This document describes the Fortran 90 interface to the netCDF library. It 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 The NetCDF Users Guide.
--- The Detailed Node Listing ---
Use of the NetCDF Library
Datasets
Groups
Dimensions
User Defined Data Types
Example
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:
NF90_CREATE ! create netCDF dataset: enter define mode ... NF90_DEF_DIM ! define dimensions: from name and length ... NF90_DEF_VAR ! define variables: from name, type, dims ... NF90_PUT_ATT ! assign attribute values ... NF90_ENDDEF ! end definitions: leave define mode ... NF90_PUT_VAR ! provide values for variable ... NF90_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 NF90_DEF_DIM is needed for each dimension created. Similarly, one call to NF90_DEF_VAR is needed for each variable creation, and one call to a member of the NF90_PUT_ATT family is needed for each attribute defined and assigned a value. To leave define mode and enter data mode, call NF90_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). Data of all types is written to a netCDF variable using the NF90_PUT_VAR subroutine. Single values, arrays, or array sections may be supplied to NF90_PUT_VAR; optional arguments allow the writing of subsampled or mapped portions of the variable. (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 NF90_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 NF90_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 NF90_SYNC or NF90_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:
NF90_OPEN ! open existing netCDF dataset ... NF90_INQ_DIMID ! get dimension IDs ... NF90_INQ_VARID ! get variable IDs ... NF90_GET_ATT ! get attribute values ... NF90_GET_VAR ! get values of variables ... NF90_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 NF90_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 NF90_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 NF90_GET_ATT for each desired attribute. Variable data values can be directly accessed from the netCDF dataset with calls to NF90_GET_VAR.
Finally, the netCDF dataset is closed with NF90_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:
NF90_OPEN ! open existing netCDF dataset ... NF90_INQUIRE ! find out what is in it ... NF90_INQUIRE_DIMENSION ! get dimension names, lengths ... NF90_INQUIRE_VARIABLE ! get variable names, types, shapes ... NF90_INQ_ATTNAME ! get attribute names ... NF90_INQUIRE_ATTRIBUTE ! get other attribute information ... NF90_GET_ATT ! get attribute values ... NF90_GET_VAR ! get values of variables ... NF90_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 NF90_INQUIRE 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 NF90_INQUIRE_DIMENSION 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 NF90_INQUIRE_VARIABLE 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 NF90_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 NF90_INQUIRE_ATTRIBUTE returns its type and length. Given the type and length, you can allocate enough space to hold the attribute values. Then a call to NF90_GET_ATT returns the attribute values.
Once the IDs and shapes of netCDF variables are known, data values can be accessed by calling NF90_GET_VAR.
With write access to an existing netCDF dataset, you can overwrite data values in existing variables or append more data to record variables along the unlimited (record) dimension. To append more data to non-record variables requires changing the shape of such variables, which means creating a new netCDF dataset, defining new variables with the desired shape, and copying data. The netCDF data model was not designed to make such "schema changes" efficient or easy, so it is best to specify the shapes of variables correctly when you create a netCDF dataset, and to anticipate which variables will later grow by using the unlimited dimension in their definition.
The following code template lists a typical sequence of calls to overwrite some existing values and add some new records to record variables in an existing netCDF dataset with known variable names:
NF90_OPEN ! open existing netCDF dataset ... NF90_INQ_VARID ! get variable IDs ... NF90_PUT_VAR ! provide new values for variables, if any ... NF90_PUT_ATT ! provide new values for attributes, if any ... NF90_CLOSE ! close netCDF dataset
A netCDF dataset is first opened by the NF90_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, but no new dimensions, variables, or attributes can be added.
Next, calls to NF90_INQ_VARID get the variable ID from the name, for each variable you want to write. Then each call to NF90_PUT_VAR writes data into a specified variable, either a single value at a time, or a whole set of values at a time, depending on which variant of the interface is used. The calls used to overwrite values of non-record variables are the same as are used to overwrite values of record variables or append new data to record variables. The difference is that, with record variables, the record dimension is extended by writing values that don't yet exist in the dataset. This extends all record variables at once, writing "fill values" for record variables for which the data has not yet been written (but see Fill Values to specify different behavior).
Calls to NF90_PUT_ATT may be used to change the values of existing attributes, although data that changes after a file is created is typically stored in variables rather than attributes.
Finally, you should explicitly close any netCDF datasets into which data has been written by calling NF90_CLOSE before program termination. Otherwise, modifications to the dataset may be lost.
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:
NF90_OPEN ! open existing netCDF dataset ... NF90_REDEF ! put it into define mode ... NF90_DEF_DIM ! define additional dimensions (if any) ... NF90_DEF_VAR ! define additional variables (if any) ... NF90_PUT_ATT ! define other attributes (if any) ... NF90_ENDDEF ! check definitions, leave define mode ... NF90_PUT_VAR ! provide new variable values ... NF90_CLOSE ! close netCDF dataset
A netCDF dataset is first opened by the NF90_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 NF90_REDEF. In define mode, call NF90_DEF_DIM to define new dimensions, NF90_DEF_VAR to define new variables, and NF90_PUT_ATT 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 NF90_ENDDEF. If you do not wish to reenter data mode, just call NF90_CLOSE, which will have the effect of first calling NF90_ENDDEF.
Until the NF90_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 NF90_ABORT. You may also use the NF90_ABORT call to restore the netCDF dataset to a consistent state if the call to NF90_ENDDEF fails. If you have called NF90_CLOSE from definition mode and the implied call to NF90_ENDDEF fails, NF90_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 NF90_SYNC function and the NF90_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 NF90_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 NF90_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.
Every Fortran 90 procedure or module which references netCDF constants or procedures must have access to the module information created when the netCDF module was compiled. The suffix for this file is “MOD” (or sometimes “mod”).
Most F90 compilers allow the user to specify the location of .MOD files, usually with the -I flag. (Some compilers, like absoft, use -p instead).
f90 -c -I/usr/local/include mymodule.f90
Starting with version 3.6.2, another method of building the netCDF fortran libraries becomes available. With the –enable-separate-fortran option to configure, the user can specify that the C library should not contain the fortran functions. In these cases an additional library, libnetcdff.a (not the extra “f”) will be built. This library contains the fortran functions.
For more information about configure options, See Specifying the Environment for Building.
Building separate fortran libraries is required for shared library builds, but is not done, by default, for static library builds.
When linking fortran programs without a separate fortran library, programs must link to the netCDF library like this:
f90 -o myprogram myprogram.o -L/usr/local/netcdf/lib -lnetcdf
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: nf90_strerror".
The function NF90_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.
function nf90_strerror(ncerr) integer, intent( in) :: ncerr character(len = 80) :: nf90_strerror
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), NF90_STRERROR returns a string indicating that there is no such error status.
Here is an example of a simple error handling function that uses NF90_STRERROR to print the error message corresponding to the netCDF error status returned from any netCDF function call and then exit:
subroutine handle_err(status) integer, intent ( in) :: status if(status /= nf90_noerr) then print *, trim(nf90_strerror(status)) stop "Stopped" end if end subroutine handle_err
The function NF90_INQ_LIBVERS returns a string identifying the version of the netCDF library, and when it was built.
function nf90_inq_libvers() character(len = 80) :: nf90_inq_libvers
This function takes no arguments, and returns no error status.
Here is an example using nf90_inq_libvers to print the version of the netCDF library with which the program is linked:
print *, trim(nf90_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.
function nf90_create(path, cmode, ncid, initialsize, bufrsize, cache_size, & cache_nelems, cache_preemption, comm, info) implicit none character (len = *), intent(in) :: path integer, intent(in) :: cmode integer, intent(out) :: ncid integer, optional, intent(in) :: initialsize integer, optional, intent(inout) :: bufrsize integer, optional, intent(in) :: cache_size, cache_nelems real, optional, intent(in) :: cache_preemption integer, optional, intent(in) :: comm, info integer :: nf90_create
path
cmode
A zero value (defined for convenience as NF90_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 NF90_NOCLOBBER means you do not want to clobber (overwrite) an existing dataset; an error (NF90_EEXIST) is returned if the specified dataset already exists.
The NF90_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 NF90_SHARE flag. (This only applies to netCDF-3 classic or 64-bit offset files.)
Setting NF90_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 the NF90_HDF5 flag causes netCDF to create a netCDF-4/HDF5 format output file.
Oring the NF90_CLASSIC_MODEL flag with the NF90_HDF5 flag causes the
resulting netCDF-4/HDF5 file to restrict itself to the classic model -
none of the new netCDF-4 data model features, such as groups or
user-defined types, are allowed in such a file.
ncid
The following optional arguments allow additional performance tuning.
initialsize
bufrsize
The library chooses a system-dependent default value if NF90_SIZEHINT_DEFAULT is supplied as input. If the "preferred I/O block size" is available from the stat() system call as member st_blksize this value is used. Lacking that, twice the system pagesize is used. Lacking a call to discover the system pagesize, the default bufrsize is set to 8192 bytes.
The bufrsize is a property of a given open netcdf descriptor ncid, it is not a persistent property of the netcdf dataset.
This is ignored for NetCDF-4/HDF5 files.
cache_size
cache_nelems
cache_premtion
comm
info
NF90_CREATE returns the value NF90_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:
use netcdf implicit none integer :: ncid, status ... status = nf90_create(path = "foo.nc", cmode = nf90_noclobber, ncid = ncid) if (status /= nf90_noerr) call handle_err(status)
The function NF90_OPEN opens an existing netCDF dataset for access.
function nf90_open(path, mode, ncid, bufrsize, cache_size, cache_nelems, & cache_preemption, comm, info) implicit none character (len = *), intent(in) :: path integer, intent(in) :: mode integer, intent(out) :: ncid integer, optional, intent(inout) :: bufrsize integer, optional, intent(in) :: cache_size, cache_nelems real, optional, intent(in) :: cache_preemption integer, optional, intent(in) :: comm, info integer :: nf90_open
path
mode
Otherwise, the open mode is NF90_WRITE, NF90_SHARE, or
NF90_WRITE|NF90_SHARE. Setting the NF90_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
NF90_SHARE flag is appropriate when one process may be writing the
dataset and one or more other processes reading the dataset
concurrently (note that this is not the same as parallel I/O); 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 NF90_SHARE flag.
ncid
The following optional argument allows additional performance tuning.
bufrsize
It Controls a space versus time trade-off, memory allocated in the netcdf library versus number of system calls. Because of internal requirements, the value may not be set to exactly the value requested. The actual value chosen is returned.
The library chooses a system-dependent default value if NF90_SIZEHINT_DEFAULT is supplied as input. If the "preferred I/O block size" is available from the stat() system call as member st_blksize this value is used. Lacking that, twice the system pagesize is used. Lacking a call to discover the system pagesize, the default bufrsize is set to 8192 bytes.
The bufrsize is a property of a given open netcdf descriptor ncid, it
is not a persistent property of the netcdf dataset.
cache_size
cache_nelems
cache_premtion
comm
info
NF90_OPEN returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_OPEN to open an existing netCDF dataset named foo.nc for read-only, non-shared access:
use netcdf implicit none integer :: ncid, status ... status = nf90_open(path = "foo.nc", mode = nf90_nowrite, ncid = ncid) if (status /= nf90_noerr) call handle_err(status)
Here is an example using NF90_OPEN to open an existing netCDF dataset for parallel I/O access. (Note the use of the comm and info parameters). This example is from test program nf_test/f90tst_parallel.f90.
use netcdf implicit none integer :: ncid, status ... ! Reopen the file. call handle_err(nf90_open(FILE_NAME, nf90_nowrite, ncid, comm = MPI_COMM_WORLD, & info = MPI_INFO_NULL))
The function NF90_REDEF puts an open netCDF dataset into define mode, so dimensions, variables, and attributes can be added or renamed and attributes can be deleted.
function nf90_redef(ncid) integer, intent( in) :: ncid integer :: nf90_redef
ncid
NF90_REDEF returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_REDEF to open an existing netCDF dataset named foo.nc and put it into define mode:
use netcdf implicit none integer :: ncid, status ... status = nf90_open("foo.nc", nf90_write, ncid) ! Open dataset if (status /= nf90_noerr) call handle_err(status) ... status = nf90_redef(ncid) ! Put the file in define mode if (status /= nf90_noerr) call handle_err(status)
The function NF90_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 NF90_SET_FILL). The netCDF dataset is then placed in data mode, so variable data can be read or written.
This call may involve copying data under some circumstances. For a more extensive discussion See File Structure and Performance.
function nf90_enddef(ncid, h_minfree, v_align, v_minfree, r_align) integer, intent( in) :: ncid integer, optional, intent( in) :: h_minfree, v_align, v_minfree, r_align integer :: nf90_enddef
ncid
The following arguments allow additional performance tuning. Note: these arguments expose internals of the netcdf version 1 file format, and may not be available in future netcdf implementations.
The current netcdf file format has three sections: the "header" section, the data section for fixed size variables, and the data section for variables which have an unlimited dimension (record variables). The header begins at the beginning of the file. The index (offset) of the beginning of the other two sections is contained in the header. Typically, there is no space between the sections. This causes copying overhead to accrue if one wishes to change the size of the sections, as may happen when changing the 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 nf90_redef or nf90_enddef by requesting that some space be available at the end of the section. The default value for both h_minfree and v_minfree is 0.
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 NF90_ALIGN_CHUNK tells the library to use the bufrsize (see above) as the align parameter. The default value for both v_align and r_align is 4 bytes.
h_minfree
v_minfree
v_align
r_align
NF90_ENDDEF returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_ENDDEF to finish the definitions of a new netCDF dataset named foo.nc and put it into data mode:
use netcdf implicit none integer :: ncid, status ... status = nf90_create("foo.nc", nf90_noclobber, ncid) if (status /= nf90_noerr) call handle_err(status) ... ! create dimensions, variables, attributes status = nf90_enddef(ncid) if (status /= nf90_noerr) call handle_err(status)
The function NF90_CLOSE closes an open netCDF dataset. If the dataset is in define mode, NF90_ENDDEF will be called before closing. (In this case, if NF90_ENDDEF returns an error, NF90_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.
function nf90_close(ncid) integer, intent( in) :: ncid integer :: nf90_close
ncid
NF90_CLOSE returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_CLOSE to finish the definitions of a new netCDF dataset named foo.nc and release its netCDF ID:
use netcdf implicit none integer :: ncid, status ... status = nf90_create("foo.nc", nf90_noclobber, ncid) if (status /= nf90_noerr) call handle_err(status) ... ! create dimensions, variables, attributes status = nf90_close(ncid) if (status /= nf90_noerr) call handle_err(status)
The NF90_INQUIRE subroutine returns information about an open netCDF dataset, given its netCDF ID. The subroutine can be called from either define mode or data mode, and returns values for any or all of the following: 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. An additional function, NF90_INQ_FORMAT, returns the (rarely needed) format version.
No I/O is performed when NF90_INQUIRE is called, since the required information is available in memory for each open netCDF dataset.
function nf90_inquire(ncid, nDimensions, nVariables, nAttributes, & unlimitedDimId, formatNum) integer, intent( in) :: ncid integer, optional, intent(out) :: nDimensions, nVariables, & nAttributes, unlimitedDimId, & formatNum integer :: nf90_inquire
ncid
nDimensions
nVariables
nAttributes
unlimitedDimID
format
Function NF90_INQUIRE returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_INQUIRE to find out about a netCDF dataset named foo.nc:
use netcdf implicit none integer :: ncid, status, nDims, nVars, nGlobalAtts, unlimDimID ... status = nf90_open("foo.nc", nf90_nowrite, ncid) if (status /= nf90_noerr) call handle_err(status) ... status = nf90_inquire(ncid, nDims, nVars, nGlobalAtts, unlimdimid) if (status /= nf90_noerr) call handle_err(status) status = nf90_inquire(ncid, nDimensions = nDims, & unlimitedDimID = unlimdimid) if (status /= nf90_noerr) call handle_err(status)
The function NF90_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 NF90_SYNC after writing and the readers call NF90_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 NF90_SHARE flag, and then it will not be necessary to call NF90_SYNC at all. However, the NF90_SYNC function still provides finer granularity than the NF90_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 NF90_SHARE flag. Use of the NF90_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 NF90_SYNC before any subsequent access.
When calling NF90_SYNC, the netCDF dataset must be in data mode. A netCDF dataset in define mode is synchronized to disk only when NF90_ENDDEF is called. A process that is reading a netCDF dataset that another process is writing may call NF90_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.
function nf90_sync(ncid) integer, intent( in) :: ncid integer :: nf90_sync
ncid
NF90_SYNC returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_SYNC to synchronize the disk writes of a netCDF dataset named foo.nc:
use netcdf implicit none integer :: ncid, status ... status = nf90_open("foo.nc", nf90_write, ncid) if (status /= nf90_noerr) call handle_err(status) ... ! write data or change attributes ... status = NF90_SYNC(ncid) if (status /= nf90_noerr) call handle_err(status)
You no longer need to call this function, since it is called automatically by NF90_CLOSE in case the dataset is in define mode and something goes wrong with committing the changes. The function NF90_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 NF90_REDEF, the netCDF dataset is restored to its state before definition mode was entered and the dataset is closed.
function nf90_abort(ncid) integer, intent( in) :: ncid integer :: nf90_abort
ncid
NF90_ABORT returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_ABORT to back out of redefinitions of a dataset named foo.nc:
use netcdf implicit none integer :: ncid, status, LatDimID ... status = nf90_open("foo.nc", nf90_write, ncid) if (status /= nf90_noerr) call handle_err(status) ... status = nf90_redef(ncid) if (status /= nf90_noerr) call handle_err(status) ... status = nf90_def_dim(ncid, "Lat", 18, LatDimID) if (status /= nf90_noerr) then ! Dimension definition failed call handle_err(status) status = nf90_abort(ncid) ! Abort redefinitions if (status /= nf90_noerr) call handle_err(status) end if ...
This function is intended for advanced usage, to optimize writes under some circumstances described below. The function NF90_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 NF90_FILL or NF90_NOFILL. The default behavior corresponding to NF90_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 NF90_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 NF90_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 NF90_SET_FILL again to explicitly set the fill mode to NF90_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.
function nf90_set_fill(ncid, fillmode, old_mode) integer, intent( in) :: ncid, fillmode integer, intent(out) :: old_mode integer :: nf90_set_fill
ncid
fillmode
old_mode
NF90_SET_FILL returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_SET_FILL to set nofill mode for subsequent writes of a netCDF dataset named foo.nc:
use netcdf implicit none integer :: ncid, status, oldMode ... status = nf90_open("foo.nc", nf90_write, ncid) if (status /= nf90_noerr) call handle_err(status) ... ! Write data with prefilling behavior ... status = nf90_set_fill(ncid, nf90_nofill, oldMode) if (status /= nf90_noerr) call handle_err(status) ... ! Write data with no prefilling ...
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 NF90_OPEN or NF90_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 NF90_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 NF90_CREATE or NF90_OPEN to create a variable in the root group. Or use NF90_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 nf90_create. (see NF90_CREATE). Groups are not compatible with the netCDF classic data model, so files created with the NF90_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.
function nf90_inq_ncid(ncid, name, grp_ncid) integer, intent(in) :: ncid character (len = *), intent(in) :: name integer, intent(out) :: grp_ncid integer :: nf90_inq_ncid
NCID
NAME
GRPID
NF90_NOERR
NF90_EBADID
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
This example is from nf90_test/ftst_groups.F.
Given a location id, return the number of groups it contains, and an array of their ncids.
function nf90_inq_grps(ncid, numgrps, ncids) integer, intent(in) :: ncid integer, intent(out) :: numgrps integer, intent(out) :: ncids integer :: nf90_inq_grps
NCID
NUMGRPS
NCIDS
NF90_NOERR
NF90_EBADID
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
Find all varids for a location.
function nf90_inq_varids(ncid, nvars, varids) integer, intent(in) :: ncid integer, intent(out) :: nvars integer, intent(out) :: varids integer :: nf90_inq_varids
NCID
VARIDS
NF90_NOERR
NF90_EBADID
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
Find all dimids for a location. This finds all dimensions in a group, or any of its parents.
function nf90_inq_dimids(ncid, ndims, dimids, include_parents) integer, intent(in) :: ncid integer, intent(out) :: ndims integer, intent(out) :: dimids integer, intent(out) :: include_parents integer :: nf90_inq_dimids
NCID
DIMIDS
INCLUDE_PARENTS
NF90_NOERR
NF90_EBADID
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
Given ncid, find length of the full name. (Root group is named "/", with length 1.)
function nf90_inq_grpname_len(ncid, len) integer, intent(in) :: ncid integer, intent(out) :: len integer :: nf90_inq_grpname_len end function nf90_inq_grpname_len
NCID
LEN
NF90_NOERR
NF90_EBADID
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
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 NF90_INQ_GRPNAME_FULL.
function nf90_inq_grpname(ncid, name) integer, intent(in) :: ncid character (len = *), intent(out) :: name integer :: nf90_inq_grpname
NCID
NAME
NF90_NOERR
NF90_EBADID
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
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 NF90_INQ_GRPNAME.
To find the length of the full name See NF90_INQ_GRPNAME_LEN.
function nf90_inq_grpname_full(ncid, len, name) integer, intent(in) :: ncid integer, intent(out) :: len character (len = *), intent(out) :: name integer :: nf90_inq_grpname_full
NCID
LEN
NAME
NF90_NOERR
NF90_EBADID
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
This example is from test program nf_test/f90tst_grps.f90.
call check(nf90_inq_grpname_full(grpid1, len, name_in)) if (name_in .ne. grp1_full_name) stop 62
Given ncid, find the ncid of the parent group.
When used with the root group, this function returns the NF90_ENOGRP error (since the root group has no parent.)
function nf90_inq_grp_parent(ncid, parent_ncid) integer, intent(in) :: ncid integer, intent(out) :: parent_ncid integer :: nf90_inq_grp_parent
NCID
PARENT_NCID
NF90_NOERR
NF90_EBADID
NF90_ENOGRP
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
Given a group name an an ncid, find the ncid of the group id.
function nf90_inq_grp_ncid(ncid, name, grpid) integer, intent(in) :: ncid character (len = *), intent(in) :: name integer, intent(out) :: grpid integer :: nf90_inq_grp_ncid nf90_inq_grp_ncid = nf_inq_grp_ncid(ncid, name, grpid) end function nf90_inq_grp_ncid
NCID
GRP_NAME
GRP_NCID
The following return codes may be returned by this function.
NF90_NOERR
NF90_EBADID
NF90_EINVAL
NF90_ENOGRP
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
This example is from test program nf_test/f90tst_grps.f90.
! Get the group ids for the newly reopened file. call check(nf90_inq_grp_ncid(ncid, GRP1_NAME, grpid1)) call check(nf90_inq_grp_ncid(grpid1, GRP2_NAME, grpid2)) call check(nf90_inq_grp_ncid(grpid2, GRP3_NAME, grpid3)) call check(nf90_inq_grp_ncid(grpid3, GRP4_NAME, grpid4))
Given a fully qualified group name an an ncid, find the ncid of the group id.
function nf90_inq_grpname_full(ncid, len, name) integer, intent(in) :: ncid integer, intent(out) :: len character (len = *), intent(out) :: name integer :: nf90_inq_grpname_full nf90_inq_grpname_full = nf_inq_grpname_full(ncid, len, name) end function nf90_inq_grpname_full
NCID
FULL_NAME
GRP_NCID
The following return codes may be returned by this function.
NF90_NOERR
NF90_EBADID
NF90_EINVAL
NF90_ENOGRP
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
This example is from test program nf_test/tstf90_grps.f90.
! Check for the groups with full group names. write(grp1_full_name, '(AA)') '/', GRP1_NAME call check(nf90_inq_grp_full_ncid(ncid, grp1_full_name, grpid1))
Create a group. Its location id is returned in new_ncid.
function nf90_def_grp(parent_ncid, name, new_ncid) integer, intent(in) :: parent_ncid character (len = *), intent(in) :: name integer, intent(out) :: new_ncid integer :: nf90_def_grp
PARENT_NCID
NAME
NEW_NCID
NF90_NOERR
NF90_EBADID
NF90_ENAMEINUSE
NF90_EMAXNAME
NF90_EBADNAME
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
NF90_EPERM
NF90_ENOTINDEFINE
C Create the netCDF file. retval = nf90_create(file_name, NF90_NETCDF4, ncid) if (retval .ne. nf90_noerr) call handle_err(retval) C Create a group and a subgroup. retval = nf90_def_grp(ncid, group_name, grpid) if (retval .ne. nf90_noerr) call handle_err(retval) retval = nf90_def_grp(grpid, sub_group_name, sub_grpid) if (retval .ne. nf90_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 (512) to the number of dimensions that can be defined in a single netCDF dataset. The limit is the value of the constant NF90_MAX_DIMS. The purpose of the limit is to make writing generic applications simpler. They need only provide an array of NF90_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 90 interface, dimension IDs are 1, 2, 3, ..., in the order in which the dimensions were defined.
Operations supported on dimensions are:
The function NF90_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.
function nf90_def_dim(ncid, name, len, dimid) integer, intent( in) :: ncid character (len = *), intent( in) :: name integer, intent( in) :: len integer, intent(out) :: dimid integer :: nf90_def_dim
ncid
name
len
dimid
NF90_DEF_DIM returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_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:
use netcdf implicit none integer :: ncid, status, LatDimID, RecordDimID ... status = nf90_create("foo.nc", nf90_noclobber, ncid) if (status /= nf90_noerr) call handle_err(status) ... status = nf90_def_dim(ncid, "Lat", 18, LatDimID) if (status /= nf90_noerr) call handle_err(status) status = nf90_def_dim(ncid, "Record", nf90_unlimited, RecordDimID) if (status /= nf90_noerr) call handle_err(status)
The function NF90_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.
function nf90_inq_dimid(ncid, name, dimid) integer, intent( in) :: ncid character (len = *), intent( in) :: name integer, intent(out) :: dimid integer :: nf90_inq_dimid
ncid
name
dimid
NF90_INQ_DIMID returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_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:
use netcdf implicit none integer :: ncid, status, LatDimID ... status = nf90_open("foo.nc", nf90_nowrite, ncid) if (status /= nf90_noerr) call handle_err(status) ... status = nf90_inq_dimid(ncid, "Lat", LatDimID) if (status /= nf90_noerr) call handle_err(status)
This function 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.
function nf90_inquire_dimension(ncid, dimid, name, len) integer, intent( in) :: ncid, dimid character (len = *), optional, intent(out) :: name integer, optional, intent(out) :: len integer :: nf90_inquire_dimension
ncid
dimid
name
len
These functions return the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_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:
use netcdf implicit none integer :: ncid, status, LatDimID, RecordDimID integer :: nLats, nRecords character(len = nf90_max_name) :: RecordDimName ... status = nf90_open("foo.nc", nf90_nowrite, ncid) if (status /= nf90_noerr) call handle_err(status) ! Get ID of unlimited dimension status = nf90_inquire(ncid, unlimitedDimId = RecordDimID) if (status /= nf90_noerr) call handle_err(status) ... status = nf90_inq_dimid(ncid, "Lat", LatDimID) if (status /= nf90_noerr) call handle_err(status) ! How many values of "lat" are there? status = nf90_inquire_dimension(ncid, LatDimID, len = nLats) if (status /= nf90_noerr) call handle_err(status) ! What is the name of the unlimited dimension, how many records are there? status = nf90_inquire_dimension(ncid, RecordDimID, & name = RecordDimName, len = Records) if (status /= nf90_noerr) call handle_err(status)
The function NF90_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.
function nf90_rename_dim(ncid, dimid, name) integer, intent( in) :: ncid character (len = *), intent( in) :: name integer, intent( in) :: dimid integer :: nf90_rename_dim
ncid
dimid
name
NF90_RENAME_DIM returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_RENAME_DIM to rename the dimension lat to latitude in an existing netCDF dataset named foo.nc:
use netcdf implicit none integer :: ncid, status, LatDimID ... status = nf90_open("foo.nc", nf90_write, ncid) if (status /= nf90_noerr) call handle_err(status) ... ! Put in define mode so we can rename the dimension status = nf90_redef(ncid) if (status /= nf90_noerr) call handle_err(status) ! Get the dimension ID for "Lat"... status = nf90_inq_dimid(ncid, "Lat", LatDimID) if (status /= nf90_noerr) call handle_err(status) ! ... and change the name to "Latitude". status = nf90_rename_dim(ncid, LatDimID, "Latitude") if (status /= nf90_noerr) call handle_err(status) ! Leave define mode status = nf90_enddef(ncid) if (status /= nf90_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 NF90_DEF_* functions described in this section. They may learn about user defined types by using the NF90_INQ_ functions defined in this section.
Once types are constructed, define variables of the new type with NF90_DEF_VAR (see NF90_DEF_VAR). Write to them with NF90_PUT_VAR (see NF90_PUT_VAR). Read data of user-defined type with NF90_GET_VAR (see NF90_GET_VAR).
Create attributes of the new type with NF90_PUT_ATT (see NF90_PUT_ATT). Read attributes of the new type with NF90_GET_ATT (see NF90_GET_ATT).
Learn the number of types defined in a group, and their IDs.
function nf90_inq_typeids(ncid, ntypes, typeids) integer, intent(in) :: ncid integer, intent(out) :: ntypes integer, intent(out) :: typeids integer :: nf90_inq_typeids
NCID
NTYPES
TYPEIDS
NF90_NOERR
NF90_BADID
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.
int nf90_inq_typeid(int ncid, char *name, nf90_type *typeidp);
ncid
name
typeidp
NF90_NOERR
NF90_EBADID
NF90_EBADTYPE
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 NF90_INQ_USER_TYPE.
function nf90_inq_type(ncid, xtype, name, size, nfields) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(out) :: name integer, intent(out) :: size integer, intent(out) :: nfields integer :: nf90_inq_type
NCID
XTYPE
NAME
SIZEP
NF90_NOERR
NF90_EBADTYPEID
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EBADGRPID
NF90_EBADID
NF90_EHDFERR
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.
function nf90_inq_user_type(ncid, xtype, name, size, base_typeid, nfields, class) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(out) :: name integer, intent(out) :: size integer, intent(out) :: base_typeid integer, intent(out) :: nfields integer, intent(out) :: class integer :: nf90_inq_user_type
NCID
XTYPE
NAME
SIZE
BASE_NF90_TYPE
NFIELDS
CLASS
NF90_NOERR
NF90_EBADTYPEID
NF90_EBADFIELDID
NF90_EHDFERR
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 NF90_PUT_VLEN_ELEMENT(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) VLEN_ELEMENT, INTEGER LEN, DATA)
NCID
XTYPE
VLEN_ELEMENT
LEN
DATA
NF90_NOERR
NF90_EBADTYPE
NF90_EBADID
NF90_EBADGRPID
This example is from nf90_test/ftst_vars4.F.
C Set up the vlen with this helper function, since F77 can't deal C with pointers. retval = nf90_put_vlen_element(ncid, vlen_typeid, vlen, & vlen_len, data1) if (retval .ne. nf90_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 NF90_GET_VLEN_ELEMENT(INTEGER NCID, INTEGER XTYPE, CHARACTER*(*) VLEN_ELEMENT, INTEGER LEN, DATA)
NCID
XTYPE
VLEN_ELEMENT
LEN
DATA
NF90_NOERR
NF90_EBADTYPE
NF90_EBADID
NF90_EBADGRPID
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 nf90_def_compound to create the type, multiple calls to nf90_insert_compound to add to the compound type, and then write data with the appropriate nf90_put_var1, nf90_put_vara, nf90_put_vars, or nf90_put_varm call.
To read data written in a compound type, you must know its structure. Use the NF90_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 NF90_INSERT_COMPOUND (see NF90_INSERT_COMPOUND). Call NF90_INSERT_COMPOUND once for each field you wish to insert into the compound type.
Note that there does not seem to be a fully portable way to read such types into structures in Fortran 90 (and there are no structures in Fortran 77). Dozens of top-notch programmers are swarming over this problem in a sub-basement of Unidata's giant underground bunker in Wyoming.
Fortran users may use character buffers to read and write compound types. User are invited to try classic Fortran features such as the equivilence and the common block statment.
function nf90_def_compound(ncid, size, name, typeid) integer, intent(in) :: ncid integer, intent(in) :: size character (len = *), intent(in) :: name integer, intent(out) :: typeid integer :: nf90_def_compound
NCID
SIZE
NAME
TYPEIDP
NF90_NOERR
NF90_EBADID
NF90_ENAMEINUSE
NF90_EMAXNAME
NF90_EBADNAME
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
NF90_EPERM
NF90_ENOTINDEFINE
Insert a named field into a compound type.
function nf90_insert_compound(ncid, xtype, name, offset, field_typeid) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(in) :: name integer, intent(in) :: offset integer, intent(in) :: field_typeid integer :: nf90_insert_compound
TYPEID
NAME
OFFSET
FIELD_TYPEID
NF90_NOERR
NF90_EBADID
NF90_ENAMEINUSE
NF90_EMAXNAME
NF90_EBADNAME
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
NF90_ENOTINDEFINE
Insert a named array field into a compound type.
function nf90_insert_array_compound(ncid, xtype, name, offset, field_typeid, & ndims, dim_sizes) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(in) :: name integer, intent(in) :: offset integer, intent(in) :: field_typeid integer, intent(in) :: ndims integer, intent(in) :: dim_sizes integer :: nf90_insert_array_compound
NCID
XTYPE
NAME
OFFSET
FIELD_TYPEID
NDIMS
DIM_SIZES
NF90_NOERR
NF90_EBADID
NF90_ENAMEINUSE
NF90_EMAXNAME
NF90_EBADNAME
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
NF90_ENOTINDEFINE
NF90_ETYPEDEFINED
Get the number of fields, length in bytes, and name of a compound type.
In addtion to the NF90_INQ_COMPOUND function, three additional functions are provided which get only the name, size, and number of fields.
function nf90_inq_compound(ncid, xtype, name, size, nfields) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(out) :: name integer, intent(out) :: size integer, intent(out) :: nfields integer :: nf90_inq_compound function nf90_inq_compound_name(ncid, xtype, name) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(out) :: name integer :: nf90_inq_compound_name function nf90_inq_compound_size(ncid, xtype, size) integer, intent(in) :: ncid integer, intent(in) :: xtype integer, intent(out) :: size integer :: nf90_inq_compound_size function nf90_inq_compound_nfields(ncid, xtype, nfields) integer, intent(in) :: ncid integer, intent(in) :: xtype integer, intent(out) :: nfields integer :: nf90_inq_compound_nfields
NCID
XTYPE
NAME
SIZEP
NFIELDSP
NF90_NOERR
NF90_EBADID
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EBADTYPE
NF90_EBADTYPEID
NF90_EHDFERR
Get information about one of the fields of a compound type.
function nf90_inq_compound_field(ncid, xtype, fieldid, name, offset, & field_typeid, ndims, dim_sizes) integer, intent(in) :: ncid integer, intent(in) :: xtype integer, intent(in) :: fieldid character (len = *), intent(out) :: name integer, intent(out) :: offset integer, intent(out) :: field_typeid integer, intent(out) :: ndims integer, intent(out) :: dim_sizes integer :: nf90_inq_compound_field function nf90_inq_compound_fieldname(ncid, xtype, fieldid, name) integer, intent(in) :: ncid integer, intent(in) :: xtype integer, intent(in) :: fieldid character (len = *), intent(out) :: name integer :: nf90_inq_compound_fieldname function nf90_inq_compound_fieldindex(ncid, xtype, name, fieldid) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(in) :: name integer, intent(out) :: fieldid integer :: nf90_inq_compound_fieldindex function nf90_inq_compound_fieldoffset(ncid, xtype, fieldid, offset) integer, intent(in) :: ncid integer, intent(in) :: xtype integer, intent(in) :: fieldid integer, intent(out) :: offset integer :: nf90_inq_compound_fieldoffset function nf90_inq_compound_fieldtype(ncid, xtype, fieldid, field_typeid) integer, intent(in) :: ncid integer, intent(in) :: xtype integer, intent(in) :: fieldid integer, intent(out) :: field_typeid integer :: nf90_inq_compound_fieldtype function nf90_inq_compound_fieldndims(ncid, xtype, fieldid, ndims) integer, intent(in) :: ncid integer, intent(in) :: xtype integer, intent(in) :: fieldid integer, intent(out) :: ndims integer :: nf90_inq_compound_fieldndims function nf90_inq_cmp_fielddim_sizes(ncid, xtype, fieldid, dim_sizes) integer, intent(in) :: ncid integer, intent(in) :: xtype integer, intent(in) :: fieldid integer, intent(out) :: dim_sizes integer :: nf90_inq_cmp_fielddim_sizes
NCID
XTYPE
FIELDID
NAME
OFFSETP
FIELD_TYPEID
NDIMSP
DIM_SIZESP
NF90_NOERR
NF90_EBADTYPEID
NF90_EHDFERR
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 NF90_CLASSIC_MODEL flag.
A variable length array is represented in C as a structure from HDF5, the nf90_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.
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.
function nf90_def_vlen(ncid, name, base_typeid, xtypeid) integer, intent(in) :: ncid character (len = *), intent(in) :: name integer, intent(in) :: base_typeid integer, intent(out) :: xtypeid integer :: nf90_def_vlen
NCID
NAME
BASE_TYPEID
XTYPEP
NF90_NOERR
NF90_EMAXNAME
NF90_ENAMEINUSE
NF90_EBADNAME
NF90_EBADID
NF90_EBADGRPID
NF90_EINVAL
NF90_ENOMEM
Use this type to learn about a vlen.
function nf90_inq_vlen(ncid, xtype, name, datum_size, base_nc_type) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(out) :: name integer, intent(out) :: datum_size integer, intent(out) :: base_nc_type integer :: nf90_inq_vlen
NCID
XTYPE
NAME
DATUM_SIZEP
BASE_NF90_TYPEP
NF90_NOERR
NF90_EBADTYPE
NF90_EBADID
NF90_EBADGRPID
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.
function nf90_free_vlen(vl) character (len = *), intent(in) :: vlen integer :: nf90_free_vlen end function nf90_free_vlen
VL
NF90_NOERR
NF90_EBADTYPE
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 NF90_DEF_OPAQUE. If encountering an enum type in a new data file, use NF90_INQ_OPAQUE to learn its name and size.
Create an opaque type. Provide a size and a name.
function nf90_def_opaque(ncid, size, name, xtype) integer, intent(in) :: ncid integer, intent(in) :: size character (len = *), intent(in) :: name integer, intent(out) :: xtype integer :: nf90_def_opaque
NCID
NAME
SIZE
TYPEIDP
NF90_NOERR
NF90_EBADTYPEID
NF90_EBADFIELDID
NF90_EHDFERR
Given a typeid, get the information about an opaque type.
function nf90_inq_opaque(ncid, xtype, name, size) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(out) :: name integer, intent(out) :: size integer :: nf90_inq_opaque
NCID
XTYPE
NAME
SIZEP
NF90_NOERR
NF90_EBADTYPEID
NF90_EBADFIELDID
NF90_EHDFERR
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 NF90_INSERT_ENUM (see NF90_INSERT_ENUM). Call NF90_INSERT_ENUM once for each value you wish to make part of the enumeration.
function nf90_def_enum(ncid, base_typeid, name, typeid) integer, intent(in) :: ncid integer, intent(in) :: base_typeid character (len = *), intent(in) :: name integer, intent(out) :: typeid integer :: nf90_def_enum
NCID
BASE_TYPEID
NAME
TYPEIDP
NF90_NOERR
NF90_EBADID
NF90_ENAMEINUSE
NF90_EMAXNAME
NF90_EBADNAME
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
NF90_EPERM
NF90_ENOTINDEFINE
Insert a named member into a enum type.
function nf90_insert_enum(ncid, xtype, name, value) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(in) :: name integer, intent(in) :: value integer :: nf90_insert_enum
NCID
TYPEID
IDENTIFIER
VALUE
NF90_NOERR
NF90_EBADID
NF90_ENAMEINUSE
NF90_EMAXNAME
NF90_EBADNAME
NF90_ENOTNC4
NF90_ESTRICTNC3
NF90_EHDFERR
NF90_ENOTINDEFINE
Get information about a user-defined enumeration type.
function nf90_inq_enum(ncid, xtype, name, base_nc_type, base_size, num_members) integer, intent(in) :: ncid integer, intent(in) :: xtype character (len = *), intent(out) :: name integer, intent(out) :: base_nc_type integer, intent(out) :: base_size integer, intent(out) :: num_members integer :: nf90_inq_enum
NCID
XTYPE
NAME
BASE_NF90_TYPE
BASE_SIZE
NUM_MEMBERS
NF90_NOERR
NF90_EBADTYPEID
NF90_EHDFERR
Get information about a member of an enum type.
function nf90_inq_enum_member(ncid, xtype, idx, name, value) integer, intent(in) :: ncid integer, intent(in) :: xtype integer, intent(in) :: idx character (len = *), intent(out) :: name integer, intent(in) :: value integer :: nf90_inq_enum_member
NCID
XTYPE
IDX
NAME
VALUE
NF90_NOERR
NF90_EBADTYPEID
NF90_EHDFERR
Get the name which is associated with an enum member value.
This is similar to NF90_INQ_ENUM_MEMBER, but instead of using the index of the member, you use the value of the member.
function nf90_inq_enum_ident(ncid, xtype, value, idx) integer, intent(in) :: ncid integer, intent(in) :: xtype integer, intent(in) :: value integer, intent(out) :: idx integer :: nf90_inq_enum_ident
NCID
XTYPE
VALUE
IDENTIFIER
NF90_NOERR
NF90_EBADTYPEID
NF90_EHDFERR
NF90_EINVAL
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 | NF90_BYTE | 8
|
| char | NF90_CHAR | 8
|
| short | NF90_SHORT | 16
|
| int | NF90_INT | 32
|
| float | NF90_FLOAT | 32
|
| double | NF90_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 90 parameter for use in netCDF functions (the parameters are defined in the netCDF Fortran 90 module netcdf.f90). 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.
NF90_DEF_VAR
The function NF90_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.
Optional arguments allow additional settings for variables in netCDF-4/HDF5 files. These parameters allow data compression and control of the layout of the data on disk for performance tuning. These parameters may also be used to set the chunk sizes to get chunked storage, or to 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.
All parameters after the varid are optional, and only supported if netCDF was built with netCDF-4 features enabled, and if the variable is in a netCDF-4/HDF5 file.
function nf90_def_var(ncid, name, xtype, dimids, varid, contiguous, & chunksizes, deflate_level, shuffle, fletcher32, endianness, & cache_size, cache_nelems, cache_preemption) integer, intent(in) :: ncid character (len = *), intent(in) :: name integer, intent( in) :: xtype integer, dimension(:), intent(in) :: dimids integer, intent(out) :: varid logical, optional, intent(in) :: contiguous integer, optional, dimension(:), intent(in) :: chunksizes integer, optional, intent(in) :: deflate_level logical, optional, intent(in) :: shuffle, fletcher32 integer, optional, intent(in) :: endianness integer, optional, intent(in) :: cache_size, cache_nelems, cache_preemption integer :: nf90_def_var
ncid
name
xtype
dimids
If an integer is passed for this parameter, a 1-D variable is created.
If this parameter is not passed (or is a 1D array of size zero) it means the variable is a scalar with no dimensions.
For classic data model files, if the ID of the unlimited dimension is included, it must be first. In expanded model netCDF4/HDF5 files, there may be any number of unlimited dimensions, and they may be used in any element of the dimids array.
This argument is optional, and if absent specifies a scalar with no
dimensions.
varid
storage
If NF90_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, shuffle, and checksums are not used.
chunksizes
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 is a very large chunk size in any case.)
If not provided, but chunked data are needed, then default chunksizes
will be chosen. For more information see The NetCDF Users Guide.
shuffle
deflate_level
fletcher32
endianness
cache_size
cache_nelems
cache_preemption
NF90_DEF_VAR returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error.
Here is an example using NF90_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:
use netcdf implicit none integer :: status, ncid integer :: LonDimId, LatDimId, TimeDimId integer :: RhVarId ... status = nf90_create("foo.nc", nf90_NoClobber, ncid) if(status /= nf90_NoErr) call handle_error(status) ... !  Define the variable status = nf90_def_var(ncid, "rh", nf90_double, & (/ LonDimId, LatDimID, TimeDimID /), RhVarId) if(status /= nf90_NoErr) call handle_error(status)
In the following example, from nf_test/f90tst_vars2.f90, chunking, checksums, and endianness control are all used in a netCDF-4/HDF5 file.
! Create the netCDF file. call check(nf90_create(FILE_NAME, nf90_netcdf4, ncid, cache_nelems = CACHE_NELEMS, & cache_size = CACHE_SIZE)) ! Define the dimensions. call check(nf90_def_dim(ncid, "x", NX, x_dimid)) call check(nf90_def_dim(ncid, "y", NY, y_dimid)) dimids = (/ y_dimid, x_dimid /) ! Define some variables. chunksizes = (/ NY, NX /) call check(nf90_def_var(ncid, VAR1_NAME, NF90_INT, dimids, varid1, chunksizes = chunksizes, & shuffle = .TRUE., fletcher32 = .TRUE., endianness = nf90_endian_big, deflate_level = DEFLATE_LEVEL)) call check(nf90_def_var(ncid, VAR2_NAME, NF90_INT, dimids, varid2, contiguous = .TRUE.)) call check(nf90_def_var(ncid, VAR3_NAME, NF90_INT64, varid3)) call check(nf90_def_var(ncid, VAR4_NAME, NF90_INT, x_dimid, varid4, contiguous = .TRUE.))
nf90_def_var_fill
The function NF90_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 NF90_ENDDEF is called.
NF90_DEF_VAR_FILL(INTEGER NCID, INTEGER VARID, INTEGER NO_FILL, FILL_VALUE);
NCID
VARID
NO_FILL
FILL_VALUE
NF90_NOERR
NF90_BADID
NF90_ENOTNC4
NF90_ENOTVAR
NF90_ELATEDEF
NF90_ENOTINDEFINE
NF90_EPERM
NF90_INQ_VAR_FILL
The function NF90_INQ_VAR_FILL returns the fill settings for a variable in a netCDF-4 file.
NF90_INQ_VAR_FILL(INTEGER NCID, INTEGER VARID, INTEGER NO_FILL, FILL_VALUE)
NCID
VARID
NO_FILL
FILL_VALUE
NF90_NOERR
NF90_BADID
NF90_ENOTNC4
NF90_ENOTVAR
NF90_INQUIRE_VARIABLE 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.
All parameters after nAtts are optional, and only supported if netCDF was built with netCDF-4 features enabled, and if the variable is in a netCDF-4/HDF5 file.
function nf90_inquire_variable(ncid, varid, name, xtype, ndims, dimids, nAtts, & contiguous, chunksizes, deflate_level, shuffle, fletcher32, endianness) integer, intent(in) :: ncid, varid character (len = *), optional, intent(out) :: name integer, optional, intent(out) :: xtype, ndims integer, dimension(:), optional, intent(out) :: dimids integer, optional, intent(out) :: nAtts logical, optional, intent(out) :: contiguous integer, optional, dimension(:), intent(out) :: chunksizes integer, optional, intent(out) :: deflate_level logical, optional, intent(out) :: shuffle, fletcher32 integer, optional, intent(out) :: endianness integer :: nf90_inquire_variable
ncid
varid
name
xtype
ndims
dimids
natts
contiguous
chunksizes
shuffle
deflate_level
fletcher32
endianness
These functions return the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_INQ_VAR to find out about a variable named rh in an existing netCDF dataset named foo.nc:
use netcdf implicit none integer :: status, ncid, & RhVarId & numDims, numAtts integer, dimension(nf90_max_var_dims) :: rhDimIds ... status = nf90_open("foo.nc", nf90_NoWrite, ncid) if(status /= nf90_NoErr) call handle_error(status) ... status = nf90_inq_varid(ncid, "rh", RhVarId) if(status /= nf90_NoErr) call handle_err(status) status = nf90_inquire_variable(ncid, RhVarId, ndims = numDims, natts = numAtts) if(status /= nf90_NoErr) call handle_err(status) status = nf90_inquire_variable(ncid, RhVarId, dimids = rhDimIds(:numDims)) if(status /= nf90_NoErr) call handle_err(status)
Given the name of a varaible, nf90_inq_varid finds the variable ID.
function nf90_inq_varid(ncid, name, varid) integer, intent(in) :: ncid character (len = *), intent( in) :: name integer, intent(out) :: varid integer :: nf90_inq_varid
ncid
name
varid
These functions return the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_INQ_VARID to find out about a variable named rh in an existing netCDF dataset named foo.nc:
use netcdf implicit none integer :: status, ncid, & RhVarId & numDims, numAtts integer, dimension(nf90_max_var_dims) :: rhDimIds ... status = nf90_open("foo.nc", nf90_NoWrite, ncid) if(status /= nf90_NoErr) call handle_error(status) ... status = nf90_inq_varid(ncid, "rh", RhVarId) if(status /= nf90_NoErr) call handle_err(status) status = nf90_inquire_variable(ncid, RhVarId, ndims = numDims, natts = numAtts) if(status /= nf90_NoErr) call handle_err(status) status = nf90_inquire_variable(ncid, RhVarId, dimids = rhDimIds(:numDims)) if(status /= nf90_NoErr) call handle_err(status)
The function NF90_PUT_VAR puts one or more data values into the variable of an open netCDF dataset that is in data mode. Required inputs are the netCDF ID, the variable ID, and one or more data values. Optional inputs may indicate the starting position of the data values in the netCDF variable (argument start), the sampling frequency with which data values are written into the netCDF variable (argument stride), and a mapping between the dimensions of the data array and the netCDF variable (argument map). 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 90 interface. Data values are converted to the external type of the variable, if necessary.
Take care when using the simplest forms of this interface with record variables (variables that use the NF90_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 specify start and count arguments for variables that use the NF90_UNLIMITED dimension.
function nf90_put_var(ncid, varid, values, start, count, stride, map) integer, intent( in) :: ncid, varid any valid type, scalar or array of any rank, & intent( in) :: values integer, dimension(:), optional, intent( in) :: start, count, stride, map integer :: nf90_put_var
ncid
varid
values
start
By default, start(:) = 1.
count
By default, count(:numDims) = shape(values) and
count(numDims + 1:) = 1, where numDims = size(shape(values)).
stride
By default, stride(:) = 1.
imap
By default, edgeLengths = shape(values), and map = (/ 1, (product(edgeLengths(:i)), i = 1, size(edgeLengths) - 1) /), that is, there is no mapping.
Use of Fortran 90 intrinsic functions (including reshape, transpose, and spread) may let you avoid using this argument.
NF90_PUT_VAR1_ type returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_PUT_VAR 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:
use netcdf implicit none integer :: ncId, rhVarId, status ... status = nf90_open("foo.nc", nf90_Write, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) status = nf90_put_var(ncid, rhVarId, 0.5, start = (/ 4, 3, 2 /) ) if(status /= nf90_NoErr) call handle_err(status)
In this example we use NF90_PUT_VAR to add or change all the values of the variable named rh to 0.5 in an existing netCDF dataset named foo.nc. We assume that we know that rh is dimensioned with lon, lat, and time. In this example we query the netCDF file to discover the lengths of the dimensions, then use the Fortran 90 intrinsic function reshape to create a temporary array of data values which is the same shape as the netCDF variable.
use netcdf implicit none integer :: ncId, rhVarId,status, & lonDimID, latDimId, timeDimId, & numLons, numLats, numTimes, & i integer, dimension(nf90_max_var_dims) :: dimIDs ... status = nf90_open("foo.nc", nf90_Write, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) ! How big is the netCDF variable, that is, what are the lengths of ! its constituent dimensions? status = nf90_inquire_variable(ncid, rhVarId, dimids = dimIDs) if(status /= nf90_NoErr) call handle_err(status) status = nf90_inquire_dimension(ncid, dimIDs(1), len = numLons) if(status /= nf90_NoErr) call handle_err(status) status = nf90_inquire_dimension(ncid, dimIDs(2), len = numLats) if(status /= nf90_NoErr) call handle_err(status) status = nf90_inquire_dimension(ncid, dimIDs(3), len = numTimes) if(status /= nf90_NoErr) call handle_err(status) ... ! Make a temporary array the same shape as the netCDF variable. status = nf90_put_var(ncid, rhVarId, & reshape( & (/ (0.5, i = 1, numLons * numLats * numTimes) /) , & shape = (/ numLons, numLats, numTimes /) ) if(status /= nf90_NoErr) call handle_err(status)
Here is an example using NF90_PUT_VAR to add or change a section 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, that there are ten lon values, five lat values, and three time values, and that we want to replace all the values at the last time.
use netcdf implicit none integer :: ncId, rhVarId, status integer, parameter :: numLons = 10, numLats = 5, numTimes = 3 real, dimension(numLons, numLats) & :: rhValues ... status = nf90_open("foo.nc", nf90_Write, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) ! Fill in all values at the last time rhValues(:, :) = 0.5 status = nf90_put_var(ncid, rhVarId,rhvalues, & start = (/ 1, 1, numTimes /), & count = (/ numLats, numLons, 1 /)) if(status /= nf90_NoErr) call handle_err(status)
Here is an example of using NF90_PUT_VAR to write every other point of a netCDF variable named rh having dimensions (6, 4).
use netcdf implicit none integer :: ncId, rhVarId, status integer, parameter :: numLons = 6, numLats = 4 real, dimension(numLons, numLats) & :: rhValues = 0.5 ... status = nf90_open("foo.nc", nf90_Write, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) ... ! Fill in every other value using an array section status = nf90_put_var(ncid, rhVarId, rhValues(::2, ::2), & stride = (/ 2, 2 /)) if(status /= nf90_NoErr) call handle_err(status)
The following map vector shows the default mapping between a 2x3x4 netCDF variable and an internal array of the same shape:
real, dimension(2, 3, 4):: a ! same shape as netCDF variable integer, dimension(3) :: map = (/ 1, 2, 6 /) ! netCDF dimension inter-element distance ! ---------------- ---------------------- ! most rapidly varying 1 ! intermediate 2 (= map(1)*2) ! most slowly varying 6 (= map(2)*3)
Using the map vector above obtains the same result as simply not passing a map vector at all.
Here is an example of using nf90_put_var to write a netCDF variable named rh whose dimensions are the transpose of the Fortran 90 array:
use netcdf implicit none integer :: ncId, rhVarId, status integer, parameter :: numLons = 6, numLats = 4 real, dimension(numLons, numLats) :: rhValues ! netCDF variable has dimensions (numLats, numLons) ... status = nf90_open("foo.nc", nf90_Write, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) ... !Write transposed values: map vector would be (/ 1, numLats /) for ! no transposition status = nf90_put_var(ncid, rhVarId,rhValues, map = (/ numLons, 1 /)) if(status /= nf90_NoErr) call handle_err(status)
The same effect can be obtained more simply using Fortran 90 intrinsic functions:
use netcdf implicit none integer :: ncId, rhVarId, status integer, parameter :: numLons = 6, numLats = 4 real, dimension(numLons, numLats) :: rhValues ! netCDF variable has dimensions (numLats, numLons) ... status = nf90_open("foo.nc", nf90_Write, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_put_var(ncid, rhVarId, transpose(rhValues)) if(status /= nf90_NoErr) call handle_err(status)
The function NF90_GET_VAR gets one or more data values from a netCDF variable of an open netCDF dataset that is in data mode. Required inputs are the netCDF ID, the variable ID, and a specification for the data values into which the data will be read. Optional inputs may indicate the starting position of the data values in the netCDF variable (argument start), the sampling frequency with which data values are read from the netCDF variable (argument stride), and a mapping between the dimensions of the data array and the netCDF variable (argument map). The values to be read are associated with the netCDF variable by assuming that the first dimension of the netCDF variable varies fastest in the Fortran 90 interface. Data values are converted from the external type of the variable, if necessary.
Take care when using the simplest forms of this interface with record variables (variables that use the NF90_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 specify the optional start and count arguments for variables that use the NF90_UNLIMITED dimension.
In netCDF classic model the maximum integer size is NF90_INT, the 4-byte signed integer. Reading variables into an eight-byte integer array from a classic model file will read from an NF90_INT. Reading variables into an eight-byte integer in a netCDF-4/HDF5 (without classic model flag) will read from an NF90_INT64
function nf90_get_var(ncid, varid, values, start, count, stride, map) integer, intent( in) :: ncid, varid any valid type, scalar or array of any rank, & intent(out) :: values integer, dimension(:), optional, intent( in) :: start, count, stride, map integer :: nf90_get_var
ncid
varid
values
start
By default, start(:) = 1.
count
By default, count(:numDims) = shape(values) and
count(numDims + 1:) = 1, where numDims = size(shape(values)).
stride
By default, stride(:) = 1.
map
By default, edgeLengths = shape(values), and map = (/ 1, (product(edgeLengths(:i)), i = 1, size(edgeLengths) - 1) /), that is, there is no mapping.
Use of Fortran 90 intrinsic functions (including reshape, transpose, and spread) may let you avoid using this argument.
NF90_GET_VAR returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
(As noted above, another possible source of error is using this interface to read all the values of a record variable without specifying the number of records. If there are more records in the file than you assume, more data will be read than you expect!)
Here is an example using NF90_GET_VAR to read the (4,3,2) element 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, so we want to read the value of rh that corresponds to the fourth lon value, the third lat value, and the second time value:
use netcdf implicit none integer :: ncId, rhVarId, status real :: rhValue ... status = nf90_open("foo.nc", nf90_NoWrite, ncid) if(status /= nf90_NoErr) call handle_err(status) - status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) status = nf90_get_var(ncid, rhVarId, rhValue, start = (/ 4, 3, 2 /) ) if(status /= nf90_NoErr) call handle_err(status)
In this example we use NF90_GET_VAR to read all the values of the variable named rh from an existing netCDF dataset named foo.nc. We assume that we know that rh is dimensioned with lon, lat, and time. In this example we query the netCDF file to discover the lengths of the dimensions, then allocate a Fortran 90 array the same shape as the netCDF variable.
use netcdf implicit none integer :: ncId, rhVarId, & lonDimID, latDimId, timeDimId, & numLons, numLats, numTimes, & status integer, dimension(nf90_max_var_dims) :: dimIDs real, dimension(:, :, :), allocatable :: rhValues ... status = nf90_open("foo.nc", nf90_NoWrite, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) ! How big is the netCDF variable, that is, what are the lengths of ! its constituent dimensions? status = nf90_inquire_variable(ncid, rhVarId, dimids = dimIDs) if(status /= nf90_NoErr) call handle_err(status) status = nf90_inquire_dimension(ncid, dimIDs(1), len = numLons) if(status /= nf90_NoErr) call handle_err(status) status = nf90_inquire_dimension(ncid, dimIDs(2), len = numLats) if(status /= nf90_NoErr) call handle_err(status) status = nf90_inquire_dimension(ncid, dimIDs(3), len = numTimes) if(status /= nf90_NoErr) call handle_err(status) allocate(rhValues(numLons, numLats, numTimes)) ... status = nf90_get_var(ncid, rhVarId, rhValues) if(status /= nf90_NoErr) call handle_err(status)
Here is an example using NF90_GET_VAR to read a section 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, that there are ten lon values, five lat values, and three time values, and that we want to replace all the values at the last time.
use netcdf implicit none integer :: ncId, rhVarId, status integer, parameter :: numLons = 10, numLats = 5, numTimes = 3 real, dimension(numLons, numLats, numTimes) & :: rhValues ... status = nf90_open("foo.nc", nf90_NoWrite, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) !Read the values at the last time by passing an array section status = nf90_get_var(ncid, rhVarId, rhValues(:, :, 3), & start = (/ 1, 1, numTimes /), & count = (/ numLons, numLats, 1 /)) if(status /= nf90_NoErr) call handle_err(status)
Here is an example of using NF90_GET_VAR to read every other point of a netCDF variable named rh having dimensions (6, 4).
use netcdf implicit none integer :: ncId, rhVarId, status integer, parameter :: numLons = 6, numLats = 4 real, dimension(numLons, numLats) & :: rhValues ... status = nf90_open("foo.nc", nf90_NoWrite, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) ... ! Read every other value into an array section status = nf90_get_var(ncid, rhVarId, rhValues(::2, ::2) & stride = (/ 2, 2 /)) if(status /= nf90_NoErr) call handle_err(status)
The following map vector shows the default mapping between a 2x3x4 netCDF variable and an internal array of the same shape:
real, dimension(2, 3, 4):: a ! same shape as netCDF variable integer, dimension(3) :: map = (/ 1, 2, 6 /) ! netCDF dimension inter-element distance ! ---------------- ---------------------- ! most rapidly varying 1 ! intermediate 2 (= map(1)*2) ! most slowly varying 6 (= map(2)*3)
Using the map vector above obtains the same result as simply not passing a map vector at all.
Here is an example of using nf90_get_var to read a netCDF variable named rh whose dimensions are the transpose of the Fortran 90 array:
use netcdf implicit none integer :: ncId, rhVarId, status integer, parameter :: numLons = 6, numLats = 4 real, dimension(numLons, numLats) :: rhValues ! netCDF variable has dimensions (numLats, numLons) ... status = nf90_open("foo.nc", nf90_NoWrite, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) ... ! Read transposed values: map vector would be (/ 1, numLats /) for ! no transposition status = nf90_get_var(ncid, rhVarId,rhValues, map = (/ numLons, 1 /)) if(status /= nf90_NoErr) call handle_err(status)
The same effect can be obtained more simply, though using more memory, using Fortran 90 intrinsic functions:
use netcdf implicit none integer :: ncId, rhVarId, status integer, parameter :: numLons = 6, numLats = 4 real, dimension(numLons, numLats) :: rhValues ! netCDF variable has dimensions (numLats, numLons) real, dimension(numLons, numLats) :: tempValues ... status = nf90_open("foo.nc", nf90_NoWrite, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_get_var(ncid, rhVarId, tempValues)) if(status /= nf90_NoErr) call handle_err(status) rhValues(:, :) = transpose(tempValues)
Character strings are not a primitive netCDF external data type under the classic netCDF data model, 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 classic interface except by convention; for example, you may treat a zero byte as terminating a character string, but you must explicitly specify the length of strings to be read from and written to netCDF variables.
Character strings as attribute values are easier to use, since the strings are treated as a single unit for access. However, the value of a character-string attribute in the classic netCDF interface is still an array of characters with an explicit length that must be specified when the attribute is defined.
When you define a variable that will have character-string values, use a character-position dimension as the most quickly varying dimension for the variable (the first dimension for the variable in Fortran 90). The length of the character-position dimension will be the maximum string length of any value to be stored in the character-string variable. Space for maximum-length strings will be allocated in the disk representation of character-string variables whether you use the space or not. If two or more variables have the same maximum length, the same character-position dimension may be used in defining the variable shapes.
To write a character-string value into a character-string variable, use either entire variable access or array access. The latter requires that you specify both a corner and a vector of edge lengths. The character-position dimension at the corner should be one for Fortran 90. If the length of the string to be written is n, then the vector of edge lengths will specify n in the character-position dimension, and one for all the other dimensions: (n, 1, 1, ..., 1).
In Fortran 90, fixed-length strings may be written to a netCDF dataset without a terminating character, to save space. Variable-length strings should follow the C convention of writing strings with a terminating zero byte so that the intended length of the string can be determined when it is later read by either C or Fortran 90 programs. It is the users responsibility to provide such null termination.
If you are writing data in the default prefill mode (see next section), you can ensure that simple strings represented as 1-dimensional character arrays are null terminated in the netCDF file by writing fewer characters than the length declared when the variable was defined. That way, the extra unwritten characters will be filled with the default character fill value, which is a null byte. The Fortran intrinsic TRIM function can be used to trim trailing blanks from the character string argument to NF90_PUT_VAR to make the argument shorter than the declared length. If prefill is not on, the data writer must explicitly provide a null terminating byte.
Here is an example illustrating this way of writing strings to character array variables:
use netcdf implicit none integer status integer :: ncid, oceanStrLenID, oceanId integer, parameter :: MaxOceanNameLen = 20 character, (len = MaxOceanNameLen):: ocean ... status = nf90_create("foo.nc", nf90_NoClobber, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_def_dim(ncid, "oceanStrLen", MaxOceanNameLen, oceanStrLenId) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_def_var(ncid, "ocean", nf90_char, (/ oceanStrLenId /), oceanId) if(status /= nf90_NoErr) call handle_err(status) ... ! Leave define mode, which prefills netCDF variables with fill values status = nf90_enddef(ncid) if (status /= nf90_noerr) call handle_err(status) ... ! Note that this assignment adds blank fill ocean = "Pacific" ! Using trim removes trailing blanks, prefill provides null ! termination, so C programs can later get intended string. status = nf90_put_var(ncid, oceanId, trim(ocean)) if(status /= nf90_NoErr) call handle_err(status)
What happens when you try to read a value that was never written in an open netCDF dataset? You might expect that this should always be an error, and that you should get an error message or an error status returned. You do get an error if you try to read data from a netCDF dataset that is not open for reading, if the variable ID is invalid for the specified netCDF dataset, or if the specified indices are not properly within the range defined by the dimension lengths of the specified variable. Otherwise, reading a value that was not written returns a special fill value used to fill in any undefined values when a netCDF variable is first written.
You may ignore fill values and use the entire range of a netCDF external data type, but in this case you should make sure you write all data values before reading them. If you know you will be writing all the data before reading it, you can specify that no prefilling of variables with fill values will occur by calling writing. This may provide a significant performance gain for netCDF writes.
The variable attribute _FillValue may be used to specify the fill value for a variable. There are default fill values for each type, defined in module netcdf: NF90_FILL_CHAR, NF90_FILL_INT1 (same as NF90_FILL_BYTE), NF90_FILL_INT2 (same as NF90_FILL_SHORT), NF90_FILL_INT, NF90_FILL_REAL (same as NF90_FILL_FLOAT), and NF90_FILL_DOUBLE
The netCDF byte and character types have different default fill values. The default fill value for characters is the zero byte, a useful value for detecting the end of variable-length C character strings. If you need a fill value for a byte variable, it is recommended that you explicitly define an appropriate _FillValue attribute, as generic utilities such as ncdump will not assume a default fill value for byte variables.
Type conversion for fill values is identical to type conversion for other values: attempting to convert a value from one type to another type that can't represent the value results in a range error. Such errors may occur on writing or reading values from a larger type (such as double) to a smaller type (such as float), if the fill value for the larger type cannot be represented in the smaller type.
The function NF90_RENAME_VAR changes the name of a netCDF variable in an open netCDF dataset. If the new name is longer than the old name, the netCDF dataset must be in define mode. You cannot rename a variable to have the name of any existing variable.
function nf90_rename_var(ncid, varid, newname) integer, intent( in) :: ncid, varid character (len = *), intent( in) :: newname integer :: nf90_rename_var
ncid
varid
newname
NF90_RENAME_VAR returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_RENAME_VAR to rename the variable rh to rel_hum in an existing netCDF dataset named foo.nc:
use netcdf implicit none integer :: ncId, rhVarId, status ... status = nf90_open("foo.nc", nf90_Write, ncid) if(status /= nf90_NoErr) call handle_err(status) ... status = nf90_inq_varid(ncid, "rh", rhVarId) if(status /= nf90_NoErr) call handle_err(status) status = nf90_redef(ncid) ! Enter define mode to change variable name if(status /= nf90_NoErr) call handle_err(status) status = nf90_rename_var(ncid, rhVarId, "rel_hum") if(status /= nf90_NoErr) call handle_err(status) status = nf90_enddef(ncid) ! Leave define mode if(status /= nf90_NoErr) call handle_err(status)
The function NF90_VAR_PAR_ACCESS changes whether read/write operations on a parallel file system are performed collectively or independently (the default) on the variable. This function can only be called if the file was created (see NF90_CREATE) or opened (see NF90_OPEN) for parallel I/O.
This function is only available if the netCDF library was built with parallel I/O enabled.
Calling this function affects only the open file - information about whether a variable is to be accessed collectively or independently is not written to the data file. Every time you open a file on a parallel file system, all variables default to independent operations. The change of a variable to collective access lasts only as long as that file is open.
The variable can be changed from collective to independent, and back, as often as desired.
Classic and 64-bit offset files, when opened for parallel access, use the parallel-netcdf (a.k.a. pnetcdf) library, which does not allow per-variable changes of access mode - the entire file must be access independently or collectively. For classic and 64-bit offset files, the nf90_var_par_access function changes the access for all variables in the file.
function nf90_var_par_access(ncid, varid, access) integer, intent(in) :: ncid integer, intent(in) :: varid integer, intent(in) :: access integer :: nf90_var_par_access end function nf90_var_par_access
ncid
varid
access
NF90_NOERR
NF90_ENOTVAR
NF90_NOPAR
This example comes from test program nf_test/f90tst_parallel.f90. For this test to be run, netCDF must have been built with a parallel-enabled HDF5, and –enable-parallel-tests must have been used when configuring netcdf.
! Reopen the file. call handle_err(nf90_open(FILE_NAME, nf90_nowrite, ncid, comm = MPI_COMM_WORLD, & info = MPI_INFO_NULL)) ! Set collective access on this variable. This will cause all ! reads/writes to happen together on every processor. call handle_err(nf90_var_par_access(ncid, varid, nf90_collective)) ! Read this processor's data. call handle_err(nf90_get_var(ncid, varid, data_in, start = start, count = count))
Attributes may be associated with each netCDF variable to specify such properties as units, special values, maximum and minimum valid values, scaling factors, and offsets. Attributes for a netCDF dataset are defined when the dataset is first created, while the netCDF dataset is in define mode. Additional attributes may be added later by reentering define mode. A netCDF attribute has a netCDF variable to which it is assigned, a name, a type, a length, and a sequence of one or more values. An attribute is designated by its variable ID and name. When an attribute name is not known, it may be designated by its variable ID and number in order to determine its name, using the function NF90_INQ_ATTNAME.
The attributes associated with a variable are typically defined immediately after the variable is created, while still in define mode. The data type, length, and value of an attribute may be changed even when in data mode, as long as the changed attribute requires no more space than the attribute as originally defined.
It is also possible to have attributes that are not associated with any variable. These are called global attributes and are identified by using NF90_GLOBAL as a variable pseudo-ID. Global attributes are usually related to the netCDF dataset as a whole and may be used for purposes such as providing a title or processing history for a netCDF dataset.
Attributes are much more useful when they follow established community conventions. See Attribute Conventions.
Operations supported on attributes are:
The function NF90_PUT_ATTadds or changes a variable attribute or global attribute of an open netCDF dataset. If this attribute is new, or if the space required to store the attribute is greater than before, the netCDF dataset must be in define mode.
Although it's possible to create attributes of all types, text and double attributes are adequate for most purposes.
function nf90_put_att(ncid, varid, name, values) integer, intent( in) :: ncid, varid character(len = *), intent( in) :: name any valid type, scalar or array of rank 1, & intent( in) :: values integer :: nf90_put_att
ncid
varid
name
values
NF90_PUT_ATT returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_PUT_ATT to add a variable attribute named valid_range for a netCDF variable named rh and a global attribute named title to an existing netCDF dataset named foo.nc:
use netcdf implicit none integer :: ncid, status, RHVarID ... status = nf90_open("foo.nc", nf90_write, ncid) if (status /= nf90_noerr) call handle_err(status) ... ! Enter define mode so we can add the attribute status = nf90_redef(ncid) if (status /= nf90_noerr) call handle_err(status) ! Get the variable ID for "rh"... status = nf90_inq_varid(ncid, "rh", RHVarID) if (status /= nf90_noerr) call handle_err(status) ! ... put the range attribute, setting it to eight byte reals... status = nf90_put_att(ncid, RHVarID, "valid_range", real((/ 0, 100 /)) ! ... and the title attribute. if (status /= nf90_noerr) call handle_err(status) status = nf90_put_att(ncid, RHVarID, "title", "example netCDF dataset") ) if (status /= nf90_noerr) call handle_err(status) ! Leave define mode status = nf90_enddef(ncid) if (status /= nf90_noerr) call handle_err(status)
The function NF90_INQUIRE_ATTRIBUTE returns information about a netCDF attribute given the variable ID and attribute name. Information about an attribute includes its type, length, name, and number. See NF90_GET_ATT for getting attribute values.
The function NF90_INQ_ATTNAME gets the name of an attribute, given its variable ID and number. This function is useful in generic applications that need to get the names of all the attributes associated with a variable, since attributes are accessed by name rather than number in all other attribute functions. The number of an attribute is more volatile than the name, since it can change when other attributes of the same variable are deleted. This is why an attribute number is not called an attribute ID.
function nf90_inquire_attribute(ncid, varid, name, xtype, len, attnum) integer, intent( in) :: ncid, varid character (len = *), intent( in) :: name integer, intent(out), optional :: xtype, len, attnum integer :: nf90_inquire_attribute function nf90_inq_attname(ncid, varid, attnum, name) integer, intent( in) :: ncid, varid, attnum character (len = *), intent(out) :: name integer :: nf90_inq_attname
ncid
varid
name
xtype
len
attnum
(If you already know an attribute name, knowing its number is not very useful, because accessing information about an attribute requires its name.)
Each function returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_INQUIRE_ATTRIBUTE to inquire about the lengths of an attribute named valid_range for a netCDF variable named rh and a global attribute named title in an existing netCDF dataset named foo.nc:
use netcdf implicit none integer :: ncid, status integer :: RHVarID ! Variable ID integer :: validRangeLength, titleLength ! Attribute lengths ... status = nf90_open("foo.nc", nf90_nowrite, ncid) if (status /= nf90_noerr) call handle_err(status) ... ! Get the variable ID for "rh"... status = nf90_inq_varid(ncid, "rh", RHVarID) if (status /= nf90_noerr) call handle_err(status) ! ... get the length of the "valid_range" attribute... status = nf90_inquire_attribute(ncid, RHVarID, "valid_range", & len = validRangeLength) if (status /= nf90_noerr) call handle_err(status) ! ... and the global title attribute. status = nf90_inquire_attribute(ncid, nf90_global, "title", len = titleLength) if (status /= nf90_noerr) call handle_err(status)
Function nf90_get_att gets the value(s) of a netCDF attribute, given its variable ID and name.
function nf90_get_att(ncid, varid, name, values) integer, intent( in) :: ncid, varid character(len = *), intent( in) :: name any valid type, scalar or array of rank 1, & intent(out) :: values integer :: nf90_get_att
ncid
varid
name
values
NF90_GET_ATT_ type returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_GET_ATT to determine the values of an attribute named valid_range for a netCDF variable named rh and a global attribute named title in an existing netCDF dataset named foo.nc. In this example, it is assumed that we don't know how many values will be returned, so we first inquire about the length of the attributes to make sure we have enough space to store them:
use netcdf implicit none integer :: ncid, status integer :: RHVarID ! Variable ID integer :: validRangeLength, titleLength ! Attribute lengths real, dimension(:), allocatable, & :: validRange character (len = 80) :: title ... status = nf90_open("foo.nc", nf90_nowrite, ncid) if (status /= nf90_noerr) call handle_err(status) ... ! Find the lengths of the attributes status = nf90_inq_varid(ncid, "rh", RHVarID) if (status /= nf90_noerr) call handle_err(status) status = nf90_inquire_attribute(ncid, RHVarID, "valid_range", & len = validRangeLength) if (status /= nf90_noerr) call handle_err(status) status = nf90_inquire_attribute(ncid, nf90_global, "title", len = titleLength) if (status /= nf90_noerr) call handle_err(status) ... !Allocate space to hold attribute values, check string lengths allocate(validRange(validRangeLength), stat = status) if(status /= 0 .or. len(title) < titleLength) print *, "Not enough space to put attribute values." exit end if ! Read the attributes. status = nf90_get_att(ncid, RHVarID, "valid_range", validRange) if (status /= nf90_noerr) call handle_err(status) status = nf90_get_att(ncid, nf90_global, "title", title) if (status /= nf90_noerr) call handle_err(status)
The function NF90_COPY_ATT copies an attribute from one open netCDF dataset to another. It can also be used to copy an attribute from one variable to another within the same netCDF dataset.
If used to copy an attribute of user-defined type, then that user-defined type must already be defined in the target file. In the case of user-defined attributes, enddef/redef is called for ncid_in and ncid_out if they are in define mode. (This is the ensure that all user-defined types are committed to the file(s) before the copy is attempted.)
function nf90_copy_att(ncid_in, varid_in, name, ncid_out, varid_out) integer, intent( in) :: ncid_in, varid_in character (len = *), intent( in) :: name integer, intent( in) :: ncid_out, varid_out integer :: nf90_copy_att
ncid_in
varid_in
name
ncid_out
varid_out
NF90_COPY_ATT returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_COPY_ATT to copy the variable attribute units from the variable rh in an existing netCDF dataset named foo.nc to the variable avgrh in another existing netCDF dataset named bar.nc, assuming that the variable avgrh already exists, but does not yet have a units attribute:
use netcdf implicit none integer :: ncid1, ncid2, status integer :: RHVarID, avgRHVarID ! Variable ID ... status = nf90_open("foo.nc", nf90_nowrite, ncid1) if (status /= nf90_noerr) call handle_err(status) status = nf90_open("bar.nc", nf90_write, ncid2) if (status /= nf90_noerr) call handle_err(status) ... ! Find the IDs of the variables status = nf90_inq_varid(ncid1, "rh", RHVarID) if (status /= nf90_noerr) call handle_err(status) status = nf90_inq_varid(ncid1, "avgrh", avgRHVarID) if (status /= nf90_noerr) call handle_err(status) ... status = nf90_redef(ncid2) ! Enter define mode if (status /= nf90_noerr) call handle_err(status) ! Copy variable attribute from "rh" in file 1 to "avgrh" in file 1 status = nf90_copy_att(ncid1, RHVarID, "units", ncid2, avgRHVarID) if (status /= nf90_noerr) call handle_err(status) status = nf90_enddef(ncid2) if (status /= nf90_noerr) call handle_err(status)
The function NF90_RENAME_ATT changes the name of an attribute. If the new name is longer than the original name, the netCDF dataset must be in define mode. You cannot rename an attribute to have the same name as another attribute of the same variable.
function nf90_rename_att(ncid, varid, curname, newname) integer, intent( in) :: ncid, varid character (len = *), intent( in) :: curname, newname integer :: nf90_rename_att
ncid
varid
curname
newname
NF90_RENAME_ATT returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_RENAME_ATT to rename the variable attribute units to Units for a variable rh in an existing netCDF dataset named foo.nc:
use netcdf implicit none integer :: ncid1, status integer :: RHVarID ! Variable ID ... status = nf90_open("foo.nc", nf90_nowrite, ncid) if (status /= nf90_noerr) call handle_err(status) ... ! Find the IDs of the variables status = nf90_inq_varid(ncid, "rh", RHVarID) if (status /= nf90_noerr) call handle_err(status) ... status = nf90_rename_att(ncid, RHVarID, "units", "Units") if (status /= nf90_noerr) call handle_err(status)
The function NF90_DEL_ATT deletes a netCDF attribute from an open netCDF dataset. The netCDF dataset must be in define mode.
function nf90_del_att(ncid, varid, name) integer, intent( in) :: ncid, varid character (len = *), intent( in) :: name integer :: nf90_del_att
ncid
varid
name
NF90_DEL_ATT returns the value NF90_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include:
Here is an example using NF90_DEL_ATT to delete the variable attribute Units for a variable rh in an existing netCDF dataset named foo.nc:
use netcdf implicit none integer :: ncid1, status integer :: RHVarID ! Variable ID ... status = nf90_open("foo.nc", nf90_nowrite, ncid) if (status /= nf90_noerr) call handle_err(status) ... ! Find the IDs of the variables status = nf90_inq_varid(ncid, "rh", RHVarID) if (status /= nf90_noerr) call handle_err(status) ... status = nf90_redef(ncid) ! Enter define mode if (status /= nf90_noerr) call handle_err(status) status = nf90_del_att(ncid, RHVarID, "Units") if (status /= nf90_noerr) call handle_err(status) status = nf90_enddef(ncid) if (status /= nf90_noerr) call handle_err(status)
Dataset Functions
function nf90_inq_libvers() character(len = 80) :: nf90_inq_libvers function nf90_strerror(ncerr) integer, intent( in) :: ncerr character(len = 80) :: nf90_strerror function nf90_create(path, cmode, ncid) character (len = *), intent(in ) :: path integer, intent(in ) :: cmode integer, optional, intent(in ) :: initialsize integer, optional, intent(inout) :: chunksize integer, intent( out) :: ncid integer :: nf90_create function nf90_open(path, mode, ncid, chunksize) character (len = *), intent(in ) :: path integer, intent(in ) :: mode integer, intent( out) :: ncid integer, optional, intent(inout) :: chunksize integer :: nf90_open function nf90_set_fill(ncid, fillmode, old_mode) integer, intent( in) :: ncid, fillmode integer, intent(out) :: old_mode integer :: nf90_set_fill function nf90_redef(ncid) integer, intent( in) :: ncid integer :: nf90_redef function nf90_enddef(ncid, h_minfree, v_align, v_minfree, r_align) integer, intent( in) :: ncid integer, optional, intent( in) :: h_minfree, v_align, v_minfree, r_align integer :: nf90_enddef function nf90_sync(ncid) integer, intent( in) :: ncid integer :: nf90_sync function nf90_abort(ncid) integer, intent( in) :: ncid integer :: nf90_abort function nf90_close(ncid) integer, intent( in) :: ncid integer :: nf90_close function nf90_Inquire(ncid, nDimensions, nVariables, nAttributes, & unlimitedDimId) integer, intent( in) :: ncid integer, optional, intent(out) :: nDimensions, nVariables, nAttributes, & unlimitedDimId integer :: nf90_Inquire
Dimension functions
function nf90_def_dim(ncid, name, len, dimid) integer, intent( in) :: ncid character (len = *), intent( in) :: name integer, intent( in) :: len integer, intent(out) :: dimid integer :: nf90_def_dim function nf90_inq_dimid(ncid, name, dimid) integer, intent( in) :: ncid character (len = *), intent( in) :: name integer, intent(out) :: dimid integer :: nf90_inq_dimid function nf90_inquire_dimension(ncid, dimid, name, len) integer, intent( in) :: ncid, dimid character (len = *), optional, intent(out) :: name integer, optional, intent(out) :: len integer :: nf90_inquire_dimension function nf90_rename_dim(ncid, dimid, name) integer, intent( in) :: ncid character (len = *), intent( in) :: name integer, intent( in) :: dimid integer :: nf90_rename_dim
Variable functions
function nf90_def_var(ncid, name, xtype, dimids, varid) integer, intent( in) :: ncid character (len = *), intent( in) :: name integer, intent( in) :: xtype integer, dimension(:), intent( in) :: dimids ! May be omitted, scalar, ! vector integer :: nf90_def_var function nf90_inq_varid(ncid, name, varid) integer, intent( in) :: ncid character (len = *), intent( in) :: name integer, intent(out) :: varid integer :: nf90_inq_varid function nf90_inquire_variable(ncid, varid, name, xtype, ndims, & dimids, nAtts) integer, intent( in) :: ncid, varid character (len = *), optional, intent(out) :: name integer, optional, intent(out) :: xtype, ndims integer, dimension(*), optional, intent(out) :: dimids integer, optional, intent(out) :: nAtts integer :: nf90_inquire_variable function nf90_put_var(ncid, varid, values, start, stride, map) integer, intent( in) :: ncid, varid any valid type, scalar or array of any rank, & intent( in) :: values integer, dimension(:), optional, intent( in) :: start, count, stride, map integer :: nf90_put_var function nf90_get_var(ncid, varid, values, start, stride, map) integer, intent( in) :: ncid, varid any valid type, scalar or array of any rank, & intent(out) :: values integer, dimension(:), optional, intent( in) :: start, count, stride, map integer :: nf90_get_var function nf90_rename_var(ncid, varid, newname) integer, intent( in) :: ncid, varid character (len = *), intent( in) :: newname integer :: nf90_rename_var
Attribute functions
function nf90_inquire_attribute(ncid, varid, name, xtype, len, attnum) integer, intent( in) :: ncid, varid character (len = *), intent( in) :: name integer, intent(out), optional :: xtype, len, attnum integer :: nf90_inquire_attribute function nf90_inq_attname(ncid, varid, attnum, name) integer, intent( in) :: ncid, varid, attnum character (len = *), intent(out) :: name integer :: nf90_inq_attname function nf90_put_att(ncid, varid, name, values) integer, intent( in) :: ncid, varid character(len = *), intent( in) :: name any valid type, scalar or array of rank 1, & intent( in) :: values integer :: nf90_put_att function nf90_get_att(ncid, varid, name, values) integer, intent( in) :: ncid, varid character(len = *), intent( in) :: name any valid type, scalar or array of rank 1, & intent(out) :: values integer :: nf90_get_att function nf90_copy_att(ncid_in, varid_in, name, ncid_out, varid_out) integer, intent( in) :: ncid_in, varid_in character (len = *), intent( in) :: name integer, intent( in) :: ncid_out, varid_out integer :: nf90_copy_att function nf90_rename_att(ncid, varid, curname, newname) integer, intent( in) :: ncid, varid character (len = *), intent( in) :: curname, newname integer :: nf90_rename_att function nf90_del_att(ncid, varid, name) integer, intent( in) :: ncid, varid character (len = *), intent( in) :: name integer :: nf90_del_att
The Fortran 90 interface to the netCDF library closely follows the FORTRAN 77 interface. In most cases, function and constant names and argument lists are the same, except that nf90_ replaces nf_ in names. The Fortran 90 interface is much smaller than the FORTRAN 77 interface, however. This has been accomplished by using optional arguments and overloaded functions wherever possible.
Because FORTRAN 77 is a subset of Fortran 90, there is no reason to modify working FORTRAN code to use the Fortran 90 interface. New code, however, can easily be patterned after existing FORTRAN while taking advantage of the simpler interface. Some compilers may provide additional support when using Fortran 90. For example, compilers may issue warnings if arguments with intent( in) are not set before they are passed to a procedure.
The Fortran 90 interface is currently implemented as a set of wrappers around the base FORTRAN subroutines in the netCDF distribution. Future versions may be implemented entirely in Fortran 90, adding additional error checking possibilities.
In the Fortran 90 interface there are two inquiry functions each for dimensions, variables, and attributes, and a single inquiry function for datasets. These functions take optional arguments, allowing users to request only the information they need. These functions replace the many-argument and single-argument inquiry functions in the FORTRAN interface.
As an example, compare the attribute inquiry functions in the Fortran 90 interface
function nf90_inquire_attribute(ncid, varid, name, xtype, len, attnum) integer, intent( in) :: ncid, varid character (len = *), intent( in) :: name integer, intent(out), optional :: xtype, len, attnum integer :: nf90_inquire_attribute function nf90_inq_attname(ncid, varid, attnum, name) integer, intent( in) :: ncid, varid, attnum character (len = *), intent(out) :: name integer :: nf90_inq_attname
with those in the FORTRAN interface
INTEGER FUNCTION NF_INQ_ATT (NCID, VARID, NAME, xtype, len) INTEGER FUNCTION NF_INQ_ATTID (NCID, VARID, NAME, attnum) INTEGER FUNCTION NF_INQ_ATTTYPE (NCID, VARID, NAME, xtype) INTEGER FUNCTION NF_INQ_ATTLEN (NCID, VARID, NAME, len) INTEGER FUNCTION NF_INQ_ATTNAME (NCID, VARID, ATTNUM, name)
The biggest simplification in the Fortran 90 is in the nf90_put_var and nf90_get_var functions. Both functions are overloaded: the values argument can be a scalar or an array any rank (7 is the maximum rank allowed by Fortran 90), and may be of any numeric type or the default character type. The netCDF library provides transparent conversion between the external representation of the data and the desired internal representation.
The start, count, stride, and map arguments to nf90_put_var and nf90_get_var are optional. By default, data is read from or written to consecutive values of starting at the origin of the netCDF variable; the shape of the argument determines how many values are read from or written to each dimension. Any or all of these arguments may be supplied to override the default behavior.
Note also that Fortran 90 allows arbitrary array sections to be passed to any procedure, which may greatly simplify programming. For examples see NF90_PUT_VAR and NF90_GET_VAR.