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/fortran/Books/. 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: