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From: tps@sdchem.UUCP
Newsgroups: comp.lang.fortran,comp.unix.questions
Subject: Re: C subroutine calls from FORTRAN
Message-ID: <639@sdchema.sdchem.UUCP>
Date: Thu, 19-Feb-87 03:25:19 EST
Article-I.D.: sdchema.639
Posted: Thu Feb 19 03:25:19 1987
Date-Received: Fri, 20-Feb-87 02:23:07 EST
References: <2324@usceast.UUCP>
Sender: news@sdchem.UUCP
Reply-To: tps@sdchemf.UUCP (Tom Stockfisch)
Organization: UC San Diego
Lines: 36
Xref: utgpu comp.lang.fortran:62 comp.unix.questions:1108

In article <2324@usceast.UUCP> still@usceast.UUCP (Bert Still) writes:
>When I try to compile and link the following routine (and a few others
>which are insignificant for this particular query), I get a bunch of
>unresolved external reference messages from the linker. This is apparently
>because when you call a routine from f77, an underscore (_) is appended to
>the fcn identifier both in front (as cc does) and BEHIND. How does one get
>around this problem ? Any ideas would be greatly appreciated.

The answer is simple.  You can't call C routines directly from fortran unless
the latter end in an underscore.  THIS IS DEFINITELY A FEATURE.  Fortran calls
by address, C by value, so 7 times out of 8 you wouldn't want to call the
C routine directly.  The answer is, for each C routine you want to call, to
write a front-end routine in C which the fortran code actually calls, which
ends in underscore, and which properly translates to call-by-value.  For
instance, isatty() has the synopsis

	isatty( fd )
		int	fd;

Write a front end which (in the C code) you call isatty_():

	isatty_( fd )
		int	*fd;	/* a POINTER, which is what fortran passes */
	{
		return	isatty( *fd );
	}

Now in your fortran code you just do
	
	integer function isatty()
	integer ifd, ttyinput

	ifd =	0
	ttyinput =	isatty(ifd)

|| Tom Stockfisch, UCSD Chemistry	tps%chem@sdcsvax.UCSD