Fwd: Re: gfortran confusing object file with source?

[Tobias Burnus <burnus at net-b dot de>]

Hello,

Jeffrey Kelling wrote:
> gfortran [...] -x f95-cpp [...] -o etsf_io etsf_io.o
>
> gfortran gives a warning:
> Warning: Reading file 'etsf_io.o' as free form

The "-x" forces the compiler (driver) to handle the given files in the
given format, overriding the suffix-based handling.

Hence, the compiler reads the .o file as free-format Fortran file, which
should be pre-processed by the C preprocessor ("cpp").

In Fortran, the common handling of compilers is to regard ".f90" files
as free-form files - and ".F90" files as the same - except that those
should additionally be processed by "cpp".

In older gfortran versions, the only way to force the compilation with
"cpp" for ".f90" files was to use "-x". Newer gfortran versions support
the option "-cpp" which otherwise not affect the handling of file suffixes.


Hence: Please replace "-x f95-cpp" by "-cpp"  (unless you have an
ancient gfortran). Otherwise: Remove "-x f95-cpp" at least when linking.


> I am not familiar with fortran, so I am do not know what 'free form' means,

As Fortran dates back to the 50s, it was initially "written" (punched)
into cards. Hence, the fixed-form format is adapted for those: If you
punch a hole in the first column, it's a comment, maximally 72
characters per line are allowed, code has to start in column 7 as the
first one are used for other purposes, spaces (outside strings) have no
semantic meaning.

As that's quite inconvenient, a free-form format was added, which feels
more "natural", "modern": You can indent the lines as you want and
spaces do have a meaning (which helps with diagnostic) - also, you can
write longer lines.

Except for the input format, both fixed/free form have all the language
features - but the compiler has to know which one is used. Most
compilers use the extension for it: ".f" for fixed form and .f90 for
free form (as it was added in Fortran 90) - both forms are valid and
fully supported in Fortran 90/95/2003/2008 and by gfortran.

Tobias