@setfilename standards.info
@settitle GNU Coding Standards
@c This date is automagically updated when you save this file:
-@set lastupdate May 26, 2012
+@set lastupdate December 17, 2013
@c %**end of header
@dircategory GNU organization
Copyright @copyright{} 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
-2011, 2012 Free Software Foundation, Inc.
+2011, 2012, 2013 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 1.3 or
@cindex programming languages
When you want to use a language that gets compiled and runs at high
-speed, the best language to use is C. Using another language is like
-using a non-standard feature: it will cause trouble for users. Even if
-GCC supports the other language, users may find it inconvenient to have
-to install the compiler for that other language in order to build your
-program. For example, if you write your program in C++, people will
-have to install the GNU C++ compiler in order to compile your program.
-
-C has one other advantage over C++ and other compiled languages: more
-people know C, so more people will find it easy to read and modify the
-program if it is written in C.
-
-So in general it is much better to use C, rather than the
-comparable alternatives.
-
-But there are two exceptions to that conclusion:
-
-@itemize @bullet
-@item
-It is no problem to use another language to write a tool specifically
-intended for use with that language. That is because the only people
-who want to build the tool will be those who have installed the other
-language anyway.
-
-@item
-If an application is of interest only to a narrow part of the community,
-then the question of which language it is written in has less effect on
-other people, so you may as well please yourself.
-@end itemize
+speed, the best language to use is C. C++ is ok too, but please don't
+make heavy use of templates. So is Java, if you compile it.
+
+When highest efficiency is not required, other languages commonly used
+in the free software community, such as Scheme, Python, Ruby, and
+Java, are OK too. Scheme, as implemented by GNU@tie{}Guile, plays a
+particular role in the GNU System: it is the preferred language to
+extend programs written in C/C++, and also a fine language for a wide
+range of applications. The more GNU components use Guile and Scheme,
+the more users are able to extend and combine them (@pxref{The Emacs
+Thesis,,, guile, GNU Guile Reference Manual}).
Many programs are designed to be extensible: they include an interpreter
for a language that is higher level than C. Often much of the program
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.
+using Guile is the path that will lead to overall consistency of the
+GNU system.
@node Compatibility
@section Compatibility with Other Implementations
-@cindex compatibility with C and @sc{posix} standards
-@cindex @sc{posix} compatibility
+@cindex compatibility with C and POSIX standards
+@cindex C compatibility
+@cindex POSIX compatibility
With occasional exceptions, utility programs and libraries for GNU
should be upward compatible with those in Berkeley Unix, and upward
compatible with Standard C if Standard C specifies their
-behavior, and upward compatible with @sc{posix} if @sc{posix} specifies
+behavior, and upward compatible with POSIX if POSIX specifies
their behavior.
When these standards conflict, it is useful to offer compatibility
modes for each of them.
@cindex options for compatibility
-Standard C and @sc{posix} prohibit many kinds of extensions. Feel
+Standard C and POSIX prohibit many kinds of extensions. Feel
free to make the extensions anyway, and include a @samp{--ansi},
@samp{--posix}, or @samp{--compatible} option to turn them off.
However, if the extension has a significant chance of breaking any real
should try to redesign its interface to make it upward compatible.
@cindex @code{POSIXLY_CORRECT}, environment variable
-Many GNU programs suppress extensions that conflict with @sc{posix} if the
+Many GNU programs suppress extensions that conflict with POSIX if the
environment variable @code{POSIXLY_CORRECT} is defined (even if it is
defined with a null value). Please make your program recognize this
variable if appropriate.
@node Standard C
@section Standard C and Pre-Standard C
-@cindex @sc{ansi} C standard
+@cindex ANSI C standard
1989 Standard C is widespread enough now that it is ok to use its
-features in new programs. There is one exception: do not ever use the
+features in programs. There is one exception: do not ever use the
``trigraph'' feature of Standard C.
-1999 Standard C is not widespread yet, so please do not require its
-features in programs. It is ok to use its features if they are present.
+The 1999 and 2011 editions of Standard C are not fully supported
+on all platforms. If you aim to support compilation by
+compilers other than GCC, you should not require these C
+features in your programs. It is ok to use these features
+conditionally when the compiler supports them.
+
+If your program is only meant to compile with GCC, then you can
+use these features if GCC supports them, when they give substantial
+benefit.
However, it is easy to support pre-standard compilers in most programs,
-so if you know how to do that, feel free. If a program you are
-maintaining has such support, you should try to keep it working.
+so if you know how to do that, feel free.
@cindex function prototypes
To support pre-standard C, instead of writing function definitions in
@cindex signal handling
The preferred signal handling facilities are the BSD variant of
-@code{signal}, and the @sc{posix} @code{sigaction} function; the
+@code{signal}, and the POSIX @code{sigaction} function; the
alternative USG @code{signal} interface is an inferior design.
-Nowadays, using the @sc{posix} signal functions may be the easiest way
+Nowadays, using the POSIX signal functions may be the easiest way
to make a program portable. If you use @code{signal}, then on GNU/Linux
systems running GNU libc version 1, you should include
@file{bsd/signal.h} instead of @file{signal.h}, so as to get BSD
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
@section Standards for Command Line Interfaces
@cindex command-line interface
@findex getopt
-It is a good idea to follow the @sc{posix} guidelines for the
+It is a good idea to follow the POSIX guidelines for the
command-line options of a program. The easiest way to do this is to use
@code{getopt} to parse them. Note that the GNU version of @code{getopt}
will normally permit options anywhere among the arguments unless the
-special argument @samp{--} is used. This is not what @sc{posix}
+special argument @samp{--} is used. This is not what POSIX
specifies; it is a GNU extension.
@cindex long-named options
Finally, here is the table of our suggested license abbreviations.
Any abbreviation can be followed by @samp{v@var{version}[+]}, meaning
that particular version, or later versions with the @samp{+}, as shown
-above.
+above. In the case of a GNU license, @emph{always} indicate the permitted
+versions in this way.
In the case of exceptions for extra permissions with the GPL, we use
@samp{/} for a separator; the version number can follow the license
@url{http://www.apache.org/@/licenses}.
@item Artistic
-The Artistic license used for Perl, @url{http://www.perlfoundation.org/@/legal}.
+The Artistic license used for Perl, @url{http://dev.perl.org/licenses/artistic.html}.
@item Expat
The Expat license, @url{http://www.jclark.com/@/xml/@/copying.txt}.
@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
+GNU Project (thanks to Sergey Poznyakoff). 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.
@section Formatting Your Source Code
@cindex formatting source code
+@cindex line length
+@cindex length of source lines
+Please keep the length of source lines to 79 characters or less, for
+maximum readability in the widest range of environments.
+
@cindex open brace
@cindex braces, in C source
@cindex function definitions, formatting
not paramount.
The primary purpose of GNU software is to run on top of the GNU kernel,
-compiled with the GNU C compiler, on various types of @sc{cpu}. So the
+compiled with the GNU C compiler, on various types of CPU. So the
kinds of portability that are absolutely necessary are quite limited.
But it is important to support Linux-based GNU systems, since they
are the form of GNU that is popular.
Avoid using the format of semi-internal data bases (e.g., directories)
when there is a higher-level alternative (@code{readdir}).
-@cindex non-@sc{posix} systems, and portability
+@cindex non-POSIX systems, and portability
As for systems that are not like Unix, such as MSDOS, Windows, VMS, MVS,
and older Macintosh systems, supporting them is often a lot of work.
When that is the case, it is better to spend your time adding features
to move your code into other GNU programs.
@node CPU Portability
-@section Portability between @sc{cpu}s
+@section Portability between CPUs
@cindex data types, and portability
@cindex portability, and data types
-Even GNU systems will differ because of differences among @sc{cpu}
+Even GNU systems will differ because of differences among CPU
types---for example, difference in byte ordering and alignment
requirements. It is absolutely essential to handle these differences.
However, don't make any effort to cater to the possibility that an
Historically, C implementations differed substantially, and many
systems lacked a full implementation of ANSI/ISO C89. Nowadays,
-however, very few systems lack a C89 compiler and GNU C supports
-almost all of C99. Similarly, most systems implement POSIX.1-1993
-libraries and tools, and many have POSIX.1-2001.
+however, all practical systems have a C89 compiler and GNU C supports
+almost all of C99 and some of C11. Similarly, most systems implement
+POSIX.1-2001 libraries and tools, and many have POSIX.1-2008.
Hence, there is little reason to support old C or non-POSIX systems,
-and you may want to take advantage of C99 and POSIX-1.2001 to write
+and you may want to take advantage of standard C and POSIX to write
clearer, more portable, or faster code. You should use standard
interfaces where possible; but if GNU extensions make your program
more maintainable, powerful, or otherwise better, don't hesitate to
@section Mmap
@findex mmap
-Don't assume that @code{mmap} either works on all files or fails
-for all files. It may work on some files and fail on others.
+If you use @code{mmap} to read or write files, don't assume it either
+works on all files or fails for all files. It may work on some files
+and fail on others.
The proper way to use @code{mmap} is to try it on the specific file for
which you want to use it---and if @code{mmap} doesn't work, fall back on
the framework for a beginner to understand the rest of the manual. The
Bison manual provides a good example of how to do this.
-To serve as a reference, a manual should have an Index that list all the
-functions, variables, options, and important concepts that are part of
-the program. One combined Index should do for a short manual, but
-sometimes for a complex package it is better to use multiple indices.
-The Texinfo manual includes advice on preparing good index entries, see
-@ref{Index Entries, , Making Index Entries, texinfo, GNU Texinfo}, and
-see @ref{Indexing Commands, , Defining the Entries of an
+To serve as a reference, a manual should have an Index that lists all
+the functions, variables, options, and important concepts that are
+part of the program. One combined Index should do for a short manual,
+but sometimes for a complex package it is better to use multiple
+indices. The Texinfo manual includes advice on preparing good index
+entries, see @ref{Index Entries, , Making Index Entries, texinfo, GNU
+Texinfo}, and see @ref{Indexing Commands, , Defining the Entries of an
Index, texinfo, GNU Texinfo}.
Don't use Unix man pages as a model for how to write GNU documentation;
@node Change Log Concepts
@subsection Change Log Concepts
+@cindex change set
+@cindex batch of changes
You can think of the change log as a conceptual ``undo list'' which
explains how earlier versions were different from the current version.
-People can see the current version; they don't need the change log
-to tell them what is in it. What they want from a change log is a
-clear explanation of how the earlier version differed.
+People can see the current version; they don't need the change log to
+tell them what is in it. What they want from a change log is a clear
+explanation of how the earlier version differed. Each @dfn{entry} in
+a change log describes either an individual change or the smallest
+batch of changes that belong together, also known as a @dfn{change
+set}.
+@cindex title, change log entry
+@cindex description, change log entry
+For later reference or for summarizing, sometimes it is useful to
+start the entry with a one-line description (sometimes called a
+@dfn{title}) to describe its overall purpose.
+
+In the past, we recommended not mentioning changes in non-software
+files (manuals, help files, media 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.
The change log file is normally called @file{ChangeLog} and covers an
entire directory. Each directory can have its own change log, or a
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. 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.
+For changes to code, 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 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, media 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.
+For changes to files that do not support a comment syntax (e.g., media
+files), it is ok to include the full explanation in the change log file,
+after the title and before the list of individual 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
-of the changed functions, variables or whatever, followed by a colon.
-Then describe the changes you made to that function or variable.
+command @kbd{M-x add-change-log-entry}. An individual change should
+have an asterisk, the name of the changed file, and then in
+parentheses the name of the changed functions, variables or whatever,
+followed by a colon. Then describe the changes you made to that
+function or variable.
+
@node Style of Change Logs
@subsection Style of Change Logs
this is not a good idea, since searching for @code{jump-to-register} or
@code{insert-register} would not find that entry.
-Separate unrelated change log entries with blank lines. When two
-entries represent parts of the same change, so that they work together,
-then don't put blank lines between them. Then you can omit the file
-name and the asterisk when successive entries are in the same file.
+Separate unrelated change log entries with blank lines. Don't put
+blank lines between individual changes of an entry. You can omit the
+file name and the asterisk when successive individual changes are in
+the same file.
Break long lists of function names by closing continued lines with
@samp{)}, rather than @samp{,}, and opening the continuation with
a certain macro is @emph{not} defined:
@example
-(gethostname) [!HAVE_SOCKETS]: Replace with winsock version.
+* host.c (gethostname) [!HAVE_SOCKETS]: Replace with winsock version.
@end example
+
@node Indicating the Part Changed
@subsection Indicating the Part Changed
@example
--prefix --exec-prefix --bindir --sbindir --libexecdir --sysconfdir
---sharedstatedir --localstatedir --libdir --includedir --oldincludedir
+--sharedstatedir --localstatedir --runstatedir
+--libdir --includedir --oldincludedir
--datarootdir --datadir --infodir --localedir --mandir --docdir
--htmldir --dvidir --pdfdir --psdir
@end example
@section Making Releases
@cindex packaging
+@cindex version numbers, for releases
You should identify each release with a pair of version numbers, a
major version and a minor. We have no objection to using more than
two numbers, but it is very unlikely that you really need them.
source files by programs under the control of the Makefile.
@cindex @file{README} file
-The distribution should contain a file named @file{README} which gives
-the name of the package, and a general description of what it does. It
-is also good to explain the purpose of each of the first-level
-subdirectories in the package, if there are any. The @file{README} file
-should either state the version number of the package, or refer to where
-in the package it can be found.
-
-The @file{README} file should refer to the file @file{INSTALL}, which
-should contain an explanation of the installation procedure.
-
-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
+The distribution should contain a file named @file{README} with a
+general overview of the package:
+
+@itemize
+@item the name of the package;
+
+@item the version number of the package, or refer to where in the
+package the version can be found;
+
+@item a general description of what the package does;
+
+@item a reference to the file @file{INSTALL}, which
+should in turn contain an explanation of the installation procedure;
+
+@item a brief explanation of any unusual top-level directories or
+files, or other hints for readers to find their way around the source;
+
+@item a reference 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.LESSER}.
+@end itemize
Naturally, all the source files must be in the distribution. It is
okay to include non-source files in the distribution along with the
with the source they are made from, and machine-independent, so that
normal building of the distribution will never modify them. We
commonly include non-source files produced by Autoconf, Automake,
-Bison, @code{lex}, @TeX{}, and @code{makeinfo}; this helps avoid
+Bison, @code{flex}, @TeX{}, and @code{makeinfo}; this helps avoid
unnecessary dependencies between our distributions, so that users can
-install whichever packages they want to install.
+install whichever versions of whichever packages they like. Do not
+induce new dependencies on other software lightly.
Non-source files that might actually be modified by building and
installing the program should @strong{never} be included in the
projects / gnulib.git / blobdiff