[Bug fortran/18428] No preprocessing option -cpp for gfortran

["c dot lemmen at fz-juelich dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From c dot lemmen at fz-juelich dot de  2005-06-12 11:36 -------
> "gfortran -x f95-cpp-input" works
> maybe this should be documented.

This is not the same.  

1) The -x <language> option states that ALL following input files should be
treated as being of type <language">

2) The former -cpp option stated that all following SOURCE files should be
preprocessed

In many legacy Makefiles, subroutines are compiled into object files, and in a
last step the main code ist compiled and linked to all dependencies in ONE step,
like

gfortran main.f90 -o main sub1.o sub2.o sub3.o

Now, for code with preprocessor directives, with other compilers you can specify
 to precompile the sources, like

f90 -cpp main.f90 -o main sub1.o sub2.o sub3.o

With gfortran and the -cpp option gone, someone who replaces the -cpp with -x
f95-cpp-input (easy to do with FLAGS), a la

gfortran -x f95-cpp-input main.f90 -o main sub1.o sub2.o sub3.o  
doesn't compile properly, since the binary object files are read as source (to
be preprocessed)
You would need to specify another -x object-input (or similar) before the object
files, that makes it significantly harder to adjust or write Makefiles. 
Alternatively, all source must be compiled first and linked in a separate step.
As stated above, this rather clean version is not considered in lots of existing
Makefiles.





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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18428