Re: how do you send a fortran character string from GCC to GFortran ?

On Thu, 02 Jan 2025 16:38:10 -0600, Lynn McGuire wrote:

On 1/2/2025 12:40 PM, Steven G. Kargl wrote:

On Thu, 02 Jan 2025 02:27:54 -0600, Lynn McGuire wrote:
 

How do you send a fortran character string from GCC to GFortran ?
>
I cannot get this to link.  I can do the reverse, send a fortran
character string from Gfortran to GCC.
>
I do have the additional complication that I do not know the length of
the fortran character string being sent from GCC to Gfortran at compile
time, only run time.  So that is a character*(*) string.
>
I am not using the ISO C binding.

 
As Thomas as indicated, ISO C binding was introduced into the
Fortran standard to address your needs.  But, if you want to
go old school with gcc/gfortran, then
 
% cat aa.c
#include <string.h>
 
void
string_(char *s, int *slen)
{
    strncpy(s, "abc", *slen);
}
 
% cat bb.f90
program foo
    external :: string
    character(len=10) str
    call string(str, len(str))
    print *, '>>' // str //'<<'
end program foo
 
% ~/work/bin/gcc -c aa.c
% gfcx -o z bb.f90 aa.o
% ./z
  >>abc<<

 
Isn't the character string length variable "slen" a value parameter and
size_t type ?
 

'int *' is a pointer to an int.  size_t may or may not be an int.

If one refuses to use the facilities of the Fortran standard,
namely ISO C binding, then one needs to experiment to determine
the type(s) and calling convention.

--
steve