@setfilename standards.info
@settitle GNU Coding Standards
@c This date is automagically updated when you save this file:
-@set lastupdate February 23, 2008
+@set lastupdate January 27, 2011
@c %**end of header
@dircategory GNU organization
The GNU coding standards, last updated @value{lastupdate}.
Copyright @copyright{} 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
-2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software
-Foundation, Inc.
+2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
+Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.2
-or any later version published by the Free Software Foundation;
-with no Invariant Sections, with no
-Front-Cover Texts, and with no Back-Cover Texts.
-A copy of the license is included in the section entitled ``GNU
-Free Documentation License''.
+under the terms of the GNU Free Documentation License, Version 1.3 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
+Texts. A copy of the license is included in the section entitled
+``GNU Free Documentation License''.
@end copying
@titlepage
even if you write in another programming language. The rules often
state reasons for writing in a certain way.
-This release of the GNU Coding Standards was last updated
-@value{lastupdate}.
-
@cindex where to obtain @code{standards.texi}
@cindex downloading this manual
If you did not obtain this file directly from the GNU project and
different formats, including the Texinfo source, PDF, HTML, DVI, plain
text, and more, at: @uref{http://www.gnu.org/prep/standards/}.
-Corrections or suggestions for this document should be sent to
-@email{bug-standards@@gnu.org}. If you make a suggestion, please include a
-suggested new wording for it; our time is limited. We prefer a context
-diff to the @file{standards.texi} or @file{make-stds.texi} files, but if
-you don't have those files, please mail your suggestion anyway.
+If you are maintaining an official GNU package, in addition to this
+document, please read and follow the GNU maintainer information
+(@pxref{Top, , Contents, maintain, Information for Maintainers of GNU
+Software}).
+
+@cindex @code{gnustandards-commit@@gnu.org} mailing list
+If you want to receive diffs for every change to these GNU documents,
+join the mailing list @code{gnustandards-commit@@gnu.org}, via the web
+interface at
+@url{http://lists.gnu.org/mailman/listinfo/gnustandards-commit}.
+Archives are also available there.
+
+@cindex @code{bug-standards@@gnu.org} email address
+@cindex Savannah repository for gnustandards
+@cindex gnustandards project repository
+Please send corrections or suggestions for this document to
+@email{bug-standards@@gnu.org}. If you make a suggestion, please
+include a suggested new wording for it, to help us consider the
+suggestion efficiently. We prefer a context diff to the Texinfo
+source, but if that's difficult for you, you can make a context diff
+for some other version of this document, or propose it in any way that
+makes it clear. The source repository for this document can be found
+at @url{http://savannah.gnu.org/projects/gnustandards}.
These standards cover the minimum of what is important when writing a
GNU package. Likely, the need for additional standards will come up.
coding standards for a trivial program.
@uref{http://www.gnu.org/software/hello/hello.html}.
+This release of the GNU Coding Standards was last updated
+@value{lastupdate}.
+
+
@node Legal Issues
@chapter Keeping Free Software Free
@cindex legal aspects
is written in that language, too. The Emacs editor pioneered this
technique.
-@cindex GUILE
-The standard extensibility interpreter for GNU software is GUILE
+@cindex Guile
+@cindex GNOME and Guile
+The standard extensibility interpreter for GNU software is Guile
(@uref{http://www.gnu.org/@/software/@/guile/}), which implements the
-language Scheme (an especially clean and simple dialect of Lisp). We
-don't reject programs written in other ``scripting languages'' such as
-Perl and Python, but using GUILE is very important for the overall
-consistency of the GNU system.
+language Scheme (an especially clean and simple dialect of Lisp).
+Guile also includes bindings for GTK+/GNOME, making it practical to
+write modern GUI functionality within Guile. We don't reject programs
+written in other ``scripting languages'' such as Perl and Python, but
+using Guile is very important for the overall consistency of the GNU
+system.
+
@node Compatibility
@section Compatibility with Other Implementations
GCC developers many hours, or even days, per year.
In the case of function-like macros like @code{REVERSIBLE_CC_MODE} in
-GCC which cannot be simply used in @code{if( ...)} statements, there is
+GCC which cannot be simply used in @code{if (...)} statements, there is
an easy workaround. Simply introduce another macro
@code{HAS_REVERSIBLE_CC_MODE} as in the following example:
* User Interfaces:: Standards about interfaces generally.
* Graphical Interfaces:: Standards for graphical interfaces.
* Command-Line Interfaces:: Standards for command line interfaces.
+* Dynamic Plug-In Interfaces:: Standards for dynamic plug-in interfaces.
* Option Table:: Table of long options.
+* OID Allocations:: Table of OID slots for GNU.
* Memory Usage:: When and how to care about memory needs.
* File Usage:: Which files to use, and where.
@end menu
avoid this problem by creating temporary files in this manner:
@example
-fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0600);
+fd = open (filename, O_WRONLY | O_CREAT | O_EXCL, 0600);
@end example
@noindent
or by using the @code{mkstemps} function from libiberty.
-In bash, use @code{set -C} to avoid this problem.
+In bash, use @code{set -C} (long name @code{noclobber}) to avoid this
+problem. In addition, the @code{mktemp} utility is a more general
+solution for creating temporary files from shell scripts
+(@pxref{mktemp invocation,,, coreutils, GNU Coreutils}).
+
@node Libraries
@section Library Behavior
@node Graphical Interfaces
@section Standards for Graphical Interfaces
@cindex graphical user interface
+@cindex interface styles
+@cindex user interface styles
-@cindex gtk+
+@cindex GTK+
When you write a program that provides a graphical user interface,
-please make it work with X Windows and the GTK+ toolkit unless the
-functionality specifically requires some alternative (for example,
-``displaying jpeg images while in console mode'').
+please make it work with the X Window System and the GTK+ toolkit
+unless the functionality specifically requires some alternative (for
+example, ``displaying jpeg images while in console mode'').
In addition, please provide a command-line interface to control the
functionality. (In many cases, the graphical user interface can be a
separate program which invokes the command-line program.) This is
so that the same jobs can be done from scripts.
-@cindex corba
-@cindex gnome
-Please also consider providing a CORBA interface (for use from GNOME), a
-library interface (for use from C), and perhaps a keyboard-driven
-console interface (for use by users from console mode). Once you are
-doing the work to provide the functionality and the graphical interface,
-these won't be much extra work.
+@cindex CORBA
+@cindex GNOME
+@cindex D-bus
+@cindex keyboard interface
+@cindex library interface
+Please also consider providing a D-bus interface for use from other
+running programs, such as within GNOME. (GNOME used to use CORBA
+for this, but that is being phased out.) In addition, consider
+providing a library interface (for use from C), and perhaps a
+keyboard-driven console interface (for use by users from console
+mode). Once you are doing the work to provide the functionality and
+the graphical interface, these won't be much extra work.
@node Command-Line Interfaces
@item LGPL
GNU Lesser General Public License, @url{http://www.gnu.org/@/licenses/@/lgpl.html}.
-@item GPL/Guile
-GNU GPL with the exception for Guile; for example, GPLv3+/Guile means
-the GNU GPL version 3 or later, with the extra exception for Guile.
-
+@item GPL/Ada
GNU GPL with the exception for Ada.
@item Apache
The license for Python, @url{http://www.python.org/@/2.0.1/@/license.html}.
@item RBSD
-The revised (3-clause) BSD, compatible with the GNU GPL,
+The revised (3-clause) BSD, compatible with the GNU GPL,@*
@url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#5}.
@item X11
The simple non-copyleft license used for most versions of the X Window
-system, @url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#3}.
+System, @url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#3}.
@item Zlib
The license for Zlib, @url{http://www.gzip.org/@/zlib/@/zlib_license.html}.
@cindex address for bug reports
@cindex bug reports
-Near the end of the @samp{--help} option's output there should be a line
-that says where to mail bug reports. It should have this format:
+Near the end of the @samp{--help} option's output, please place lines
+giving the email address for bug reports, the package's home page
+(normally @indicateurl{http://www.gnu.org/software/@var{pkg}}, and the
+general page for help using GNU programs. The format should be like this:
@example
-Report bugs to @var{mailing-address}.
+Report bugs to: @var{mailing-address}
+@var{pkg} home page: <http://www.gnu.org/software/@var{pkg}/>
+General help using GNU software: <http://www.gnu.org/gethelp/>
@end example
+It is ok to mention other appropriate mailing lists and web pages.
+
+
+@node Dynamic Plug-In Interfaces
+@section Standards for Dynamic Plug-in Interfaces
+@cindex plug-ins
+@cindex dynamic plug-ins
+
+Another aspect of keeping free programs free is encouraging
+development of free plug-ins, and discouraging development of
+proprietary plug-ins. Many GNU programs will not have anything like
+plug-ins at all, but those that do should follow these
+practices.
+
+First, the general plug-in architecture design should closely tie the
+plug-in to the original code, such that the plug-in and the base
+program are parts of one extended program. For GCC, for example,
+plug-ins receive and modify GCC's internal data structures, and so
+clearly form an extended program with the base GCC.
+
+@vindex plugin_is_GPL_compatible
+Second, you should require plug-in developers to affirm that their
+plug-ins are released under an appropriate license. This should be
+enforced with a simple programmatic check. For GCC, again for
+example, a plug-in must define the global symbol
+@code{plugin_is_GPL_compatible}, thus asserting that the plug-in is
+released under a GPL-compatible license (@pxref{Plugins,, Plugins,
+gccint, GCC Internals}).
+
+By adding this check to your program you are not creating a new legal
+requirement. The GPL itself requires plug-ins to be free software,
+licensed compatibly. As long as you have followed the first rule above
+to keep plug-ins closely tied to your original program, the GPL and AGPL
+already require those plug-ins to be released under a compatible
+license. The symbol definition in the plug-in---or whatever equivalent
+works best in your program---makes it harder for anyone who might
+distribute proprietary plug-ins to legally defend themselves. If a case
+about this got to court, we can point to that symbol as evidence that
+the plug-in developer understood that the license had this requirement.
+
@node Option Table
@section Table of Long Options
@samp{-v} in @code{gawk}.
@item assume-new
-@samp{-W} in Make.
+@samp{-W} in @code{make}.
@item assume-old
-@samp{-o} in Make.
+@samp{-o} in @code{make}.
@item auto-check
@samp{-a} in @code{recode}.
@samp{-d} in @code{touch}.
@item debug
-@samp{-d} in Make and @code{m4};
+@samp{-d} in @code{make} and @code{m4};
@samp{-t} in Bison.
@item define
@samp{-X} in @code{strip}.
@item dry-run
-@samp{-n} in Make.
+@samp{-n} in @code{make}.
@item ed
@samp{-e} in @code{diff}.
@samp{-N} in @code{diff}.
@item environment-overrides
-@samp{-e} in Make.
+@samp{-e} in @code{make}.
@item eof
@samp{-e} in @code{xargs}.
@samp{-E} in @code{m4}.
@item file
-@samp{-f} in @code{info}, @code{gawk}, Make, @code{mt}, and @code{tar};
-@samp{-n} in @code{sed};
-@samp{-r} in @code{touch}.
+@samp{-f} in @code{gawk}, @code{info}, @code{make}, @code{mt},
+@code{sed}, and @code{tar}.
@item field-separator
@samp{-F} in @code{gawk}.
@samp{-i} in @code{diff} and @code{wdiff}.
@item ignore-errors
-@samp{-i} in Make.
+@samp{-i} in @code{make}.
@item ignore-file
@samp{-i} in @code{ptx}.
@samp{-I} in @code{m4}.
@item include-dir
-@samp{-I} in Make.
+@samp{-I} in @code{make}.
@item incremental
@samp{-G} in @code{tar}.
Used in @code{date}
@item jobs
-@samp{-j} in Make.
+@samp{-j} in @code{make}.
@item just-print
-@samp{-n} in Make.
+@samp{-n} in @code{make}.
@item keep-going
-@samp{-k} in Make.
+@samp{-k} in @code{make}.
@item keep-files
@samp{-k} in @code{csplit}.
@samp{-N} in @code{ls}.
@item load-average
-@samp{-l} in Make.
+@samp{-l} in @code{make}.
@item login
Used in @code{su}.
@samp{-d} in @code{cpio}.
@item makefile
-@samp{-f} in Make.
+@samp{-f} in @code{make}.
@item mapped
Used in GDB.
@samp{-l} in @code{xargs}.
@item max-load
-@samp{-l} in Make.
+@samp{-l} in @code{make}.
@item max-procs
@samp{-P} in @code{xargs}.
@samp{-a} in @code{shar}.
@item new-file
-@samp{-W} in Make.
+@samp{-W} in @code{make}.
@item no-builtin-rules
-@samp{-r} in Make.
+@samp{-r} in @code{make}.
@item no-character-count
@samp{-w} in @code{shar}.
@samp{-2} in @code{wdiff}.
@item no-keep-going
-@samp{-S} in Make.
+@samp{-S} in @code{make}.
@item no-lines
@samp{-l} in Bison.
@samp{-o} in @code{tar}.
@item old-file
-@samp{-o} in Make.
+@samp{-o} in @code{make}.
@item one-file-system
@samp{-l} in @code{tar}, @code{cp}, and @code{du}.
@samp{-L} in @code{cmp}.
@item print-data-base
-@samp{-p} in Make.
+@samp{-p} in @code{make}.
@item print-directory
-@samp{-w} in Make.
+@samp{-w} in @code{make}.
@item print-file-name
@samp{-o} in @code{nm}.
@samp{-X} in @code{shar}.
@item question
-@samp{-q} in Make.
+@samp{-q} in @code{make}.
@item quiet
Used in many programs to inhibit the usual output. Every
Used in GDB.
@item recon
-@samp{-n} in Make.
+@samp{-n} in @code{make}.
@item record-number
@samp{-R} in @code{tar}.
Used in @code{chgrp}, @code{chown}, @code{cp}, @code{ls}, @code{diff},
and @code{rm}.
-@item reference-limit
-Used in @code{makeinfo}.
+@item reference
+@samp{-r} in @code{touch}.
@item references
@samp{-r} in @code{ptx}.
@samp{-S} in @code{shar}.
@item stop
-@samp{-S} in Make.
+@samp{-S} in @code{make}.
@item strict
@samp{-s} in @code{recode}.
@samp{-c} in @code{du}.
@item touch
-@samp{-t} in Make, @code{ranlib}, and @code{recode}.
+@samp{-t} in @code{make}, @code{ranlib}, and @code{recode}.
@item trace
@samp{-t} in @code{m4}.
@samp{-V} in @code{tar}.
@item what-if
-@samp{-W} in Make.
+@samp{-W} in @code{make}.
@item whole-size-limit
@samp{-l} in @code{shar}.
@samp{-z} in @code{gprof}.
@end table
+@node OID Allocations
+@section OID Allocations
+@cindex OID allocations for GNU
+@cindex SNMP
+@cindex LDAP
+@cindex X.509
+
+The OID (object identifier) 1.3.6.1.4.1.11591 has been assigned to the
+GNU Project (thanks to Werner Koch). These are used for SNMP, LDAP,
+X.509 certificates, and so on. The web site
+@url{http://www.alvestrand.no/objectid} has a (voluntary) listing of
+many OID assignments.
+
+If you need a new slot for your GNU package, write
+@email{maintainers@@gnu.org}. Here is a list of arcs currently
+assigned:
+
+@example
+@include gnu-oids.texi
+@end example
+
+
@node Memory Usage
@section Memory Usage
@cindex memory usage
If your program creates complicated data structures, just make them in
memory and give a fatal error if @code{malloc} returns zero.
+@pindex valgrind
+@cindex memory leak
+Memory leak detectors such as @command{valgrind} can be useful, but
+don't complicate a program merely to avoid their false alarms. For
+example, if memory is used until just before a process exits, don't
+free it simply to silence a leak detector.
+
@node File Usage
@section File Usage
@cindex file usage
If you want to do this, then do. The compiler should be your servant,
not your master.
+@pindex clang
+@pindex lint
+Don't make the program ugly just to placate static analysis tools such
+as @command{lint}, @command{clang}, and GCC with extra warnings
+options such as @option{-Wconversion} and @option{-Wundef}. These
+tools can help find bugs and unclear code, but they can also generate
+so many false alarms that that it hurts readability to silence them
+with unnecessary casts, wrappers, and other complications. For
+example, please don't insert casts to @code{void} or calls to
+do-nothing functions merely to pacify a lint checker.
+
Declarations of external functions and functions to appear later in the
source file should all go in one place near the beginning of the file
(somewhere before the first function definition in the file), or else
all its uses. This makes the program even cleaner.
Don't use local variables or parameters that shadow global identifiers.
+GCC's @samp{-Wshadow} option can detect this problem.
@cindex multiple variables in a line
Don't declare multiple variables in one declaration that spans lines.
fatal ("virtual memory exhausted");
@end example
-@pindex lint
-Don't make the program ugly to placate @code{lint}. Please don't insert any
-casts to @code{void}. Zero without a cast is perfectly fine as a null
-pointer constant, except when calling a varargs function.
+This example uses zero without a cast as a null pointer constant.
+This is perfectly fine, except that a cast is needed when calling a
+varargs function or when using @code{sizeof}.
@node Names
@section Naming Variables, Functions, and Files
The change log file is normally called @file{ChangeLog} and covers an
entire directory. Each directory can have its own change log, or a
-directory can use the change log of its parent directory--it's up to
+directory can use the change log of its parent directory---it's up to
you.
Another alternative is to record change log information with a version
to a @file{ChangeLog} file using @code{rcs2log}; in Emacs, the command
@kbd{C-x v a} (@code{vc-update-change-log}) does the job.
-There's no need to describe the full purpose of the changes or how they
-work together. If you think that a change calls for explanation, you're
-probably right. Please do explain it---but please put the explanation
-in comments in the code, where people will see it whenever they see the
-code. For example, ``New function'' is enough for the change log when
-you add a function, because there should be a comment before the
-function definition to explain what it does.
+There's no need to describe the full purpose of the changes or how
+they work together. However, sometimes it is useful to write one line
+to describe the overall purpose of a change or a batch of changes. If
+you think that a change calls for explanation, you're probably right.
+Please do explain it---but please put the full explanation in comments
+in the code, where people will see it whenever they see the code. For
+example, ``New function'' is enough for the change log when you add a
+function, because there should be a comment before the function
+definition to explain what it does.
In the past, we recommended not mentioning changes in non-software
files (manuals, help files, etc.) in change logs. However, we've been
advised that it is a good idea to include them, for the sake of
copyright records.
-However, sometimes it is useful to write one line to describe the
-overall purpose of a batch of changes.
-
The easiest way to add an entry to @file{ChangeLog} is with the Emacs
command @kbd{M-x add-change-log-entry}. An entry should have an
asterisk, the name of the changed file, and then in parentheses the name
is more authoritative. The note should say how to access the Texinfo
documentation.
-Be sure that man pages include a copyright statement and free
-license. The simple all-permissive license is appropriate for simple
-man pages:
-
-@example
-Copying and distribution of this file, with or without modification,
-are permitted in any medium without royalty provided the copyright
-notice and this notice are preserved.
-@end example
+Be sure that man pages include a copyright statement and free license.
+The simple all-permissive license is appropriate for simple man pages
+(@pxref{License Notices for Other Files,,,maintain,Information for GNU
+Maintainers}).
For long man pages, with enough explanation and documentation that
they can be considered true manuals, use the GFDL (@pxref{License for
Each GNU distribution should come with a shell script named
@code{configure}. This script is given arguments which describe the
kind of machine and system you want to compile the program for.
-
The @code{configure} script must record the configuration options so
that they affect compilation.
-One way to do this is to make a link from a standard name such as
-@file{config.h} to the proper configuration file for the chosen system.
-If you use this technique, the distribution should @emph{not} contain a
-file named @file{config.h}. This is so that people won't be able to
-build the program without configuring it first.
+The description here is the specification of the interface for the
+@code{configure} script in GNU packages. Many packages implement it
+using GNU Autoconf (@pxref{Top,, Introduction, autoconf, Autoconf})
+and/or GNU Automake (@pxref{Top,, Introduction, automake, Automake}),
+but you do not have to use these tools. You can implement it any way
+you like; for instance, by making @code{configure} be a wrapper around
+a completely different configuration system.
+
+Another way for the @code{configure} script to operate is to make a
+link from a standard name such as @file{config.h} to the proper
+configuration file for the chosen system. If you use this technique,
+the distribution should @emph{not} contain a file named
+@file{config.h}. This is so that people won't be able to build the
+program without configuring it first.
Another thing that @code{configure} can do is to edit the Makefile. If
you do this, the distribution should @emph{not} contain a file named
CC=gcc ./configure
@end example
as it helps to recreate the same configuration later with
-@file{config.status}.
+@file{config.status}. However, both methods should be supported.
@end table
All @code{configure} scripts should accept all of the ``detail''
The @file{README} file should also refer to the file which contains the
copying conditions. The GNU GPL, if used, should be in a file called
@file{COPYING}. If the GNU LGPL is used, it should be in a file called
-@file{COPYING.LIB}.
+@file{COPYING.LESSER}.
Naturally, all the source files must be in the distribution. It is okay
to include non-source files in the distribution, provided they are
distribution. So if you do distribute non-source files, always make
sure they are up to date when you make a new distribution.
-Make sure that the directory into which the distribution unpacks (as
-well as any subdirectories) are all world-writable (octal mode 777).
-This is so that old versions of @code{tar} which preserve the
-ownership and permissions of the files from the tar archive will be
-able to extract all the files even if the user is unprivileged.
-
-Make sure that all the files in the distribution are world-readable.
+Make sure that all the files in the distribution are world-readable, and
+that directories are world-readable and world-searchable (octal mode 755).
+We used to recommend that all directories in the distribution also be
+world-writable (octal mode 777), because ancient versions of @code{tar}
+would otherwise not cope when extracting the archive as an unprivileged
+user. That can easily lead to security issues when creating the archive,
+however, so now we recommend against that.
Don't include any symbolic links in the distribution itself. If the tar
file contains symbolic links, then people cannot even unpack it on
By contrast, it is ok to refer to journal articles and textbooks in
the comments of a program for explanation of how it functions, even
though they are non-free. This is because we don't include such
-things in the GNU system even they are free---they are outside the
+things in the GNU system even if they are free---they are outside the
scope of what a software distribution needs to include.
Referring to a web site that describes or recommends a non-free
time-stamp-start: "@set lastupdate "
time-stamp-end: "$"
time-stamp-format: "%:b %:d, %:y"
-compile-command: "make just-standards"
+compile-command: "cd work.s && make"
End:
projects / gnulib.git / blobdiff