preprocessor - Gfortran pre-processor directives for Different Operating systems

Question

Could you tell me please how can I do the following:

#if __unix__
#define path_sep='/'
#elif __windows__
#define path_sep=''
#else
#error "path_sep not defined."
#endif

using gfortran compiler.

Answer 1

This can be done in combination with conditional compilation and using the "D" option on the command line. Here is some example code:

program test_Dopt
character (len=1) :: pathsep
pathsep = "?"
#ifdef WOS
   pathsep = ""
#endif
#ifdef UOS
   pathsep = "/"
#endif

write (*, '( "pathsep is >", A1, "<")' )  pathsep

end program test_Dopt

Name the program with filetype F90 to cause gfortran to run the preprocessor or use -cpp on the compile line. Then pass options to the prepreprocessor by including them after D on the compile line, e.g., gfortran -DWOS. (This is more general then gfortran -- most Fortran compilers will process C-style pre-processor directives.) Then you can identify the OS outside of Fortran and pass the information to the Fortran program.

You can compile your code via using the filetype F90 or -cpp.