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This document describes the FORTRAN-77 interface to the netCDF library. This document applies to netCDF version 4.0. This document was last updated in 27 June 2008.
For a complete description of the netCDF format and utilities see Top (The NetCDF Users Guide).
--- 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 (The NetCDF Users Guide).) 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: nc_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)
NCERRIf 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 nc_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)
PATHCMODEA 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 (The NetCDF Users Guide).
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 (The NetCDF Users Guide).
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.
ncidNF_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 CHUNKSIZEHINT, INTEGER ncid)
PATHCMODESetting 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.
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 (The NetCDF Users Guide).
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 (The NetCDF Users Guide).
initialszchunksizehintpBecause 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 chunksize to 8192.
The chunksize is a property of a given open netcdf descriptor
ncid, it is not a persistent property of the netcdf dataset.
ncidNF__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, CHUNKSIZEHINT
...
INITIALSZ = 2048
CHUNKSIZEHINT = 1024
STATUS = NF_CREATE('foo.nc', NF_NOCLOBBER, INITIALSZ, CHUNKSIZEHINT, NCID)
IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
This function is a variant of nc_create, nc_create_par allows users to open a file on a MPI/IO or MPI/Posix parallel file system.
The parallel parameters are not written to the data file, they are only used for so long as the file remains open after an nc_create_par.
This function creates a new netCDF dataset, returning a netCDF ID that can subsequently be used to refer to the netCDF dataset in other netCDF function calls. The new netCDF dataset opened for write access and placed in define mode, ready for you to add dimensions, variables, and attributes.
This function is only available for netCDF-4 files. The creation mode flag must include NC_NETCDF4.
When a netCDF-4 file is created for parallel access, collective operations are the default. To use independent 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)
PATHCMODESetting 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_COMMMPI_INFOncidNF_CREATE returns the value NF_NOERR if no errors occurred. Possible causes of errors include:
The function NF_OPEN opens an existing netCDF dataset for access.
INTEGER FUNCTION NF_OPEN(CHARACTER*(*) PATH, INTEGER OMODE, INTEGER ncid)
PATHOMODEOtherwise, 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.
ncidNF_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
CHUNKSIZEHINT, INTEGER ncid)
PATHOMODEOtherwise, 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.
CHUNKSIZEHINTBecause 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 chunksize to 8192.
The chunksize is a property of a given open netcdf descriptor
ncid, it is not a persistent property of the netcdf dataset.
ncidNF__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, CHUNKSIZEHINT
...
CHUNKSIZEHINT = 1024
STATUS = NF_OPEN('foo.nc', 0, CHUNKSIZEHINT, NCID)
IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
This function opens a netCDF-4 dataset for parallel access.
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 NC_NETCDF4 in the creation mode).
This function is only available if netCDF-4 was configured with the .use-parallel option before being built. Also HDF5 parallel must be installed (before netCDF-4 is installed.)
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)
PATHOMODEOtherwise, 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_COMMMPI_INFOncidNF_OPEN returns the value NF_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
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)
NCIDNF_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 (NetCDF Users' Guide).
INTEGER FUNCTION NF_ENDDEF(INTEGER NCID)
NCIDNF_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 (NetCDF Users' Guide).
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 nc_redef, nc_enddef by requesting that minfree bytes be available at the end of the section.
The align parameters allow one to set the alignment of the beginning of the corresponding sections. The beginning of the section is rounded up to an index which is a multiple of the align parameter. The flag value ALIGN_CHUNK tells the library to use the chunksize (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,
nc_enddef(ncid);
is equivalent to
nc_enddef(ncid, 0, 4, 0, 4);
The file format does not contain a "record size" value, this is calculated from the sizes of the record variables. This unfortunate fact prevents us from providing minfree and alignment control of the "records" in a netcdf file. If you add a variable which has an unlimited dimension, the third section will always be copied with the new variable added.
INTEGER FUNCTION NF_ENDDEF(INTEGER NCID, INTEGER H_MINFREE, INTEGER V_ALIGN,
INTEGER V_MINFREE, INTEGER R_ALIGN)
NCIDH_MINFREEV_ALIGNV_MINFREER_ALIGNNF__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)
NCIDNF_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)
NCIDndimsnvarsngattsunlimdimidformatAll 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)
NCIDNF_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)
NCIDNF_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)
NCIDFILLMODEold_modeNF_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.
Starting in version 3.6, netCDF introduced a new data format, the first change in the underlying binary data format since the netCDF interface was released. The new format, 64-bit offset format, was introduced to greatly relax the limitations on creating very large files.
Users are warned that creating files in the 64-bit offset format makes them unreadable by the netCDF library prior to version 3.6.0. For reasons of compatibility, users should continue to create files in netCDF classic format.
Users who do want to use 64-bit offset format files can create them directory from 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 64-bit offset formation without changing all calls the NF_CREATE. See Large File Support (The NetCDF Users Guide).
Once the default format is set, all future created files will be in the desired format.
Two constants are provided in the netcdf.inc file to be used with this function, nf_format_64bit and nf_format_classic.
Using NF_CREATE with a cmode including nf_64bit_offset overrides the default format, and creates a 64-bit offset file.
INTEGER FUNCTION NF_SET_DEFAULT_FORMAT(INTEGER FORMAT, INTEGER OLD_FORMT)
FORMATOLD_FORMATNF_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 STATUS, OLD_FORMAT
...
STATUS = NF_SET_DEFAULT_FORMAT(nf_format_64bit, OLD_FORMAT)
IF (STATUS .NE. NF_NOERR) CALL HANDLE_ERR(STATUS)
...
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 NC_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)
NCIDNAMEGRPIDNF_NOERRNF_EBADIDNF_ENOTNC4NF_ESTRICTNC3NF_EHDFERRThis 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)
NCIDNUMGRPSNCIDSNF_NOERRNF_EBADIDNF_ENOTNC4NF_ESTRICTNC3NF_EHDFERRThis 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)
NCIDVARIDSNF_NOERRNF_EBADIDNF_ENOTNC4NF_ESTRICTNC3NF_EHDFERRThis 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)
NCIDDIMIDSINCLUDE_PARENTSNF_NOERRNF_EBADIDNF_ENOTNC4NF_ESTRICTNC3NF_EHDFERRThis 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)
NCIDLENNF_NOERRNF_EBADIDNF_ENOTNC4NF_ESTRICTNC3NF_EHDFERRThis 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)
NCIDNAMENF_NOERRNF_EBADIDNF_ENOTNC4NF_ESTRICTNC3NF_EHDFERRThis 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)
NCIDLENNAMENF_NOERRNF_EBADIDNF_ENOTNC4NF_ESTRICTNC3NF_EHDFERRThis 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)
NCIDPARENT_NCIDNF_NOERRNF_EBADIDNF_ENOGRPNF_ENOTNC4NF_ESTRICTNC3NF_EHDFERRThis 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)
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_NCIDNAMENEW_NCIDNF_NOERRNF_EBADIDNF_ENAMEINUSENF_EMAXNAMENF_EBADNAMENF_ENOTNC4NF_ESTRICTNC3NF_EHDFERRNF_EPERMNF_ENOTINDEFINEIn 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)
NCIDNAMELENdimidNF_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)
NCIDNAMEdimidNF_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)
NCIDDIMIDNAMElenThese 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)
NCIDDIMIDNAMENF_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 typevariable length array typeopaque typeenum typeUsers 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.
Learn the number of types defined in a group, and their IDs.
INTEGER FUNCTION NF_INQ_TYPEIDS(INTEGER NCID, INTEGER NTYPES,
INTEGER TYPEIDS)
NCIDNTYPESTYPEIDSNF_NOERRNF_BADIDThe 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 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)
NCIDXTYPENAMESIZEPNF_NOERRNF_EBADTYPEIDNF_ENOTNC4NF_ESTRICTNC3