Question

I think title says what I need. I know we can use “asd” function to do this, but for some reasons I need to do the allocation in Fortran (i.e. in subroutine “asd_”). Here is the C code:

#include <stdio.h>

void asd(float **c) {
  *c = (float *) malloc (2*sizeof(float));
  **c =123;
  *(*c+1)=1234;
}

void asd_(float **c);

main () {
  float *c;
  asd_(&c);
// asd(&c); would do the job perfectly
  printf("%f %f \n",c[0],c[1]);
  return 0;
}

And here is the Fortran code:

  subroutine asd(c)

  implicit none

  real, pointer, allocatable ::c(:)

  print *, associated(c)
  if(.not. associated(c))  allocate(c(2))

  end subroutine 

This randomly gives segmentation fault. Any help would be appreciated.

Answer 1

Here is also another solution, if you want to use Fortran intrinsic types. This was my case, since I needed to call routines from an external library, using the pre-specified data types. This is basically done with a wrapper Fortran subroutine. Here is the C code:

void mywrap_(void **);
void myprint_(void *);

main () {
  void *d;
  mywrap_(&d);
  myprint_(d);
  return 0;
}

And here is the wrapper:

  subroutine mywrap(b)
  implicit none
  include "h.h"     
  type(st), target, save :: a
  integer, pointer :: b
  interface 
     subroutine alloc(a)
        include "h.h"
        type(st) a
     end subroutine alloc
  end interface

  call alloc(a)
  b => a%i
  end

And the Fortran codes:

  subroutine alloc(a)
  implicit none 
  include "h.h"
  type(st) a

  a%i = 2
  a%r = 1.5
  if (allocated(a%s)) deallocate(a%s)
  allocate(a%s(2))
  a%s(1) = 1.23
  a%s(2) = 1234
  end
  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  subroutine myprint(a)
  implicit none
  include "h.h"     
  type(st) a

  print *,"INT: ", a%i
  print *,"REAL: ", a%r
  print *,"ALLOC: ", a%s
  end

And the header file “h.h”:

  type st
     sequence
     integer i
     real r
     real, allocatable :: s(:)
  end type

Note, this way all the objects are opaque in the C.