Re: Guile, C++, and Mac OS X 10.4 (powerpc)

[Hans Aberg]

On 28 Jul 2010, at 21:49, Mike Solomon wrote:

> Hey guile users,
>    Trying to compile the simple example bessel.c from
> Writing-Guile-Extensions.html (renamed bessel.cc because I'm using g+ 
> +), I
> encountered the following error:
>
> bessel.cc: In function 'void init_bessel()':
> bessel.cc:13: error: invalid conversion from 'scm_unused_struct*
> (*)(scm_unused_struct*)' to 'scm_unused_struct* (*)(...)'
> bessel.cc:13: error:   initializing argument 5 of 'scm_unused_struct*
> scm_c_define_gsubr(const char*, int, int, int, scm_unused_struct* (*) 
> (...))'

The SCM type is a pointer to an undefined C type - C hack, which  
clashes with C++. Clever in C, but bad for C++ users.

> This even comes up when I put everything in extern "C" { ... }.  I  
> have seen
> other postings on the net for other software (lilypond, swig) that  
> speaks of
> the same issue, and some suggest that it is a problem with g++ and not
> guile.  I'm using powerpc-apple-darwin8-g++-4.0.1 (GCC) 4.0.1 (Apple
> Computer, Inc. build 5370)

When you use g++, all stuff is compiled as C++. So use gcc and add c++  
libraries when linking.

Then in formally correct C++, main() must be C++. Gcc accepts calling C 
++ from C, but attempting to pass an exception through a C function is  
converted to a termination exception.

So I wrote a C++ function scm::init_guile() calling scm_init_guile()  
and other stuff that needs to be initialized. Then
  int main(int argc, char** argv) {
    init_guile();

    try {
      ...
    }
    ...
  }

Then write a header bessel.h

#ifndef BESSEL_H
#define BESSEL_H

/* Copyright ...
   Free Software Foundation GNU General Public License <http://www.gnu.org/licenses/ 
>
 */

#ifdef __cplusplus
extern "C" {
#endif

void init_bessel();
...

#ifdef __cplusplus
} // extern "C"
#endif

#endif BESSEL_H


The file bessel.c is compiled as C, but your C++ files include bessel.h.

  Hans