detecting gfortran with ifdef

[Brooks Moses]

Steven Bosscher wrote:
> On Thursday 26 October 2006 23:12, Warren Turkal wrote:
>>Is there a preprocessor symbol defined when using gfortran that can be used
>>to conditionally compile code only when using gfortran?
> 
> No, there isn't.
> 
> Note that gfortran does not have an integrated preprocessor, like
> e.g. Cray Fortran does.  The program you call to compile your
> programs is the driver program called gfortran.  This driver calls
> the compiler (f951), and for some files it calls the preprocessor
> before the compiler.
> 
> If your Fortran source file has the extensions .F, .fpp, .FPP, .F90,
> or .F95, gfortran (the compiler driver) calls the C preprocessor in
> traditional (i.e. pre ANSI C) mode.  The driver adds one command
> line #define to the command line: -D_LANGUAGE_FORTRAN.
> 
> So the closest thing to what you want, probably is _LANGUAGE_FORTRAN.

An alternate option is __GNUC__.  This, of course, does not distinguish 
between things compiled with gfortran and things compiled with gcc or 
other gcc drivers, but those can be trivially distinguished by what 
language they're in, so that's probably irrelevant.

This does, however, have the failure mode that it will most likely be 
defined by any compilation process that uses the GNU C preprocessor.  On 
the other hand, it's unlikely to be defined by any compilers that aren't 
using the GNU toolchain somehow, so it could be a better option there.

- Brooks