Update

[gnulib.git] / doc / standards.texi

diff --git a/doc/standards.texi b/doc/standards.texi
index 6c9532c..75c154c 100644 (file)
--- a/doc/standards.texi
+++ b/doc/standards.texi
@@ -3,7 +3,7 @@
 @setfilename standards.info
 @settitle GNU Coding Standards
 @c This date is automagically updated when you save this file:
 @setfilename standards.info
 @settitle GNU Coding Standards
 @c This date is automagically updated when you save this file:

-@set lastupdate November 29, 2004
+@set lastupdate February 8, 2006

 @c %**end of header
 
 @dircategory GNU organization
 @c %**end of header
 
 @dircategory GNU organization


@@ -33,7 +33,7 @@
 The GNU coding standards, last updated @value{lastupdate}.
 
 Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
 The GNU coding standards, last updated @value{lastupdate}.
 
 Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,

-2001, 2002, 2003, 2004 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
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.1


@@ -239,9 +239,9 @@ C'' as a label for the compiler rather than for the language.
 
 Please don't use ``win'' as an abbreviation for Microsoft Windows in
 GNU software or documentation.  In hacker terminology, calling
 
 Please don't use ``win'' as an abbreviation for Microsoft Windows in
 GNU software or documentation.  In hacker terminology, calling

-something a "win" is a form of praise.  If you wish to praise
+something a ``win'' is a form of praise.  If you wish to praise

 Microsoft Windows when speaking on your own, by all means do so, but
 Microsoft Windows when speaking on your own, by all means do so, but

-not in GNU software.  Usually we write the word ``windows'' in full,
+not in GNU software.  Usually we write the name ``Windows'' in full,

 but when brevity is very important (as in file names and sometimes
 symbol names), we abbreviate it to ``w''.  For instance, the files and
 functions in Emacs that deal with Windows start with @samp{w32}.
 but when brevity is very important (as in file names and sometimes
 symbol names), we abbreviate it to ``w''.  For instance, the files and
 functions in Emacs that deal with Windows start with @samp{w32}.


@@ -518,6 +518,8 @@ software.  It also describes general standards for error messages, the
 command line interface, and how libraries should behave.
 
 @menu
 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
 * Semantics::                   Writing robust programs
 * Libraries::                   Library behavior
 * Errors::                      Formatting error messages


@@ -529,6 +531,50 @@ command line interface, and how libraries should behave.
 * File Usage::                  Which files to use, and where
 @end menu
 
 * 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
 
 @node Semantics
 @section Writing Robust Programs
 


@@ -850,7 +896,7 @@ All programs should support two standard options: @samp{--version}
 and @samp{--help}.  CGI programs should accept these as command-line
 options, and also if given as the @env{PATH_INFO}; for instance,
 visiting @url{http://example.org/p.cgi/--help} in a browser should
 and @samp{--help}.  CGI programs should accept these as command-line
 options, and also if given as the @env{PATH_INFO}; for instance,
 visiting @url{http://example.org/p.cgi/--help} in a browser should

-output the same information as inokving @samp{p.cgi --help} from the
+output the same information as invoking @samp{p.cgi --help} from the

 command line.
 
 @table @code
 command line.
 
 @table @code


@@ -1492,9 +1538,7 @@ Used in @code{gawk}.
 Used in @code{su}.
 
 @item machine
 Used in @code{su}.
 
 @item machine

-No listing of which programs already use this;
-someone should check to
-see if any actually do, and tell @email{gnu@@gnu.org}.
+Used in @code{uname}.

 
 @item macro-name
 @samp{-M} in @code{ptx}.
 
 @item macro-name
 @samp{-M} in @code{ptx}.


@@ -2144,6 +2188,8 @@ when writing GNU software.
 * CPU Portability::             Supporting the range of CPU types
 * System Functions::            Portability and ``standard'' library functions
 * Internationalization::        Techniques for internationalization
 * CPU Portability::             Supporting the range of CPU types
 * System Functions::            Portability and ``standard'' library functions
 * Internationalization::        Techniques for internationalization

+* Character Set::               Use ASCII by default.
+* Quote Characters::            Use `...' in the C locale.

 * Mmap::                        How you can safely use @code{mmap}.
 @end menu
 
 * Mmap::                        How you can safely use @code{mmap}.
 @end menu
 


@@ -2154,21 +2200,20 @@ when writing GNU software.
 @cindex open brace
 @cindex braces, in C source
 It is important to put the open-brace that starts the body of a C
 @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
 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,
 definitions, and may also help certain tools recognize them.  Thus,

-the proper format is this:
+using Standard C syntax, the format is this:

 
 @example
 static char *
 
 @example
 static char *

-concat (s1, s2)        /* Name starts in column zero here */
-     char *s1, *s2;
-@{                     /* Open brace in column zero here */
+concat (char *s1, char *s2)
+@{

   @dots{}
 @}
 @end example
   @dots{}
 @}
 @end example


@@ -2179,8 +2224,9 @@ this:
 
 @example
 static char *
 
 @example
 static char *

-concat (char *s1, char *s2)
-@{
+concat (s1, s2)        /* Name starts in column one here */
+     char *s1, *s2;
+@{                     /* Open brace in column one here */

   @dots{}
 @}
 @end example
   @dots{}
 @}
 @end example


@@ -2298,7 +2344,13 @@ page.  The formfeeds should appear alone on lines by themselves.
 @cindex commenting
 
 Every program should start with a comment saying briefly what it is for.
 @cindex commenting
 
 Every program should start with a comment saying briefly what it is for.

-Example: @samp{fmt - filter for simple filling of text}.
+Example: @samp{fmt - filter for simple filling of text}.  This comment
+should be at the top of the source file containing the @samp{main}
+function of the program.
+
+Also, please write a brief comment at the start of each source file,
+with the file name and a line or two about the overall purpose of the
+file.

 
 Please write the comments in a GNU program in English, because English
 is the one language that nearly all programmers in all countries can
 
 Please write the comments in a GNU program in English, because English
 is the one language that nearly all programmers in all countries can


@@ -2576,7 +2628,7 @@ constants.
 @cindex file-name limitations
 @pindex doschk
 You might want to make sure that none of the file names would conflict
 @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
 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


@@ -2618,11 +2670,11 @@ 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
 when there is a higher-level alternative (@code{readdir}).
 
 @cindex non-@sc{posix} systems, and portability

-As for systems that are not like Unix, such as MSDOS, Windows, the
-Macintosh, VMS, and MVS, supporting them is often a lot of work.  When
-that is the case, it is better to spend your time adding features that
-will be useful on GNU and GNU/Linux, rather than on supporting other
-incompatible systems.
+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
+that will be useful on GNU and GNU/Linux, rather than on supporting
+other incompatible systems.

 
 If you do support Windows, please do not abbreviate it as ``win''.  In
 hacker terminology, calling something a ``win'' is a form of praise.
 
 If you do support Windows, please do not abbreviate it as ``win''.  In
 hacker terminology, calling something a ``win'' is a form of praise.


@@ -2667,7 +2719,7 @@ printf ("diff = %ld\n", (long) (pointer2 - pointer1));
 @end example
 
 1989 Standard C requires this to work, and we know of only one
 @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.
 
 leave it to those who want to port GNU programs to that environment
 to figure out how to do it.
 


@@ -2687,37 +2739,50 @@ while ((c = getchar()) != EOF)
   write(file_descriptor, &c, 1);
 @end example
 
   write(file_descriptor, &c, 1);
 @end example
 

-When calling functions, you need not worry about the difference between
-pointers of various types, or between pointers and integers.  On most
-machines, there's no difference anyway.  As for the few machines where
-there is a difference, all of them support Standard C prototypes, so you can
-use prototypes (perhaps conditionalized to be active only in Standard C)
-to make the code work on those systems.
+It used to be ok to not worry about the difference between pointers
+and integers when passing arguments to functions.  However, on most
+modern 64-bit machines pointers are wider than @code{int}.
+Conversely, integer types like @code{long long int} and @code{off_t}
+are wider than pointers on most modern 32-bit machines.  Hence it's
+often better nowadays to use prototypes to define functions whose
+argument types are not trivial.

 
 

-In certain cases, it is ok to pass integer and pointer arguments
-indiscriminately to the same function, and use no prototype on any
-system.  For example, many GNU programs have error-reporting functions
-that pass their arguments along to @code{printf} and friends:
+In particular, if functions accept varying argument counts or types
+they should be declared using prototypes containing @samp{...} and
+defined using @file{stdarg.h}.  For an example of this, please see the
+@uref{http://www.gnu.org/software/gnulib/, Gnulib} error module, which
+declares and defines the following function:

 
 @example
 
 @example

-error (s, a1, a2, a3)
-     char *s;
-     char *a1, *a2, *a3;
-@{
-  fprintf (stderr, "error: ");
-  fprintf (stderr, s, a1, a2, a3);
-@}
+/* Print a message with `fprintf (stderr, FORMAT, ...)';
+   if ERRNUM is nonzero, follow it with ": " and strerror (ERRNUM).
+   If STATUS is nonzero, terminate the program with `exit (STATUS)'.  */
+
+void error (int status, int errnum, const char *format, ...);

 @end example
 
 @end example
 

-@noindent
-In practice, this works on all machines, since a pointer is generally
-the widest possible kind of argument; it is much simpler than any
-``correct'' alternative.  Be sure @emph{not} to use a prototype for such
-functions.
+A simple way to use the Gnulib error module is to obtain the two
+source files @file{error.c} and @file{error.h} from the Gnulib library
+source code repository at
+@uref{http://savannah.gnu.org/cgi-bin/viewcvs/gnulib/gnulib/lib/}.
+Here's a sample use:
+
+@example
+#include "error.h"
+#include <errno.h>
+#include <stdio.h>
+
+char *program_name = "myprogram";

 
 

-If you have decided to use Standard C, then you can instead define
-@code{error} using @file{stdarg.h}, and pass the arguments along to
-@code{vfprintf}.
+FILE *
+xfopen (char const *name)
+@{
+  FILE *fp = fopen (name, "r");
+  if (! fp)
+    error (1, errno, "cannot read %s", name);
+  return fp;
+@}
+@end example

 
 @cindex casting pointers to integers
 Avoid casting pointers to integers if you can.  Such casts greatly
 
 @cindex casting pointers to integers
 Avoid casting pointers to integers if you can.  Such casts greatly


@@ -2958,6 +3023,63 @@ printf (f->tried_implicit
         : "#  Implicit rule search has not been done.\n");
 @end example
 
         : "#  Implicit rule search has not been done.\n");
 @end example
 

+
+@node Character Set
+@section Character Set
+@cindex character set
+@cindex encodings
+@cindex ASCII characters
+@cindex non-ASCII characters
+
+Sticking to the ASCII character set (plain text, 7-bit characters) is
+preferred in GNU source code comments, text documents, and other
+contexts, unless there is good reason to do something else because of
+the application domain.  For example, if source code deals with the
+French Revolutionary calendar, it is OK if its literal strings contain
+accented characters in month names like ``Flor@'eal''.  Also, it is OK
+to use non-ASCII characters to represent proper names of contributors in
+change logs (@pxref{Change Logs}).
+
+If you need to use non-ASCII characters, you should normally stick with
+one encoding, as one cannot in general mix encodings reliably.
+
+
+@node Quote Characters
+@section Quote Characters
+@cindex quote characters
+@cindex locale-specific quote characters
+@cindex left quote
+@cindex grave accent
+
+In the C locale, GNU programs should stick to plain ASCII for quotation
+characters in messages to users: preferably 0x60 (@samp{`}) for left
+quotes and 0x27 (@samp{'}) for right quotes.  It is ok, but not
+required, to use locale-specific quotes in other locales.
+
+The @uref{http://www.gnu.org/software/gnulib/, Gnulib} @code{quote} and
+@code{quotearg} modules provide a reasonably straightforward way to
+support locale-specific quote characters, as well as taking care of
+other issues, such as quoting a filename that itself contains a quote
+character.  See the Gnulib documentation for usage details.
+
+In any case, the documentation for your program should clearly specify
+how it does quoting, if different than the preferred method of @samp{`}
+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 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 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.
+
+

 @node Mmap
 @section Mmap
 @findex mmap
 @node Mmap
 @section Mmap
 @findex mmap


@@ -3076,9 +3198,9 @@ 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
 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, The GNU Texinfo
-Manual}, and see @ref{Indexing Commands, , Defining the Entries of an
-Index, texinfo, The GNU Texinfo manual}.
+@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;
 most of them are terse, badly structured, and give inadequate
 
 Don't use Unix man pages as a model for how to write GNU documentation;
 most of them are terse, badly structured, and give inadequate


@@ -3587,20 +3709,21 @@ For example, an Athlon-based GNU/Linux system might be
 
 The @code{configure} script needs to be able to decode all plausible
 alternatives for how to describe a machine.  Thus,
 
 The @code{configure} script needs to be able to decode all plausible
 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{ftp://ftp.gnu.org/gnu/config/config.sub, @file{config.sub}}
-that you can use
-as a subroutine to validate system types and canonicalize aliases.
+@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,
+@file{config.sub}} that you can use as a subroutine to validate system
+types and canonicalize aliases.

 
 The @code{configure} script should also take the option
 @option{--build=@var{buildtype}}, which should be equivalent to a
 plain @var{buildtype} argument.  For example, @samp{configure
 --build=i686-pc-linux-gnu} is equivalent to @samp{configure
 i686-pc-linux-gnu}.  When the build type is not specified by an option
 
 The @code{configure} script should also take the option
 @option{--build=@var{buildtype}}, which should be equivalent to a
 plain @var{buildtype} argument.  For example, @samp{configure
 --build=i686-pc-linux-gnu} is equivalent to @samp{configure
 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{ftp://ftp.gnu.org/gnu/config/config.guess, @file{config.guess}}.
+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,
+@file{config.guess}}.

 
 @cindex optional features, configure-time
 Other options are permitted to specify in more detail the software
 
 @cindex optional features, configure-time
 Other options are permitted to specify in more detail the software


@@ -3784,9 +3907,11 @@ advertise them to new potential customers.  Proprietary software is a
 social and ethical problem, and the point of GNU is to solve that
 problem.
 
 social and ethical problem, and the point of GNU is to solve that
 problem.
 

-The GNU definition of free software is found in
-@url{http://www.gnu.org/philosophy/free-sw.html}, with a list of
-important licenses and whether they qualify as free in
+The GNU definition of free software is found on the GNU web site at
+@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
 ``free'' and ``non-free'', used in this document, refer to that
 definition.  If it is not clear whether a license qualifies as free
 @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


@@ -3843,7 +3968,7 @@ scope of an operating system project.
 Referring to a web site that describes or recommends a non-free
 program is in effect promoting that software, so please do not make
 links (or mention by name) web sites that contain such material.  This
 Referring to a web site that describes or recommends a non-free
 program is in effect promoting that software, so please do not make
 links (or mention by name) web sites that contain such material.  This

-policy is relevant particulary for the web pages for a GNU package.
+policy is relevant particularly for the web pages for a GNU package.

 
 Following links from nearly any web site can lead to non-free
 software; this is an inescapable aspect of the nature of the web, and
 
 Following links from nearly any web site can lead to non-free
 software; this is an inescapable aspect of the nature of the web, and