Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!slb-sdr!saito
From: saito@sdr.slb.com (Naoki Saito)
Newsgroups: comp.lang.c++
Subject: How to call C++ functions from Fortran with C++ 2.0
Message-ID: <1990Mar13.172657.277@sdr.slb.com>
Date: 13 Mar 90 17:26:57 GMT
Reply-To: saito@slb-sdr.UUCP ()
Organization: Schlumberger-Doll Research, Ridgefield CT
Lines: 54


	Last year, Jeff Filo @ Purdue Univ, posted the article about how to
call C++ from C and Fortran.  Switching to C++ 2.0, however, makes the problem
messier.  Of course, calling Fortran subroutines from C++ is easy, but the
reverse is not.  The following artificial programs illustrate the situation.

Fortran main program (I want to use C++ square function):
	program test
c
	integer*4 i, j
	i = 100
	call square(i, j)
	write(6,*) i, j
	end

C++ program:
void square(int& i, int& j)
{
  j = i*i;
}

In order to make executable image, I had to
(1) Translate the C++ program to the C program.
The translation changes function name in C++ 2.0 as follows:
char square__FRiT1 (__0i , __0j )
int *__0i ;
int *__0j ;
{ 
((*__0j ))= (((*__0i ))* ((*__0i )));
}

(2) Modify the function name which is callable from Fortran.
Fortran is not case sensitive. The underscore must be appended too.
in C++,
char square__FRiT1 (__0i , __0j ) ==> char square__frit1_ (__0i , __0j )
 						   ^^^^^^
in Fortran,
call square(i, j) ==> call square__frit1(i, j)

(3) Finally, compile and link them.

Of course, the above example is very artificial and stupid, but the process
is rather complicated.  This kind of situation sometimes occurs if we have
developed classes in C++ and want to plug them in the old existing Fortran
programs such as graphics systems.
Does anyone have good idea about this?  I would like to emphasize again:
calling Fortran subroutines or C functions from C++ is "easy".  However,
the reverse, especially, calling C++ 2.0 from Fortran doesn't seem easy.

Thanks in advance,

-- 
Naoki Saito (saito@sdr.slb.com)
Schlumberger-Doll Research