Sample Program: C Calling Fortran

A C program can call a Fortran function or subroutine.

The following example illustrates how program units written in different languages can be combined to create a single program. It also demonstrates parameter passing between C and Fortran subroutines with different data types as arguments.

#include <iostream.h>
extern double add(int *, double [],
int *, double []);

double ar1[4]={1.0, 2.0, 3.0, 4.0};
double ar2[4]={5.0, 6.0, 7.0, 8.0};
main()
{
int x, y;
double z;

x = 3;

z = add(&x, ar1, y, ar2); /* Call Fortran add routine */
/* Note: Fortran indexes arrays 1..n*/
/* C indexes arrays 0..(n-1) */

printf("The sum of %1.0f and %1.0f is %2.0f \n",
ar1[x-1], ar2[y-1], z);

}

The Fortran subroutine is:

C Fortran function add.f - for C interlanguage call example
C Compile separately, then link to C program
REAL FUNCTION ADD*8 (A, B, C, D)
REAL*8 B,D
INTEGER*4 A,C
DIMENSION B(4), D(4)
ADD = B(A) + D(C)
RETURN
END

Interlanguage Calling Conventions
Corresponding Data Types
Using the Subroutine Linkage Conventions in Interlanguage Calls