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2.5 NF90_CREATE

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

A creation mode flag specifies whether to overwrite any existing dataset with the same name and whether access to the dataset is shared.

Usage

      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
path
The file name of the new netCDF dataset.
cmode
The creation mode flag. The following flags are available: NF90_NOCLOBBER, NF90_SHARE, and NF90_64BIT_OFFSET.

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.

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.

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.

ncid
Returned netCDF ID.

The following optional arguments allow additional performance tuning.

initialsize
The initial size of the file (in bytes) at creation time. A value of 0 causes the file size to be computed when nf90_enddef is called.
chunksize
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 chunksize is set to 8192 bytes.

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

Errors

NF90_CREATE returns the value NF90_NOERR if no errors occurred. Possible causes of errors include:

Example

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)