Technical data

Chapter 3: Fortran Program Interfaces

Note the following:

• Avoid calling Fortran functions of type FLOAT, COMPLEX, and

CHARACTER from C.

• You cannot write a C function so that it will return a COMPLEX value

to Fortran.

• A character-valued Fortran subprogram is equivalent to a C language

routine with two extra initial arguments: a data address and a length.

However, if the length is one, no extra argument is needed and the

single character result is returned as in a normal numeric function.

Thus

character*15 function g(…)

is equivalent to

char result [1];

long int length;

g_(result, length, …)

…

and could be invoked in C by

char chars[15]

g_(chars, 15, …);

and

character function h(…)

could be invoked in C by

char c, h();

c=h_(…);

Arguments

The following rules apply to arguments passed between Fortran and C:

• All explicit arguments must be passed by reference. All routines must

specify an address rather than a value. Thus, to pass constants or

expressions to Fortran, the C routine must ﬁrst store their values into

variables and then pass the address of the variable. (The only exception

occurs when passing the length of a string from C to a Fortran

subroutine with a parameter of type CHARACTER.)