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USING SUBSCRIPTS TO ACCESS NDF SECTIONS   

As well as providing the programmer with explicit facilities for creating NDF sections, the NDF_ system also allows both the user and the writer of applications to specify sections (subsets and super-sets) when giving the names of NDF data structures to be processed. To see how this works, consider an application which requests access to an NDF data structure as follows:

      CALL NDF_ASSOC( 'IN', 'READ', INDF, STATUS )

and suppose this results in a prompt asking for the name of an NDF:

   IN - Input NDF data structure > name

If you were to respond simply with the name of an HDS object (denoted here by ``name''), then NDF_ASSOC would return a base NDF identifier for the specified data structure via its INDF argument. However, if a set of subscripts is also supplied, thus:

   IN - Input NDF data structure > name(3:256,-8:4)

then NDF_ASSOC will return an identifier for the specified NDF section instead.

This process may be applied when accessing a pre-existing data structure in any situation where an NDF name alone would suffice (e.g. on the command line when invoking an application, or as a default in an interface file, etc.). Writers of applications may also use this method of selecting NDF sections when passing the names of datasets to NDF_ routines which access them (see §[*]).



 

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Starlink User Note 33
R.F. Warren-Smith
11th January 2000
E-mail:rfws@star.rl.ac.uk

Copyright © 2000 Council for the Central Laboratory of the Research Councils