@setfilename standards.info
@settitle GNU Coding Standards
@c This date is automagically updated when you save this file:
-@set lastupdate February 17, 2010
+@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, 2009, 2010 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 1.3 or
@url{http://lists.gnu.org/mailman/listinfo/gnustandards-commit}.
Archives are also available there.
-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.
+@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.
* 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.
@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.
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}.
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
@cindex long option names
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
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
projects / gnulib.git / blobdiff