Return Values

A Fortran subroutine is a C function with a void return type. A C procedure called as a function must return a value whose type corresponds to the type the Fortran program expects (except for character, complex, and double-complex data types). The table below shows this correspondence.

Return Value Data Type

Fortran Type	C Type
integer	int;
integer*1	signed char;
integer*2	short;
integer*4	long int x;
integer*8 x	long long x; or _int64
logical	int;
logical*1	char;
logical*2	short;
logical*4x	long int x;
logical*8	long long x; or _int64
real	float;
real*r x	float x;
real*8 x	double x;
real*16	No equivalent
double precision	double;

Example below shows Fortran code for a return value function called cfunct and the corresponding C routine.

Example of Returning Values from C to Fortran

Fortran code
integer iret, cfunct
iret = cfunct()

Corresponding C Routine
int cfunct ()
{
...program text...
return i;
}