By-passing the gfortran driver

[ivan-pi]

From the gfortran pages:

When running gfortran one actually does not run the compiler, but the compiler driver. This driver interprets the command line options given, and hands the work off to the actual compiler, the assembler, and the linker. By default, this compiler driver decides by the extensions of the given file names what to do. A file named foo.c is handed to the C compiler and a file named foo.f90 is handed to the Fortran 95 compiler, etc. To overrule this behavior, one has to precede the filename by the argument -x lang where lang is a string identifying the requested language. For Fortran 95 this is f95

I was just wondering if there might by any reason to cut the gfortran compiler driver out of the picture, and use the "low-level" gcc compiler commands directly. I'm not sure how this affects Fortran-specific flags.

So far I only have one (nasty) reason, why you would want to do this - to force using the C preprocessor (in general this is a bad idea). Say I want to gain access to some macros defined in a C header:

! main.F90
#include <limits.h>
program main
implicit none
print *, "size of C CHAR_BIT = ", CHAR_BIT
end program

I can then run only the C preprocessor with the command

$ gcc -x c -E -P main.F90
program main
implicit none
print *, "size of C CHAR_BIT = ", 8
end program

where the -P flags instructs the preprocessor to omit generation of linemarkes.

Something similar can be done with Intel compilers:

$ icc -EP main.F90 | grep "\S"
program main
implicit none
print *, "size of C CHAR_BIT = ", 8
end program

The -EP flag causes the preprocessor to output to stdout omitting the line directives. The additional grep command is to remove the empty lines, which were left by header expansion and omitting linemarkers (annoyingly, the behavior of gcc and icc differs).