Passing functions from C++ DLD to Fortran and vise versa

[Thomas Treichl]

Hi,

I've a (hopefully simple) problem that I can't figure out. I'm trying to pass a 
function pointer from C++ to a Fortran routine and vise versa. But at the step 
of compilation I fail and don't know what to do at the moment:

$ mkoctfile ex4a.f ex4a.cc
ex4a.cc: In function 'octave_value_list Fex4a(const octave_value_list&, int)':
ex4a.cc:16: error: invalid conversion from 'void (*)(int*, double*)' to 'void*'
ex4a.cc:16: error: initializing argument 3 of 'void ffuncall_(int*, double*, 
void*)'

Can somebody help please? The files I'm using are attached.

 Thomas

C Example 4a, function ffuncall ()
      subroutine ffuncall (vn, vd, vp)
      integer vn
      double precision vd
      external vp
C
      print *, '  Example 4a: Fortran side: numbers are', vn, vd
C
      call vp (vn, vd)
      return
      end

/* Example 4a, Interfacing Fortran function ffuncall () */
#include <octave/oct.h>
#include <iostream>
     
extern "C" void F77_FUNC (ffuncall, FFUNCALL) (int *vn, double *vd, void *vp);

extern "C" void F77_FUNC (ffun, FFUN) (int *vint, double *vdbl) {
  printf ("   Example 4a: C side: Fortran called C function ffon with numbers 
%d %f\n",
          *vint, *vdbl);
}
    
DEFUN_DLD (ex4a, args, nargout, "ex4a") {
  int vnum = 11;
  double vdob = 22.22;
  F77_FUNC (ffuncall, FFUNCALL) (&vnum, &vdob, F77_FUNC (ffun, FFUN));
  std::cout << "   Example 4a: C++ side: Fortran function finished, back in C++ 
function\n";
}