@setfilename standards.info
@settitle GNU Coding Standards
@c This date is automagically updated when you save this file:
-@set lastupdate August 18, 2005
+@set lastupdate August 19, 2006
@c %**end of header
@dircategory GNU organization
The GNU coding standards, last updated @value{lastupdate}.
Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
-2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
+2001, 2002, 2003, 2004, 2005, 2006 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 1.1
+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.
* Managing Releases:: The Release Process
* References:: References to Non-Free Software or Documentation
* Copying This Manual:: How to Make Copies of This Manual
-* Index::
+* Index::
@end menu
more maintainable by others.
The GNU Hello program serves as an example of how to follow the GNU
-coding standards for a trivial program which prints @samp{Hello,
-world!}. @uref{http://www.gnu.org/software/hello/hello.html}.
+coding standards for a trivial program.
+@uref{http://www.gnu.org/software/hello/hello.html}.
@node Legal Issues
@chapter Keeping Free Software Free
Trademark acknowledgements are the statements that such-and-such is a
trademark of so-and-so. The GNU Project has no objection to the basic
-idea of trademarks, but these acknowledgements feel like kowtowing,
+idea of trademarks, but these acknowledgements feel like kowtowing,
and there is no legal requirement for them, so we don't use them.
What is legally required, as regards other people's trademarks, is to
technique.
@cindex GUILE
-The standard extensibility interpreter for GNU software is GUILE, which
-implements the language Scheme (an especially clean and simple dialect
-of Lisp). @uref{http://www.gnu.org/software/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.
+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.
@node Compatibility
@section Compatibility with Other Implementations
command line interface, and how libraries should behave.
@menu
+* Non-GNU Standards:: We consider standards such as POSIX;
+ we don't "obey" them.
* Semantics:: Writing robust programs
* Libraries:: Library behavior
* Errors:: Formatting error messages
* File Usage:: Which files to use, and where
@end menu
+@node Non-GNU Standards
+@section Non-GNU Standards
+
+The GNU Project regards standards published by other organizations as
+suggestions, not orders. We consider those standards, but we do not
+``obey'' them. In developing a GNU program, you should implement
+an outside standard's specifications when that makes the GNU system
+better overall in an objective sense. When it doesn't, you shouldn't.
+
+In most cases, following published standards is convenient for
+users---it means that their programs or scripts will work more
+portably. For instance, GCC implements nearly all the features of
+Standard C as specified by that standard. C program developers would
+be unhappy if it did not. And GNU utilities mostly follow
+specifications of POSIX.2; shell script writers and users would be
+unhappy if our programs were incompatible.
+
+But we do not follow either of these specifications rigidly, and there
+are specific points on which we decided not to follow them, so as to
+make the GNU system better for users.
+
+For instance, Standard C says that nearly all extensions to C are
+prohibited. How silly! GCC implements many extensions, some of which
+were later adopted as part of the standard. If you want these
+constructs to give an error message as ``required'' by the standard,
+you must specify @samp{--pedantic}, which was implemented only so that
+we can say ``GCC is a 100% implementation of the standard,'' not
+because there is any reason to actually use it.
+
+POSIX.2 specifies that @samp{df} and @samp{du} must output sizes by
+default in units of 512 bytes. What users want is units of 1k, so
+that is what we do by default. If you want the ridiculous behavior
+``required'' by POSIX, you must set the environment variable
+@samp{POSIXLY_CORRECT} (which was originally going to be named
+@samp{POSIX_ME_HARDER}).
+
+GNU utilities also depart from the letter of the POSIX.2 specification
+when they support long-named command-line options, and intermixing
+options with ordinary arguments. This minor incompatibility with
+POSIX is never a problem in practice, and it is very useful.
+
+In particular, don't reject a new feature, or remove an old one,
+merely because a standard says it is ``forbidden'' or ``deprecated.''
+
@node Semantics
@section Writing Robust Programs
@example
@var{source-file-name}:@var{lineno}:@var{column}: @var{message}
-@var{source-file-name}:@var{lineno}.@var{column}: @var{message}
+@var{source-file-name}:@var{lineno}.@var{column}: @var{message}
@end example
(preferably @samp{-o} or @samp{--output}). Even if you allow an output
file name as an ordinary argument for compatibility, try to provide an
option as another way to specify it. This will lead to more consistency
-among GNU utilities, and fewer idiosyncracies for users to remember.
+among GNU utilities, and fewer idiosyncrasies for users to remember.
@cindex standard command-line options
@cindex options, standard command-line
which changes were made---there's no need to list the years for previous
versions' changes. You don't have to mention the name of the program in
these notices, if that is inconvenient, since it appeared in the first
-line.
+line. (The rules are different for copyright notices in source files;
+see @ref{Copyright Notices,,,maintain,Information for GNU Maintainers}.)
Translations of the above lines must preserve the validity of the
copyright notices (@pxref{Internationalization}). If the translation's
character set supports it, the @samp{(C)} should be replaced with the
copyright symbol, as follows:
-@ifinfo
-(the official copyright symbol, which is the letter C in a circle);
-@end ifinfo
-@ifnotinfo
+@ifinfo
+(the official copyright symbol, which is the letter C in a circle);
+@end ifinfo
+@ifnotinfo
@copyright{}
-@end ifnotinfo
+@end ifnotinfo
Write the word ``Copyright'' exactly like that, in English. Do not
translate it into another language. International treaties recognize
@item socket
Specify a file descriptor for a network server to use for its socket,
instead of opening and binding a new socket. This provides a way to
-run, in a nonpriveledged process, a server that normally needs a
+run, in a non-privileged process, a server that normally needs a
reserved port number.
@item sort
@cindex open brace
@cindex braces, in C source
It is important to put the open-brace that starts the body of a C
-function in column zero, and avoid putting any other open-brace or
-open-parenthesis or open-bracket in column zero. Several tools look
-for open-braces in column zero to find the beginnings of C functions.
+function in column one, and avoid putting any other open-brace or
+open-parenthesis or open-bracket in column one. Several tools look
+for open-braces in column one to find the beginnings of C functions.
These tools will not work on code not formatted that way.
It is also important for function definitions to start the name of the
-function in column zero. This helps people to search for function
+function in column one. This helps people to search for function
definitions, and may also help certain tools recognize them. Thus,
using Standard C syntax, the format is this:
@end example
@noindent
-or, if you want to use Standard C syntax, format the definition like
+or, if you want to use traditional C syntax, format the definition like
this:
@example
static char *
-concat (s1, s2) /* Name starts in column zero here */
+concat (s1, s2) /* Name starts in column one here */
char *s1, *s2;
-@{ /* Open brace in column zero here */
+@{ /* Open brace in column one here */
@dots{}
@}
@end example
@cindex file-name limitations
@pindex doschk
You might want to make sure that none of the file names would conflict
-the files were loaded onto an MS-DOS file system which shortens the
+if the files were loaded onto an MS-DOS file system which shortens the
names. You can use the program @code{doschk} to test for this.
Some GNU programs were designed to limit themselves to file names of 14
@end example
1989 Standard C requires this to work, and we know of only one
-counterexample: 64-bit programs on Microsoft Windows IA-64. We will
+counterexample: 64-bit programs on Microsoft Windows. We will
leave it to those who want to port GNU programs to that environment
to figure out how to do it.
name} for the package. The text domain name is used to separate the
translations for this package from the translations for other packages.
Normally, the text domain name should be the same as the name of the
-package---for example, @samp{fileutils} for the GNU file utilities.
+package---for example, @samp{coreutils} for the GNU core utilities.
@cindex message text, and internationalization
To enable gettext to work well, avoid writing code that makes
Here is an example of what not to do:
-@example
-printf ("%d file%s processed", nfiles,
- nfiles != 1 ? "s" : "");
-@end example
+@smallexample
+printf ("%s is full", capacity > 5000000 ? "disk" : "floppy disk");
+@end smallexample
-@noindent
-The problem with that example is that it assumes that plurals are made
-by adding `s'. If you apply gettext to the format string, like this,
+If you apply gettext to all strings, like this,
-@example
-printf (gettext ("%d file%s processed"), nfiles,
- nfiles != 1 ? "s" : "");
-@end example
+@smallexample
+printf (gettext ("%s is full"),
+ capacity > 5000000 ? gettext ("disk") : gettext ("floppy disk"));
+@end smallexample
@noindent
-the message can use different words, but it will still be forced to use
-`s' for the plural. Here is a better way:
-
-@example
-printf ((nfiles != 1 ? "%d files processed"
- : "%d file processed"),
- nfiles);
-@end example
+the translator will hardly know that "disk" and "floppy disk" are meant to
+be substituted in the other string. Worse, in some languages (like French)
+the construction will not work: the translation of the word "full" depends
+on the gender of the first part of the sentence; it happens to be not the
+same for "disk" as for "floppy disk".
-@noindent
-This way, you can apply gettext to each of the two strings
-independently:
+Complete sentences can be translated without problems:
@example
-printf ((nfiles != 1 ? gettext ("%d files processed")
- : gettext ("%d file processed")),
- nfiles);
+printf (capacity > 5000000 ? gettext ("disk is full")
+ : gettext ("floppy disk is full"));
@end example
-@noindent
-This can be any method of forming the plural of the word for ``file'', and
-also handles languages that require agreement in the word for
-``processed''.
-
A similar problem appears at the level of sentence structure with this
code:
Adding @code{gettext} calls to this code cannot give correct results for
all languages, because negation in some languages requires adding words
at more than one place in the sentence. By contrast, adding
-@code{gettext} calls does the job straightfowardly if the code starts
+@code{gettext} calls does the job straightforwardly if the code starts
out like this:
@example
: "# Implicit rule search has not been done.\n");
@end example
+Another example is this one:
+
+@example
+printf ("%d file%s processed", nfiles,
+ nfiles != 1 ? "s" : "");
+@end example
+
+@noindent
+The problem with this example is that it assumes that plurals are made
+by adding `s'. If you apply gettext to the format string, like this,
+
+@example
+printf (gettext ("%d file%s processed"), nfiles,
+ nfiles != 1 ? "s" : "");
+@end example
+
+@noindent
+the message can use different words, but it will still be forced to use
+`s' for the plural. Here is a better way, with gettext being applied to
+the two strings independently:
+
+@example
+printf ((nfiles != 1 ? gettext ("%d files processed")
+ : gettext ("%d file processed")),
+ nfiles);
+@end example
+
+@noindent
+But this still doesn't work for languages like Polish, which has three
+plural forms: one for nfiles == 1, one for nfiles == 2, 3, 4, 22, 23, 24, ...
+and one for the rest. The GNU @code{ngettext} function solves this problem:
+
+@example
+printf (ngettext ("%d files processed", "%d file processed", nfiles),
+ nfiles);
+@end example
+
@node Character Set
@section Character Set
and @samp{'}. This is especially important if the output of your
program is ever likely to be parsed by another program.
-Quotation characters are a difficult area in the computing world at this
-time: there are no true left or right quote characters in ASCII, or even
-Latin1; the @samp{`} character we use was standardized as a grave
+Quotation characters are a difficult area in the computing world at
+this time: there are no true left or right quote characters in Latin1;
+the @samp{`} character we use was standardized there as a grave
accent. Moreover, Latin1 is still not universally usable.
Unicode contains the unambiguous quote characters required, and its
-common encoding UTF-8 is upward compatible with ASCII@. However,
-Unicode and UTF-8 are not universally well-supported, either.
+common encoding UTF-8 is upward compatible with Latin1. However,
+Unicode and UTF-8 are not universally well-supported, either.
This may change over the next few years, and then we will revisit
this.
converted automatically into Texinfo. It is ok to produce the Texinfo
documentation by conversion this way, as long as it gives good results.
-Programmers often find it most natural to structure the documentation
-following the structure of the implementation, which they know. But
-this structure is not necessarily good for explaining how to use the
-program; it may be irrelevant and confusing for a user.
-
-At every level, from the sentences in a paragraph to the grouping of
-topics into separate manuals, the right way to structure documentation
-is according to the concepts and questions that a user will have in mind
-when reading it. Sometimes this structure of ideas matches the
+Make sure your manual is clear to a reader who knows nothing about the
+topic and reads it straight through. This means covering basic topics
+at the beginning, and advanced topics only later. This also means
+defining every specialized term when it is first used.
+
+Programmers tend to carry over the structure of the program as the
+structure for its documentation. But this structure is not
+necessarily good for explaining how to use the program; it may be
+irrelevant and confusing for a user.
+
+Instead, the right way to structure documentation is according to the
+concepts and questions that a user will have in mind when reading it.
+This principle applies at every level, from the lowest (ordering
+sentences in a paragraph) to the highest (ordering of chapter topics
+within the manual). Sometimes this structure of ideas matches the
structure of the implementation of the software being documented---but
-often they are different. Often the most important part of learning to
-write good documentation is learning to notice when you are structuring
-the documentation like the implementation, and think about better
-alternatives.
+often they are different. An important part of learning to write good
+documentation is to learn to notice when you have unthinkingly
+structured the documentation like the implementation, stop yourself,
+and look for better alternatives.
For example, each program in the GNU system probably ought to be
documented in one manual; but this does not mean each program should
a computer program. Please use ``invalid'' for this, and reserve the
term ``illegal'' for activities prohibited by law.
+Please do not write @samp{()} after a function name just to indicate
+it is a function. @code{foo ()} is not a function, it is a function
+call with no arguments.
+
@node Doc Strings and Manuals
@section Doc Strings and Manuals
variables. The previous descriptions of functions and variables in the
section will also have given information about the topic. A description
written to stand alone would repeat some of that information; this
-redundance looks bad. Meanwhile, the informality that is acceptable in
+redundancy looks bad. Meanwhile, the informality that is acceptable in
a documentation string is totally unacceptable in a manual.
The only good way to use documentation strings in writing a good manual
history of how the conflicting concepts arose and who they came from.
@menu
-* Change Log Concepts::
-* Style of Change Logs::
-* Simple Changes::
-* Conditional Changes::
+* Change Log Concepts::
+* Style of Change Logs::
+* Simple Changes::
+* Conditional Changes::
* Indicating the Part Changed::
@end menu
alternatives for how to describe a machine. Thus,
@samp{athlon-pc-gnu/linux} would be a valid alias. There is a shell
script called
-@uref{http://savannah.gnu.org/cgi-bin/viewcvs/*checkout*/config/config/config.sub,
+@uref{http://savannah.gnu.org/@/cgi-bin/@/viewcvs/@/*checkout*/@/config/@/config/@/config.sub,
@file{config.sub}} that you can use as a subroutine to validate system
types and canonicalize aliases.
i686-pc-linux-gnu}. When the build type is not specified by an option
or argument, the @code{configure} script should normally guess it using
the shell script
-@uref{http://savannah.gnu.org/cgi-bin/viewcvs/*checkout*/config/config/config.guess,
+@uref{http://savannah.gnu.org/@/cgi-bin/@/viewcvs/@/*checkout*/@/config/@/config/@/config.guess,
@file{config.guess}}.
@cindex optional features, configure-time
Other options are permitted to specify in more detail the software
-or hardware present on the machine, and include or exclude optional
-parts of the package:
+or hardware present on the machine, to include or exclude optional parts
+of the package, or to adjust the name of some tools or arguments to them:
@table @samp
@item --enable-@var{feature}@r{[}=@var{parameter}@r{]}
Do not use a @samp{--with} option to specify the file name to use to
find certain files. That is outside the scope of what @samp{--with}
options are for.
+
+@item @var{variable}=@var{value}
+Set the value of the variable @var{variable} to @var{value}. This is
+used to override the default values of commands or arguments in the
+build process. For example, the user could issue @samp{configure
+CFLAGS=-g CXXFLAGS=-g} to build with debugging information and without
+the default optimization.
+
+Specifying variables as arguments to @code{configure}, like this:
+@example
+./configure CC=gcc
+@end example
+is preferable to setting them in environment variables:
+@example
+CC=gcc ./configure
+@end example
+as it helps to recreate the same configuration later with
+@file{config.status}.
@end table
-All @code{configure} scripts should accept all of these ``detail''
-options, whether or not they make any difference to the particular
-package at hand. In particular, they should accept any option that
-starts with @samp{--with-} or @samp{--enable-}. This is so users will
-be able to configure an entire GNU source tree at once with a single set
-of options.
+All @code{configure} scripts should accept all of the ``detail''
+options and the variable settings, whether or not they make any
+difference to the particular package at hand. In particular, they
+should accept any option that starts with @samp{--with-} or
+@samp{--enable-}. This is so users will be able to configure an
+entire GNU source tree at once with a single set of options.
You will note that the categories @samp{--with-} and @samp{--enable-}
are narrow: they @strong{do not} provide a place for any sort of option
problem.
The GNU definition of free software is found on the GNU web site at
-@url{http://www.gnu.org/philosophy/free-sw.html}. A list of
+@url{http://www.gnu.org/philosophy/free-sw.html}, and the definition
+of free documentation is found at
+@url{http://www.gnu.org/philosophy/free-doc.html}. A list of
important licenses and whether they qualify as free is in
-@url{http://www.gnu.org/licenses/license-list.html}. The terms
+@url{http://www.gnu.org/@/licenses/@/license-list.html}. The terms
``free'' and ``non-free'', used in this document, refer to that
definition. If it is not clear whether a license qualifies as free
under this definition, please ask the GNU Project by writing to
projects / gnulib.git / blobdiff