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Function: presentn

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

Category: UTILITY

File: present.c

Author: K.G. Begeman

Use: LOGICAL PRESENTN( NUMARG ) Input any type except character

PRESENTN Returns true if argument is present, false if not.
NUMARG Numeric argument in argument list which is
checked for its presence.

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

Example: C SHELTRAN example to demonstrate use of presentn

PROGRAM MAINF
INTEGER NULLN
COMMON /NOARGN/ NULLN
...
CALL SUB( NULLN )
...
STOP
END
SUBROUTINE SUB( ARG )
REAL ARG
LOGICAL PRESENTN
IF (PRESENTN( ARG ))
THEN
...
CIF
RETURN
END

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

void sub( float *arg )
{
if (presentn_c( arg )) {
...
}
}

main()
{
...
sub( NULL );
...
}

Warnings: System dependent!

Notes: For character arguments use PRESENTC.

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