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From: "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu>
Newsgroups: comp.lang.fortran
Subject: Re: nasty link problem with Gfortran and G++ (C++) ???
Date: Tue, 7 Jan 2025 22:40:18 -0000 (UTC)
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On Tue, 07 Jan 2025 15:35:38 -0600, Lynn McGuire wrote:

> I just ran into a nasty problem with GFortran and G++ (C++).  Probably
> not a bug ???  I am using GCC 14.1.
> 
> I have a lot of code in C++ (over 100,000 lines).  I have 750,000 lines
> of code in GFortran.  I have to extern "C" this code in C++ to make it
> callable by GFortran code.
> 
> I missed declaring a couple of C++ functions as extern "C" which means
> that they kept their C++ mangled link names.  But these C++ functions
> were declared as integer*8 and external in the GFortran code (old F77
> code).
> 
> So, the GCC linker did not report to me that it did not have a link for
> the G++ functions.  This may be a bug, I am not sure.
> 
> When I ran the program, the C++ functions were not called by the
> GFortran code.  Instead, the GFortran code treated the C++ functions as
> integer*8 scalar variables.
> 
> If needful, I can probably put together a small code sample that
> exhibits the problem.  Maybe.  It could be that the size of my code
> affects the GCC linker.
> 
> I removed the Gfortran code "external" keywords, extern "C" the C++
> functions, added the C++ function to my module list, and got a working
> link.


Need to see some actual code.

% cat > foo.c
int
foo(void)
{
   return (1);
}
% gcc14 -c foo.c
% nm foo.o
0000000000000000 T foo
% g++14 -c foo.c
% nm foo.o
0000000000000000 T _Z3foov
% cat > foo.f90
integer*8 function foo()
   foo = 1
end
% gfortran14 -c foo.f90
% nm foo.o
0000000000000000 T foo_

So, with gcc, you get the symbol foo. With g++, you get the mangled
named _Z3foov.  With gfortran, you get foo_.



-- 
steve