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<H1><A NAME="SECTION000120000000000000000"></A><A NAME="xref_subroutines_and_functions_as_arguments"></A><A NAME="f77_externalargs"></A>
<BR>
Subroutines and Functions as Arguments
</H1>

<P>
Macros are provided to handle subroutine and function names passed as
arguments. They correspond closely to the macros for handling normal data
type arguments.
The following example shows how to pass the name of an INTEGER function from
a C program to a FORTRAN subroutine.

<P>

<A NAME="cook_namectof"></A>
<DIV ALIGN="CENTER">
Example
- Passing names from C to FORTRAN.

</DIV>
A C program which calls a FORTRAN subroutine which needs the name of an INTEGER
function as an argument.
<FONT SIZE="-1"><BLOCKQUOTE> </FONT><PRE>
#include "f77.h"

extern F77_SUBROUTINE(tst_ifun)( INTEGER_FUNCTION(name),
                                 INTEGER(status) );

extern F77_INTEGER_FUNCTION(ifun)();

main(){
DECLARE_INTEGER(status);

   status = 0;

   F77_CALL(tst_ifun)( INTEGER_FUNCTION_ARG(ifun),
                        INTEGER_ARG(&amp;status) );

   printf( "Status set is: %d\n", status );

}
</PRE><FONT SIZE="-1"> </BLOCKQUOTE></FONT>
The FORTRAN subroutine:
<FONT SIZE="-1"><BLOCKQUOTE> </FONT><PRE>
*+ TST_IFUN - Call an integer function
      SUBROUTINE TST_IFUN( NAME, STATUS )

      INTEGER NAME
      EXTERNAL NAME
      INTEGER STATUS

      INTEGER I

      STATUS = NAME( STATUS )

      END
</PRE><FONT SIZE="-1"> </BLOCKQUOTE></FONT>
The INTEGER function:
<FONT SIZE="-1"><BLOCKQUOTE> </FONT><PRE>
*+ IFUN - A very simple FORTRAN INTEGER FUNCTION
      INTEGER FUNCTION IFUN( STATUS )

      INTEGER STATUS

      IFUN = STATUS + 99

      END
</PRE><FONT SIZE="-1"> </BLOCKQUOTE></FONT>
Corresponding macros are defined for other types of function and for 
FORTRAN subroutines.

<P>
Now suppose in the above example the subroutine TST_IFUN was written in C to 
be called from FORTRAN. The code would be something like:

<P>

<A NAME="cook_nameftoc"></A>
<DIV ALIGN="CENTER">
Example
- Passing names from FORTRAN to C.

</DIV>

<P>
<FONT SIZE="-1"><BLOCKQUOTE> </FONT><PRE>
*+ TESTIFUN - Call a SUBROUTINE which requires a function name argument.
      PROGRAM TSTIFUN

      EXTERNAL IFUN
      INTEGER STATUS

      CALL TST_IFUN( IFUN, STATUS )
      PRINT *, 'STATUS is: ', STATUS

      END
</PRE><FONT SIZE="-1"> </BLOCKQUOTE></FONT>
<FONT SIZE="-1"><BLOCKQUOTE> </FONT><PRE>
#include "f77.h"

F77_INTEGER_FUNCTION(ifun)();

F77_SUBROUTINE(tst_ifun)(INTEGER_FUNCTION(name), INTEGER(status) ){

GENPTR_INTEGER_FUNCTION(name)
GENPTR_INTEGER(status)

*status = F77_EXTERNAL_NAME(name)( INTEGER_ARG(status) );
</PRE><FONT SIZE="-1"> </BLOCKQUOTE></FONT>

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<ADDRESS>
<I>CNF and F77 Mixed Language Programming -- FORTRAN and C<BR>Starlink User Note 209<BR>P.M. Allan<BR>A.J. Chipperfield<BR>R.F. Warren-Smith<BR>19 January 2000<BR>E-mail:<A HREF="mailto:ussc@star.rl.ac.uk">ussc@star.rl.ac.uk</A></I>
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