This document describes the FORTRAN-77 interface to the netCDF library. This document applies to netCDF version 4.1.3. This document was last updated in 30 June 2011.
For a complete description of the netCDF format and utilities see Top.
--- The Detailed Node Listing ---
Use of the NetCDF Library
Datasets
Groups
Dimensions
User Defined Data Types
Compound Types Introduction
Variable Length Array Introduction
Opaque Type Introduction
Example
Enum Type Introduction
Variables
Attributes
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 are needed if you use the ncgen utility to create the dataset before running a program using netCDF library calls to write data. See ncgen.) 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.
Here is a typical sequence of netCDF calls used to create a new netCDF dataset:
NF_CREATE ! create netCDF dataset: enter define mode ... NF_DEF_DIM ! define dimensions: from name and length ... NF_DEF_VAR ! define variables: from name, type, dims ... NF_PUT_ATT ! assign attribute values ... NF_ENDDEF ! end definitions: leave define mode ... NF_PUT_VAR ! provide values for variable ... NF_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 NF_DEF_DIM is needed for each dimension created. Similarly, one call to NF_DEF_VAR is needed for each variable creation, and one call to a member of the NF_PUT_ATT family is needed for each attribute defined and assigned a value. To leave define mode and enter data mode, call NF_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 NF_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 NF_PUT_VAR family. Arrays or array cross-sections of a variable may be written using members of the NF_PUT_VARA family. Subsampled array sections may be written using members of the NF_PUT_VARS family. Mapped array sections may be written using members of the NF_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 NF_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 NF_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 NF_SYNC or NF_CLOSE is called.
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:
NF_OPEN ! open existing netCDF dataset ... NF_INQ_DIMID ! get dimension IDs ... NF_INQ_VARID ! get variable IDs ... NF_GET_ATT ! get attribute values ... NF_GET_VAR ! get values of variables ... NF_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 NF_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 NF_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 NF_GET_ATT family (typically NF_GET_ATT_TEXT or NF_GET_ATT_DOUBLE) for each desired attribute. Variable data values can be directly accessed from the netCDF dataset with calls to members of the NF_GET_VAR1 family for single values, the NF_GET_VAR family for entire variables, or various other members of the NF_GET_VARA, NF_GET_VARS, or NF_GET_VARM families for array, subsampled or mapped access.
Finally, the netCDF dataset is closed with NF_CLOSE. There is no need to close a dataset open only for reading.
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:
NF_OPEN ! open existing netCDF dataset ... NF_INQ ! find out what is in it ... NF_INQ_DIM ! get dimension names, lengths ... NF_INQ_VAR ! get variable names, types, shapes ... NF_INQ_ATTNAME ! get attribute names ... NF_INQ_ATT ! get attribute values ... NF_GET_ATT ! get attribute values ... NF_GET_VAR ! get values of variables ... NF_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 NF_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 1. 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 1, 2, 3, ... up to the number of dimensions. For each dimension ID, a call to the inquire function NF_INQ_DIM returns the dimension name and length.
Variable IDs are also assigned from consecutive integers 1, 2, 3, ... up to the number of variables. These can be used in NF_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 NF_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 NF_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 NF_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 NF_GET_VAR1 family for single values, or members of the NF_GET_VAR, NF_GET_VARA, NF_GET_VARS, or NF_GET_VARM for various kinds of array access.
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:
NF_OPEN ! open existing netCDF dataset ... NF_REDEF ! put it into define mode ... NF_DEF_DIM ! define additional dimensions (if any) ... NF_DEF_VAR ! define additional variables (if any) ... NF_PUT_ATT ! define other attributes (if any) ... NF_ENDDEF ! check definitions, leave define mode ... NF_PUT_VAR ! provide new variable values ... NF_CLOSE ! close netCDF dataset
A netCDF dataset is first opened by the NF_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 NF_REDEF.In define mode, call NF_DEF_DIM to define new dimensions, NF_DEF_VAR to define new variables, and a member of the NF_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 NF_ENDDEF. If you do not wish to reenter data mode, just call NF_CLOSE, which will have the effect of first calling NF_ENDDEF.
Until the NF_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 NF_ABORT. You may also use the NF_ABORT call to restore the netCDF dataset to a consistent state if the call to NF_ENDDEF fails. If you have called NF_CLOSE from definition mode and the implied call to NF_ENDDEF fails, NF_ABORT will automatically be called to close the netCDF dataset and leave it in its previous consistent state (before you entered define mode).
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 NF_SYNC function and the NF_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 NF_SYNC before the next access.
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 to handle any errors.
The NF_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.
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, and where the netCDF library and include files are installed. 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 FORTRAN file that references netCDF functions or constants must contain an appropriate INCLUDE statement before the first such reference:
INCLUDE 'netcdf.inc'
Unless the netcdf.inc file is installed in a standard directory where the FORTRAN compiler always looks, you must use the -I option when invoking the compiler, to specify a directory where netcdf.inc is installed, for example:
f77 -c -I/usr/local/netcdf/include myprogram.f
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. For example:
f77 -o myprogram myprogram.o -L/usr/local/netcdf/lib -lnetcdf
Alternatively, you could specify an absolute path name for the library:
f77 -o myprogram myprogram.o -l/usr/local/netcdf/lib/libnetcdf.
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 nonnegative 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:
The operations supported on a netCDF dataset as a single object are:
Each interface description for a particular netCDF function in this and later chapters contains:
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 Section 5.2 "Get error message corresponding to error status: nf_strerror".
The function NF_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.
CHARACTER*80 FUNCTION NF_STRERROR(INTEGER NCERR)
NCERR
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), NF_STRERROR returns a string indicating that there is no such error status.
Here is an example of a simple error handling function that uses NF_STRERROR to print the error message corresponding to the netCDF error status returned from any netCDF function call and then exit:
INCLUDE 'netcdf.inc' ... SUBROUTINE HANDLE_ERR(STATUS) INTEGER STATUS IF (STATUS .NE. NF_NOERR) THEN PRINT *, NF_STRERROR(STATUS) STOP 'Stopped' ENDIF END
The function NF_INQ_LIBVERS returns a string identifying the version of the netCDF library, and when it was built.
CHARACTER*80 FUNCTION NF_INQ_LIBVERS()
This function takes no arguments, and thus no errors are possible in its invocation.
Here is an example using nf_inq_libvers to print the version of the netCDF library with which the program is linked:
INCLUDE 'netcdf.inc' ... PRINT *, NF_INQ_LIBVERS()
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.
INTEGER FUNCTION NF_CREATE (CHARACTER*(*) PATH, INTEGER CMODE, INTEGER ncid)
PATH
CMODE
A zero value (defined for convenience as NF_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 NF_NOCLOBBER means you do not want to clobber (overwrite) an existing dataset; an error (NF_EEXIST) is returned if the specified dataset already exists.
The NF_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 NF_SHARE flag. This only applied to classic and 64-bit offset format files.
Setting NF_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.
Setting NF_NETCDF4 causes netCDF to create a netCDF-4/HDF5 format
file. Oring NF_CLASSIC_MODEL with NF_NETCDF4 causes the netCDF library
to create a netCDF-4/HDF5 data file, with the netCDF classic model
enforced - none of the new features of the netCDF-4 data model may be
usedin such a file, for example groups and user-defined types.
ncid
NF_CREATE returns the value NF_NOERR if no errors occurred. Possible causes of errors include:
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.inc' ... INTEGER NCID, STATUS ... STATUS = NF_CREATE('foo.nc', NF_NOCLOBBER, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
This function is a variant of NF_CREATE, NF__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 NF__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.
INTEGER FUNCTION NF__CREATE (CHARACTER*(*) PATH, INTEGER CMODE, INTEGER INITIALSZ, INTEGER BUFRSIZEHINT, INTEGER ncid)
PATH
CMODE
Setting NF_NOCLOBBER means you do not want to clobber (overwrite) an existing dataset; an error (NF_EEXIST) is returned if the specified dataset already exists.
The NF_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 NF_SHARE flag. This flag has no effect with netCDF-4/HDF5 files.
Setting NF_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.
Setting NF_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 NF_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 guarenteed to work with existing netCDF software.
A zero value (defined for convenience as NF_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.
INITIALSZ
BUFRSIZEHINT
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 NF_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.
ncid
NF__CREATE returns the value NF_NOERR if no errors occurred. Possible causes of errors include:
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.inc' ... INTEGER NCID, STATUS, INITIALSZ, BUFRSIZEHINT ... INITIALSZ = 2048 BUFRSIZEHINT = 1024 STATUS = NF__CREATE('foo.nc', NF_NOCLOBBER, INITIALSZ, BUFRSIZEHINT, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
This function is a variant of nf_create, nf_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 nf_create_par.
This function is only available if the netCDF library was built with parallel I/O.
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.
When a netCDF-4 file is created for parallel access, independent operations are the default. To use collective access on a variable, See NF_VAR_PAR_ACCESS.
INTEGER FUNCTION NF_CREATE_PAR(CHARACTER*(*) PATH, INTEGER CMODE, INTEGER MPI_COMM, INTEGER MPI_INFO, INTEGER ncid)
PATH
CMODE
Setting NF_NETCDF4 causes netCDF to create a netCDF-4/HDF5 format file. Oring NF_CLASSIC_MODEL with NF_NETCDF4 causes the netCDF library to create a netCDF-4/HDF5 data file, with the netCDF classic model enforced - none of the new features of the netCDF-4 data model may be usedin such a file, for example groups and user-defined types.
Only netCDF-4/HDF5 files may be used with parallel I/O.
MPI_COMM
MPI_INFO
ncid
NF_CREATE returns the value NF_NOERR if no errors occurred. Possible causes of errors include:
This example is from test program nf_test/ftst_parallel.F.
! Create the netCDF file. mode_flag = IOR(nf_netcdf4, nf_classic_model) retval = nf_create_par(FILE_NAME, mode_flag, MPI_COMM_WORLD, $ MPI_INFO_NULL, ncid) if (retval .ne. nf_noerr) stop 2
The function NF_OPEN opens an existing netCDF dataset for access.
INTEGER FUNCTION NF_OPEN(CHARACTER*(*) PATH, INTEGER OMODE, INTEGER ncid)
PATH
OMODE
Otherwise, the creation mode is NF_WRITE, NF_SHARE, or
OR(NF_WRITE, NF_SHARE). Setting the NF_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 NF_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 NF_SHARE flag.
ncid
NF_OPEN returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_OPEN to open an existing netCDF dataset named foo.nc for read-only, non-shared access:
INCLUDE 'netcdf.inc' ... INTEGER NCID, STATUS ... STATUS = NF_OPEN('foo.nc', 0, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The function NF)_OPEN opens an existing netCDF dataset for access, with a performance tuning parameter.
INTEGER FUNCTION NF__OPEN(CHARACTER*(*) PATH, INTEGER OMODE, INTEGER BUFRSIZEHINT, INTEGER ncid)
PATH
OMODE
Otherwise, the creation mode is NF_WRITE, NF_SHARE, or
OR(NF_WRITE,NF_SHARE). Setting the NF_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 NF_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 NF_SHARE flag.
BUFRSIZEHINT
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 NF_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.
ncid
NF__OPEN returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF__OPEN to open an existing netCDF dataset named foo.nc for read-only, non-shared access:
INCLUDE 'netcdf.inc' ... INTEGER NCID, STATUS, BUFRSIZEHINT ... BUFRSIZEHINT = 1024 STATUS = NF_OPEN('foo.nc', 0, BUFRSIZEHINT, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
This function opens a netCDF-4 dataset for parallel access.
This function is only available if the netCDF library was built with a HDF5 library for which –enable-parallel was used, and which was linked (like HDF5) to MPI libraries.
This opens the file using either MPI-IO or MPI-POSIX. The file must be a netCDF-4 file. (That is, it must have been created using NF_NETCDF4 in the creation mode).
This function is only available if netCDF-4 was build with a version of the HDF5 library which was built with –enable-parallel.
Before either HDF5 or netCDF-4 can be installed with support for parallel programming, and MPI layer must also be installed on the machine, and usually a parallel file system.
NetCDF-4 exposes the parallel access functionality of HDF5. For more information about what is required to install and use the parallel access functions, see the HDF5 web site.
When a netCDF-4 file is opened for parallel access, collective operations are the default. To use independent access on a variable, See NF_VAR_PAR_ACCESS.
INTEGER FUNCTION NF_OPEN_PAR(CHARACTER*(*) PATH, INTEGER OMODE, INTEGER MPI_COMM, INTEGER MPI_INFO, INTEGER ncid)
PATH
OMODE
Otherwise, the mode may be NF_WRITE. Setting the NF_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.)
Setting NF_NETCDF4 is not necessary (or allowed). The file type is
detected automatically.
MPI_COMM
MPI_INFO
ncid
NF_OPEN returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
This example is from the test program nf_test/ftst_parallel.F.
! Reopen the file. retval = nf_open_par(FILE_NAME, nf_nowrite, MPI_COMM_WORLD, $ MPI_INFO_NULL, ncid) if (retval .ne. nf_noerr) stop 2
The function NF_REDEF puts an open netCDF dataset into define mode, so dimensions, variables, and attributes can be added or renamed and attributes can be deleted.
INTEGER FUNCTION NF_REDEF(INTEGER NCID)
NCID
NF_REDEF returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_REDEF to open an existing netCDF dataset named foo.nc and put it into define mode:
INCLUDE 'netcdf.inc' ... INTEGER NCID, STATUS ... STATUS = NF_OPEN('foo.nc', NF_WRITE, NCID) ! open dataset IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_REDEF(NCID) ! put in define mode IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The function NF_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 NF_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. See File Structure and Performance.
INTEGER FUNCTION NF_ENDDEF(INTEGER NCID)
NCID
NF_ENDDEF returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_ENDDEF to finish the definitions of a new netCDF dataset named foo.nc and put it into data mode:
INCLUDE 'netcdf.inc' ... INTEGER NCID, STATUS ... STATUS = NF_CREATE('foo.nc', NF_NOCLOBBER, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... ! create dimensions, variables, attributes STATUS = NF_ENDDEF(NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The function NF__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 NF_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. See File Structure and Performance.
This function assumes specific characteristics of the netcdf version 1 and version 2 file formats. Users should use nf_enddef in most circumstances. Although this function will be available in future netCDF implementations, it may not continue to have any effect on performance.
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 nf_redef, nf_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.
The file format requires mod 4 alignment, so the align parameters are silently rounded up to multiples of 4. The usual call,
nf_enddef(ncid);
is equivalent to
nf_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.
INTEGER FUNCTION NF_ENDDEF(INTEGER NCID, INTEGER H_MINFREE, INTEGER V_ALIGN, INTEGER V_MINFREE, INTEGER R_ALIGN)
NCID
H_MINFREE
V_ALIGN
V_MINFREE
R_ALIGN
NF__ENDDEF returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF__ENDDEF to finish the definitions of a new netCDF dataset named foo.nc and put it into data mode:
INCLUDE 'netcdf.inc' ... INTEGER NCID, STATUS, H_MINFREE, V_ALIGN, V_MINFREE, R_ALIGN ... STATUS = NF_CREATE('foo.nc', NF_NOCLOBBER, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... ! create dimensions, variables, attributes H_MINFREE = 512 V_ALIGN = 512 V_MINFREE = 512 R_ALIGN = 512 STATUS = NF_ENDDEF(NCID, H_MINFREE, V_ALIGN, V_MINFREE, R_ALIGN) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The function NF_CLOSE closes an open netCDF dataset. If the dataset is in define mode, NF_ENDDEF will be called before closing. (In this case, if NF_ENDDEF returns an error, NF_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.
INTEGER FUNCTION NF_CLOSE(INTEGER NCID)
NCID
NF_CLOSE returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_CLOSE to finish the definitions of a new netCDF dataset named foo.nc and release its netCDF ID:
INCLUDE 'netcdf.inc' ... INTEGER NCID, STATUS ... STATUS = NF_CREATE('foo.nc', NF_NOCLOBBER, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... ! create dimensions, variables, attributes STATUS = NF_CLOSE(NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
Members of the NF_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, NF_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 FORTRAN, these functions include NF_INQ, NF_INQ_NDIMS, NF_INQ_NVARS, NF_INQ_NATTS, and NF_INQ_UNLIMDIM. An additional function, NF_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.
INTEGER FUNCTION NF_INQ (INTEGER NCID, INTEGER ndims, INTEGER nvars,INTEGER ngatts, INTEGER unlimdimid) INTEGER FUNCTION NF_INQ_NDIMS (INTEGER NCID, INTEGER ndims) INTEGER FUNCTION NF_INQ_NVARS (INTEGER NCID, INTEGER nvars) INTEGER FUNCTION NF_INQ_NATTS (INTEGER NCID, INTEGER ngatts) INTEGER FUNCTION NF_INQ_UNLIMDIM (INTEGER NCID, INTEGER unlimdimid) INTEGER FUNCTION NF_INQ_FORMAT (INTEGER NCID, INTEGER format)
NCID
ndims
nvars
ngatts
unlimdimid
format
All members of the NF_INQ family return the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_INQ to find out about a netCDF dataset named foo.nc:
INCLUDE 'netcdf.inc' ... INTEGER STATUS, NCID, NDIMS, NVARS, NGATTS, UNLIMDIMID ... STATUS = NF_OPEN('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ(NCID, NDIMS, NVARS, NGATTS, UNLIMDIMID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The function NF_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:
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 NF_SYNC after writing and the readers call NF_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 NF_SHARE flag, and then it will not be necessary to call NF_SYNC at all. However, the NF_SYNC function still provides finer granularity than the NF_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 NF_SHARE flag. Use of the NF_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 NF_SYNC before any subsequent access.
When calling NF_SYNC, the netCDF dataset must be in data mode. A netCDF dataset in define mode is synchronized to disk only when NF_ENDDEF is called. A process that is reading a netCDF dataset that another process is writing may call NF_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.
INTEGER FUNCTION NF_SYNC(INTEGER NCID)
NCID
NF_SYNC returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_SYNC to synchronize the disk writes of a netCDF dataset named foo.nc:
INCLUDE 'netcdf.inc' ... INTEGER STATUS, NCID ... STATUS = NF_OPEN('foo.nc', NF_WRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... ! write data or change attributes ... STATUS = NF_SYNC(NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
You no longer need to call this function, since it is called automatically by NF_CLOSE in case the dataset is in define mode and something goes wrong with committing the changes. The function NF_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 NF_REDEF, the netCDF dataset is restored to its state before definition mode was entered and the dataset is closed.
INTEGER FUNCTION NF_ABORT(INTEGER NCID)
NCID
NF_ABORT returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_ABORT to back out of redefinitions of a dataset named foo.nc:
INCLUDE 'netcdf.inc' ... INTEGER STATUS, NCID, LATID ... STATUS = NF_OPEN('foo.nc', NF_WRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_REDEF(NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_DEF_DIM(NCID, 'LAT', 18, LATID) IF (STATUS .NE. NF_NOERR) THEN ! dimension definition failed CALL HANDLE_ERR(STATUS) STATUS = NF_ABORT(NCID) ! abort redefinitions IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ENDIF ...
This function is intended for advanced usage, to optimize writes under some circumstances described below. The function NF_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 NF_FILL or NF_NOFILL. The default behavior corresponding to NF_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. See Fill Values, for more information on the use of fill values. See Attribute Conventions, for information about how to define your own fill values.
The behavior corresponding to NF_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 NF_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 NF_SET_FILL again to explicitly set the fill mode to NF_FILL.
There are three situations where it is advantageous to set nofill mode:
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.
INTEGER FUNCTION NF_SET_FILL(INTEGER NCID, INTEGER FILLMODE, INTEGER old_mode)
NCID
FILLMODE
old_mode
NF_SET_FILL returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_SET_FILL to set nofill mode for subsequent writes of a netCDF dataset named foo.nc:
INCLUDE 'netcdf.inc' ... INTEGER NCID, STATUS, OMODE ... STATUS = NF_OPEN('foo.nc', NF_WRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... ! write data with default prefilling behavior ... STATUS = NF_SET_FILL(NCID, NF_NOFILL, OMODE) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... ! write data with no prefilling ...
This function is intended for advanced users.
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.
In version 4.0, another new binary format was introduced: netCDF-4/HDF5.
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, and creating files in netcdf-4/HDF5 format makes them unreadable by the netCDF library prior to version 4.0. For reasons of compatibility, users should continue to create files in netCDF classic format.
Users who do want to use 64-bit offset or netCDF-4/HDF5 format files can create them directory from NF_CREATE, using the proper cmode flag. (see NF_CREATE).
The function NF_SET_DEFAULT_FORMAT allows the user to change the format of the netCDF file to be created by future calls to NF_CREATE without changing the cmode flag.
This allows the user to convert a program to use the new formats without changing all calls the NF_CREATE.
Once the default format is set, all future created files will be in the desired format.
Constants are provided in the netcdf.inc file to be used with this function: nf_format_classic, nf_format_64bit, nf_format_netcdf4 and nf_format_netcdf4_classic.
INTEGER FUNCTION NF_SET_DEFAULT_FORMAT(INTEGER FORMAT, INTEGER OLD_FORMT)
FORMAT
OLD_FORMAT
The following error codes may be returned by this function:
INCLUDE 'netcdf.inc' ... INTEGER STATUS, OLD_FORMAT ... STATUS = NF_SET_DEFAULT_FORMAT(nf_format_64bit, OLD_FORMAT) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ...
This function changes the chunk cache settings in the HDF5 library. The settings apply for subsequent file opens/creates. This function does not change the chunk cache settings of already open files.
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 H5Pset_cache() function in the HDF5 library at the HDF5 website: http://hdfgroup.org/HDF5/.
INTEGER NF_SET_CHUNK_CACHE(INTEGER SIZE, INTEGER NELEMS, INTEGER PREEMPTION);
SIZE
NELEMS
PREEMPTION
NF_NOERR
NF_EINVAL
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/.
INTEGER NC_GET_CHUNK_CACHE(INTEGER SIZE, INTEGER NELEMS, INTEGER PREEMPTION);
SIZE
NELEMS
PREEMPTION
NC_NOERR
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 NF_OPEN or NF_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 NF_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 NF_CREATE or NF_OPEN to create a variable in the root group. Or use NF_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 defined in whichever group is refered to by the ncid.
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 nf_create. (see NF_CREATE). Groups are not compatible with the netCDF classic data model, so files created with the NF_CLASSIC_MODEL file cannot contain groups (except the root group).
Given an ncid and group name (NULL or "" gets root group), return ncid of the named group.
INTEGER FUNCTION NF_INQ_NCID(INTEGER NCID, CHARACTER*(*) NAME, INTEGER GRPID)
NCID
NAME
GRPID
NF_NOERR
NF_EBADID
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
This example is from nf_test/ftst_groups.F.
C Check getting the group by name retval = nf_inq_ncid(ncid, group_name, grpid_in) if (retval .ne. nf_noerr) call handle_err(retval)
Given a location id, return the number of groups it contains, and an array of their ncids.
INTEGER FUNCTION NF_INQ_GRPS(INTEGER NCID, INTEGER NUMGRPS, INTEGER NCIDS)
NCID
NUMGRPS
NCIDS
NF_NOERR
NF_EBADID
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
This example is from nf_test/ftst_groups.F.
C What groups are there from the root group? retval = nf_inq_grps(ncid, ngroups_in, grpids) if (retval .ne. nf_noerr) call handle_err(retval)
Find all varids for a location.
INTEGER FUNCTION NF_INQ_VARIDS(INTEGER NCID, INTEGERS VARIDS)
NCID
VARIDS
NF_NOERR
NF_EBADID
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
This example is from nf_test/ftst_groups.F.
C Check varids in subgroup. retval = nf_inq_varids(subgrp_in, nvars, varids_in) if (retval .ne. nf_noerr) call handle_err(retval)
Find all dimids for a location. This finds all dimensions in a group, or any of its parents.
INTEGER FUNCTION NF_INQ_DIMIDS(INTEGER NCID, INTEGER DIMIDS, INTEGER INCLUDE_PARENTS)
NCID
DIMIDS
INCLUDE_PARENTS
NF_NOERR
NF_EBADID
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
This example is from nf_test/ftst_groups.F.
C Check dimids in subgroup. retval = nf_inq_dimids(subgrp_in, ndims, dimids_in, 0) if (retval .ne. nf_noerr) call handle_err(retval) if (ndims .ne. 2 .or. dimids_in(1) .ne. dimids(1) .or. & dimids_in(2) .ne. dimids(2)) stop 2
Given ncid, find length of the full name. (Root group is named "/", with length 1.)
INTEGER FUNCTION NF_INQ_GRPNAME_LEN(INTEGER NCID, INTEGER LEN)
NCID
LEN
NF_NOERR
NF_EBADID
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
This example is from nf_test/ftst_groups.F.
C Check the length of the full name. retval = nf_inq_grpname_len(grpids(1), full_name_len) if (retval .ne. nf_noerr) call handle_err(retval)
Given ncid, find relative name of group. (Root group is named "/").
The name provided by this function is relative to the parent group. For a full path name for the group is, with all parent groups included, separated with a forward slash (as in Unix directory names) See NF_INQ_GRPNAME_FULL.
INTEGER FUNCTION NF_INQ_GRPNAME(INTEGER NCID, CHARACTER*(*) NAME)
NCID
NAME
NF_NOERR
NF_EBADID
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
This example is from nf_test/ftst_groups.F.
C Check the name of the root group. retval = nf_inq_grpname(ncid, name_in) if (retval .ne. nf_noerr) call handle_err(retval) if (name_in(1:1) .ne. '/') stop 2
Given ncid, find complete name of group. (Root group is named "/").
The name provided by this function is a full path name for the group is, with all parent groups included, separated with a forward slash (as in Unix directory names). For a name relative to the parent group See NF_INQ_GRPNAME.
To find the length of the full name See NF_INQ_GRPNAME_LEN.
INTEGER FUNCTION NF_INQ_GRPNAME_FULL(INTEGER NCID, INTEGER LEN, CHARACTER*(*) NAME)
NCID
LEN
NAME
NF_NOERR
NF_EBADID
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
This example is from nf_test/ftst_groups.F.
C Check the full name. retval = nf_inq_grpname_full(grpids(1), full_name_len, name_in2) if (retval .ne. nf_noerr) call handle_err(retval)
Given ncid, find the ncid of the parent group.
When used with the root group, this function returns the NF_ENOGRP error (since the root group has no parent.)
INTEGER FUNCTION NF_INQ_GRP_PARENT(INTEGER NCID, INTEGER PARENT_NCID)
NCID
PARENT_NCID
NF_NOERR
NF_EBADID
NF_ENOGRP
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
This example is from nf_test/ftst_groups.F.
C Check the parent ncid. retval = nf_inq_grp_parent(grpids(1), grpid_in) if (retval .ne. nf_noerr) call handle_err(retval)
Given a group name an an ncid, find the ncid of the group id.
INTEGER FUNCTION NF_INQ_GRP_NCID(INTEGER NCID, CHARACTER GRP_NAME, INTEGER GRP_NCID)
NCID
GRP_NAME
GRP_NCID
The following return codes may be returned by this function.
NF_NOERR
NF_EBADID
NF_EINVAL
NF_ENOGRP
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
This example is from nf_test/ftst_types3.F.
C Go to a child group and find the id of our type. retval = nf_inq_grp_ncid(ncid, group_name, sub_grpid) if (retval .ne. nf_noerr) call handle_err(retval)
Given a fully qualified group name an an ncid, find the ncid of the group id.
INTEGER FUNCTION NF_INQ_GRP_FULL_NCID(INTEGER NCID, CHARACTER FULL_NAME, INTEGER GRP_NCID)
NCID
FULL_NAME
GRP_NCID
The following return codes may be returned by this function.
NF_NOERR
NF_EBADID
NF_EINVAL
NF_ENOGRP
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
This example is from nf_test/ftst_groups.F.
C Check the full name of the root group (also "/"). retval = nf_inq_grpname_full(ncid, full_name_len, name_in) if (retval .ne. nf_noerr) call handle_err(retval)
Create a group. Its location id is returned in new_ncid.
INTEGER FUNCTION NF_DEF_GRP(INTEGER PARENT_NCID, CHARACTER*(*) NAME, INTEGER NEW_NCID)
PARENT_NCID
NAME
NEW_NCID
NF_NOERR
NF_EBADID
NF_ENAMEINUSE
NF_EMAXNAME
NF_EBADNAME
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
NF_EPERM
NF_ENOTINDEFINE
In this exampe rom nf_test/ftst_groups.F, a groups is reated, and then a sub-group is created in that group.
C Create the netCDF file. retval = nf_create(file_name, NF_NETCDF4, ncid) if (retval .ne. nf_noerr) call handle_err(retval) C Create a group and a subgroup. retval = nf_def_grp(ncid, group_name, grpid) if (retval .ne. nf_noerr) call handle_err(retval) retval = nf_def_grp(grpid, sub_group_name, sub_grpid) if (retval .ne. nf_noerr) call handle_err(retval)
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. At most one dimension in a netCDF dataset can have the unlimited length, which means variables using this dimension can grow along this dimension.
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 NF_MAX_DIMS. The purpose of the limit is to make writing generic applications simpler. They need only provide an array of NF_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.
A netCDF dimension in an open netCDF dataset is referred to by a small integer called a dimension ID. In the FORTRAN interface, dimension IDs are 1, 2, 3, ..., in the order in which the dimensions were defined.
Operations supported on dimensions are:
The function NF_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 netCDF dataset.
INTEGER FUNCTION NF_DEF_DIM (INTEGER NCID, CHARACTER*(*) NAME, INTEGER LEN, INTEGER dimid)
NCID
NAME
LEN
dimid
NF_DEF_DIM returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_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.inc' ... INTEGER STATUS, NCID, LATID, RECID ... STATUS = NF_CREATE('foo.nc', NF_NOCLOBBER, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_DEF_DIM(NCID, 'lat', 18, LATID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_DEF_DIM(NCID, 'rec', NF_UNLIMITED, RECID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The function NF_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 1 and ndims.
INTEGER FUNCTION NF_INQ_DIMID (INTEGER NCID, CHARACTER*(*) NAME, INTEGER dimid)
NCID
NAME
dimid
NF_INQ_DIMID returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_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.inc' ... INTEGER STATUS, NCID, LATID ... STATUS = NF_OPEN('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_DIMID(NCID, 'lat', LATID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
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 NF_INQ_DIM, NF_INQ_DIMNAME, and NF_INQ_DIMLEN. The function NF_INQ_DIM returns all the information about a dimension; the other functions each return just one item of information.
INTEGER FUNCTION NF_INQ_DIM (INTEGER NCID, INTEGER DIMID, CHARACTER*(*) name, INTEGER len) INTEGER FUNCTION NF_INQ_DIMNAME (INTEGER NCID, INTEGER DIMID, CHARACTER*(*) name) INTEGER FUNCTION NF_INQ_DIMLEN (INTEGER NCID, INTEGER DIMID, INTEGER len)
NCID
DIMID
NAME
len
These functions return the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_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.inc' ... INTEGER STATUS, NCID, LATID, LATLEN, RECID, NRECS CHARACTER*(NF_MAX_NAME) LATNAM, RECNAM ... STATUS = NF_OPEN('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ! get ID of unlimited dimension STATUS = NF_INQ_UNLIMDIM(NCID, RECID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_DIMID(NCID, 'lat', LATID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ! get lat length STATUS = NF_INQ_DIMLEN(NCID, LATID, LATLEN) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ! get unlimited dimension name and current length STATUS = NF_INQ_DIM(NCID, RECID, RECNAME, NRECS) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The function NF_RENAME_DIM renames an existing dimension in a netCDF dataset open for writing. If the new name is longer than the old name, the netCDF dataset must be in define mode. You cannot rename a dimension to have the same name as another dimension.
INTEGER FUNCTION NF_RENAME_DIM (INTEGER NCID, INTEGER DIMID, CHARACTER*(*) NAME)
NCID
DIMID
NAME
NF_RENAME_DIM returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_RENAME_DIM to rename the dimension lat to latitude in an existing netCDF dataset named foo.nc:
INCLUDE 'netcdf.inc' ... INTEGER STATUS, NCID, LATID ... STATUS = NF_OPEN('foo.nc', NF_WRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... ! put in define mode to rename dimension STATUS = NF_REDEF(NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_INQ_DIMID(NCID, 'lat', LATID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_RENAME_DIM(NCID, LATID, 'latitude') IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ! leave define mode STATUS = NF_ENDDEF(NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
NetCDF-4 has added support for four different user defined data types.
compound type
variable length array type
opaque type
enum type
Users may construct user defined type with the various NF_DEF_* functions described in this section. They may learn about user defined types by using the NF_INQ_ functions defined in this section.
Once types are constructed, define variables of the new type with NF_DEF_VAR (see NF_DEF_VAR). Write to them with NF_PUT_VAR1, NF_PUT_VAR, NF_PUT_VARA, or NF_PUT_VARS (see Variables). Read data of user-defined type with NF_GET_VAR1, NF_GET_VAR, NF_GET_VARA, or NF_GET_VARS (see Variables).
Create attributes of the new type with NF_PUT_ATT (see NF_PUT_ATT_ type). Read attributes of the new type with NF_GET_ATT (see NF_GET_ATT_ type).
Learn the number of types defined in a group, and their IDs.
INTEGER FUNCTION NF_INQ_TYPEIDS(INTEGER NCID, INTEGER NTYPES, INTEGER TYPEIDS)
NCID
NTYPES
TYPEIDS
NF_NOERR
NF_BADID
The following example is from the test program nf_test/ftst_vars3.F.
retval = nf_inq_typeids(ncid, num_types, typeids) if (retval .ne. nf_noerr) call handle_err(retval)
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.
INTEGER FUNCTION NF_INQ_TYPEID(INTEGER NCID, CHARACTER NAME, NF_TYPE TYPEIDP)
NCID
NAME
TYPEIDP
NF_NOERR
NF_EBADID
NF_EBADTYPE
The following example is from nf_test/ftst_types3.F:
C Go to a child group and find the id of our type. retval = nf_inq_grp_ncid(ncid, group_name, sub_grpid) if (retval .ne. nf_noerr) call handle_err(retval) retval = nf_inq_typeid(sub_grpid, type_name, typeid_in) if (retval .ne. nf_noerr) call handle_err(retval)
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 NF_INQ_USER_TYPE.
INTEGER FUNCTION NF_INQ_TYPE(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) NAME, INTEGER SIZE)
NCID
XTYPE
NAME
SIZEP
NF_NOERR
NF_EBADTYPEID
NF_ENOTNC4
NF_ESTRICTNC3
NF_EBADGRPID
NF_EBADID
NF_EHDFERR
This example is from the test program nf_test/ftst_vars3.F, and it uses all the possible inquiry functions on an enum type.
C Check the enum type. retval = NF_INQ_TYPEIDS(ncid, num_types, typeids) if (retval .ne. nf_noerr) call handle_err(retval) if (num_types .ne. MAX_TYPES) stop 2 retval = nf_inq_enum(ncid, typeids(1), type_name, base_type, & base_size, num_members) if (retval .ne. nf_noerr) call handle_err(retval) if (base_type .ne. NF_INT .or. num_members .ne. 2) stop 2 retval = nf_inq_enum_member(ncid, typeids(1), 1, member_name, & member_value) if (retval .ne. nf_noerr) call handle_err(retval) if (member_name(1:len(one_name)) .ne. one_name) stop 2
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.
INTEGER FUNCTION NF_INQ_USER_TYPE(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) NAME, INTEGER SIZE, INTEGER BASE_NF_TYPE, INTEGER NFIELDS, INTEGER CLASS)
NCID
XTYPE
NAME
SIZE
BASE_NF_TYPE
NFIELDS
CLASS
NF_NOERR
NF_EBADTYPEID
NF_EBADFIELDID
NF_EHDFERR
This example is from nf_test/ftst_types2.F.
C Check the type. retval = nf_inq_user_type(ncid, typeids(1), name_in, size_in, & base_type_in, nfields_in, class_in) if (retval .ne. nf_noerr) call handle_err(retval)
NetCDF-4 added support for compound types, which allow users to construct a new type - a combination of other types, like a C struct.
Compound types are not supported in classic or 64-bit offset format files.
To write data in a compound type, first use nf_def_compound to create the type, multiple calls to nf_insert_compound to add to the compound type, and then write data with the appropriate nf_put_var1, nf_put_vara, nf_put_vars, or nf_put_varm call.
To read data written in a compound type, you must know its structure. Use the NF_INQ_COMPOUND functions to learn about the compound type.
In Fortran a character buffer must be used for the compound data. The user must read the data from within that buffer in the same way that the C compiler which compiled netCDF would store the structure.
The use of compound types introduces challenges and portability issues for Fortran users.
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 NF_INSERT_COMPOUND (see NF_INSERT_COMPOUND). Call NF_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).
Fortran users may use character buffers to read and write compound types.
INTEGER FUNCTION NF_DEF_COMPOUND(INTEGER NCID, INTEGER SIZE, CHARACTER*(*) NAME, INTEGER TYPEIDP)
NCID
SIZE
NAME
TYPEIDP
NF_NOERR
NF_EBADID
NF_ENAMEINUSE
NF_EMAXNAME
NF_EBADNAME
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
NF_EPERM
NF_ENOTINDEFINE
This example is from nf_test/ftst_types2.F.
C Define a compound type. retval = nf_def_compound(ncid, cmp_size, type_name, & cmp_typeid) if (retval .ne. nf_noerr) call handle_err(retval)
Insert a named field into a compound type.
INTEGER FUNTION NF_INSERT_COMPOUND(INTEGER TYPEID, CHARACTER*(*) NAME, INTEGER OFFSET, INTEGER FIELD_TYPEID)
TYPEID
NAME
OFFSET
FIELD_TYPEID
NF_NOERR
NF_EBADID
NF_ENAMEINUSE
NF_EMAXNAME
NF_EBADNAME
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
NF_ENOTINDEFINE
This example is from nf_test/ftst_types.F.
C Define a compound type. retval = nf_def_compound(ncid, WIND_T_SIZE, type_name, & wind_typeid) if (retval .ne. nf_noerr) call handle_err(retval) retval = nf_insert_compound(ncid, wind_typeid, u_name, 0, NF_INT) if (retval .ne. nf_noerr) call handle_err(retval) retval = nf_insert_compound(ncid, wind_typeid, v_name, 4, NF_INT) if (retval .ne. nf_noerr) call handle_err(retval)
Insert a named array field into a compound type.
INTEGER FUNCTION NF_INSERT_ARRAY_COMPOUND(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) NAME, INTEGER OFFSET, INTEGER FIELD_TYPEID, INTEGER NDIMS, INTEGER DIM_SIZES)
NCID
XTYPE
NAME
OFFSET
FIELD_TYPEID
NDIMS
DIM_SIZES
NF_NOERR
NF_EBADID
NF_ENAMEINUSE
NF_EMAXNAME
NF_EBADNAME
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
NF_ENOTINDEFINE
NF_ETYPEDEFINED
This example is from nf_test/ftst_types2.F.
C Define a compound type. retval = nf_def_compound(ncid, cmp_size, type_name, & cmp_typeid) if (retval .ne. nf_noerr) call handle_err(retval) C Include an array. dim_sizes(1) = NX dim_sizes(2) = NY retval = nf_insert_array_compound(ncid, cmp_typeid, ary_name, 0, & NF_INT, NDIMS, dim_sizes) if (retval .ne. nf_noerr) call handle_err(retval)
Get the number of fields, length in bytes, and name of a compound type.
In addtion to the NF_INQ_COMPOUND function, three additional functions are provided which get only the name, size, and number of fields.
INTEGER FUNCTION NF_INQ_COMPOUND(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) NAME, INTEGER SIZEP, INTEGER NFIELDSP) INTEGER FUNCTION NF_INQ_COMPOUND_NAME(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) NAME) INTEGER FUNCTION NF_INQ_COMPOUND_SIZE(INTEGER NCID, INTEGER XTYPE, INTEGER SIZEP) INTEGER FUNCTION NF_INQ_COMPOUND_NFIELDS(INTEGER NCID, INTEGER XTYPE, INTEGER NFIELDSP)
NCID
XTYPE
NAME
SIZEP
NFIELDSP
NF_NOERR
NF_EBADID
NF_ENOTNC4
NF_ESTRICTNC3
NF_EBADTYPE
NF_EBADTYPEID
NF_EHDFERR
This example is from nf_test/ftst_types.F.
C Check it differently. retval = nf_inq_compound(ncid, typeids(1), name_in, size_in, & nfields_in) if (retval .ne. nf_noerr) call handle_err(retval) if (name_in(1:len(type_name)) .ne. type_name .or. & size_in .ne. WIND_T_SIZE .or. nfields_in .ne. 2) stop 2 C Check it one piece at a time. retval = nf_inq_compound_nfields(ncid, typeids(1), nfields_in) if (retval .ne. nf_noerr) call handle_err(retval) if (nfields_in .ne. 2) stop 2 retval = nf_inq_compound_size(ncid, typeids(1), size_in) if (retval .ne. nf_noerr) call handle_err(retval) if (size_in .ne. WIND_T_SIZE) stop 2 retval = nf_inq_compound_name(ncid, typeids(1), name_in) if (retval .ne. nf_noerr) call handle_err(retval) if (name_in(1:len(type_name)) .ne. type_name) stop 2
Get information about one of the fields of a compound type.
INTEGER FUNCTION NF_INQ_COMPOUND_FIELD(INTEGER NCID, INTEGER XTYPE, INTEGER FIELDID, CHARACTER*(*) NAME, INTEGER OFFSETP, INTEGER FIELD_TYPEIDP, INTEGER NDIMSP, INTEGER DIM_SIZESP) INTEGER FUNCTION NF_INQ_COMPOUND_FIELDNAME(INTEGER TYPEID, INTEGER FIELDID, CHARACTER*(*) NAME) INTEGER FUNCTION NF_INQ_COMPOUND_FIELDINDEX(INTEGER TYPEID, CHARACTER*(*) NAME, INTEGER FIELDIDP) INTEGER FUNCTION NF_INQ_COMPOUND_FIELDOFFSET(INTEGER TYPEID, INTEGER FIELDID, INTEGER OFFSETP) INTEGER FUNCTION NF_INQ_COMPOUND_FIELDTYPE(INTEGER TYPEID, INTEGER FIELDID, INTEGER FIELD_TYPEIDP) INTEGER FUNCTION NF_INQ_COMPOUND_FIELDNDIMS(INTEGER NCID, INTEGER XTYPE, INTEGER FIELDID, INTEGER NDIMSP) INTEGER FUNCTION NF_INQ_COMPOUND_FIELDDIM_SIZES(INTEGER NCID, INTEGER XTYPE, INTEGER FIELDID, INTEGER DIM_SIZES)
NCID
XTYPE
FIELDID
NAME
OFFSETP
FIELD_TYPEID
NDIMSP
DIM_SIZESP
NF_NOERR
NF_EBADTYPEID
NF_EHDFERR
This example is from nf_test/fst_types.F.
C Check the first field of the compound type. retval = nf_inq_compound_field(ncid, typeids(1), 1, name_in, & offset_in, field_typeid_in, ndims_in, dim_sizes_in) if (retval .ne. nf_noerr) call handle_err(retval) if (name_in(1:len(u_name)) .ne. u_name .or. offset_in .ne. 0 .or. & field_typeid_in .ne. NF_INT .or. ndims_in .ne. 0) stop 2 retval = nf_inq_compound_fieldname(ncid, typeids(1), 1, name_in) if (retval .ne. nf_noerr) call handle_err(retval) if (name_in(1:len(u_name)) .ne. u_name) stop 2 retval = nf_inq_compound_fieldoffset(ncid, typeids(1), 1, & offset_in) if (retval .ne. nf_noerr) call handle_err(retval) if (offset_in .ne. 0) stop 2 retval = nf_inq_compound_fieldtype(ncid, typeids(1), 1, & field_typeid_in) if (retval .ne. nf_noerr) call handle_err(retval) if (field_typeid_in .ne. NF_INT) stop 2 retval = nf_inq_compound_fieldndims(ncid, typeids(1), 1, & ndims_in) if (retval .ne. nf_noerr) call handle_err(retval) if (ndims_in .ne. 0) stop 2
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 NF_CLASSIC_MODEL flag.
A variable length array is represented in C as a structure from HDF5, the nf_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. The only way to handle this in Fortran is with a character buffer sized correctly for the platform.
The extra access functions NF_GET_VLEN_ELEMENT and NF_PUT_VLEN_ELEMENT to get and put one VLEN element. (That is, one array of variable length.) When calling the put, the data are not copied from the source. When calling the get the data are copied from VLEN allocated memory, which must still be freed (see below).
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.
Compression is permitted but may not be effective for VLEN data, because the compression is applied to the nc_vlen_t structures, rather than the actual data.
Use this function to define a variable length array type.
INTEGER FUNCTION NF_DEF_VLEN(INTEGER NCID, CHARACTER*(*) NAME, INTEGER BASE_TYPEID, INTEGER XTYPEP)
NCID
NAME
BASE_TYPEID
XTYPEP
NF_NOERR
NF_EMAXNAME
NF_ENAMEINUSE
NF_EBADNAME
NF_EBADID
NF_EBADGRPID
NF_EINVAL
NF_ENOMEM
This example is from nf_test/ftst_vars4.F.
C Create the vlen type. retval = nf_def_vlen(ncid, vlen_type_name, nf_int, vlen_typeid) if (retval .ne. nf_noerr) call handle_err(retval)
Use this type to learn about a vlen.
INTEGER FUNCTION NF_INQ_VLEN(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) NAME, INTEGER DATUM_SIZEP, INTEGER BASE_NF_TYPEP)
NCID
XTYPE
NAME
DATUM_SIZEP
BASE_NF_TYPEP
NF_NOERR
NF_EBADTYPE
NF_EBADID
NF_EBADGRPID
This example is from nf_test/ftst_vars4.F.
C Use nf_inq_vlen and make sure we get the same answers as we did C with nf_inq_user_type. retval = nf_inq_vlen(ncid, typeids(1), type_name, base_size, & base_type) if (retval .ne. nf_noerr) call handle_err(retval)
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.
INTEGER FUNCTION NF_FREE_VLEN(CHARACTER VL);
VL
NF_NOERR
NF_EBADTYPE
Use this to set the element of the (potentially) n-dimensional array of VLEN. That is, this sets the data in one variable length array.
INTEGER FUNCTION NF_PUT_VLEN_ELEMENT(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) VLEN_ELEMENT, INTEGER LEN, DATA)
NCID
XTYPE
VLEN_ELEMENT
LEN
DATA
NF_NOERR
NF_EBADTYPE
NF_EBADID
NF_EBADGRPID
This example is from nf_test/ftst_vars4.F.
C Set up the vlen with this helper function, since F77 can't deal C with pointers. retval = nf_put_vlen_element(ncid, vlen_typeid, vlen, & vlen_len, data1) if (retval .ne. nf_noerr) call handle_err(retval)
Use this to set the element of the (potentially) n-dimensional array of VLEN. That is, this sets the data in one variable length array.
INTEGER FUNCTION NF_GET_VLEN_ELEMENT(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) VLEN_ELEMENT, INTEGER LEN, DATA)
NCID
XTYPE
VLEN_ELEMENT
LEN
DATA
NF_NOERR
NF_EBADTYPE
NF_EBADID
NF_EBADGRPID
This example is from nf_test/ftst_vars4.F.
C Read the vlen attribute. retval = nf_get_att(ncid, NF_GLOBAL, 'att1', vlen_in) if (retval .ne. nf_noerr) call handle_err(retval) C Get the data from the vlen we just read. retval = nf_get_vlen_element(ncid, vlen_typeid, vlen_in, & vlen_len_in, data1_in) if (retval .ne. nf_noerr) call handle_err(retval)
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 NF_DEF_OPAQUE. If encountering an enum type in a new data file, use NF_INQ_OPAQUE to learn its name and size.
Create an opaque type. Provide a size and a name.
INTEGER FUNCTION NF_DEF_OPAQUE(INTEGER NCID, INTEGER SIZE, CHARACTER*(*) NAME, INTEGER TYPEIDP)
NCID
SIZE
NAME
TYPEIDP
NF_NOERR
NF_EBADTYPEID
NF_EBADFIELDID
NF_EHDFERR
This example is from nf_test/ftst_vars3.F.
C Create the opaque type. retval = nf_def_opaque(ncid, opaque_size, opaque_type_name, & opaque_typeid) if (retval .ne. nf_noerr) call handle_err(retval)
Given a typeid, get the information about an opaque type.
INTEGER FUNCTION NF_INQ_OPAQUE(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) NAME, INTEGER SIZEP)
NCID
XTYPE
NAME
SIZEP
NF_NOERR
NF_EBADTYPEID
NF_EBADFIELDID
NF_EHDFERR
This example is from nf_test/ftst_vars3.F.
C Use nf_inq_opaque and make sure we get the same answers as we did C with nf_inq_user_type. retval = nf_inq_opaque(ncid, typeids(2), type_name, base_size) if (retval .ne. nf_noerr) call handle_err(retval)
NetCDF-4 added support for the enum type. This is not supported in classic or 64-bit offset files.
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 NF_INSERT_ENUM (see NF_INSERT_ENUM). Call NF_INSERT_ENUM once for each value you wish to make part of the enumeration.
INTEGER FUNCTION NF_DEF_ENUM(INTEGER NCID, INTEGER BASE_TYPEID, CHARACTER*(*) NAME, INTEGER TYPEIDP)
NCID
BASE_TYPEID
NAME
TYPEIDP
NF_NOERR
NF_EBADID
NF_ENAMEINUSE
NF_EMAXNAME
NF_EBADNAME
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
NF_EPERM
NF_ENOTINDEFINE
This example is from nf_test/ftst_vars3.F.
C Create the enum type. retval = nf_def_enum(ncid, NF_INT, enum_type_name, enum_typeid) if (retval .ne. nf_noerr) call handle_err(retval)
Insert a named member into a enum type.
INTEGER FUNCTION NF_INSERT_ENUM(INTEGER NCID, INTEGER XTYPE, CHARACTER IDENTIFIER, INTEGER VALUE)
NCID
TYPEID
IDENTIFIER
VALUE
NF_NOERR
NF_EBADID
NF_ENAMEINUSE
NF_EMAXNAME
NF_EBADNAME
NF_ENOTNC4
NF_ESTRICTNC3
NF_EHDFERR
NF_ENOTINDEFINE
This example is from nf_test/ftst_vars3.F.
one = 1 zero = 0 retval = nf_insert_enum(ncid, enum_typeid, zero_name, zero) if (retval .ne. nf_noerr) call handle_err(retval) retval = nf_insert_enum(ncid, enum_typeid, one_name, one) if (retval .ne. nf_noerr) call handle_err(retval)
Get information about a user-defined enumeration type.
INTEGER FUNCTION NF_INQ_ENUM(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) NAME, INTEGER BASE_NF_TYPE, INTEGER BASE_SIZE, INTEGER NUM_MEMBERS)
NCID
XTYPE
NAME
BASE_NF_TYPE
BASE_SIZE
NUM_MEMBERS
NF_NOERR
NF_EBADTYPEID
NF_EHDFERR
In this example from nf_test/ftst_vars3.F, an enum type is created and then examined:
retval = nf_inq_enum(ncid, typeids(1), type_name, base_type, & base_size, num_members) if (retval .ne. nf_noerr) call handle_err(retval) if (base_type .ne. NF_INT .or. num_members .ne. 2) stop 2
Get information about a member of an enum type.
INTEGER FUNCTION NF_INQ_ENUM_MEMBER(INTEGER NCID, INTEGER XTYPE, INTEGER IDX, CHARACTER*(*) NAME, INTEGER VALUE)
NCID
XTYPE
IDX
NAME
VALUE
NF_NOERR
NF_EBADTYPEID
NF_EHDFERR
This example is from nf_test/ftst_vars3.F:
C Check the members of the enum type. retval = nf_inq_enum_member(ncid, typeids(1), 1, member_name, & member_value) if (retval .ne. nf_noerr) call handle_err(retval) if (member_name(1:len(zero_name)) .ne. zero_name .or. & member_value .ne. 0) stop 2 retval = nf_inq_enum_member(ncid, typeids(1), 2, member_name, & member_value) if (retval .ne. nf_noerr) call handle_err(retval) if (member_name(1:len(one_name)) .ne. one_name .or. & member_value .ne. 1) stop 2
Get the name which is associated with an enum member value.
This is similar to NF_INQ_ENUM_MEMBER, but instead of using the index of the member, you use the value of the member.
INTEGER FUNCTION NF_INQ_ENUM_IDENT(INTEGER NCID, INTEGER XTYPE, INTEGER VALUE, CHARACTER*(*) IDENTIFIER)
NCID
XTYPE
VALUE
IDENTIFIER
NF_NOERR
NF_EBADTYPEID
NF_EHDFERR
NF_EINVAL
In this example from nf_test/ftst_vars3.F, the values for 0 and 1 are checked in an enum.
retval = nf_inq_enum_ident(ncid, typeids(1), 0, member_name) if (retval .ne. nf_noerr) call handle_err(retval) if (member_name(1:len(zero_name)) .ne. zero_name) stop 2 retval = nf_inq_enum_ident(ncid, typeids(1), 1, member_name) if (retval .ne. nf_noerr) call handle_err(retval) if (member_name(1:len(one_name)) .ne. one_name) stop 2
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 1, 2, 3,..., 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:
The following table gives the netCDF external data types and the corresponding type constants for defining variables in the FORTRAN interface:
| Type | FORTRAN API Mnemonic | Bits
|
| byte | NF_BYTE | 8
|
| char | NF_CHAR | 8
|
| short | NF_SHORT | 16
|
| int | NF_INT | 32
|
| float | NF_FLOAT | 32
|
| double | NF_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 FORTRAN parameter for use in netCDF functions (the parameters are defined in the netCDF FORTRAN include-file netcdf.inc). The last column gives the number of bits used in the external representation of values of the corresponding type.
Note that there are no netCDF types corresponding to 64-bit integers or to characters wider than 8 bits in the current version of the netCDF library.
NF_DEF_VAR
The function NF_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.
INTEGER FUNCTION NF_DEF_VAR(INTEGER NCID, CHARACTER*(*) NAME, INTEGER XTYPE, INTEGER NVDIMS, INTEGER VDIMS(*), INTEGER varid)
NCID
NAME
XTYPE
NVDIMS
VDIMS
varid
NF_DEF_VAR returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_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.inc' ...  STATUS = NF_CREATE ('foo.nc', NF_NOCLOBBER, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... ! define dimensions STATUS = NF_DEF_DIM(NCID, 'lat', 5, LATDIM) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_DEF_DIM(NCID, 'lon', 10, LONDIM) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_DEF_DIM(NCID, 'time', NF_UNLIMITED, TIMDIM) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... ! define variable RHDIMS(1) = LONDIM RHDIMS(2) = LATDIM RHDIMS(3) = TIMDIM STATUS = NF_DEF_VAR (NCID, 'rh', NF_DOUBLE, 3, RHDIMS, RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
NF_DEF_VAR_CHUNKING
The function NF_DEF_VAR_CHUNKING sets the storage 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.
NF_DEF_VAR_CHUNKING(INTEGER NCID, INTEGER VARID, INTEGER STORAGE, INTEGER CHUNKSIZES)
ncid
varid
storage
If NF_CHUNKED, then chunked storage is used for this variable. Chunk sizes may be specified with the chunksizes parameter. Default sizes will be used if chunking is required and this function is not called.
By default contiguous storage is used for fix-sized variables when
conpression, chunking, checksums, or endianness control are not used.
chunksizes
NF_DEF_VAR_CHUNKING returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error.
Possible return codes include:
NF_NOERR
NF_BADID
NF_EINVAL
NF_ENOTNC4
NF_ENOTVAR
NF_ELATEDEF
NF_ENOTINDEFINE
NF_ESTRICTNC3
In this example from nf_test/ftst_vars.F, a file is created, two dimensions and a variable are defined, and the chunksizes of the data are set to the size of the data (that is, data will be written in one chunk).
C Create the netCDF file. retval = nf_create(FILE_NAME, NF_NETCDF4, ncid) if (retval .ne. nf_noerr) call handle_err(retval) C Define the dimensions. retval = nf_def_dim(ncid, "x", NX, x_dimid) if (retval .ne. nf_noerr) call handle_err(retval) retval = nf_def_dim(ncid, "y", NY, y_dimid) if (retval .ne. nf_noerr) call handle_err(retval) C Define the variable. dimids(1) = y_dimid dimids(2) = x_dimid retval = NF_DEF_VAR(ncid, "data", NF_INT, NDIMS, dimids, varid) if (retval .ne. nf_noerr) call handle_err(retval) C Turn on chunking. chunks(1) = NY chunks(2) = NX retval = NF_DEF_VAR_chunking(ncid, varid, NF_CHUNKED, chunks) if (retval .ne. nf_noerr) call handle_err(retval)
NF_INQ_VAR_CHUNKING
The function NF_INQ_VAR_CHUNKING returns the chunking settings for a variable in a netCDF-4 file.
NF_INQ_VAR_CHUNKING(INTEGER NCID, INTEGER VARID, INTEGER STORAGE, INTEGER CHUNKSIZES);
NCID
VARID
STORAGE
CHUNKSIZES
NF_INQ_VAR_CHUNKING returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error.
Possible return codes include:
NF_NOERR
NF_BADID
NF_ENOTNC4
NF_ENOTVAR
In this example from nf_test/ftst_vars.F, a variable with chunked storage is checked to ensure that the chunksizes are set to expected values.
C Is everything set that is supposed to be? retval = nf_inq_var_chunking(ncid, varid, storage, chunks_in) if (retval .ne. nf_noerr) call handle_err(retval) if (storage .ne. NF_CHUNKED) stop 2 if (chunks(1) .ne. chunks_in(1)) stop 2 if (chunks(2) .ne. chunks_in(2)) stop 2
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/.
nc_set_var_chunk_cache(int ncid, int varid, size_t size, size_t nelems, float preemption);
ncid
varid
size
nelems
preemption
NF_NOERR
NF_EINVAL
This example is from nf_test/ftst_vars2.F:
include 'netcdf.inc' ... C These will be used to set the per-variable chunk cache. integer CACHE_SIZE, CACHE_NELEMS, CACHE_PREEMPTION parameter (CACHE_SIZE = 8, CACHE_NELEMS = 571) parameter (CACHE_PREEMPTION = 42) ... C Set variable caches. retval = nf_set_var_chunk_cache(ncid, varid(i), CACHE_SIZE, & CACHE_NELEMS, CACHE_PREEMPTION) if (retval .ne. nf_noerr) call handle_err(retval)
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/.
INTEGER NF_GET_VAR_CHUNK_CACHE(INTEGER NCID, INTEGER VARID, INTEGER SIZE, INTEGER NELEMS, INTEGER PREEMPTION);
ncid
varid
sizep
nelemsp
preemptionp
NC_NOERR
This example is from nf_test/ftst_vars2.c:
include 'netcdf.inc' ... C These will be used to set the per-variable chunk cache. integer CACHE_SIZE, CACHE_NELEMS, CACHE_PREEMPTION parameter (CACHE_SIZE = 8, CACHE_NELEMS = 571) parameter (CACHE_PREEMPTION = 42) C These will be used to check the setting of the per-variable chunk C cache. integer cache_size_in, cache_nelems_in, cache_preemption_in ... retval = nf_get_var_chunk_cache(ncid, varid(i), cache_size_in, & cache_nelems_in, cache_preemption_in) if (retval .ne. nf_noerr) call handle_err(retval) if (cache_size_in .ne. CACHE_SIZE .or. cache_nelems_in .ne. & CACHE_NELEMS .or. cache_preemption .ne. CACHE_PREEMPTION) & stop 8
nf_def_var_fill
The function NF_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 NF_ENDDEF is called.
NF_DEF_VAR_FILL(INTEGER NCID, INTEGER VARID, INTEGER NO_FILL, FILL_VALUE);
NCID
VARID
NO_FILL
FILL_VALUE
NF_NOERR
NF_BADID
NF_ENOTNC4
NF_ENOTVAR
NF_ELATEDEF
NF_ENOTINDEFINE
NF_EPERM
NF_INQ_VAR_FILL
The function NF_INQ_VAR_FILL returns the fill settings for a variable in a netCDF-4 file.
NF_INQ_VAR_FILL(INTEGER NCID, INTEGER VARID, INTEGER NO_FILL, FILL_VALUE)
NCID
VARID
NO_FILL
FILL_VALUE
NF_NOERR
NF_BADID
NF_ENOTNC4
NF_ENOTVAR
NF_DEF_VAR_DEFLATE
The function NF_DEF_VAR_DEFLATE sets the deflate parameters for a variable in a netCDF-4 file.
When using parallel I/O for writing data, deflate cannot be used. This is because the compression makes it impossible for the HDF5 library to exactly map the data to disk location.
(Deflated data can be read with parallel I/O).
NF_DEF_VAR_DEFLATE must be called after the variable is defined, but before NF_ENDDEF is called.
NF_DEF_VAR_DEFLATE(INTEGER NCID, INTEGER VARID, INTEGER SHUFFLE, INTEGER DEFLATE, INTEGER DEFLATE_LEVEL);
NCID
VARID
SHUFFLE
DEFLATE
DEFLATE_LEVEL
If set to zero, no deflation takes place and the def_var_deflate call is ignored. This is slightly different from HDF5 handing of 0 deflate, which turns on the filter but makes only trivial changes to the data.
Informal testing at NetCDF World Headquarters suggests that there is little to be gained (with the limited set of test data used here), in setting the deflate level above 2 or 3.
NF_DEF_VAR_DEFLATE returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error.
Possible return codes include:
NF_NOERR
NF_BADID
NF_ENOTNC4
NF_ENOTVAR
NF_ELATEDEF
NF_ENOTINDEFINE
NF_EPERM
NF_EINVAL
In this example from nf_test/ftst_vars.F, a file is created with two dimensions and one variable. Chunking, deflate, and the fletcher32 filter are turned on. The deflate level is set to 4 below.
C Create the netCDF file. retval = nf_create(FILE_NAME, NF_NETCDF4, ncid) if (retval .ne. nf_noerr) call handle_err(retval) C Define the dimensions. retval = nf_def_dim(ncid, "x", NX, x_dimid) if (retval .ne. nf_noerr) call handle_err(retval) retval = nf_def_dim(ncid, "y", NY, y_dimid) if (retval .ne. nf_noerr) call handle_err(retval) C Define the variable. dimids(1) = y_dimid dimids(2) = x_dimid retval = NF_DEF_VAR(ncid, "data", NF_INT, NDIMS, dimids, varid) if (retval .ne. nf_noerr) call handle_err(retval) C Turn on chunking. chunks(1) = NY chunks(2) = NX retval = NF_DEF_VAR_CHUNKING(ncid, varid, NF_CHUNKED, chunks) if (retval .ne. nf_noerr) call handle_err(retval) C Turn on deflate compression, fletcher32 checksum. retval = NF_DEF_VAR_deflate(ncid, varid, 0, 1, 4) if (retval .ne. nf_noerr) call handle_err(retval) retval = NF_DEF_VAR_FLETCHER32(ncid, varid, NF_FLETCHER32) if (retval .ne. nf_noerr) call handle_err(retval)
NF_INQ_VAR_DEFLATE
The function NF_INQ_VAR_DEFLATE returns the deflate settings for a variable in a netCDF-4 file.
It is not necessary to know the deflate settings to read the variable. (Deflate is completely transparent to readers of the data).
NF_INQ_VAR_DEFLATE(INTEGER NCID, INTEGER VARID, INTEGER SHUFFLE, INTEGER DEFLATE, INTEGER DEFLATE_LEVEL);
NCID
VARID
SHUFFLE
DEFLATE
DEFLATE_LEVEL
NF_INQ_VAR_DEFLATE returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error.
Possible return codes include:
NF_NOERR
NF_BADID
NF_ENOTNC4
NF_ENOTVAR
In this example code from nf_test/ftst_vars.F, a file with a variable using deflate is opened, and the deflate level checked.
C Is everything set that is supposed to be? retval = nf_inq_var_deflate(ncid, varid, shuffle, deflate, + deflate_level) if (retval .ne. nf_noerr) call handle_err(retval) if (shuffle .ne. 0 .or. deflate .ne. 1 .or. + deflate_level .ne. 4) stop 2
NF_INQ_VAR_SZIP
The function NF_INQ_VAR_SZIP returns the szip settings for a variable in a netCDF-4 file.
It is not necessary to know the szip settings to read the variable. (Szip is completely transparent to readers of the data).
NF_INQ_VAR_SZIP(INTEGER NCID, INTEGER VARID, INTEGER OPTION_MASK, PIXELS_PER_BLOCK);
NCID
VARID
OPTION_MASK
PIXELS_PER_BLOCK
NF_INQ_VAR_SZIP returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error.
Possible return codes include:
NF_NOERR
NF_BADID
NF_ENOTNC4
NF_ENOTVAR
NF_DEF_VAR_FLETCHER32
The function NF_DEF_VAR_FLETCHER32 sets the checksum property for a variable in a netCDF-4 file.
This function may only be called after the variable is defined, but before NF_ENDDEF is called.
NF_DEF_VAR_FLETCHER32(INTEGER NCID, INTEGER VARID, INTEGER CHECKSUM);
NCID
VARID
CHECKSUM
NF_DEF_VAR_FLETCHER32 returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error.
Possible return codes include:
NF_NOERR
NF_BADID
NF_ENOTNC4
NF_ENOTVAR
NF_ELATEDEF
NF_ENOTINDEFINE
NF_EPERM
In this example from nf_test/ftst_vars.F, the variable in a file has the Fletcher32 checksum filter turned on.
C Create the netCDF file. retval = nf_create(FILE_NAME, NF_NETCDF4, ncid) if (retval .ne. nf_noerr) call handle_err(retval) C Define the dimensions. retval = nf_def_dim(ncid, "x", NX, x_dimid) if (retval .ne. nf_noerr) call handle_err(retval) retval = nf_def_dim(ncid, "y", NY, y_dimid) if (retval .ne. nf_noerr) call handle_err(retval) C Define the variable. dimids(1) = y_dimid dimids(2) = x_dimid retval = NF_DEF_VAR(ncid, "data", NF_INT, NDIMS, dimids, varid) if (retval .ne. nf_noerr) call handle_err(retval) C Turn on chunking. chunks(1) = NY chunks(2) = NX retval = NF_DEF_VAR_CHUNKING(ncid, varid, NF_CHUNKED, chunks) if (retval .ne. nf_noerr) call handle_err(retval) C Turn on deflate compression, fletcher32 checksums. retval = NF_DEF_VAR_DEFLATE(ncid, varid, 0, 1, 4) if (retval .ne. nf_noerr) call handle_err(retval) retval = NF_DEF_VAR_FLETCHER32(ncid, varid, NF_FLETCHER32) if (retval .ne. nf_noerr) call handle_err(retval)
NF_INQ_VAR_FLETCHER32
The function NF_INQ_VAR_FLETCHER32 returns the checksum settings for a variable in a netCDF-4 file.
NF_INQ_VAR_FLETCHER32(INTEGER NCID, INTEGER VARID, INTEGER CHECKSUM);
NCID
VARID
CHECKSUM
NF_INQ_VAR_FLETCHER32 returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error.
Possible return codes include:
NF_NOERR
NF_BADID
NF_ENOTNC4
NF_ENOTVAR
In this example from nf_test/ftst_vars.F the checksum filter is checked for a file. Since it was turned on for this variable, the checksum variable is set to NF_FLETCHER32.
retval = nf_inq_var_fletcher32(ncid, varid, checksum) if (retval .ne. nf_noerr) call handle_err(retval) if (checksum .ne. NF_FLETCHER32) stop 2
NF_DEF_VAR_ENDIAN
The function NF_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 NF_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.
NF_DEF_VAR_ENDIAN(INTEGER NCID, INTEGER VARID, INTEGER ENDIAN)
NCID
VARID
ENDIAN
NF_DEF_VAR_ENDIAN returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error.
Possible return codes include:
NF_NOERR
NF_BADID
NF_ENOTNC4
NF_ENOTVAR
NF_ELATEDEF
NF_ENOTINDEFINE
NF_EPERM
In this example from nf_test/ftst_vars.c, a file is created with one variable, and its endianness is set to NF_ENDIAN_BIG.
C Create the netCDF file. retval = nf_create(FILE_NAME, NF_NETCDF4, ncid) if (retval .ne. nf_noerr) call handle_err(retval) C Define the dimensions. retval = nf_def_dim(ncid, "x", NX, x_dimid) if (retval .ne. nf_noerr) call handle_err(retval) retval = nf_def_dim(ncid, "y", NY, y_dimid) if (retval .ne. nf_noerr) call handle_err(retval) C Define the variable. dimids(1) = y_dimid dimids(2) = x_dimid retval = NF_DEF_VAR(ncid, "data", NF_INT, NDIMS, dimids, varid) if (retval .ne. nf_noerr) call handle_err(retval) C Turn on chunking. chunks(1) = NY chunks(2) = NX retval = NF_DEF_VAR_chunking(ncid, varid, 0, chunks) if (retval .ne. nf_noerr) call handle_err(retval) C Set variable to big-endian (default is whatever is native to C writing machine). retval = NF_DEF_VAR_endian(ncid, varid, NF_ENDIAN_BIG) if (retval .ne. nf_noerr) call handle_err(retval)
NF_INQ_VAR_ENDIAN
The function NF_INQ_VAR_ENDIAN returns the endianness settings for a variable in a netCDF-4 file.
NF_INQ_VAR_ENDIAN(INTEGER NCID, INTEGER VARID, INTEGER ENDIAN)
NCID
VARID
ENDIAN
NF_INQ_VAR_ENDIAN returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error.
Possible return codes include:
NF_NOERR
NF_BADID
NF_ENOTNC4
NF_ENOTVAR
In this example from nf_test/ftst_vars.F, the endianness of a variable is checked to make sure it is NF_ENDIAN_BIG.
retval = nf_inq_var_endian(ncid, varid, endianness) if (retval .ne. nf_noerr) call handle_err(retval) if (endianness .ne. NF_ENDIAN_BIG) stop 2
The function NF_INQ_VARID returns the ID of a netCDF variable, given its name.
INTEGER FUNCTION NF_INQ_VARID(INTEGER NCID, CHARACTER*(*) NAME, INTEGER varid)
NCID
NAME
varid
NF_INQ_VARID returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_INQ_VARID to find out the ID of a variable named rh in an existing netCDF dataset named foo.nc:
INCLUDE 'netcdf.inc' ... INTEGER STATUS, NCID, RHID ... STATUS = NF_OPEN ('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID (NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
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 NF_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 NF_INQ_VARNAME, NF_INQ_VARTYPE, NF_INQ_VARNDIMS, NF_INQ_VARDIMID, and NF_INQ_VARNATTS.
INTEGER FUNCTION NF_INQ_VAR (INTEGER NCID, INTEGER VARID, CHARACTER*(*) name, INTEGER xtype, INTEGER ndims, INTEGER dimids(*), INTEGER natts) INTEGER FUNCTION NF_INQ_VARNAME (INTEGER NCID, INTEGER VARID, CHARACTER*(*) name) INTEGER FUNCTION NF_INQ_VARTYPE (INTEGER NCID, INTEGER VARID, INTEGER xtype) INTEGER FUNCTION NF_INQ_VARNDIMS (INTEGER NCID, INTEGER VARID, INTEGER ndims) INTEGER FUNCTION NF_INQ_VARDIMID (INTEGER NCID, INTEGER VARID, INTEGER dimids(*)) INTEGER FUNCTION NF_INQ_VARNATTS (INTEGER NCID, INTEGER VARID, INTEGER natts)
NCID
VARID
NAME
xtype
ndims
dimids
natts
These functions return the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_INQ_VAR to find out about a variable named rh in an existing netCDF dataset named foo.nc:
INCLUDE 'netcdf.inc' ... INTEGER STATUS, NCID INTEGER RHID ! variable ID CHARACTER*31 RHNAME ! variable name INTEGER RHTYPE ! variable type INTEGER RHN ! number of dimensions INTEGER RHDIMS(NF_MAX_VAR_DIMS) ! variable shape INTEGER RHNATT ! number of attributes ... STATUS = NF_OPEN ('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID (NCID, 'rh', RHID) ! get ID IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_INQ_VAR (NCID, RHID, RHNAME, RHTYPE, RHN, RHDIMS, RHNATT) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The functions NF_PUT_VAR1_type (for various types) 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.
INTEGER FUNCTION NF_PUT_VAR1_TEXT(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), CHARACTER CHVAL) INTEGER FUNCTION NF_PUT_VAR1_INT1(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), INTEGER*1 I1VAL) INTEGER FUNCTION NF_PUT_VAR1_INT2(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), INTEGER*2 I2VAL) INTEGER FUNCTION NF_PUT_VAR1_INT (INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), INTEGER IVAL) INTEGER FUNCTION NF_PUT_VAR1_REAL(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), REAL RVAL) INTEGER FUNCTION NF_PUT_VAR1_DOUBLE(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), DOUBLE DVAL) INTEGER FUNCTION NF_PUT_VAR1(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), *)
NCID
VARID
INDEX
CHVAL
I1VAL
I2VAL
IVAL
RVAL
DVAL
NF_PUT_VAR1_ type returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_PUT_VAR1_DOUBLE to set the (4,3,2) 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 lon, lat, and time, so we want to set the value of rh that corresponds to the fourth lon value, the third lat value, and the second time value:
INCLUDE 'netcdf.inc' ... INTEGER STATUS ! error status INTEGER NCID INTEGER RHID ! variable ID INTEGER RHINDX(3) ! where to put value DATA RHINDX /4, 3, 2/ ... STATUS = NF_OPEN ('foo.nc', NF_WRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID (NCID, 'rh', RHID) ! get ID IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_PUT_VAR1_DOUBLE (NCID, RHID, RHINDX, 0.5) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The NF_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 (variables that use the NF_UNLIMITED dimension) 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 the values of a record variable from an array but there are more records in the file than you assume, more in-memory data will be accessed than you expect, which may cause a segmentation violation. To avoid such problems, it is better to use the NF_PUT_VARA_type interfaces for variables that use the NF_UNLIMITED dimension. See NF_PUT_VARA_ type.
INTEGER FUNCTION NF_PUT_VAR_TEXT (INTEGER NCID, INTEGER VARID, CHARACTER*(*) TEXT) INTEGER FUNCTION NF_PUT_VAR_INT1 (INTEGER NCID, INTEGER VARID, INTEGER*1 I1VALS(*)) INTEGER FUNCTION NF_PUT_VAR_INT2 (INTEGER NCID, INTEGER VARID, INTEGER*2 I2VALS(*)) INTEGER FUNCTION NF_PUT_VAR_INT (INTEGER NCID, INTEGER VARID, INTEGER IVALS(*)) INTEGER FUNCTION NF_PUT_VAR_REAL (INTEGER NCID, INTEGER VARID, REAL RVALS(*)) INTEGER FUNCTION NF_PUT_VAR_DOUBLE(INTEGER NCID, INTEGER VARID, DOUBLE DVALS(*)) INTEGER FUNCTION NF_PUT_VAR (INTEGER NCID, INTEGER VARID, VALS(*))
NCID
VARID
TEXT
I1VALS
I2VALS
IVALS
RVALS
DVALS
VALS
Members of the NF_PUT_VAR_ type family return the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_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 lon and lat, and that there are ten lon values and five lat values.
INCLUDE 'netcdf.inc' ... PARAMETER (LATS=5, LONS=10) ! dimension lengths INTEGER STATUS, NCID INTEGER RHID ! variable ID DOUBLE RHVALS(LONS, LATS) ... STATUS = NF_OPEN ('foo.nc', NF_WRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID (NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) DO 10 ILON = 1, LONS DO 10 ILAT = 1, LATS RHVALS(ILON, ILAT) = 0.5 10 CONTINUE STATUS = NF_PUT_var_DOUBLE (NCID, RHID, RHVALS) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The function NF_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 first dimension of the netCDF variable varies fastest in the FORTRAN interface. The netCDF dataset must be in data mode.
INTEGER FUNCTION NF_PUT_VARA_TEXT(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), CHARACTER*(*) TEXT) INTEGER FUNCTION NF_PUT_VARA_INT1(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER*1 I1VALS(*)) INTEGER FUNCTION NF_PUT_VARA_INT2(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER*2 I2VALS(*)) INTEGER FUNCTION NF_PUT_VARA_INT (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER IVALS(*)) INTEGER FUNCTION NF_PUT_VARA_REAL(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), REAL RVALS(*)) INTEGER FUNCTION NF_PUT_VARA_DOUBLE(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), DOUBLE DVALS(*)) INTEGER FUNCTION NF_PUT_VARA (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), VALS(*))
NCID
VARID
START
COUNT
Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.
TEXT
I1VALS
I2VALS
IVALS
RVALS
DVALS
VALS
NF_PUT_VARA_ type returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_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.inc' ... PARAMETER (NDIMS=3) ! number of dimensions PARAMETER (TIMES=3, LATS=5, LONS=10) ! dimension lengths INTEGER STATUS, NCID, TIMES INTEGER RHID ! variable ID INTEGER START(NDIMS), COUNT(NDIMS) DOUBLE RHVALS(LONS, LATS, TIMES) DATA START /1, 1, 1/ ! start at first value DATA COUNT /LONS, LATS, TIMES/ ... STATUS = NF_OPEN ('foo.nc', NF_WRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID (NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) DO 10 ILON = 1, LONS DO 10 ILAT = 1, LATS DO 10 ITIME = 1, TIMES RHVALS(ILON, ILAT, ITIME) = 0.5 10 CONTINUE STATUS = NF_PUT_VARA_DOUBLE (NCID, RHID, START, COUNT, RHVALS) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
Each member of the family of functions NF_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.
INTEGER FUNCTION NF_PUT_VARS_TEXT (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*),CHARACTER*(*) TEXT) INTEGER FUNCTION NF_PUT_VARS_INT1 (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*),INTEGER*1 I1VALS(*)) INTEGER FUNCTION NF_PUT_VARS_INT2 (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*),INTEGER*2 I2VALS(*)) INTEGER FUNCTION NF_PUT_VARS_INT (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IVALS(*)) INTEGER FUNCTION NF_PUT_VARS_REAL (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), REAL RVALS(*)) INTEGER FUNCTION NF_PUT_VARS_DOUBLE(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), DOUBLE DVALS(*)) INTEGER FUNCTION NF_PUT_VARS (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), VALS(*))
NCID
VARID
START
COUNT
Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.
STRIDE
TEXT
I1VALS
I2VALS
IVALS
RVALS
DVALS
VALS
NF_PUT_VARS_ type returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example of using NF_PUT_VARS_REAL to write – from an internal array – every other point of a netCDF variable named rh which is described by the FORTRAN declaration REAL RH(6,4) (note the size of the dimensions):
INCLUDE 'netcdf.inc' ...  STATUS = NF_OPEN('foo.nc', NF_WRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID(NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_PUT_VARS_REAL(NCID, RHID, START, COUNT, STRIDE, RH) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The NF_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.
INTEGER FUNCTION NF_PUT_VARM_TEXT (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), CHARACTER*(*) TEXT) INTEGER FUNCTION NF_PUT_VARM_INT1 (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), INTEGER*1 I1VALS(*)) INTEGER FUNCTION NF_PUT_VARM_INT2 (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), INTEGER*2 I2VALS(*)) INTEGER FUNCTION NF_PUT_VARM_INT (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), INTEGER IVALS(*)) INTEGER FUNCTION NF_PUT_VARM_REAL (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), REAL RVALS(*)) INTEGER FUNCTION NF_PUT_VARM_DOUBLE(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), DOUBLE DVALS(*))
NCID
VARID
START
COUNT
Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.
STRIDE
IMAP
TEXT
I1VALS
I2VALS
IVALS
RVALS
DVALS
NF_PUT_VARM_ type returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
The following IMAP vector maps in the trivial way a 2x3x4 netCDF variable and an internal array of the same shape:
REAL A(2,3,4) ! same shape as netCDF variable INTEGER IMAP(3) DATA IMAP /1, 2, 6/ ! netCDF dimension inter-element distance ! ---------------- ---------------------- ! most rapidly varying 1 ! intermediate 2 (=IMAP(1)*2) ! most slowly varying 6 (=IMAP(2)*3)
Using the IMAP vector above with NF_PUT_VARM_REAL obtains the same result as simply using NF_PUT_VAR_REAL.
Here is an example of using NF_PUT_VARM_REAL to write – from a transposed, internal array – a netCDF variable named rh which is described by the FORTRAN declaration REAL RH(4,6) (note the size and order of the dimensions):
INCLUDE 'netcdf.inc' ...  NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID(NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_PUT_VARM_REAL(NCID, RHID, START, COUNT, STRIDE, IMAP, RH) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
Here is another example of using NF_PUT_VARM_REAL 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.inc' ...  STATUS = NF_OPEN('foo.nc', NF_WRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID(NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_PUT_VARM_REAL(NCID, RHID, START, COUNT, STRIDE, IMAP, RH) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The functions NF_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.
INTEGER FUNCTION NF_GET_VAR1_TEXT(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), CHARACTER CHVAL) INTEGER FUNCTION NF_GET_VAR1_INT1(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), INTEGER*1 I1VAL) INTEGER FUNCTION NF_GET_VAR1_INT2(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), INTEGER*2 I2VAL) INTEGER FUNCTION NF_GET_VAR1_INT (INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), INTEGER IVAL) INTEGER FUNCTION NF_GET_VAR1_REAL(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), REAL RVAL) INTEGER FUNCTION NF_GET_VAR1_DOUBLE(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), DOUBLE DVAL) INTEGER FUNCTION NF_GET_VAR1(INTEGER NCID, INTEGER VARID, INTEGER INDEX(*), VAL)
NCID
VARID
INDEX
CHVAL
I1VAL
I2VAL
IVAL
RVAL
DVAL
VAL
NF_GET_VAR1_ type returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_GET_VAR1_DOUBLE to get the (4,3,2) 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 lon, lat, and time, so we want to get the value of rh that corresponds to the fourth lon value, the third lat value, and the second time value:
INCLUDE 'netcdf.inc' ... INTEGER STATUS, NCID INTEGER RHID ! variable ID INTEGER RHINDX(3) ! where to get value DOUBLE PRECISION RHVAL ! put it here DATA RHINDX /4, 3, 2/ ... STATUS = NF_OPEN ('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID (NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_GET_VAR1_DOUBLE (NCID, RHID, RHINDX, RHVAL) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The members of the NF_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 first dimension varying fastest. The netCDF dataset must be in data mode.
Take care when using the simplest forms of this interface with record variables (variables that use the NF_UNLIMITED dimension) 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. To avoid such problems, it is better to use the NF_GET_VARA_type interfaces for variables that use the NF_UNLIMITED dimension. See NF_GET_VARA_ type.
INTEGER FUNCTION NF_GET_VAR_TEXT (INTEGER NCID, INTEGER VARID, CHARACTER*(*) text) INTEGER FUNCTION NF_GET_VAR_INT1 (INTEGER NCID, INTEGER VARID, INTEGER*1 i1vals(*)) INTEGER FUNCTION NF_GET_VAR_INT2 (INTEGER NCID, INTEGER VARID, INTEGER*2 i2vals(*)) INTEGER FUNCTION NF_GET_VAR_INT (INTEGER NCID, INTEGER VARID, INTEGER ivals(*)) INTEGER FUNCTION NF_GET_VAR_REAL (INTEGER NCID, INTEGER VARID, REAL rvals(*)) INTEGER FUNCTION NF_GET_VAR_DOUBLE(INTEGER NCID, INTEGER VARID, DOUBLE dvals(*)) INTEGER FUNCTION NF_GET_VAR (INTEGER NCID, INTEGER VARID, vals(*))
NCID
VARID
TEXT
I1VALS
I2VALS
IVALS
RVALS
DVALS
VALS
NF_GET_VAR_ type returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_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 lon and lat, and that there are ten lon values and five lat values.
INCLUDE 'netcdf.inc' ... PARAMETER (LATS=5, LONS=10) ! dimension lengths INTEGER STATUS, NCID INTEGER RHID ! variable ID DOUBLE RHVALS(LONS, LATS) ... STATUS = NF_OPEN ('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID (NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_GET_VAR_DOUBLE (NCID, RHID, RHVALS) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The members of the NF_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 first dimension varying fastest. The netCDF dataset must be in data mode.
INTEGER FUNCTION NF_GET_VARA_TEXT(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), CHARACTER*(*) text) INTEGER FUNCTION NF_GET_VARA_INT1(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER*1 i1vals(*)) INTEGER FUNCTION NF_GET_VARA_INT2(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER*2 i2vals(*)) INTEGER FUNCTION NF_GET_VARA_INT (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER ivals(*)) INTEGER FUNCTION NF_GET_VARA_REAL(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), REAL rvals(*)) INTEGER FUNCTION NF_GET_VARA_DOUBLE(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), DOUBLE dvals(*))
NCID
VARID
START
COUNT
Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.
text
i1vals
i2vals
ivals
rvals
dvals
NF_GET_VARA_ type returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_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 lon, lat, and time, and that there are ten lon values, five lat values, and three time values.
INCLUDE 'netcdf.inc' ... PARAMETER (NDIMS=3) ! number of dimensions PARAMETER (TIMES=3, LATS=5, LONS=10) ! dimension lengths INTEGER STATUS, NCID INTEGER RHID ! variable ID INTEGER START(NDIMS), COUNT(NDIMS) DOUBLE RHVALS(LONS, LATS, TIMES) DATA START /1, 1, 1/ ! start at first value DATA COUNT /LONS, LATS, TIMES/ ! get all the values ... STATUS = NF_OPEN ('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID (NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_GET_VARA_DOUBLE (NCID, RHID, START, COUNT, RHVALS) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The NF_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 first dimension of the netCDF variable varying fastest. The netCDF dataset must be in data mode.
INTEGER FUNCTION NF_GET_VARS_TEXT (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*),CHARACTER*(*) text) INTEGER FUNCTION NF_GET_VARS_INT1 (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*),INTEGER*1 i1vals(*)) INTEGER FUNCTION NF_GET_VARS_INT2 (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*),INTEGER*2 i2vals(*)) INTEGER FUNCTION NF_GET_VARS_INT (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER ivals(*)) INTEGER FUNCTION NF_GET_VARS_REAL (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), REAL rvals(*)) INTEGER FUNCTION NF_GET_VARS_DOUBLE(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), DOUBLE dvals(*))
NCID
VARID
START
COUNT
Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.
STRIDE
text
i1vals
i2vals
ivals
rvals
dvals
NF_GET_VARS_ type returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF_GET_VARS_DOUBLE to read every other value in each dimension of the variable named rh from an existing netCDF dataset named foo.nc. Values are assigned, using the same dimensional strides, to a 2-parameter array. For simplicity in this example, we assume that we know that rh is dimensioned with lon, lat, and time, and that there are ten lon values, five lat values, and three time values.
INCLUDE 'netcdf.inc' ... PARAMETER (NDIMS=3) ! number of dimensions PARAMETER (TIMES=3, LATS=5, LONS=10) ! dimension lengths INTEGER STATUS, NCID INTEGER RHID ! variable ID INTEGER START(NDIMS), COUNT(NDIMS), STRIDE(NDIMS) DOUBLE DATA(LONS, LATS, TIMES) DATA START /1, 1, 1/ ! start at first value DATA COUNT /LONS, LATS, TIMES/ DATA STRIDE /2, 2, 2/ ... STATUS = NF_OPEN ('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID (NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) STATUS = NF_GET_VARS_DOUBLE(NCID,RHID,START,COUNT,STRIDE,DATA(1,1,1)) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
The NF_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.
INTEGER FUNCTION NF_GET_VARM_TEXT (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), CHARACTER*(*) text) INTEGER FUNCTION NF_GET_VARM_INT1 (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), INTEGER*1 i1vals(*)) INTEGER FUNCTION NF_GET_VARM_INT2 (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), INTEGER*2 i2vals(*)) INTEGER FUNCTION NF_GET_VARM_INT (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), INTEGER ivals(*)) INTEGER FUNCTION NF_GET_VARM_REAL (INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), REAL rvals(*)) INTEGER FUNCTION NF_GET_VARM_DOUBLE(INTEGER NCID, INTEGER VARID, INTEGER START(*), INTEGER COUNT(*), INTEGER STRIDE(*), INTEGER IMAP(*), DOUBLE dvals(*))
NCID
VARID
START
COUNT
Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.
STRIDE
IMAP
text
i1vals
i2vals
ivals
rvals
dvals
NF_GET_VARM_ type returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
The following IMAP vector maps in the trivial way a 2x3x4 netCDF variable and an internal array of the same shape:
REAL A(2,3,4) ! same shape as netCDF variable INTEGER IMAP(3) DATA IMAP /1, 2, 6/ ! netCDF dimension inter-element distance ! ---------------- ---------------------- ! most rapidly varying 1 ! intermediate 2 (=IMAP(1)*2) ! most slowly varying 6 (=IMAP(2)*3)
Using the IMAP vector above with NF_GET_VARM_REAL obtains the same result as simply using NF_GET_VAR_REAL.
Here is an example of using NF_GET_VARM_REAL to transpose a netCDF variable named rh which is described by the FORTRAN declaration REAL RH(4,6) (note the size and order of the dimensions):
INCLUDE 'netcdf.inc' ...  STATUS = NF_OPEN('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID(NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_GET_VARM_REAL(NCID, RHID, START, COUNT, STRIDE, IMAP, RH) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
Here is another example of using NF_GET_VARM_REAL to simultaneously transpose and subsample the same netCDF variable, by accessing every other point of the netCDF variable:
INCLUDE 'netcdf.inc' ...  STATUS = NF_OPEN('foo.nc', NF_NOWRITE, NCID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_INQ_VARID(NCID, 'rh', RHID) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS) ... STATUS = NF_GET_VARM_REAL(NCID, RHID, START, COUNT, STRIDE, IMAP, RH) IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
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.