5.4 ncgen
The ncgen tool generates a netCDF file or a C or FORTRAN program that
creates a netCDF dataset. If no options are specified in invoking
ncgen, the program merely checks the syntax of the CDL input,
producing error messages for any violations of CDL syntax.
In the current release, the ncgen utility can only generate
classic-model netCDF-4 files or programs. A separate experimental
utility, ncgen4 (built when –enable-ncgen4 is specified at build
time), can be used to generate netCDF-4 files or C code for the
enhanced data model. The ncgen4 utility also handles the special
virtual attributes produced by the ncdump '-s' option to describe
implementation characteristics such as compression and chunking. It
does not yet generate Fortran code.
UNIX syntax for invoking ncgen:
ncgen [-b] [-o netcdf-file] [-c] [-f] [-v2|-v3] [-x] [input-file]
where:
-b- Create a (binary) netCDF file. If the '-o' option is absent, a default
file name will be constructed from the netCDF name (specified after
the netcdf keyword in the input) by appending the '.nc'
extension. Warning: if a file already exists with the specified name
it will be overwritten.
-o netcdf-file- Name for the netCDF file created. If this option is specified, it
implies the '-b' option. (This option is necessary because netCDF
files are direct-access files created with seek calls, and hence
cannot be written to standard output.)
-c- Generate C source code that will create a netCDF dataset matching the
netCDF specification. The C source code is written to standard
output. This is only useful for relatively small CDL files, since all
the data is included in variable initializations in the generated
program.
-f- Generate FORTRAN source code that will create a netCDF dataset
matching the netCDF specification. The FORTRAN source code is written
to standard output. This is only useful for relatively small CDL
files, since all the data is included in variable initializations in
the generated program.
-v2- The generated netCDF file or program will use the version of the
format with 64-bit offsets, to allow for the creation of very large
files. These files are not as portable as classic format netCDF
files, because they require version 3.6.0 or later of the netCDF
library.
-v3- The generated netCDF file will be in netCDF-4/HDF5 format. These files
are not as portable as classic format netCDF files, because they
require version 4.0 or later of the netCDF library.
-x- Use “no fill” mode, omitting the initialization of variable values
with fill values. This can make the creation of large files much
faster, but it will also eliminate the possibility of detecting the
inadvertent reading of values that haven't been written.
Examples
Check the syntax of the CDL file foo.cdl:
ncgen foo.cdl
From the CDL file foo.cdl, generate an equivalent binary netCDF file
named bar.nc:
ncgen -o bar.nc foo.cdl
From the CDL file foo.cdl, generate a C program containing netCDF
function invocations that will create an equivalent binary netCDF
dataset:
ncgen -c foo.cdl > foo.c
