Includes revealing with Fortran preprocessor

Question

I would like to understand how the preprocessor inlines includes into the code in Fortran. With C, it's pretty simple:

Test.c:

#include <stdio.h>

int main(void) {
    return 0;
}

Then I compile using:

gcc -E test.c

Then it displays the content generated by the C preprocessor, as expected.

Now assume I have this Fortran code:

Test.f:

program test
include "mpif.h"
call mpi_init
call mpi_finalize
end

Then I run:

gfortran -E -cpp test.f // For some reason I need -cpp when using -E in Fortran

But I won't have the expected result, which is the generated include embedded into the code.

Instead, I have this:

# 1 "test.f"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "test.f"
   program test
   include  'mpif.h'

   call mpi_init

   call mpi_finalize
   end

What am I doing wrong here?

Answer 1

Fortran has its own include directive which must not be confused with the preprocessor directive #include. As far as I understand it, the included code is not embedded into the master file, but the compiler instead continues to compile from the include file, and returns to the master file at the end of that file. From here:

The INCLUDE statement directs the compiler to stop reading statements from the current file and read statements in an included file or text module.

Also, included files are not preprocessed further, while #included ones are.

Note, that there is also a naming convention that enables the preprocessor only on files with capital suffixes *.F and *.F90. If you want to preprocess *.f or *.f90 files, you need to specify that in a compile option, e.g. -cpp for gfortran, and -fpp for ifort.