How to generate *.f90 files from *.F90 files in gfortran? - fortran

Question

I have a small fortran program with some pre-processor directives written in a *.F90 file. Now, I would like to generate a *.f90 fortran file from it, which removes all the extra code in the *.F90 file corresponding to the other non-activated directives.
In pgifortran, all I have to do is :
pgf90 -F file_name.F90
And that is it! It produces a *.f90 file having the lines relevant to the active directives.
How can I do this in gfortran?

Answer 1

GNU Fortran options
See https://gcc.gnu.org/onlinedocs/gfortran/Preprocessing-Options.html for full details, but you may observe that the option -E preprocesses foo.F90 to stdout (you can, of course, pipe it to e.g. foo.f90).
The -E option is valid for the GNU compiler front-ends in general, and works for C, C++ and Fortran.
While preprocessing is enabled by default for files with the extentions .fpp, .FPP, .F, .FOR, .FTN, .F90, .F95, .F03 or .F08, you can enable it manually with -cpp. You can also disable it manually with -nocpp.
Example Program
program main
implicit none
#ifdef USER_MACRO
print*,'USER_MACRO was defined'
#endif
#ifdef __GFORTRAN__
print*,'I am GNU Fortran (aka gfortran)!'
#endif
#ifdef __GNUC__
print*,'I am GNU C (or its preprocessor)!'
#endif
end program main
Result from GNU C preprocessor (cpp)
$ cpp -E fpp.F90
# 1 "fpp.F90"
# 1 "<built-in>" 1
# 1 "<built-in>" 3
# 324 "<built-in>" 3
# 1 "<command line>" 1
# 1 "<built-in>" 2
# 1 "fpp.F90" 2
program main
implicit none
print*,'I am GNU C (or its preprocessor)!'
end program main
Result from GNU Fortran
$ gfortran -E fpp.F90
# 1 "fpp.F90"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "fpp.F90"
program main
implicit none
print*,'I am GNU Fortran (aka gfortran)!'
print*,'I am GNU C (or its preprocessor)!'
end program main
Obviously, you can see how user-defined symbols are preprocessed, too:
$ gfortran -E -DUSER_MACRO fpp.F90
# 1 "fpp.F90"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "fpp.F90"
program main
implicit none
print*,'USER_MACRO was defined'
print*,'I am GNU Fortran (aka gfortran)!'
print*,'I am GNU C (or its preprocessor)!'
end program main
Result from Intel Fortran
In case it is of interest, Intel compilers support the same options as GCC:
$ ifort -E -DUSER_MACRO fpp.F90
# 1 "fpp.F90"
program main
implicit none
print*,'USER_MACRO was defined'
# 8
# 11
end program main
Preprocessing with IBM XL Fortran
The IBM XL Fortran man pages have the full details, but it is important to note that preprocessor symbols must be provided via -WF,-DUSER_MACRO instead of -DUSER_MACRO.