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Date: Mon, 10 May 1999 11:31:16 -0500 (CDT)
From: Mumit Khan <khan AT xraylith DOT wisc DOT edu>
Reply-To: Mumit Khan <khan AT xraylith DOT wisc DOT edu>
To: "J.C. Ng" <j DOT c DOT ng AT ic DOT ac DOT uk>
cc: cygwin AT sourceware DOT cygnus DOT com
Subject: Re: No underscore option for g77 or f77 
In-Reply-To: <Pine.SGI.3.96.990510164906.25468C-100000@buccaneer.ae.ic.ac.uk>
Message-ID: <Pine.SUN.3.93.990510112134.14165I-100000@modi.xraylith.wisc.edu>
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Content-Type: TEXT/PLAIN; charset=US-ASCII

On Mon, 10 May 1999, J.C. Ng wrote:

> The library was compiled using egcs 1.1.2 in Cygwin. I used nm to check
> the symbols within the library and all of them was prepended an
> underscore.
> Thanks for your help.

So you're trying to call g77 compiled routines from C/C++ and vice versa
and running the "underscore issue". There is lots of info on the net on
how to semi-portably do this, and I won't rehash that here. Here's a quick
summary of what I do:

1. at compile time (via configuration utility), check if the f77 compiler
   tacks an underscore at the end. If so, define F77_APPEND_UNDERSCORE to
   be 1, or else 0 (or undefine it).

2. In C headers, when prototyping the functions, I use this macro to
   declare the externals:
     
     #if F77_APPEND_UNDERSCORE
     # define F77_FUNCTION(f) f##_
     #else
     # define F77_FUNCTION(f) f
     #endif

     extern int F77_FUNCTION(f77func1) (int *, int *);

   or, if you want to define or undefine F77_UNDERSCORE (instead of giving
   it a value),

     #if defined(F77_APPEND_UNDERSCORE)
     # define F77_FUNCTION(f) f##_
     #else
     # define F77_FUNCTION(f) f
     #endif

     extern int F77_FUNCTION(f77func1) (int *, int *);

You can simply build all your C code with -DF77_APPEND_UNDERSCORE=1 and
you're all set.

G77, thanks to compatibility with f2c, has one more issue -- it appends
*TWO* underscores if the name already has an underscore. Of course, names
with underscores are not legal in f77, so f2c is free to do as it wishes.

There are good portability packages out there that may help. Lots of
people use CFORTRAN, which is a terrific package that hides lots of this
magic. You need to get version 3.5. Also search the mailing list for
what else you may need.

Regards,
Mumit




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