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Conditional NDF Creation   

It is sometimes necessary to determine whether an NDF exists before deciding to create a new one. The routine NDF_EXIST is provided to allow this by associating an existing NDF with a parameter and returning an NDF identifier for it, if it exists. If the NDF does not exist, then no error results, but the routine returns with a ``null'' identifier value of NDF__NOID (defined in the include file NDF_PAR). In effect, this routine behaves identically to NDF_ASSOC, except that if the NDF does not exist, control is returned to the calling routine rather than re-prompting the user to supply a new name. The following illustrates how NDF_EXIST might be used:

      INCLUDE 'NDF_PAR'

      ...

      CALL NDF_EXIST( 'OUT', 'UPDATE', INDF, STATUS )
      IF ( INDF .EQ. NDF__NOID ) THEN
         CALL NDF_CREAT( 'OUT', '_INTEGER', NDIM, LBND, UBND, INDF, STATUS )
      END IF

Here, an existing NDF is accessed if it exists, otherwise a new structure is created and used instead.



next up previous
Next: Creating Primitive NDFs
Up: ACCESSING NDFS FOR OUTPUT
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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