp`
`sp`
`ip`
`lp`
`fp`
`dp`
  Pointer to location for returned attribute value(s). All elements of the vector of attribute values are returned, so you must allocate enough space to hold them. For attributes of type NC_CHAR, you should not assume that the returned values include a trailing zero byte; they won't if the attribute was stored without a trailing zero byte, for example from a FORTRAN program. Before using the value as a C string, make sure it is null-terminated. If you don't know how much space to reserve, call nc_inq_attlen first to find out the length of the attribute.

### Errors

nc_get_att_ type returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The variable ID is invalid for the specified netCDF dataset.
- The specified attribute does not exist.
- The specified netCDF ID does not refer to an open netCDF dataset.
- One or more of the attribute values are out of the range of values representable by the desired type.

### Example

Here is an example using nc_get_att_double to determine the values of a variable attribute named valid_range for a netCDF variable named rh and a global attribute named title in an existing netCDF dataset named foo.nc. In this example, it is assumed that we don't know how many values will be returned, but that we do know the types of the attributes. Hence, to allocate enough space to store them, we must first inquire about the length of the attributes.

         #include <netcdf.h>
            ...
         int  status;               /* error status */
         int  ncid;                 /* netCDF ID */
         int  rh_id;                /* variable ID */
         int  vr_len, t_len;        /* attribute lengths */
         double *vr_val;            /* ptr to attribute values */
         char *title;               /* ptr to attribute values */
         extern char *malloc();     /* memory allocator */

            ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         /* find out how much space is needed for attribute values */
         status = nc_inq_attlen (ncid, rh_id, "valid_range", &vr_len);
         if (status != NC_NOERR) handle_error(status);
         status = nc_inq_attlen (ncid, NC_GLOBAL, "title", &t_len);
         if (status != NC_NOERR) handle_error(status);

         /* allocate required space before retrieving values */
         vr_val = (double *) malloc(vr_len * sizeof(double));
         title = (char *) malloc(t_len + 1);  /* + 1 for trailing null */

         /* get attribute values */
         status = nc_get_att_double(ncid, rh_id, "valid_range", vr_val);
         if (status != NC_NOERR) handle_error(status);
         status = nc_get_att_text(ncid, NC_GLOBAL, "title", title);
         if (status != NC_NOERR) handle_error(status);
         title[t_len] = '\0';       /* null terminate */
            ...

Next: nc_rename_att, Previous: nc_get_att_ type, Up: Attributes

### 7.5 Copy Attribute from One NetCDF to Another: nc_copy_att

The function nc_copy_att copies an attribute from one open netCDF dataset to another. It can also be used to copy an attribute from one variable to another within the same netCDF.

If used to copy an attribute of user-defined type, then that user-defined type must already be defined in the target file. In the case of user-defined attributes, enddef/redef is called for ncid_in and ncid_out if they are in define mode. (This is the ensure that all user-defined types are committed to the file(s) before the copy is attempted.)

### Usage

         int nc_copy_att (int ncid_in, int varid_in, const char *name,
                          int ncid_out, int varid_out);

`ncid_in`
  The netCDF ID of an input netCDF dataset from which the attribute will be copied, from a previous call to nc_open or nc_create.
`varid_in`
  ID of the variable in the input netCDF dataset from which the attribute will be copied, or NC_GLOBAL for a global attribute.
`name`
  Name of the attribute in the input netCDF dataset to be copied.
`ncid_out`
  The netCDF ID of the output netCDF dataset to which the attribute will be copied, from a previous call to nc_open or nc_create. It is permissible for the input and output netCDF IDs to be the same. The output netCDF dataset should be in define mode if the attribute to be copied does not already exist for the target variable, or if it would cause an existing target attribute to grow.
`varid_out`
  ID of the variable in the output netCDF dataset to which the attribute will be copied, or NC_GLOBAL to copy to a global attribute.

### Errors

nc_copy_att returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The input or output variable ID is invalid for the specified netCDF dataset.
- The specified attribute does not exist.
- The output netCDF is not in define mode and the attribute is new for the output dataset is larger than the existing attribute.
- The input or output netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_copy_att to copy the variable attribute units from the variable rh in an existing netCDF dataset named foo.nc to the variable avgrh in another existing netCDF dataset named bar.nc, assuming that the variable avgrh already exists, but does not yet have a units attribute:

         #include <netcdf.h>
            ...
         int  status;               /* error status */
         int  ncid1, ncid2;         /* netCDF IDs */
         int  rh_id, avgrh_id;      /* variable IDs */
            ...
         status = nc_open("foo.nc", NC_NOWRITE, ncid1);
         if (status != NC_NOERR) handle_error(status);
         status = nc_open("bar.nc", NC_WRITE, ncid2);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid1, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
         status = nc_inq_varid (ncid2, "avgrh", &avgrh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_redef(ncid2);  /* enter define mode */
         if (status != NC_NOERR) handle_error(status);
         /* copy variable attribute from "rh" to "avgrh" */
         status = nc_copy_att(ncid1, rh_id, "units", ncid2, avgrh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_enddef(ncid2); /* leave define mode */
         if (status != NC_NOERR) handle_error(status);

Next: nc_del_att, Previous: nc_copy_att, Up: Attributes

### 7.6 Rename an Attribute: nc_rename_att

The function nc_rename_att changes the name of an attribute. If the new name is longer than the original name, the netCDF dataset must be in define mode. You cannot rename an attribute to have the same name as another attribute of the same variable.

### Usage

         int nc_rename_att (int ncid, int varid, const char* name,
                            const char* newname);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create
`varid`
  ID of the attribute's variable, or NC_GLOBAL for a global attribute
`name`
  The current attribute name.
`newname`
  The new name to be assigned to the specified attribute. If the new name is longer than the current name, the netCDF dataset must be in define mode.

### Errors

nc_rename_att returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The specified variable ID is not valid.
- The new attribute name is already in use for another attribute of the specified variable.
- The specified netCDF dataset is in data mode and the new name is longer than the old name.
- The specified attribute does not exist.
- The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_rename_att to rename the variable attribute units to Units for a variable rh in an existing netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int  status;      /* error status */
         int  ncid;        /* netCDF ID */
         int  rh_id;       /* variable id */
            ...
         status = nc_open("foo.nc", NC_NOWRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         /* rename attribute */
         status = nc_rename_att(ncid, rh_id, "units", "Units");
         if (status != NC_NOERR) handle_error(status);

Previous: nc_rename_att, Up: Attributes

### 7.7 Delete an Attribute: nc_del_att

The function nc_del_att deletes a netCDF attribute from an open netCDF dataset. The netCDF dataset must be in define mode.

### Usage

int nc_del_att (int ncid, int varid, const char* name);

`ncid`
  NetCDF ID, from a previous call to nc_open or nc_create.
`varid`
  ID of the attribute's variable, or NC_GLOBAL for a global attribute.
`name`
  The name of the attribute to be deleted.

### Errors

nc_del_att returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:

- The specified variable ID is not valid.
- The specified netCDF dataset is in data mode.
- The specified attribute does not exist.
- The specified netCDF ID does not refer to an open netCDF dataset.

### Example

Here is an example using nc_del_att to delete the variable attribute Units for a variable rh in an existing netCDF dataset named foo.nc:

         #include <netcdf.h>
            ...
         int  status;      /* error status */
         int  ncid;        /* netCDF ID */
         int  rh_id;       /* variable ID */
            ...
         status = nc_open("foo.nc", NC_WRITE, &ncid);
         if (status != NC_NOERR) handle_error(status);
            ...
         status = nc_inq_varid (ncid, "rh", &rh_id);
         if (status != NC_NOERR) handle_error(status);
            ...
         /* delete attribute */
         status = nc_redef(ncid);        /* enter define mode */
         if (status != NC_NOERR) handle_error(status);
         status = nc_del_att(ncid, rh_id, "Units");
         if (status != NC_NOERR) handle_error(status);
         status = nc_enddef(ncid);       /* leave define mode */
         if (status != NC_NOERR) handle_error(status);

Next: NetCDF 3 Transition Guide, Previous: Attributes, Up: Top

## Appendix A Summary of C Interface

         const char* nc_inq_libvers (void);
         const char* nc_strerror    (int ncerr);

         int nc_create         (const char *path, int cmode, int *ncidp);
         int nc_open           (const char *path, int mode, int *ncidp);
         int nc_set_fill       (int ncid, int fillmode, int *old_modep);
         int nc_redef          (int ncid);
         int nc_enddef         (int ncid);
         int nc_sync           (int ncid);
         int nc_abort          (int ncid);
         int nc_close          (int ncid);
         int nc_inq            (int ncid, int *ndimsp, int *nvarsp,
                                int *ngattsp, int *unlimdimidp);
         int nc_inq_ndims      (int ncid, int *ndimsp);
         int nc_inq_nvars      (int ncid, int *nvarsp);
         int nc_inq_natts      (int ncid, int *ngattsp);
         int nc_inq_unlimdim   (int ncid, int *unlimdimidp);

         int nc_def_dim        (int ncid, const char *name, size_t len,
                                int *idp);
         int nc_inq_dimid      (int ncid, const char *name, int *idp);
         int nc_inq_dim        (int ncid, int dimid, char *name, size_t *lenp);
         int nc_inq_dimname    (int ncid, int dimid, char *name);
         int nc_inq_dimlen     (int ncid, int dimid, size_t *lenp);
         int nc_rename_dim     (int ncid, int dimid, const char *name);

         int nc_def_var        (int ncid, const char *name, nc_type xtype,
                                int ndims, const int *dimidsp, int *varidp);
         int nc_inq_var        (int ncid, int varid, char *name,
                                nc_type *xtypep, int *ndimsp, int *dimidsp,
                                int *nattsp);
         int nc_inq_varid      (int ncid, const char *name, int *varidp);
         int nc_inq_varname    (int ncid, int varid, char *name);
         int nc_inq_vartype    (int ncid, int varid, nc_type *xtypep);
         int nc_inq_varndims   (int ncid, int varid, int *ndimsp);
         int nc_inq_vardimid   (int ncid, int varid, int *dimidsp);
         int nc_inq_varnatts   (int ncid, int varid, int *nattsp);
         int nc_rename_var     (int ncid, int varid, const char *name);
         int nc_put_var_text   (int ncid, int varid, const char *op);
         int nc_get_var_text   (int ncid, int varid,       char *ip);
         int nc_put_var_uchar  (int ncid, int varid, const unsigned char *op);
         int nc_get_var_uchar  (int ncid, int varid,       unsigned char *ip);
         int nc_put_var_schar  (int ncid, int varid, const signed char *op);
         int nc_get_var_schar  (int ncid, int varid,       signed char *ip);
         int nc_put_var_short  (int ncid, int varid, const short *op);
         int nc_get_var_short  (int ncid, int varid,       short *ip);
         int nc_put_var_int    (int ncid, int varid, const int *op);
         int nc_get_var_int    (int ncid, int varid,       int *ip);
         int nc_put_var_long   (int ncid, int varid, const long *op);
         int nc_get_var_long   (int ncid, int varid,       long *ip);
         int nc_put_var_float  (int ncid, int varid, const float *op);
         int nc_get_var_float  (int ncid, int varid,       float *ip);
         int nc_put_var_double (int ncid, int varid, const double *op);
         int nc_get_var_double (int ncid, int varid,       double *ip);
         int nc_put_var1_text  (int ncid, int varid, const size_t *indexp,
                                const char *op);
         int nc_get_var1_text  (int ncid, int varid, const size_t *indexp,
                                char *ip);
         int nc_put_var1_uchar (int ncid, int varid, const size_t *indexp,
                                const unsigned char *op);
         int nc_get_var1_uchar (int ncid, int varid, const size_t *indexp,
                                unsigned char *ip);
         int nc_put_var1_schar (int ncid, int varid, const size_t *indexp,
                                const signed char *op);
         int nc_get_var1_schar (int ncid, int varid, const size_t *indexp,
                                signed char *ip);
         int nc_put_var1_short (int ncid, int varid, const size_t *indexp,
                                const short *op);
         int nc_get_var1_short (int ncid, int varid, const size_t *indexp,
                                short *ip);
         int nc_put_var1_int   (int ncid, int varid, const size_t *indexp,
                                const int *op);
         int nc_get_var1_int   (int ncid, int varid, const size_t *indexp,
                                int *ip);
         int nc_put_var1_long  (int ncid, int varid, const size_t *indexp,
                                const long *op);
         int nc_get_var1_long  (int ncid, int varid, const size_t *indexp,
                                long *ip);
         int nc_put_var1_float (int ncid, int varid, const size_t *indexp,
                                const float *op);
         int nc_get_var1_float (int ncid, int varid, const size_t *indexp,
                                float *ip);
         int nc_put_var1_double(int ncid, int varid, const size_t *indexp,
                                const double *op);
         int nc_get_var1_double(int ncid, int varid, const size_t *indexp,
                                double *ip);
         int nc_put_vara_text  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const char *op);
         int nc_get_vara_text  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, char *ip);
         int nc_put_vara_uchar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const unsigned char *op);
         int nc_get_vara_uchar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, unsigned char *ip);
         int nc_put_vara_schar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const signed char *op);
         int nc_get_vara_schar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, signed char *ip);
         int nc_put_vara_short (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const short *op);
         int nc_get_vara_short (int ncid, int varid, const size_t *startp,
                                const size_t *countp, short *ip);
         int nc_put_vara_int   (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const int *op);
         int nc_get_vara_int   (int ncid, int varid, const size_t *startp,
                                const size_t *countp, int *ip);
         int nc_put_vara_long  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const long *op);
         int nc_get_vara_long  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, long *ip);
         int nc_put_vara_float (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const float *op);
         int nc_get_vara_float (int ncid, int varid, const size_t *startp,
                                const size_t *countp, float *ip);
         int nc_put_vara_double(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const double *op);
         int nc_get_vara_double(int ncid, int varid, const size_t *startp,
                                const size_t *countp, double *ip);
         int nc_put_vars_text  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const char *op);
         int nc_get_vars_text  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                char *ip);
         int nc_put_vars_uchar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const unsigned char *op);
         int nc_get_vars_uchar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                unsigned char *ip);
         int nc_put_vars_schar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const signed char *op);
         int nc_get_vars_schar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                signed char *ip);
         int nc_put_vars_short (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const short *op);
         int nc_get_vars_short (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                short *ip);
         int nc_put_vars_int   (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const int *op);
         int nc_get_vars_int   (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                int *ip);
         int nc_put_vars_long  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const long *op);
         int nc_get_vars_long  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                long *ip);
         int nc_put_vars_float (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const float *op);
         int nc_get_vars_float (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                float *ip);
         int nc_put_vars_double(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const double *op);
         int nc_get_vars_double(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                double *ip);
         int nc_put_varm_text  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, const char *op);
         int nc_get_varm_text  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, char *ip);
         int nc_put_varm_uchar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, const unsigned char *op);
         int nc_get_varm_uchar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, unsigned char *ip);
         int nc_put_varm_schar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, const signed char *op);
         int nc_get_varm_schar (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, signed char *ip);
         int nc_put_varm_short (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, const short *op);
         int nc_get_varm_short (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, short *ip);
         int nc_put_varm_int   (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, const int *op);
         int nc_get_varm_int   (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, int *ip);
         int nc_put_varm_long  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, const long *op);
         int nc_get_varm_long  (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, long *ip);
         int nc_put_varm_float (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, const float *op);
         int nc_get_varm_float (int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, float *ip);
         int nc_put_varm_double(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t *imapp, const double *op);
         int nc_get_varm_double(int ncid, int varid, const size_t *startp,
                                const size_t *countp, const ptrdiff_t *stridep,
                                const ptrdiff_t * imap, double *ip);

         int nc_inq_att        (int ncid, int varid, const char *name,
                                nc_type *xtypep, size_t *lenp);
         int nc_inq_attid      (int ncid, int varid, const char *name, int *idp);
         int nc_inq_atttype    (int ncid, int varid, const char *name,
                                nc_type *xtypep);
         int nc_inq_attlen     (int ncid, int varid, const char *name,
                                size_t *lenp);
         int nc_inq_attname    (int ncid, int varid, int attnum, char *name);
         int nc_copy_att       (int ncid_in, int varid_in, const char *name,
                                int ncid_out, int varid_out);
         int nc_rename_att     (int ncid, int varid, const char *name,
                                const char *newname);
         int nc_del_att        (int ncid, int varid, const char *name);
         int nc_put_att_text   (int ncid, int varid, const char *name, size_t len,
                                const char *op);
         int nc_get_att_text   (int ncid, int varid, const char *name, char *ip);
         int nc_put_att_uchar  (int ncid, int varid, const char *name,
                                nc_type xtype, size_t len, const unsigned char *op);
         int nc_get_att_uchar  (int ncid, int varid, const char *name,
                                unsigned char *ip);
         int nc_put_att_schar  (int ncid, int varid, const char *name,
                                nc_type xtype, size_t len, const signed char *op);
         int nc_get_att_schar  (int ncid, int varid, const char *name,
                                signed char *ip);
         int nc_put_att_short  (int ncid, int varid, const char *name,
                                nc_type xtype, size_t len, const short *op);
         int nc_get_att_short  (int ncid, int varid, const char *name, short *ip);
         int nc_put_att_int    (int ncid, int varid, const char *name,
                                nc_type xtype,size_t len, const int *op);
         int nc_get_att_int    (int ncid, int varid, const char *name, int *ip);
         int nc_put_att_long   (int ncid, int varid, const char *name,
                                nc_type xtype, size_t len, const long *op);
         int nc_get_att_long   (int ncid, int varid, const char *name, long *ip);
         int nc_put_att_float  (int ncid, int varid, const char *name,
                                 nc_type xtype, size_t len, const float *op);
         int nc_get_att_float  (int ncid, int varid, const char *name, float *ip);
         int nc_put_att_double (int ncid, int varid, const char *name,
                                nc_type xtype, size_t len, const double *op);
         int nc_get_att_double (int ncid, int varid, const char *name,
                                double *ip);

Next: NetCDF 2 C Transition Guide, Previous: Summary of C Interface, Up: Top

## Appendix B NetCDF 3 to NetCDF 4 Transition Guide

### B.1 Introduction

The release of netCDF-4 represents a substantial increase in the capabilities of the netCDF C and Fortran APIs.

The netCDF-4.0 release (June, 2008) allows the use of the popular HDF5 data format as a storage layer. The HDF5 format has many features, and only a subset of them are exposed in the netCDF-4 API. This represents a deliberate selection process by netCDF-4 developers to choose the most useful features of the HDF5 model, while retaining the simplicity of the netCDF APIs.

Despite many new features, full backward compatibility is assured (and extensively tested). Existing software and data files will continue to work with netCDF-4.0, just as with previous releases of the netCDF library.

The use of netCDF-4 files allows the use of the expanded data model, including user-defined types, groups, the new unsigned, 64-bit, and string types.

Using netCDF-4 files also allows the use of such features as endianness control, per-variable data compression, chunking, parallel I/O, and checksums. These features fit neatly within the classic netCDF data model.

Although the expanded data model offers many exciting new features, we expect and encourage users to proceed with care - it also allows the creation of needlessly, even horribly complex files. This would decrease interoperability and increase the work of the poor programmers trying to use the data file.

There are many netCDF-4 features which fit comfortably within the classic netCDF model. Existing programs can be very quickly converted to use features such as compression, endianness control, and chunking. This allows users to gain immediate performance pay off, with minimal software development effort.

### B.2 NetCDF-4 and HDF5

NetCDF-4 depends on HDF5 to deliver the new features of the expanded data model, as well as the features required to support the classic data model.

NetCDF-4 users must have at least HDF5 version 1.8.1 (and at least zlib-1.2.3) to use HDF5 with netCDF-4.0. If these packages are not found when netCDF is built, then the netCDF library may still be built (without the –enable-netcdf-4 option), but will not allow users to create netCDF-4/HDF5 files, or use the expanded data model. Only classic and 64-bit offset format netCDF files will be created or readable. (see Configure).

The HDF5 files created by netCDF-4 will be readable (and writable) by any HDF5 application. However, netCDF-4.0 cannot read any HDF5 file, only those created by netCDF-4.

### B.3 Backward Compatibility

In the context of netCDF, backward compatibility has several meanings.

`Data Compatibility`
  NetCDF-4 provides backward compatibility for existing data. All netCDF data files remain readable and writable to the netCDF library. When a file is opened, the library detects the underlying format of the file; this is transparent to the programmer and user.
`Code Compatibility`
  NetCDF-4 provides backward compatibility for existing software. Programs using the 4.0 release can use it as a drop-in replacement for netCDF-3.x. Existing programs will continue to create netCDF classic or 64-bit offset files.
`Model Compatibility`
  NetCDF-4 introduces an expanded model of a netCDF data file (include such new elements as groups, user-defined types, multiple-unlimited dimensions, etc.) This expanded model is a super-set of the classic netCDF model. Everything that works in the classic model works in the expanded model as well. (The reverse is not true - code using the expanded data model will fail if run on classic model netCDF files.)

### B.4 The Classic and the Expanded NetCDF Data Models

The classic netCDF data model consists of variables, dimensions, and attributes.

The netCDF-4.0 release introduces an expanded data model, which offers many new features. These features will only work on files which have been created with the NC_NETCDF4 flag, and without the NC_CLASSIC_MODEL flag (see nc_create).

`New Types`
  New data types are introduced: NC_UBYTE, NC_USHORT, NC_UINT, NC_INT64, NC_UINT64, and NC_STRING. These types many be used for attributes and variables. See nc_def_var.
`Groups`
  NetCDF objects may now be organizes into a hierarchical set of groups. Groups are organized much line a UNIX file system, with each group capable of containing more groups. Within each group a classic model netCDF “file” exists, with its own dimensions, variables, and attributes. See nc_def_grp.
`User Defined Types`
  NetCDF-4 allows the user to define new data types, including a compound type (see nc_def_compound), a variable length array type (see nc_def_vlen), an enumerated type (see nc_def_enum), and an opaque type (see nc_def_opaque).
`Multiple Unlimited Dimensions`
  NetCDF-4/HDF5 data files may use multiple unlimited dimensions with a file, and even within a variable.

### B.5 Using NetCDF-4.0 with the Classic and 64-bit Offset Formats

Prior to the 4.0 release, two underlying data formats were available for the netCDF user, the classic, and the 64-bit offset format. (The 64-bit offset format was introduced in the 3.6.0 release, and allows the use of larger variables and files).

Software using netCDF, relinked against the netCDF-4.0 library, will continue to work exactly as before. Since the default create mode in nc_create is to create a classic format file, using unmodified netCDF-3 code with the netCDF-4 library will result in the exact same output - a classic netCDF file or 64-bit offset file.

When writing or reading classic and 64-bit offset files, the netCDF-4.0 library relies on the core netCDF-3.x code.

### B.6 Creating a NetCDF-4/HDF5 File

The extra features of netCDF-4 can only be accessed by adding the NC_NETCDF4 flag to the create mode of nc_create. Files created with the NC_NETCDF4 flag can have multiple unlimited dimensions, use the new atomic types, use compound and opaque types, and take advantage of the other features of netCDF-4. (see nc_create).

### B.7 Using NetCDF-4.0 with the Classic Model

By changing your nc_create call to create a netCDF-4/HDF5 file you gain access to many new features - perhaps too many! Using groups or user-defined types will make the file unreadable to existing netCDF applications, until they are updated to handle the new netCDF-4 model.

Using the NC_CLASSIC_MODEL flag with the NC_NETCDF4 flag tells the library to create a netCDF-4/HDF5 file which must abide by the rules of the classic netCDF data model. Such a file many not contain groups, user defined types, multiple unlimited dimensions, etc.

But a classic model file is guaranteed to be compatible with existing netCDF software, once relinked to the netCDF 4.0 library.

Some features of netCDF-4 are transparent to the user when the file is read. For example, a netCDF-4/HDF5 file may contain compressed data. When such a file is read, the decompression of the data takes place transparently. This means that data may use the data compression feature, and still conform to the classic netCDF data model, and thus retain compatibility with existing netCDF software (see nc_def_var_deflate). The same applies for control of endianness (see nc_def_var_endian), chunking (see nc_def_var_chunking), checksums (see nc_def_var_fletcher32), and parallel I/O, if netCDF-4 was built on a system with the MPI libraries.

To use these feature, change your nc_create calls to use the NC_NETCDF4 and NC_CLASSIC_MODEL flags. Then call the appropriate nc_dev_var_* function after the variable is defined, but before the next call to nc_enddef.

### B.8 Use of the Expanded Model Impacts Fortran Portability

Using expanded model features impacts portability for Fortran programmers.

Fortran compilers do not always agree as to how data should be laid out in memory. This makes handling compound and variable length array types compiler and platform dependant.

(This is also true for C, but the clever HDF5 configuration has solved this problem for C. Alas, not for Fortran.)

Despite this, Fortran programs can take advantage of the new data model. The portability challenge is no different from that which Fortran programmers already deal with when doing data I/O.

### B.9 The C++ API Does Not Handle Expanded Model in this Release

Unfortunately, the C++ API does not support the netCDF-4 expanded data model. A new C++ API is being developed and may be built by adventurous users using the –enable-cxx4 option to configure (see Configure).

Next: NetCDF-3 Error Codes, Previous: NetCDF 3 Transition Guide, Up: Top

## Appendix C NetCDF 2 to NetCDF 3 C Transition Guide

### C.1 Overview of C interface changes

NetCDF version 3 includes a complete rewrite of the netCDF library. It is about twice as fast as the previous version. The netCDF file format is unchanged, so files written with version 3 can be read with version 2 code and vice versa.

The core library is now written in ANSI C. For example, prototypes are used throughout as well as const qualifiers where appropriate. You must have an ANSI C compiler to compile this version.

Rewriting the library offered an opportunity to implement improved C and FORTRAN interfaces that provide some significant benefits:

type safety, by eliminating the need to use generic void* pointers;

automatic type conversions, by eliminating the undesirable coupling between the language-independent external netCDF types (NC_BYTE, ..., NC_DOUBLE) and language-dependent internal data types (char, ..., double);

support for future enhancements, by eliminating obstacles to the clean addition of support for packed data and multithreading;

more standard error behavior, by uniformly communicating an error status back to the calling program in the return value of each function.

It is not necessary to rewrite programs that use the version 2 C interface, because the netCDF-3 library includes a backward compatibility interface that supports all the old functions, globals, and behavior. We are hoping that the benefits of the new interface will be an incentive to use it in new netCDF applications. It is possible to convert old applications to the new interface incrementally, replacing netCDF-2 calls with the corresponding netCDF-3 calls one at a time. If you want to check that only netCDF-3 calls are used in an application, a preprocessor macro (NO_NETCDF_2) is available for that purpose.

Other changes in the implementation of netCDF result in improved portability, maintainability, and performance on most platforms. A clean separation between I/O and type layers facilitates platform-specific optimizations. The new library no longer uses a vendor-provided XDR library, which simplifies linking programs that use netCDF and speeds up data access significantly in most cases.

### C.2 The New C Interface

First, here's an example of C code that uses the netCDF-2 interface:

         void *bufferp;
         nc_type xtype;
         ncvarinq(ncid, varid, ..., &xtype, ...
         ...
         /* allocate bufferp based on dimensions and type */
         ...
         if (ncvarget(ncid, varid, start, count, bufferp) == -1) {
             fprintf(stderr, "Can't get data, error code = %d\n",ncerr);
             /* deal with it */
             ...
         }
         switch(xtype) {
             /* deal with the data, according to type */
         ...
         case  NC_FLOAT:
             fanalyze((float *)bufferp);
             break;
         case NC_DOUBLE:
             danalyze((double *)bufferp);
             break;
         }

Here's how you might handle this with the new netCDF-3 C interface:

         /*
          * I want to use doubles for my analysis.
          */
         double dbuf[NDOUBLES];
         int status;

         /* So, I use the function that gets the data as doubles. */
         status = nc_get_vara_double(ncid, varid, start, count, dbuf)
         if (status != NC_NOERR) {
            fprintf(stderr, "Can't get data: %s\n", nc_strerror(status));
             /* deal with it */
             ...
         }
         danalyze(dbuf);

The example above illustrates changes in function names, data type conversion, and error handling, discussed in detail in the sections below.

### C.3 Function Naming Conventions

The netCDF-3 C library employs a new naming convention, intended to make netCDF programs more readable. For example, the name of the function to rename a variable is now nc_rename_var instead of the previous ncvarrename.

All netCDF-3 C function names begin with the nc_ prefix. The second part of the name is a verb, like get, put, inq (for inquire), or open. The third part of the name is typically the object of the verb: for example dim, var, or att for functions dealing with dimensions, variables, or attributes. To distinguish the various I/O operations for variables, a single character modifier is appended to var:

var
  entire variable access
var1
  single value access
vara
  array or array section access
vars
  strided access to a subsample of values
varm
  mapped access to values not contiguous in memory

At the end of the name for variable and attribute functions, there is a component indicating the type of the final argument: text, uchar, schar, short, int, long, float, or double. This part of the function name indicates the type of the data container you are using in your program: character string, unsigned char, signed char, and so on.

Also, all macro names in the public C interface begin with the prefix NC_. For example, the macro which was formerly MAX_NC_NAME is now NC_MAX_NAME, and the former FILL_FLOAT is now NC_FILL_FLOAT.

As previously mentioned, all the old names are still supported for backward compatibility.

### C.4 Type Conversion

With the new interface, users need not be aware of the external type of numeric variables, since automatic conversion to or from any desired numeric type is now available. You can use this feature to simplify code, by making it independent of external types. The elimination of void* pointers provides detection of type errors at compile time that could not be detected with the previous interface. Programs may be made more robust with the new interface, because they need not be changed to accommodate a change to the external type of a variable.

If conversion to or from an external numeric type is necessary, it is handled by the library. This automatic conversion and separation of external data representation from internal data types will become even more important in netCDF version 4, when new external types will be added for packed data for which there is no natural corresponding internal type, for example, arrays of 11-bit values.

Converting from one numeric type to another may result in an error if the target type is not capable of representing the converted value. (In netCDF-2, such overflows can only happen in the XDR layer.) For example, a float may not be able to hold data stored externally as an NC_DOUBLE (an IEEE floating-point number). When accessing an array of values, an NC_ERANGE error is returned if one or more values are out of the range of representable values, but other values are converted properly.

Note that mere loss of precision in type conversion does not return an error. Thus, if you read double precision values into an int, for example, no error results unless the magnitude of the double precision value exceeds the representable range of ints on your platform. Similarly, if you read a large integer into a float incapable of representing all the bits of the integer in its mantissa, this loss of precision will not result in an error. If you want to avoid such precision loss, check the external types of the variables you access to make sure you use an internal type that has a compatible precision.

The new interface distinguishes arrays of characters intended to represent text strings from arrays of 8-bit bytes intended to represent small integers. The interface supports the internal types text, uchar, and schar, intended for text strings, unsigned byte values, and signed byte values.

The _uchar and _schar functions were introduced in netCDF-3 to eliminate an ambiguity, and support both signed and unsigned byte data. In netCDF-2, whether the external NC_BYTE type represented signed or unsigned values was left up to the user. In netcdf-3, we treat NC_BYTE as signed for the purposes of conversion to short, int, long, float, or double. (Of course, no conversion takes place when the internal type is signed char.) In the _uchar functions, we treat NC_BYTE as if it were unsigned. Thus, no NC_ERANGE error can occur converting between NC_BYTE and unsigned char.

### C.5 Error handling

The new interface handles errors differently than netCDF-2. In the old interface, the default behavior when an error was detected was to print an error message and exit. To get control of error handling, you had to set flag bits in a global variable, ncopts, and to determine the cause of an error, you had to test the value of another global variable ncerr.

In the new interface, functions return an integer status that indicates not only success or failure, but also the cause of the error. The global variables ncerr and ncopt have been eliminated. The library will never try to print anything, nor will it call exit (unless you are using the netCDF version 2 compatibility functions). You will have to check the function return status and do this yourself. We eliminated these globals in the interest of supporting parallel (multiprocessor) execution cleanly, as well as reducing the number of assumptions about the environment where netCDF is used. The new behavior should provide better support for using netCDF as a hidden layer in applications that have their own GUI interface.

### C.6 NC_LONG and NC_INT

Where the netCDF-2 interface used NC_LONG to identify an external data type corresponding to 32-bit integers, the new interface uses NC_INT instead. NC_LONG is defined to have the same value as NC_INT for backward compatibility, but it should not be used in new code. With new 64-bit platforms using long for 64-bit integers, we would like to reduce the confusion caused by this name clash. Note that there is still no netCDF external data type corresponding to 64-bit integers.

### C.7 What's Missing?

The new C interface omits three "record I/O" functions, ncrecput, ncrecget, and ncrecinq, from the netCDF-2 interface, although these functions are still supported via the netCDF-2 compatibility interface.

This means you may have to replace one record-oriented call with multiple type-specific calls, one for each record variable. For example, a single call to ncrecput can always be replaced by multiple calls to the appropriate nc_put_var functions, one call for each variable accessed. The record-oriented functions were omitted, because there is no simple way to provide type-safety and automatic type conversion for such an interface.

There is no function corresponding to the nctypelen function from the version 2 interface. The separation of internal and external types and the new type-conversion interfaces make nctypelen unnecessary. Since users read into and write out of native types, the sizeof operator is perfectly adequate to determine how much space to allocate for a value.

In the previous library, there was no checking that the characters used in the name of a netCDF object were compatible with CDL restrictions. The ncdump and ncgen utilities now properly escape and handle escaped special characters in names, so that all valid netCDF names are representable in CDL.

### C.8 Other Changes

There are two new functions in netCDF-3 that don't correspond to any netCDF-2 functions: nc_inq_libvers and nc_strerror. The version of the netCDF library in use is returned as a string by nc_inq_libvers. An error message corresponding to the status returned by a netCDF function call is returned as a string by the nc_strerror function.

A new NC_SHARE flag is available for use in an nc_open or nc_create call, to suppress the default buffering of accesses. The use of NC_SHARE for concurrent access to a netCDF dataset means you don't have to call nc_sync after every access to make sure that disk updates are synchronous. It is important to note that changes to ancillary data, such as attribute values, are not propagated automatically by use of the NC_SHARE flag. Use of the nc_sync function is still required for this purpose.

The version 2 interface had a single inquiry function, ncvarinq for getting the name, type, and shape of a variable. Similarly, only a single inquiry function was available for getting information about a dimension, an attribute, or a netCDF dataset. When you only wanted a subset of this information, you had to provide NULL arguments as placeholders for the unneeded information. The new interface includes additional inquire functions that return each item separately, so errors are less likely from miscounting arguments.

The previous implementation returned an error when 0-valued count components were specified in ncvarput and ncvarget calls. This restriction has been removed, so that now functions in the nc_put_var and nc_get_var families may be called with 0-valued count components, resulting in no data being accessed. Although this may seem useless, it simplifies some programs to not treat 0-valued counts as a special case.

The previous implementation returned an error when the same dimension was used more than once in specifying the shape of a variable in ncvardef. This restriction is relaxed in the netCDF-3 implementation, because an auto-correlation matrix is a good example where using the same dimension twice makes sense.

In the new interface, units for the imap argument to the nc_put_varm and nc_get_varm families of functions are now in terms of the number of data elements of the desired internal type, not in terms of bytes as in the netCDF version-2 mapped access interfaces.

Following is a table of netCDF-2 function names and names of the corresponding netCDF-3 functions. For parameter lists of netCDF-2 functions, see the netCDF-2 User's Guide.

`ncabort`
  nc_abort
`ncattcopy`
  nc_copy_att
`ncattdel`
  nc_del_att
`ncattget`
  nc_get_att_double, nc_get_att_float, nc_get_att_int, nc_get_att_long, nc_get_att_schar, nc_get_att_short, nc_get_att_text, nc_get_att_uchar
`ncattinq`
  nc_inq_att, nc_inq_attid, nc_inq_attlen, nc_inq_atttype
`ncattname`
  nc_inq_attname
`ncattput`
  nc_put_att_double, nc_put_att_float, nc_put_att_int, nc_put_att_long, nc_put_att_schar, nc_put_att_short, nc_put_att_text, nc_put_att_uchar
`ncattrename`
  nc_rename_att
`ncclose`
  nc_close
`nccreate`
  nc_create
`ncdimdef`
  nc_def_dim
`ncdimid`
  nc_inq_dimid
`ncdiminq`
  nc_inq_dim, nc_inq_dimlen, nc_inq_dimname
`ncdimrename`
  nc_rename_dim
`ncendef`
  nc_enddef
`ncinquire`
  nc_inq, nc_inq_natts, nc_inq_ndims, nc_inq_nvars, nc_inq_unlimdim
`ncopen`
  nc_open
`ncrecget`
  (none)
`ncrecinq`
  (none)
`ncrecput`
  (none)
`ncredef`
  nc_redef
`ncsetfill`
  nc_set_fill
`ncsync`
  nc_sync
`nctypelen`
  (none)
`ncvardef`
  nc_def_var
`ncvarget`
  nc_get_vara_double, nc_get_vara_float, nc_get_vara_int, nc_get_vara_long, nc_get_vara_schar, nc_get_vara_short, nc_get_vara_text, nc_get_vara_uchar
`ncvarget1`
  nc_get_var1_double, nc_get_var1_float, nc_get_var1_int, nc_get_var1_long, nc_get_var1_schar, nc_get_var1_short, nc_get_var1_text, nc_get_var1_uchar
`ncvargetg`
  nc_get_varm_double, nc_get_varm_float, nc_get_varm_int, nc_get_varm_long, nc_get_varm_schar, nc_get_varm_short, nc_get_varm_text, nc_get_varm_uchar, nc_get_vars_double, nc_get_vars_float, nc_get_vars_int, nc_get_vars_long, nc_get_vars_schar, nc_get_vars_short, nc_get_vars_text, nc_get_vars_uchar
`ncvarid`
  nc_inq_varid
`ncvarinq`
  nc_inq_var, nc_inq_vardimid, nc_inq_varname, nc_inq_varnatts, nc_inq_varndims, nc_inq_vartype
`ncvarput`
  nc_put_vara_double, nc_put_vara_float, nc_put_vara_int, nc_put_vara_long, nc_put_vara_schar, nc_put_vara_short, nc_put_vara_text, nc_put_vara_uchar
`ncvarput1`
  nc_put_var1_double, nc_put_var1_float, nc_put_var1_int, nc_put_var1_long, nc_put_var1_schar, nc_put_var1_short, nc_put_var1_text, nc_put_var1_uchar
`ncvarputg`
  nc_put_varm_double, nc_put_varm_float, nc_put_varm_int, nc_put_varm_long, nc_put_varm_schar, nc_put_varm_short, nc_put_varm_text, nc_put_varm_uchar, nc_put_vars_double, nc_put_vars_float, nc_put_vars_int, nc_put_vars_long, nc_put_vars_schar, nc_put_vars_short, nc_put_vars_text, nc_put_vars_uchar
`ncvarrename`
  nc_rename_var
`(none)`
  nc_inq_libvers
`(none)`
  nc_strerror

Next: NetCDF-4 Error Codes, Previous: NetCDF 2 C Transition Guide, Up: Top

## Appendix D NetCDF-3 Error Codes

         #define NC_NOERR        0       /* No Error */

         #define NC_EBADID       (-33)   /* Not a netcdf id */
         #define NC_ENFILE       (-34)   /* Too many netcdfs open */
         #define NC_EEXIST       (-35)   /* netcdf file exists && NC_NOCLOBBER */
         #define NC_EINVAL       (-36)   /* Invalid Argument */
         #define NC_EPERM        (-37)   /* Write to read only */
         #define NC_ENOTINDEFINE (-38)   /* Operation not allowed in data mode */
         #define NC_EINDEFINE    (-39)   /* Operation not allowed in define mode */
         #define NC_EINVALCOORDS (-40)   /* Index exceeds dimension bound */
         #define NC_EMAXDIMS     (-41)   /* NC_MAX_DIMS exceeded */
         #define NC_ENAMEINUSE   (-42)   /* String match to name in use */
         #define NC_ENOTATT      (-43)   /* Attribute not found */
         #define NC_EMAXATTS     (-44)   /* NC_MAX_ATTRS exceeded */
         #define NC_EBADTYPE     (-45)   /* Not a netcdf data type */
         #define NC_EBADDIM      (-46)   /* Invalid dimension id or name */
         #define NC_EUNLIMPOS    (-47)   /* NC_UNLIMITED in the wrong index */
         #define NC_EMAXVARS     (-48)   /* NC_MAX_VARS exceeded */
         #define NC_ENOTVAR      (-49)   /* Variable not found */
         #define NC_EGLOBAL      (-50)   /* Action prohibited on NC_GLOBAL varid */
         #define NC_ENOTNC       (-51)   /* Not a netcdf file */
         #define NC_ESTS         (-52)   /* In Fortran, string too short */
         #define NC_EMAXNAME     (-53)   /* NC_MAX_NAME exceeded */
         #define NC_EUNLIMIT     (-54)   /* NC_UNLIMITED size already in use */
         #define NC_ENORECVARS   (-55)   /* nc_rec op when there are no record vars */
         #define NC_ECHAR        (-56)   /* Attempt to convert between text & numbers */
         #define NC_EEDGE        (-57)   /* Edge+start exceeds dimension bound */
         #define NC_ESTRIDE      (-58)   /* Illegal stride */
         #define NC_EBADNAME     (-59)   /* Attribute or variable name
                                                  contains illegal characters */
         /* N.B. following must match value in ncx.h */
         #define NC_ERANGE       (-60)   /* Math result not representable */
         #define NC_ENOMEM       (-61)   /* Memory allocation (malloc) failure */

         #define NC_EVARSIZE     (-62)   /* One or more variable sizes violate
                                            format constraints */
         #define NC_EDIMSIZE     (-63)   /* Invalid dimension size */
         #define NC_ETRUNC       (-64)   /* File likely truncated or possibly corrupted */

Next: DAP Error Codes, Previous: NetCDF-3 Error Codes, Up: Top

## Appendix E NetCDF-4 Error Codes

NetCDF-4 uses all error codes from NetCDF-3 (see NetCDF-3 Error Codes). The following additional error codes were added for new errors unique to netCDF-4.

         #define NC_EHDFERR       (-101)
         #define NC_ECANTREAD     (-102)
         #define NC_ECANTWRITE    (-103)
         #define NC_ECANTCREATE   (-104)
         #define NC_EFILEMETA     (-105)
         #define NC_EDIMMETA      (-106)
         #define NC_EATTMETA      (-107)
         #define NC_EVARMETA      (-108)
         #define NC_ENOCOMPOUND   (-109)
         #define NC_EATTEXISTS    (-110)
         #define NC_ENOTNC4       (-111) /* Attempting netcdf-4 operation on netcdf-3 file. */
         #define NC_ESTRICTNC3    (-112) /* Attempting netcdf-4 operation on strict nc3 netcdf-4 file. */
         #define NC_EBADGRPID     (-113) /* Bad group id. Bad! */
         #define NC_EBADTYPEID    (-114) /* Bad type id. */
         #define NC_EBADFIELDID   (-115) /* Bad field id. */
         #define NC_EUNKNAME      (-116)

Next: Combined Index, Previous: NetCDF-4 Error Codes, Up: Top

## Appendix F DAP Error Codes

If the DAP client is enabled, then the following additional error codes may occur.

         #define NC_EDAP         (-66)   /* Generic DAP error */
         #define NC_ECURL        (-67)   /* Generic libcurl error */
         #define NC_EIO          (-68)   /* Generic IO error */
         #define NC_ENODATA      (-69)   /* Attempt to access variable with no data */
         #define NC_EDAPSVC      (-70)   /* DAP Server side error */
         #define NC_EDAS         (-71)   /* Malformed or inaccessible DAS */
         #define NC_EDDS         (-72)   /* Malformed or inaccessible DDS */
         #define NC_EDATADDS     (-73)   /* Malformed or inaccessible DATADDS */
         #define NC_EDAPURL      (-74)   /* Malformed DAP URL */
         #define NC_EDAPCONSTRAINT (-75) /* Malformed DAP Constraint*/
         #define NC_EDAP         (-66)   /* Generic DAP error */
         #define NC_ECURL        (-67)   /* Generic libcurl error */
         #define NC_EIO          (-68)   /* Generic IO error */
         #define NC_ENODATA      (-69)   /* Attempt to access variable with no data */
         #define NC_EDAPSVC      (-70)   /* DAP Server side error */
         #define NC_EDAS         (-71)   /* Malformed or inaccessible DAS */
         #define NC_EDDS         (-72)   /* Malformed or inaccessible DDS */
         #define NC_EDATADDS     (-73)   /* Malformed or inaccessible DATADDS */
         #define NC_EDAPURL      (-74)   /* Malformed DAP URL */
         #define NC_EDAPCONSTRAINT (-75) /* Malformed DAP Constraint*/

Previous: DAP Error Codes, Up: Top

## 7 Index

- abnormal termination: Use of the NetCDF Library
- aborting define mode: Adding
- aborting definitions: Adding
- adding attributes: Adding
- adding attributes using nc_redef: nc_redef
- adding dimensions: Adding
- adding dimensions using nc_redef: nc_redef
- adding variables: Adding
- adding variables using nc_redef: nc_redef
- API, C summary: Summary of C Interface
- appending data to variable: Variable Introduction
- array section, reading mapped: nc_get_vara_ type
- array section, reading subsampled: nc_get_vars_ type
- array section, writing: nc_put_vara_ type
- array section, writing mapped: nc_get_vara_ type
- array section, writing subsampled: nc_get_vars_ type
- array, writing mapped: nc_put_varm_ type
- `attnum`: nc_inq_att Family
- `attnump`: nc_inq_att Family
- attributes, adding: Adding
- attributes, array of strings: Strings
- attributes, character string: Classic Strings
- attributes, copying: nc_copy_att
- attributes, creating: nc_put_att_ type
- attributes, deleting: nc_del_att
- attributes, deleting, introduction: Adding
- attributes, finding length: nc_inq_att Family
- attributes, getting information about: nc_inq_att Family
- attributes, ID: nc_inq_att Family
- attributes, inquiring about: nc_inq_att Family
- attributes, introduction: Attributes Introduction
- attributes, number of: nc_inq Family
- attributes, operations on: Attributes Introduction
- attributes, reading: nc_get_att_ type
- attributes, renaming: nc_rename_att
- attributes, writing: nc_put_att_ type
- backing out of definitions: nc_abort
- backward compatibility with v2 API: NetCDF 2 C Transition Guide
- big-endian: nc_def_var_endian
- bit lengths of data types: Variable Types
- bit lengths of netcdf-3 data types: NetCDF-3 Variable Types
- bit lengths of netcdf-4 data types: NetCDF-4 Atomic Types
- byte vs. char fill values: Fill Values
- byte, zero: Classic Strings
- C API summary: Summary of C Interface
- call sequence, typical: Use of the NetCDF Library
- canceling definitions: nc_abort
- character-string data, writing: Classic Strings
- checksum: nc_def_var_fletcher32
- chunking: nc_def_var_chunking
- code templates: Use of the NetCDF Library
- compiling with netCDF library: Compiling
- compound types, overview: Compound Types
- compression, setting parameters: nc_def_var_deflate
- contiguous: nc_def_var_chunking
- copying attributes: nc_copy_att
- create flag, setting default: nc_set_default_format
- creating a dataset: Use of the NetCDF Library
- creating variables: nc_def_var
- DAP error codes: DAP Error Codes
- datasets, overview: Datasets
- deflate: nc_def_var_deflate
- deleting attributes: nc_del_att
- dimensions, adding: Adding
- dimensions, number of: nc_inq Family
- endianness: nc_def_var_endian
- entire variable, reading: nc_get_var_ type
- entire variable, writing: nc_put_var_ type
- enum type: Enum Type
- error codes: nc_strerror
- error codes, DAP: DAP Error Codes
- error codes, netcdf-3: NetCDF-3 Error Codes
- error codes, netcdf-4: NetCDF-4 Error Codes
- error handling: Errors
- fill: nc_def_var_fill
- fill values: Fill Values
- fletcher32: nc_def_var_fletcher32
- format version: nc_inq Family
- groups, overview: Groups
- `handle_err`: nc_strerror
- HDF5 chunk cache: nc_get_var_chunk_cache
- HDF5 chunk cache: nc_get_chunk_cache
- HDF5 chunk cache: nc_set_chunk_cache
- HDF5 chunk cache, per-variable: nc_set_var_chunk_cache
- HDF5 errors, first create: nc_open
- HDF5 errors, first create: nc_create
- inquiring about attributes: nc_inq_att Family
- inquiring about variables: nc_inq_varid
- interface descriptions: Interface Descriptions
- length of attributes: nc_inq_att Family
- `lenp`: nc_inq_att Family
- linking to netCDF library: Compiling
- little-endian: nc_def_var_endian
- mapped array section, writing: nc_get_varm_ type
- mapped array, writing: nc_put_varm_ type
- `name`: nc_inq_att Family
- `NC_64BIT_OFFSET`: nc__create
- `NC_64BIT_OFFSET`: nc_create
- `nc__create`: nc__create
- nc__create, example: nc__create
- nc__create, flags: nc__create
- `nc__enddef`: nc__enddef
- nc__enddef, example: nc__enddef
- `nc__open`: nc__open
- nc__open, example: nc__open
- `nc_abort`: nc_abort
- nc_abort, example: nc_abort
- `NC_CLOBBER`: nc_create_par
- `NC_CLOBBER`: nc__create
- `NC_CLOBBER`: nc_create
- `nc_close`: nc_close
- nc_close, example: nc_close
- nc_close, root group: nc_close
- `nc_close, typical use`: Use of the NetCDF Library
- `nc_copy_att`: nc_copy_att
- nc_copy_att, example: nc_copy_att
- `nc_copy_var`: nc_copy_var
- `nc_create`: nc_create
- nc_create, example: nc_create
- nc_create, flags: nc_create
- `nc_create, typical use`: Use of the NetCDF Library
- `nc_create_par`: nc_create_par
- nc_create_par, example: nc_create_par
- nc_create_par, flags: nc_create_par
- `nc_def_compound`: nc_def_compound
- `nc_def_dim`: nc_def_dim
- nc_def_dim, example: nc_def_dim
- `nc_def_dim, typical use`: Adding
- `nc_def_dim, typical use`: Use of the NetCDF Library
- `nc_def_enum`: nc_def_enum
- `nc_def_grp`: nc_def_grp
- `nc_def_opaque`: nc_def_opaque
- `nc_def_var`: nc_def_var
- nc_def_var, example: nc_def_var
- `nc_def_var, typical use`: Use of the NetCDF Library
- `nc_def_var_chunking`: nc_def_var_chunking
- `nc_def_var_deflate`: nc_def_var_deflate
- `nc_def_var_endian`: nc_def_var_endian
- `nc_def_var_fill`: nc_def_var_fill
- `nc_def_var_fletcher32`: nc_def_var_fletcher32
- `nc_def_vlen`: nc_inq_vlen
- `nc_def_vlen`: nc_def_vlen
- `nc_del_att`: nc_del_att
- nc_del_att, example: nc_del_att
- `nc_enddef`: nc_enddef
- nc_enddef, example: nc_enddef
- `nc_enddef, typical use`: Use of the NetCDF Library
- `nc_free_string`: nc_free_string
- `nc_free_vlen`: nc_free_vlens
- `nc_free_vlen`: nc_free_vlen
- `nc_get_att, typical use`: Reading Unknown
- `nc_get_att, typical use`: Reading Known
- `nc_get_att_ type`: nc_get_att_ type
- nc_get_att_ type, example: nc_get_att_ type
- `nc_get_chunk_cache`: nc_get_var_chunk_cache
- `nc_get_chunk_cache`: nc_get_chunk_cache
- `nc_get_var`: nc_get_var_ type
- `nc_get_var, typical use`: Reading Unknown
- `nc_get_var, typical use`: Reading Known
- `nc_get_var1`: nc_get_var1_ type
- `nc_get_var1_ type`: nc_get_var1_ type
- nc_get_var1_ type, example: nc_get_var1_ type
- `nc_get_var1_double`: nc_get_var1_ type
- `nc_get_var1_float`: nc_get_var1_ type
- `nc_get_var1_int`: nc_get_var1_ type
- `nc_get_var1_long`: nc_get_var1_ type
- `nc_get_var1_longlong`: nc_get_var1_ type
- `nc_get_var1_schar`: nc_get_var1_ type
- `nc_get_var1_short`: nc_get_var1_ type
- `nc_get_var1_string`: nc_get_var1_ type
- `nc_get_var1_text`: nc_get_var1_ type
- `nc_get_var1_ubyte`: nc_get_var1_ type
- `nc_get_var1_uchar`: nc_get_var1_ type
- `nc_get_var1_uint`: nc_get_var1_ type
- `nc_get_var1_ulonglong`: nc_get_var1_ type
- `nc_get_var1_ushort`: nc_get_var1_ type
- `nc_get_var_ type`: nc_get_var_ type
- nc_get_var_ type, example: nc_get_var_ type
- `nc_get_var_double`: nc_get_var_ type
- `nc_get_var_float`: nc_get_var_ type
- `nc_get_var_int`: nc_get_var_ type
- `nc_get_var_long`: nc_get_var_ type
- `nc_get_var_longlong`: nc_get_var_ type
- `nc_get_var_schar`: nc_get_var_ type
- `nc_get_var_short`: nc_get_var_ type
- `nc_get_var_string`: nc_get_var_ type
- `nc_get_var_text`: nc_get_var_ type
- `nc_get_var_ubyte`: nc_get_var_ type
- `nc_get_var_uchar`: nc_get_var_ type
- `nc_get_var_uint`: nc_get_var_ type
- `nc_get_var_ulonglong`: nc_get_var_ type
- `nc_get_var_ushort`: nc_get_var_ type
- `nc_get_vara`: nc_get_vara_ type
- `nc_get_vara_ type`: nc_get_vara_ type
- nc_get_vara_ type, example: nc_get_vara_ type
- `nc_get_vara_double`: nc_get_vara_ type
- `nc_get_vara_float`: nc_get_vara_ type
- `nc_get_vara_int`: nc_get_vara_ type
- `nc_get_vara_long`: nc_get_vara_ type
- `nc_get_vara_longlong`: nc_get_vara_ type
- `nc_get_vara_schar`: nc_get_vara_ type
- `nc_get_vara_short`: nc_get_vara_ type
- `nc_get_vara_string`: nc_get_vara_ type
- `nc_get_vara_text`: nc_get_vara_ type
- `nc_get_vara_ubyte`: nc_get_vara_ type
- `nc_get_vara_uchar`: nc_get_vara_ type
- `nc_get_vara_uint`: nc_get_vara_ type
- `nc_get_vara_ulonglong`: nc_get_vara_ type
- `nc_get_vara_ushort`: nc_get_vara_ type
- `nc_get_varm`: nc_get_varm_ type
- `nc_get_varm_ type`: nc_get_varm_ type
- nc_get_varm_ type, example: nc_get_varm_ type
- `nc_get_varm_double`: nc_get_varm_ type
- `nc_get_varm_float`: nc_get_varm_ type
- `nc_get_varm_int`: nc_get_varm_ type
- `nc_get_varm_long`: nc_get_varm_ type
- `nc_get_varm_longlong`: nc_get_varm_ type
- `nc_get_varm_schar`: nc_get_varm_ type
- `nc_get_varm_short`: nc_get_varm_ type
- `nc_get_varm_string`: nc_get_varm_ type
- `nc_get_varm_text`: nc_get_varm_ type
- `nc_get_varm_ubyte`: nc_get_varm_ type
- `nc_get_varm_uchar`: nc_get_varm_ type
- `nc_get_varm_uint`: nc_get_varm_ type
- `nc_get_varm_ulonglong`: nc_get_varm_ type
- `nc_get_varm_ushort`: nc_get_varm_ type
- `nc_get_vars`: nc_get_vars_ type
- `nc_get_vars_ type`: nc_get_vars_ type
- nc_get_vars_ type, example: nc_get_vars_ type
- `nc_get_vars_double`: nc_get_vars_ type
- `nc_get_vars_float`: nc_get_vars_ type
- `nc_get_vars_int`: nc_get_vars_ type
- `nc_get_vars_long`: nc_get_vars_ type
- `nc_get_vars_longlong`: nc_get_vars_ type
- `nc_get_vars_schar`: nc_get_vars_ type
- `nc_get_vars_short`: nc_get_vars_ type
- `nc_get_vars_string`: nc_get_vars_ type
- `nc_get_vars_text`: nc_get_vars_ type
- `nc_get_vars_ubyte`: nc_get_vars_ type
- `nc_get_vars_uchar`: nc_get_vars_ type
- `nc_get_vars_uint`: nc_get_vars_ type
- `nc_get_vars_ulonglong`: nc_get_vars_ type
- `nc_get_vars_ushort`: nc_get_vars_ type
- `nc_inq Family`: nc_inq Family
- nc_inq Family, example: nc_inq Family
- `nc_inq, typical use`: Reading Unknown
- `nc_inq_att Family`: nc_inq_att Family
- nc_inq_att Family, example: nc_inq_att Family
- `nc_inq_att, typical use`: Reading Unknown
- `nc_inq_compound`: nc_inq_compound
- `nc_inq_compound_field`: nc_inq_compound_field
- `nc_inq_compound_fielddim_sizes`: nc_inq_compound_fielddim_sizes
- `nc_inq_compound_fieldindex`: nc_inq_compound_fieldindex
- `nc_inq_compound_fieldname`: nc_inq_compound_fieldname
- `nc_inq_compound_fieldndims`: nc_inq_compound_fieldndims
- `nc_inq_compound_fieldoffset`: nc_inq_compound_fieldoffset
- `nc_inq_compound_fieldtype`: nc_inq_compound_fieldtype
- `nc_inq_compound_name`: nc_inq_compound_name
- `nc_inq_compound_nfields`: nc_inq_compound_nfields
- `nc_inq_compound_size`: nc_inq_compound_size
- `nc_inq_dim`: nc_inq_dim Family
- `nc_inq_dim Family`: nc_inq_dim Family
- nc_inq_dim Family, example: nc_inq_dim Family
- `nc_inq_dim, typical use`: Reading Unknown
- `nc_inq_dimid`: nc_inq_dim Family
- `nc_inq_dimid`: nc_inq_dimid
- nc_inq_dimid, example: nc_inq_dimid
- `nc_inq_dimid, typical use`: Reading Known
- `nc_inq_dimids`: nc_inq_dim Family
- `nc_inq_dimids`: nc_inq_dimids
- `nc_inq_dimlen`: nc_inq_dim Family
- `nc_inq_dimname`: nc_inq_dim Family
- `nc_inq_enum`: nc_inq_enum
- `nc_inq_enum_ident`: nc_inq_enum_ident
- `nc_inq_enum_member`: nc_inq_enum_member
- `nc_inq_format`: nc_inq Family
- `nc_inq_grp_parent`: nc_inq_grp_full_ncid
- `nc_inq_grp_parent`: nc_inq_grp_ncid
- `nc_inq_grp_parent`: nc_inq_grp_parent
- `nc_inq_grpname`: nc_inq_grpname
- `nc_inq_grpname_full`: nc_inq_grpname_full
- `nc_inq_grpname_len`: nc_inq_grpname_len
- `nc_inq_grps`: nc_inq_grps
- `nc_inq_libvers`: nc_inq_libvers
- nc_inq_libvers, example: nc_inq_libvers
- `nc_inq_natts`: nc_inq Family
- `nc_inq_ncid`: nc_inq_ncid
- `nc_inq_ndims`: nc_inq Family
- `nc_inq_nvars`: nc_inq Family
- `nc_inq_opaque`: nc_inq_opaque
- `nc_inq_type`: nc_inq_type
- `nc_inq_typeid`: nc_inq_typeid
- `nc_inq_typeids`: nc_inq_typeids
- `nc_inq_unlimdim`: nc_inq Family
- `nc_inq_unlimdims`: nc_inq_unlimdims
- `nc_inq_user_type`: nc_inq_user_type
- `nc_inq_var`: nc_inq_var
- nc_inq_var, example: nc_inq_var
- `nc_inq_var, typical use`: Reading Unknown
- `nc_inq_var_chunking`: nc_inq_var_chunking
- `nc_inq_var_deflate`: nc_inq_var_deflate
- `nc_inq_var_endian`: nc_inq_var_endian
- `nc_inq_var_fill`: nc_inq_var_fill
- `nc_inq_var_fletcher32`: nc_inq_var_fletcher32
- `nc_inq_var_szip`: nc_inq_var_szip
- `nc_inq_varid`: nc_inq_varid
- nc_inq_varid, example: nc_inq_varid
- `nc_inq_varid, typical use`: Reading Known
- `nc_inq_varids`: nc_inq_varids
- `nc_inq_varname`: nc_inq_var
- `nc_inq_varnatts`: nc_inq_var
- `nc_inq_varndims`: nc_inq_var
- `nc_inq_vartype`: nc_inq_var
- `nc_insert_array_compound`: nc_insert_array_compound
- `nc_insert_compound`: nc_insert_compound
- `nc_insert_enum`: nc_insert_enum
- `NC_MPIIO`: nc_create_par
- `NC_MPIPOSIX`: nc_create_par
- `NC_NETCDF4`: nc_open_par
- `NC_NOCLOBBER`: nc_create_par
- `NC_NOCLOBBER`: nc__create
- `NC_NOCLOBBER`: nc_create
- `NC_NOWRITE`: nc_open_par
- `NC_NOWRITE`: nc__open
- `NC_NOWRITE`: nc_open
- `nc_open`: nc_open
- nc_open, example: nc_open
- `nc_open_par`: nc_open_par
- `nc_put_att, typical use`: Adding
- `nc_put_att, typical use`: Use of the NetCDF Library
- `nc_put_att_ type`: nc_put_att_ type
- nc_put_att_ type, example: nc_put_att_ type
- `nc_put_var`: nc_put_var_ type
- `nc_put_var, typical use`: Use of the NetCDF Library
- `nc_put_var1`: nc_put_var1_ type
- `nc_put_var1_ type`: nc_put_var1_ type
- nc_put_var1_ type, example: nc_put_var1_ type
- `nc_put_var1_double`: nc_put_var1_ type
- `nc_put_var1_float`: nc_put_var1_ type
- `nc_put_var1_int`: nc_put_var1_ type
- `nc_put_var1_long`: nc_put_var1_ type
- `nc_put_var1_longlong`: nc_put_var1_ type
- `nc_put_var1_schar`: nc_put_var1_ type
- `nc_put_var1_short`: nc_put_var1_ type
- `nc_put_var1_string`: nc_put_var1_ type
- `nc_put_var1_text`: nc_put_var1_ type
- `nc_put_var1_ubyte`: nc_put_var1_ type
- `nc_put_var1_uchar`: nc_put_var1_ type
- `nc_put_var1_uint`: nc_put_var1_ type
- `nc_put_var1_ulonglong`: nc_put_var1_ type
- `nc_put_var1_ushort`: nc_put_var1_ type
- `nc_put_var_ type`: nc_put_var_ type
- nc_put_var_ type, example: nc_put_var_ type
- `nc_put_var_double`: nc_put_var_ type
- `nc_put_var_float`: nc_put_var_ type
- `nc_put_var_int`: nc_put_var_ type
- `nc_put_var_long`: nc_put_var_ type
- `nc_put_var_longlong`: nc_put_var_ type
- `nc_put_var_schar`: nc_put_var_ type
- `nc_put_var_short`: nc_put_var_ type
- `nc_put_var_string`: nc_put_var_ type
- `nc_put_var_text`: nc_put_var_ type
- `nc_put_var_ubyte`: nc_put_var_ type
- `nc_put_var_uchar`: nc_put_var_ type
- `nc_put_var_uint`: nc_put_var_ type
- `nc_put_var_ulonglong`: nc_put_var_ type
- `nc_put_var_ushort`: nc_put_var_ type
- `nc_put_vara`: nc_put_vara_ type
- `nc_put_vara_ type`: nc_put_vara_ type
- nc_put_vara_ type, example: nc_put_vara_ type
- `nc_put_vara_double`: nc_put_vara_ type
- `nc_put_vara_float`: nc_put_vara_ type
- `nc_put_vara_int`: nc_put_vara_ type
- `nc_put_vara_long`: nc_put_vara_ type
- `nc_put_vara_longlong`: nc_put_vara_ type
- `nc_put_vara_schar`: nc_put_vara_ type
- `nc_put_vara_short`: nc_put_vara_ type
- `nc_put_vara_string`: nc_put_vara_ type
- `nc_put_vara_text`: nc_put_vara_ type
- `nc_put_vara_ubyte`: nc_put_vara_ type
- `nc_put_vara_uchar`: nc_put_vara_ type
- `nc_put_vara_uint`: nc_put_vara_ type
- `nc_put_vara_ulonglong`: nc_put_vara_ type
- `nc_put_vara_ushort`: nc_put_vara_ type
- `nc_put_varm`: nc_put_varm_ type
- `nc_put_varm_ type`: nc_put_varm_ type
- nc_put_varm_ type, example: nc_put_varm_ type
- `nc_put_varm_double`: nc_put_varm_ type
- `nc_put_varm_float`: nc_put_varm_ type
- `nc_put_varm_int`: nc_put_varm_ type
- `nc_put_varm_long`: nc_put_varm_ type
- `nc_put_varm_longlong`: nc_put_varm_ type
- `nc_put_varm_schar`: nc_put_varm_ type
- `nc_put_varm_short`: nc_put_varm_ type
- `nc_put_varm_string`: nc_put_varm_ type
- `nc_put_varm_text`: nc_put_varm_ type
- `nc_put_varm_ubyte`: nc_put_varm_ type
- `nc_put_varm_uchar`: nc_put_varm_ type
- `nc_put_varm_uint`: nc_put_varm_ type
- `nc_put_varm_ulonglong`: nc_put_varm_ type
- `nc_put_varm_ushort`: nc_put_varm_ type
- `nc_put_vars`: nc_put_vars_ type
- `nc_put_vars_ type`: nc_put_vars_ type
- nc_put_vars_ type, example: nc_put_vars_ type
- `nc_put_vars_double`: nc_put_vars_ type
- `nc_put_vars_float`: nc_put_vars_ type
- `nc_put_vars_int`: nc_put_vars_ type
- `nc_put_vars_long`: nc_put_vars_ type
- `nc_put_vars_longlong`: nc_put_vars_ type
- `nc_put_vars_schar`: nc_put_vars_ type
- `nc_put_vars_short`: nc_put_vars_ type
- `nc_put_vars_string`: nc_put_vars_ type
- `nc_put_vars_text`: nc_put_vars_ type
- `nc_put_vars_ubyte`: nc_put_vars_ type
- `nc_put_vars_uchar`: nc_put_vars_ type
- `nc_put_vars_uint`: nc_put_vars_ type
- `nc_put_vars_ulonglong`: nc_put_vars_ type
- `nc_put_vars_ushort`: nc_put_vars_ type
- `nc_redef`: nc_redef
- nc_redef, example: nc_redef
- `nc_redef, typical use`: Adding
- `nc_rename_att`: nc_rename_att
- nc_rename_att, example: nc_rename_att
- `nc_rename_dim`: nc_rename_dim
- nc_rename_dim, example: nc_rename_dim
- `nc_rename_var`: nc_rename_var
- nc_rename_var, example: nc_rename_var
- `nc_set_chunk_cache`: nc_set_chunk_cache
- `nc_set_default_format`: nc_set_default_format
- nc_set_default_format, example: nc_set_default_format
- `nc_set_fill`: nc_set_fill
- nc_set_fill, example: nc_set_fill
- `nc_set_var_chunk_cache`: nc_set_var_chunk_cache
- `NC_SHARE`: nc__create
- `NC_SHARE`: nc_create
- NC_SHARE: Adding
- `NC_SHARE, and buffering`: Use of the NetCDF Library
- `NC_SHARE, in nc__open`: nc__open
- `NC_SHARE, in nc_open`: nc_open
- `nc_strerror`: nc_strerror
- nc_strerror, example: nc_strerror
- `nc_strerror, introduction`: Errors
- NC_STRING, freeing: nc_free_string
- NC_STRING, using: Arrays of Strings
- `nc_sync`: nc_sync
- nc_sync, example: nc_sync
- `nc_var_par_access`: nc_var_par_access
- nc_var_par_access, example: nc_var_par_access
- `NC_WRITE`: nc_open_par
- `NC_WRITE`: nc__open
- `NC_WRITE`: nc_open
- `ncid`: nc_inq_att Family
- netCDF 2 transition guide: NetCDF 2 C Transition Guide
- netCDF library version: nc_inq_libvers
- netcdf-3 error codes: NetCDF-3 Error Codes
- netcdf-4 error codes: NetCDF-4 Error Codes
- opaque type: Opaque Type
- parallel access: parallel access
- parallel example: parallel access
- reading attributes: nc_get_att_ type
- reading entire variable: nc_get_var_ type
- reading netCDF dataset with known names: Reading Known
- reading netCDF dataset with unknown names: Reading Unknown
- reading single value: nc_get_var1_ type
- renaming attributes: nc_rename_att
- renaming variable: nc_rename_var
- single value, reading: nc_get_var1_ type
- string arrays: Strings
- strings in classic model: Classic Strings
- subsampled array, writing: nc_put_vars_ type
- templates, code: Use of the NetCDF Library
- transition guide, netCDF 2: NetCDF 2 C Transition Guide
- user defined types: User Defined Data Types
- user defined types, overview: User Defined Types
- variable length array type, overview: User Defined Data Types
- variable length arrays: Variable Length Array
- variable, copying: nc_copy_var
- variable, renaming: nc_rename_var
- variable, writing entire: nc_put_var_ type
- variables, adding: Adding
- variables, checksum: nc_def_var_fletcher32
- variables, chunking: nc_def_var_chunking
- variables, contiguous: nc_def_var_chunking
- variables, creating: nc_def_var
- variables, endian: nc_def_var_endian
- variables, fill: nc_def_var_fill
- variables, fletcher32: nc_def_var_fletcher32
- variables, getting name: nc_inq_var
- variables, inquiring about: nc_inq_varid
- variables, number of: nc_inq Family
- variables, setting deflate: nc_def_var_deflate
- `varid`: nc_inq_att Family
- version of netCDF, discovering: nc_inq_libvers
- version, format: nc_inq Family
- VLEN: Variable Length Array
- VLEN, defining: nc_free_vlens
- VLEN, defining: nc_free_vlen
- VLEN, defining: nc_inq_vlen
- VLEN, defining: nc_def_vlen
- write errors: Errors
- write fill mode, setting: nc_set_fill
- writing array section: nc_put_vara_ type
- writing attributes: nc_put_att_ type
- writing character-string data: Classic Strings
- writing entire variable: nc_put_var_ type
- writing mapped array: nc_put_varm_ type
- writing mapped array section: nc_get_varm_ type
- writing single value: nc_put_var1_ type
- writing subsampled array: nc_put_vars_ type
- XDR library: NetCDF 2 C Transition Guide
- `xtypep`: nc_inq_att Family
- zero byte: Classic Strings
- zero length edge: NetCDF 2 C Transition Guide
- zero valued count vector: NetCDF 2 C Transition Guide