g77 Manual Page
g77 - GNU project Fortran Compiler (v0.5.24)
g77 [option | filename ]...
The information in this man page is an extract from the
full documentation of the GNU Fortran compiler (version
0.5.24), and is limited to the meaning of some of the
This man page is not up to date, since no volunteers want
to maintain it. If you find a discrepancy between the man
page and the software, please check the Info file, which
is the authoritative documentation.
If we find that the things in this man page that are out
of date cause significant confusion or complaints, we will
stop distributing the man page. The alternative, updating
the man page when we update the Info file, is impractical
because the rest of the work of maintaining GNU Fortran
leaves us no time for that. The GNU project regards man
pages as obsolete and should not let them take time away
from other things.
For complete and current documentation, refer to the Info
file `g77' or the manual Using and Porting GNU Fortran
(for version 0.5.24). Both are made from the Texinfo
source file g77.texi.
If your system has the `info' command installed, the com-
mand `info g77' should work, unless g77 has not been prop-
erly installed. If your system lacks `info', or you wish
to avoid using it for now, the command `more
/usr/info/g77.info*' should work, unless g77 has not been
If g77 has not been properly installed, so that you cannot
easily access the Info file for it, ask your system admin-
istrator, or the installer of g77 (if you know who that
is) to fix the problem.
The C and F77 compilers are integrated; g77 is a program
to call gcc with options to recognize programs written in
Fortran (ANSI FORTRAN 77, also called F77). gcc processes
input files through one or more of four stages: prepro-
cessing, compilation, assembly, and linking. This man
page contains full descriptions for only F77-specific
aspects of the compiler, though it also contains summaries
of some general-purpose options. For a fuller explanation
of the compiler, see gcc(1).
For complete documentation on GNU Fortran, type `info
F77 source files use the suffix `.f', `.for', or `.FOR';
F77 files to be preprocessed by cpp(1) use the suffix
`.F', `.fpp', or `.FPP'; Ratfor source files use the suf-
fix `.r' (though ratfor itself is not supplied as part of
There are many command-line options, including options to
control details of optimization, warnings, and code gener-
ation, which are common to both gcc and g77. For full
information on all options, see gcc(1).
Options must be separate: `-dr' is quite different from
`-d -r '.
Most `-f' and `-W' options have two contrary forms: -fname
and -fno-name (or -Wname and -Wno-name). Only the non-
default forms are shown here.
-c Compile or assemble the source files, but do not
link. The compiler output is an object file corre-
sponding to each source file.
Define macro macro with the string `1' as its defi-
Define macro macro as defn.
-E Stop after the preprocessing stage; do not run the
compiler proper. The output is preprocessed source
code, which is sent to the standard output.
-g Produce debugging information in the operating sys-
tem's native format (for DBX or SDB or DWARF). GDB
also can work with this debugging information. On
most systems that use DBX format, `-g' enables use
of extra debugging information that only GDB can
Unlike most other Fortran compilers, GNU Fortran
allows you to use `-g' with `-O'. The shortcuts
taken by optimized code may occasionally produce
surprising results: some variables you declared may
not exist at all; flow of control may briefly move
where you did not expect it; some statements may
not be executed because they compute constant
results or their values were already at hand; some
statements may execute in different places because
they were moved out of loops.
Nevertheless it proves possible to debug optimized
output. This makes it reasonable to use the opti-
mizer for programs that might have bugs.
-Idir Append directory dir to the list of directories
searched for include files.
-Ldir Add directory dir to the list of directories to be
searched for `-l'.
Use the library named library when linking.
Do not search the standard system directories for
header files. Only the directories you have speci-
fied with -I options (and the current directory, if
appropriate) are searched.
-O Optimize. Optimizing compilation takes somewhat
more time, and a lot more memory for a large func-
tion. See the GCC documentation for further opti-
misation options. Loop unrolling, in particular,
may be worth investigating for typical numerical
Place output in file file.
-S Stop after the stage of compilation proper; do not
assemble. The output is an assembler code file for
each non-assembler input file specified.
Undefine macro macro.
-v Print (on standard error output) the commands exe-
cuted to run the stages of compilation. Also print
the version number of the compiler driver program
and of the preprocessor and the compiler proper.
The version numbers of g77 itself and the GCC dis-
tribution on which it is based are distinct.
-Wall Issue warnings for conditions which pertain to
usage that we recommend avoiding and that we
believe is easy to avoid, even in conjunction with
file.h C header (preprocessor) file
file.f Fortran source file
file.for Fortran source file
file.FOR Fortran source file
file.F preprocessed Fortran source file
file.fpp preprocessed Fortran source file
file.FPP preprocessed Fortran source file
file.r Ratfor source file (ratfor not included)
file.s assembly language file
file.o object file
a.out link edited output
TMPDIR/cc* temporary files
LIBDIR/libg2c.a Fortran run-time library
LIBDIR/libgcc.a GCC subroutine library
/lib/crt[01n].o start-up routine
/lib/libc.a standard C library, see intro(3)
/usr/include standard directory for #include files
LIBDIR/include standard gcc directory for #include
LIBDIR is usually /usr/local/lib/machine/version.
TMPDIR comes from the environment variable TMPDIR (default
/usr/tmp if available, else /tmp).
gcc(1), cpp(1), as(1), ld(1), gdb(1), adb(1), dbx(1),
`g77', `gcc', `cpp', `as', `ld', and `gdb' entries in
Using and Porting GNU Fortran (for version 0.5.24), James
Craig Burley; Using and Porting GNU CC (for version 2.0),
Richard M. Stallman; The C Preprocessor, Richard M. Stall-
man; Debugging with GDB: the GNU Source-Level Debugger,
Richard M. Stallman and Roland H. Pesch; Using as: the GNU
Assembler, Dean Elsner, Jay Fenlason & friends; gld: the
GNU linker, Steve Chamberlain and Roland Pesch.
For instructions on how to report bugs, type `info g77 -n
Copyright (c) 1991-1998 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim
copies of this manual provided the copyright notice and
this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified ver-
sions of this manual under the conditions for verbatim
copying, provided that the entire resulting derived work
is distributed under the terms of a permission notice
identical to this one.
Permission is granted to copy and distribute translations
of this manual into another language, under the above con-
ditions for modified versions, except that this permission
notice may be included in translations approved by the
Free Software Foundation instead of in the original
See the GNU CC Manual for the contributors to GNU CC. See
the GNU Fortran Manual for the contributors to GNU For-