GNU Fortran supports a variety of extensions to, and dialects of, the Fortran language. Its primary base is the ANSI FORTRAN 77 standard, currently available on the network at http://www.fortran.com/fortran/F77_std/rjcnf0001.html or as monolithic text at http://www.fortran.com/fortran/F77_std/f77_std.html. It offers some extensions that are popular among users of UNIX f77 and f2c compilers, some that are popular among users of other compilers (such as Digital products), some that are popular among users of the newer Fortran 90 standard, and some that are introduced by GNU Fortran.
(If you need a text on Fortran, a few freely available electronic references have pointers from http://www.fortran.com/F/books.html. There is a `cooperative net project', User Notes on Fortran Programming at ftp://vms.huji.ac.il/fortran/ and mirrors elsewhere; some of this material might not apply specifically to g77.)
Part of what defines a particular implementation of a Fortran system, such as g77, is the particular characteristics of how it supports types, constants, and so on. Much of this is left up to the implementation by the various Fortran standards and accepted practice in the industry.
The GNU Fortran language is described below. Much of the material is organized along the same lines as the ANSI FORTRAN 77 standard itself.
See Other Dialects, for information on features g77 supports that are not part of the GNU Fortran language.
Note: This portion of the documentation definitely needs a lot of work!
Relationship to the ANSI FORTRAN 77 standard:
Extensions to the ANSI FORTRAN 77 standard: