Many Fortran compilers including GNU Fortran allow passing the source code through a C preprocessor (CPP; sometimes also called the Fortran preprocessor, FPP) to allow for conditional compilation. In the case of GNU Fortran, this is the GNU C Preprocessor in the traditional mode. On systems with case-preserving file names, the preprocessor is automatically invoked if the filename extension is .F
, .FOR
, .FTN
, .fpp
, .FPP
, .F90
, .F95
, .F03
or .F08
. To manually invoke the preprocessor on any file, use -cpp
, to disable preprocessing on files where the preprocessor is run automatically, use -nocpp
.
If a preprocessed file includes another file with the Fortran INCLUDE
statement, the included file is not preprocessed. To preprocess included files, use the equivalent preprocessor statement #include
.
If GNU Fortran invokes the preprocessor, __GFORTRAN__
is defined and __GNUC__
, __GNUC_MINOR__
and __GNUC_PATCHLEVEL__
can be used to determine the version of the compiler. See Overview for details.
While CPP is the de-facto standard for preprocessing Fortran code, Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines Conditional Compilation, which is not widely used and not directly supported by the GNU Fortran compiler. You can use the program coco to preprocess such files (http://www.daniellnagle.com/coco.html).
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-4.9.3/gfortran/Preprocessing-and-conditional-compilation.html