Fortran call C, deal with double**

test.c

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

/* This is a C function to be called from Fortran
 * input s: the size of the array
 * output x: the array of float point numbers in double precision
 */
void call_fc(double *(*x), int s)
{
    double *y = malloc(s*sizeof(double));
    int i;
    for(i=0; i < s; i++)
    {
        y[i]= sin((double)i);
    }
    *x = y;
}

test.f90

PROGRAM FORT_C
   use iso_c_binding
   IMPLICIT NONE

   ! interoperate with C
   interface
      subroutine call_fc(pX,s) bind(C,name='call_fc')
         import
         integer(c_int),value :: s   ! int s
         type(c_ptr)          :: pX  ! double **x
      end subroutine
   end interface

   integer(c_int)           :: i
   integer(c_int)           :: s
   real(c_double), pointer  :: X(:)  ! double **x in Fortran
   type(C_ptr)              :: pX    ! double **x in C

   s = 10
   call call_fc(pX,s)
   call c_f_pointer(pX,X,(/s/))      ! convert C pointer to Fortran pointer(s)

   do i=1,s
      write(*,'(a4,1x,I2,1x,a2,1x,F15.8)') 'sin(', i, ') =', x(i)
   end do

END program