Function:     presentc

Purpose:      Logical function checking the 'presence' of a character
              argument in a subroutine/function call.

Category:     UTILITY

File:         present.c

Author:       K.G. Begeman

Use:          LOGICAL PRESENTC( CHARARG )   Input    CHARACTER*(*)

              PRESENTC  Returns true is argument is present, false if not.
              CHARARG   Character argument in argument list which is
                        checked for its presence.

Description:  PRESENTC is intended to be used in routines which perform
              a different action depending on the 'presence' or
              'absence' of certain character arguments.
              In C procedures a character argument is considered not
              present if the calling routine/program assigns NULL to
              the character pointer of the fchar struct, in
              FORTRAN or SHELTRAN one has to put the first element of
              the common block NOARGC in the argument list.

Example:      C     SHELTRAN example to demonstrate use of presentc

                    PROGRAM MAINF
                    CHARACTER NULLC
                    COMMON /NOARGC/ NULLC
                    ...
                    CALL SUB( NULLC )
                    ...
                    STOP
                    END
                    SUBROUTINE SUB( ARG )
                    CHARACTER*(*) ARG
                    LOGICAL PRESENTC
                    IF (PRESENTC( ARG ))
                    THEN
                       ...
                    CIF
                    RETURN
                    END

              C example to demonstrate use of presentc
              #include "gipsyc.h"
              #include "presentc.h"

              void sub( fchar arg )
              {
                 if (presentc_c( arg )) {
                    ...
                 }
              }

              main()
              {
                 static fchar nullc = { NULL, 0 };
                 ...
                 sub( nullc );
                 ...
              }

Warnings:     System dependent!

Notes:        Use PRESENTN for numeric arguments.

Updates:      Jul 21, 1988: JPT, Original document.
              Jul 12, 1989: KGB, Converted to ANSI C.
              Apr 23, 1991: KGB, implemented for HP.