CODEWITHSUNDEEP
cfortrangfortranfortran-iso-c-binding
leoleson
leoleson

Reputation: 43

C Wrapper Calling Fortran Functions

I'm trying to write a C wrapper to call a set of functions in a Fortran module. I'm starting with something basic but I'm missing something important.

I've tried appending/prepending different numbers of underscores. I've also tried linking with gcc instead of gfortran. What I show below gives the simplest error(s).

I'm working on a Mac running Yosemite 10.10.3, GNU Fortran 5.1.0, and the C compiler that comes with Xcode.

main.c

#include "stdio.h"

int main(void) 
{
    int a;
    float b;
    char c[30];
    extern int _change_integer(int *a);

    printf("Please input an integer: ");
    scanf("%d", &a);

    printf("You new integer is: %d\n", _change_integer(&a));

    return 0;
}

intrealstring.f90

module intrealstring
use iso_c_binding
implicit none

contains

integer function change_integer(n)
    implicit none

    integer, intent(in) :: n
    integer, parameter :: power = 2

    change_integer = n ** power
end function change_integer

end module intrealstring

Here is how I'm compiling, along with the error:

$ gcc -c main.c
$ gfortran -c intrealstring.f90
$ gfortran main.o intrealstring.o -o cwrapper
Undefined symbols for architecture x86_64:
  "__change_integer", referenced from:
      _main in main.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
$

Upvotes: 4

Views: 2125

Answers (1)

LPs
LPs

Reputation: 16213

You have to bind fortran to c:

module intrealstring
use iso_c_binding
implicit none

contains

integer (C_INT) function change_integer(n) bind(c)
    implicit none

    integer (C_INT), intent(in) :: n
    integer (C_INT), parameter :: power = 2

    change_integer = n ** power
end function change_integer

end module intrealstring

Your c file has to modified as follows:

#include "stdio.h"

int change_integer(int *n);

int main(void) 
{
    int a;
    float b;
    char c[30];

    printf("Please input an integer: ");
    scanf("%d", &a);

    printf("You new integer is: %d\n", change_integer(&a));

    return 0;
}

The you can do:

$ gcc -c main.c
$ gfortran -c intrealstring.f90
$ gfortran main.o intrealstring.o -o cwrapper

Upvotes: 4

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