HP Fortran Programmer's Guide (B3908-90031; September 2011)

Calling C routines from HP Fortran
Data types
Chapter 8186
The Fortran source file for such a scenario is shown below in the example pass_complex.f90.
Example 8-1 pass_complex.f90
PROGRAM main
! This program passes a complex number to a C function
! that squares it and returns the result. The C
! function has the following declaration prototype:
!
! complex sqr_complex(complex cmx_val);
!
! "complex" is not an intrinsic type for C but it
! creates a typedef for one, using a struct.
COMPLEX :: result, cmx_num = (2.5, 3.5)
! We have to declare the C function because we’re calling it
! as a function rather than a subroutine. If we didn’t
! declare it, Fortran would use the implicit typing rules
! by default and assume from the name, sqr_complex, that it
! returns a real.
COMPLEX sqr_complex
PRINT *, 'C will square this complex number: ', cmx_num
! Use the %VAL built-in function to indicate that cmx_num
! is being passed by value, as C expects it to be, and
! and not by reference, as Fortran does by default
result = sqr_complex(%VAL(cmx_num))
PRINT *, 'The squared result is: ', result
END PROGRAM main
The following is the C source file.
Example 8-2 sqr_complex.c
#include <stdio.h>
/* simulate Fortran’s complex number */
typedef struct
{
float real;
float imag;
}COMPLEX;
/* returns the square of the complex argument */
COMPLEX sqr_complex(COMPLEX cmx_val)