Technical data

Chapter 3: Fortran Program Interfaces

Fortran/C Interface

When writing Fortran programs that call C functions, consider procedure

and function declaration conventions for both languages. Also, consider the

rules for argument passing, array handling, and accessing common blocks

of data.

Procedure and Function Declarations

This section discusses items to consider before calling C functions from

Fortran.

Names

When calling a Fortran subprogram from C, the C program must append an

underscore (_) to the name of the Fortran subprogram. For example, if the

name of the subprogram is matrix, then call it by the name matrix_. When

Fortran is calling a C function, the name of the C function must also end with

an underscore.

The Fortran compiler changes all its subprogram names to lowercase. Thus,

all of the following subprograms refer to the same function matrix when

interfacing with C:

subroutine MATRIX

subroutine Matrix

subroutine matrix

The exception to this rule is when the –u option to f77 is used. This option

causes case to be preserved.