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* standards.texi, make-stds.texi: Update to FSF version of May 13.

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@ -1,3 +1,7 @@
2000-05-18 Martin von Loewis <loewis@informatik.hu-berlin.de>
* standards.texi, make-stds.texi: Update to FSF version of May 13.
Mon Nov 23 16:46:10 1998 Kaveh R. Ghazi <ghazi@caip.rutgers.edu>
* configure.in: Use AC_PREREQ(2.12.1).

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etc/make-stds.texi
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@ -21,6 +21,8 @@ chapter
@end ifclear
@end iftex
describes conventions for writing the Makefiles for GNU programs.
Using Automake will help you write a Makefile that follows these
conventions.
@menu
* Makefile Basics:: General Conventions for Makefiles
@ -280,8 +282,8 @@ installed.
Installation directories should always be named by variables, so it is
easy to install in a nonstandard place. The standard names for these
variables are described below. They are based on a standard filesystem
layout; variants of it are used in SVR4, 4.4BSD, Linux, Ultrix v4, and
other modern operating systems.
layout; variants of it are used in SVR4, 4.4BSD, GNU/Linux, Ultrix v4,
and other modern operating systems.
These two variables set the root for the installation. All the other
installation directories should be subdirectories of one of these two,

549
etc/standards.texi
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@ -3,7 +3,7 @@
@setfilename standards.info
@settitle GNU Coding Standards
@c This date is automagically updated when you save this file:
@set lastupdate March 13, 1998
@set lastupdate May 13, 2000
@c %**end of header
@ifinfo
@ -28,7 +28,7 @@ END-INFO-DIR-ENTRY
@ifinfo
GNU Coding Standards
Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998 Free Software Foundation, Inc.
Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
@ -84,13 +84,14 @@ Last updated @value{lastupdate}.
@end ifinfo
@menu
* Preface:: About the GNU Coding Standards
* Intellectual Property:: Keeping Free Software Free
* Design Advice:: General Program Design
* Program Behavior:: Program Behavior for All Programs
* Writing C:: Making The Best Use of C
* Documentation:: Documenting Programs
* Managing Releases:: The Release Process
* Preface:: About the GNU Coding Standards
* Legal Issues:: Keeping Free Software Free
* Design Advice:: General Program Design
* Program Behavior:: Program Behavior for All Programs
* Writing C:: Making The Best Use of C
* Documentation:: Documenting Programs
* Managing Releases:: The Release Process
* References:: References to Non-Free Software or Documentation
@end menu
@node Preface
@ -113,15 +114,16 @@ you don't have those files, please mail your suggestion anyway.
This release of the GNU Coding Standards was last updated
@value{lastupdate}.
@node Intellectual Property
@node Legal Issues
@chapter Keeping Free Software Free
This @value{CHAPTER} discusses how you can make sure that GNU software
remains unencumbered.
avoids legal difficulties, and other related issues.
@menu
* Reading Non-Free Code:: Referring to Proprietary Programs
* Contributions:: Accepting Contributions
* Trademarks:: How We Deal with Trademark Issues
@end menu
@node Reading Non-Free Code
@ -157,15 +159,15 @@ Or turn some parts of the program into independently usable libraries.
Or use a simple garbage collector instead of tracking precisely when
to free memory, or use a new GNU facility such as obstacks.
@node Contributions
@section Accepting Contributions
If someone else sends you a piece of code to add to the program you are
working on, we need legal papers to use it---the same sort of legal
papers we will need to get from you. @emph{Each} significant
contributor to a program must sign some sort of legal papers in order
for us to have clear title to the program. The main author alone is not
If the program you are working on is copyrighted by the Free Software
Foundation, then when someone else sends you a piece of code to add to
the program, we need legal papers to use it---just as we asked you to
sign papers initially. @emph{Each} person who makes a nontrivial
contribution to a program must sign some sort of legal papers in order
for us to have clear title to the program; the main author alone is not
enough.
So, before adding in any contributions from other people, please tell
@ -181,16 +183,17 @@ This also applies to comments and documentation files. For copyright
law, comments and code are just text. Copyright applies to all kinds of
text, so we need legal papers for all kinds.
We know it is frustrating to ask for legal papers; it's frustrating for
us as well. But if you don't wait, you are going out on a limb---for
example, what if the contributor's employer won't sign a disclaimer?
You might have to take that code out again!
You don't need papers for changes of a few lines here or there, since
they are not significant for copyright purposes. Also, you don't need
papers if all you get from the suggestion is some ideas, not actual code
which you use. For example, if you write a different solution to the
problem, you don't need to get papers.
We know this is frustrating; it's frustrating for us as well. But if
you don't wait, you are going out on a limb---for example, what if the
contributor's employer won't sign a disclaimer? You might have to take
that code out again!
which you use. For example, if someone send you one implementation, but
you write a different implementation of the same idea, you don't need to
get papers.
The very worst thing is if you forget to tell us about the other
contributor. We could be very embarrassed in court some day as a
@ -200,39 +203,113 @@ We have more detailed advice for maintainers of programs; if you have
reached the stage of actually maintaining a program for GNU (whether
released or not), please ask us for a copy.
@node Trademarks
@section Trademarks
Please do not include any trademark acknowledgements in GNU software
packages or documentation.
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, so
we don't use them. There is no legal requirement for them.
What is legally required, as regards other people's trademarks, is to
avoid using them in ways which a reader might read as naming or labeling
our own programs or activities. For example, since ``Objective C'' is
(or at least was) a trademark, we made sure to say that we provide a
``compiler for the Objective C language'' rather than an ``Objective C
compiler''. The latter is meant to be short for the former, but it does
not explicitly state the relationship, so it could be misinterpreted as
using ``Objective C'' as a label for the compiler rather than for the
language.
@node Design Advice
@chapter General Program Design
This @value{CHAPTER} discusses some of the issues you should take into
account when designing your program.
@c Standard or ANSI C
@c
@c In 1989 the American National Standards Institute (ANSI) standardized
@c C as standard X3.159-1989. In December of that year the
@c International Standards Organization ISO adopted the ANSI C standard
@c making minor changes. In 1990 ANSI then re-adopted ISO standard
@c C. This version of C is known as either ANSI C or Standard C.
@menu
* Source Language:: Which languges to use.
* Compatibility:: Compatibility with other implementations
* Using Extensions:: Using non-standard features
* ANSI C:: Using ANSI C features
* Source Language:: Using languages other than C
* Standard C:: Using Standard (ANSI 1989) C features
@end menu
@node Source Language
@section Which Languages to Use
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 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
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
is written in that language, too. The Emacs editor pioneered this
technique.
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.
@node Compatibility
@section Compatibility with Other Implementations
With occasional exceptions, utility programs and libraries for GNU
should be upward compatible with those in Berkeley Unix, and upward
compatible with @sc{ansi} C if @sc{ansi} C specifies their behavior, and
upward compatible with @sc{POSIX} if @sc{POSIX} specifies their
behavior.
compatible with 1989 Standard C if 1989 Standard C specifies their
behavior, and upward compatible with @sc{posix} if @sc{posix} specifies
their behavior.
When these standards conflict, it is useful to offer compatibility
modes for each of them.
@sc{ansi} C and @sc{POSIX} prohibit many kinds of extensions. Feel free
to make the extensions anyway, and include a @samp{--ansi},
1989 Standard C and @sc{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
programs or scripts, then it is not really upward compatible. Try to
redesign its interface.
programs or scripts, then it is not really upward compatible. So you
should try to redesign its interface to make it upward compatible.
Many GNU programs suppress extensions that conflict with POSIX if the
Many GNU programs suppress extensions that conflict with @sc{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.
@ -243,7 +320,8 @@ completely with something totally different and better. (For example,
@code{vi} is replaced with Emacs.) But it is nice to offer a compatible
feature as well. (There is a free @code{vi} clone, so we offer it.)
Additional useful features not in Berkeley Unix are welcome.
Additional useful features are welcome regardless of whether
there is any precedent for them.
@node Using Extensions
@section Using Non-standard Features
@ -267,29 +345,28 @@ straightforwardly do without them, but to use the extensions if they
are a big improvement.
An exception to this rule are the large, established programs (such as
Emacs) which run on a great variety of systems. Such programs would
be broken by use of GNU extensions.
Emacs) which run on a great variety of systems. Using GNU extensions in
such programs would make many users unhappy, so we don't do that.
Another exception is for programs that are used as part of
compilation: anything that must be compiled with other compilers in
order to bootstrap the GNU compilation facilities. If these require
the GNU compiler, then no one can compile them without having them
installed already. That would be no good.
Another exception is for programs that are used as part of compilation:
anything that must be compiled with other compilers in order to
bootstrap the GNU compilation facilities. If these require the GNU
compiler, then no one can compile them without having them installed
already. That would be extremely troublesome in certain cases.
@node ANSI C
@section @sc{ansi} C and pre-@sc{ansi} C
@node Standard C
@section 1989 Standard C and Pre-Standard C
Do not ever use the ``trigraph'' feature of @sc{ansi} C.
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
``trigraph'' feature of 1989 Standard C.
@sc{ansi} C is widespread enough now that it is ok to write new programs
that use @sc{ansi} C features (and therefore will not work in
non-@sc{ansi} compilers). And if a program is already written in
@sc{ansi} C, there's no need to convert it to support non-@sc{ansi}
compilers.
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.
However, it is easy to support non-@sc{ansi} compilers in most programs,
so you might still consider doing so when you write a program. Instead
of writing function definitions in @sc{ansi} prototype form,
To support pre-standard C, instead of writing function definitions in
standard prototype form,
@example
int
@ -298,7 +375,7 @@ foo (int x, int y)
@end example
@noindent
write the definition in pre-@sc{ansi} style like this,
write the definition in pre-standard style like this,
@example
int
@ -315,56 +392,42 @@ int foo (int, int);
@end example
You need such a declaration anyway, in a header file, to get the benefit
of @sc{ansi} C prototypes in all the files where the function is called.
And once you have it, you lose nothing by writing the function
definition in the pre-@sc{ansi} style.
of prototypes in all the files where the function is called. And once
you have the declaration, you normally lose nothing by writing the
function definition in the pre-standard style.
If you don't know non-@sc{ansi} C, there's no need to learn it; just
write in @sc{ansi} C.
This technique does not work for integer types narrower than @code{int}.
If you think of an argument as being of a type narrower than @code{int},
declare it as @code{int} instead.
@node Source Language
@section Using Languages Other Than C
There are a few special cases where this technique is hard to use. For
example, if a function argument needs to hold the system type
@code{dev_t}, you run into trouble, because @code{dev_t} is shorter than
@code{int} on some machines; but you cannot use @code{int} instead,
because @code{dev_t} is wider than @code{int} on some machines. There
is no type you can safely use on all machines in a non-standard
definition. The only way to support non-standard C and pass such an
argument is to check the width of @code{dev_t} using Autoconf and choose
the argument type accordingly. This may not be worth the trouble.
Using a language other than C 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 C++ compiler
in order to compile your program. Thus, it is better if you write in C.
In order to support pre-standard compilers that do not recognize
prototypes, you may want to use a preprocessor macro like this:
But there are three situations when there is no disadvantage in using
some other language:
@itemize @bullet
@item
It is okay to use another language if your program contains an
interpreter for that language.
For example, if your program links with GUILE, it is ok to write part of
the program in Scheme or another language supported by GUILE.
@item
It is okay to use another language in a tool specifically intended for
use with that language.
This is okay 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 to a narrow community, then perhaps
it's not important if the application is inconvenient to install.
@end itemize
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.
@example
/* Declare the prototype for a general external function. */
#if defined (__STDC__) || defined (WINDOWSNT)
#define P_(proto) proto
#else
#define P_(proto) ()
#endif
@end example
@node Program Behavior
@chapter Program Behavior for All Programs
This @value{CHAPTER} describes how to write robust software. It also
describes general standards for error messages, the command line interface,
and how libraries should behave.
This @value{CHAPTER} describes conventions for writing robust
software. It also describes general standards for error messages, the
command line interface, and how libraries should behave.
@menu
* Semantics:: Writing robust programs
@ -384,9 +447,13 @@ all data structures dynamically. In most Unix utilities, ``long lines
are silently truncated''. This is not acceptable in a GNU utility.
Utilities reading files should not drop NUL characters, or any other
nonprinting characters @emph{including those with codes above 0177}. The
only sensible exceptions would be utilities specifically intended for
interface to certain types of printers that can't handle those characters.
nonprinting characters @emph{including those with codes above 0177}.
The only sensible exceptions would be utilities specifically intended
for interface to certain types of terminals or printers
that can't handle those characters.
Whenever possible, try to make programs work properly with
sequences of bytes that represent multibyte characters, using encodings
such as UTF-8 and others.
Check every system call for an error return, unless you know you wish to
ignore errors. Include the system error text (from @code{perror} or
@ -428,11 +495,18 @@ Try to avoid low-level interfaces to obscure Unix data structures (such
as file directories, utmp, or the layout of kernel memory), since these
are less likely to work compatibly. If you need to find all the files
in a directory, use @code{readdir} or some other high-level interface.
These will be supported compatibly by GNU.
These are supported compatibly by GNU.
By default, the GNU system will provide the signal handling functions of
@sc{BSD} and of @sc{POSIX}. So GNU software should be written to use
these.
The preferred signal handling facilities are the BSD variant of
@code{signal}, and the @sc{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
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
behavior. It is up to you whether to support systems where
@code{signal} has only the USG behavior, or give up on them.
In error checks that detect ``impossible'' conditions, just abort.
There is usually no point in printing any message. These checks
@ -452,6 +526,20 @@ If you make temporary files, check the @code{TMPDIR} environment
variable; if that variable is defined, use the specified directory
instead of @file{/tmp}.
In addition, be aware that there is a possible security problem when
creating temporary files in directories world-writable directories. In
C, you can avoid this problem by creating temporary files in this
manner:
@example
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.
@node Libraries
@section Library Behavior
@ -490,6 +578,20 @@ Error messages from compilers should look like this:
@var{source-file-name}:@var{lineno}: @var{message}
@end example
@noindent
If you want to mention the column number, use this format:
@example
@var{source-file-name}:@var{lineno}:@var{column}: @var{message}
@end example
@noindent
Line numbers should start from 1 at the beginning of the file, and
column numbers should start from 1 at the beginning of the line. (Both
of these conventions are chosen for compatibility.) Calculate column
numbers assuming that space and all ASCII printing characters have
equal width, and assuming tab stops every 8 columns.
Error messages from other noninteractive programs should look like this:
@example
@ -506,6 +608,12 @@ when there is an appropriate source file, or like this:
@noindent
when there is no relevant source file.
If you want to mention the column number, use this format:
@example
@var{program}:@var{source-file-name}:@var{lineno}:@var{column}: @var{message}
@end example
In an interactive program (one that is reading commands from a
terminal), it is better not to include the program name in an error
message. The place to indicate which program is running is in the
@ -533,8 +641,10 @@ to select among the alternate behaviors.
Likewise, please don't make the behavior of the program depend on the
type of output device it is used with. Device independence is an
important principle of the system's design; do not compromise it
merely to save someone from typing an option now and then.
important principle of the system's design; do not compromise it merely
to save someone from typing an option now and then. (Variation in error
message syntax when using a terminal is ok, because that is a side issue
that people do not depend on.)
If you think one behavior is most useful when the output is to a
terminal, and another is most useful when the output is a file or a
@ -550,11 +660,11 @@ output device type. For example, we provide a @code{dir} program much
like @code{ls} except that its default output format is always
multi-column format.
It is a good idea to follow the @sc{POSIX} guidelines for the
It is a good idea to follow the @sc{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 @sc{posix}
specifies; it is a GNU extension.
Please define long-named options that are equivalent to the
@ -581,7 +691,7 @@ and @samp{--help}.
@table @code
@item --version
This option should direct the program to information about its name,
This option should direct the program to print information about its name,
version, origin and legal status, all on standard output, and then exit
successfully. Other options and arguments should be ignored once this
is seen, and the program should not perform its normal function.
@ -738,6 +848,9 @@ and @code{unexpand}.
@item avoid-wraps
@samp{-n} in @code{wdiff}.
@item background
For server programs, run in the background.
@item backward-search
@samp{-B} in @code{ctags}.
@ -862,6 +975,9 @@ Used in @code{tar} and @code{cpio}.
@item dereference-args
@samp{-D} in @code{du}.
@item device
Specify an I/O device (special file name).
@item diacritics
@samp{-d} in @code{recode}.
@ -994,6 +1110,11 @@ Used in @code{makeinfo}.
@item force-prefix
@samp{-F} in @code{shar}.
@item foreground
For server programs, run in the foreground;
in other words, don't do anything special to run the server
in the background.
@item format
Used in @code{ls}, @code{time}, and @code{ptx}.
@ -1039,6 +1160,9 @@ Used to ask for brief usage information.
@item hide-control-chars
@samp{-q} in @code{ls}.
@item html
In @code{makeinfo}, output HTML.
@item idle
@samp{-u} in @code{who}.
@ -1099,6 +1223,10 @@ Used to ask for brief usage information.
@item info
@samp{-i}, @samp{-l}, and @samp{-m} in Finger.
@item init-file
In some programs, specify the name of the file to read as the user's
init file.
@item initial
@samp{-i} in @code{expand}.
@ -1117,6 +1245,9 @@ Used to ask for brief usage information.
@item intermix-type
@samp{-p} in @code{shar}.
@item iso-8601
Used in @code{date}
@item jobs
@samp{-j} in Make.
@ -1352,6 +1483,10 @@ Used in GDB.
@item only-time
@samp{-F} in @code{gprof}.
@item options
@samp{-o} in @code{getopt}, @code{fdlist}, @code{fdmount},
@code{fdmountd}, and @code{fdumount}.
@item output
In various programs, specify the output file name.
@ -1436,6 +1571,9 @@ Used in @code{tar} and @code{cp}.
@item prompt
@samp{-p} in @code{ed}.
@item proxy
Specify an HTTP proxy.
@item query-user
@samp{-X} in @code{shar}.
@ -1564,6 +1702,12 @@ Used in many programs to inhibit the usual output.
@item size
@samp{-s} in @code{ls}.
@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
reserved port number.
@item sort
Used in @code{ls}.
@ -1662,6 +1806,9 @@ Used in GDB and @code{objdump}.
@item time
Used in @code{ls} and @code{touch}.
@item timeout
Specify how long to wait before giving up on some operation.
@item to-stdout
@samp{-O} in @code{tar}.
@ -1813,7 +1960,8 @@ concat (s1, s2) /* Name starts in column zero here */
@end example
@noindent
or, if you want to use @sc{ansi} C, format the definition like this:
or, if you want to use Standard C syntax, format the definition like
this:
@example
static char *
@ -1823,7 +1971,7 @@ concat (char *s1, char *s2)
@}
@end example
In @sc{ansi} C, if the arguments don't fit nicely on one line,
In Standard C, if the arguments don't fit nicely on one line,
split it like this:
@example
@ -1833,7 +1981,17 @@ lots_of_args (int an_integer, long a_long, short a_short,
@dots{}
@end example
For the body of the function, we prefer code formatted like this:
The rest of this section gives our recommendations for other aspects of
C formatting style. We don't think of them as requirements, because it
causes no problems for users if two different programs have different
formatting styles.
But whatever style you use, please use it consistently, since a mixture
of styles within one program tends to look ugly. If you are
contributing changes to an existing program, please follow the style of
that program.
For the body of the function, our recommended style looks like this:
@example
if (x < foo (y, z))
@ -1879,14 +2037,15 @@ mode = ((inmode[j] == VOIDmode
Insert extra parentheses so that Emacs will indent the code properly.
For example, the following indentation looks nice if you do it by hand,
but Emacs would mess it up:
@example
v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
+ rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000;
@end example
But adding a set of parentheses solves the problem:
@noindent
but Emacs would alter it. Adding a set of parentheses produces
something that looks equally nice, and which Emacs will preserve:
@example
v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
@ -1908,7 +2067,6 @@ pages at logical places (but not within a function). It does not matter
just how long the pages are, since they do not have to fit on a printed
page. The formfeeds should appear alone on lines by themselves.
@node Comments
@section Commenting Your Work
@ -2007,6 +2165,13 @@ but, by contrast, write the comments this way for a @samp{#ifndef}:
Please explicitly declare all arguments to functions.
Don't omit them just because they are @code{int}s.
Some programmers like to use the GCC @samp{-Wall} option, and change the
code whenever it issues a warning. If you want to do this, then do.
Other programmers prefer not to use @samp{-Wall}, because it gives
warnings for valid and legitimate code which they do not want to change.
If you want to do this, then do. The compiler should be your servant,
not your master.
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
@ -2128,7 +2293,7 @@ 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.
@node Names
@node Names
@section Naming Variables and Functions
The names of global variables and functions in a program serve as
@ -2140,6 +2305,10 @@ comments.
Local variable names can be shorter, because they are used only within
one context, where (presumably) comments explain their purpose.
Try to limit your use of abbreviations in symbol names. It is ok to
make a few abbreviations, explain what they mean, and then use them
frequently, but don't use lots of obscure abbreviations.
Please use underscores to separate words in a name, so that the Emacs
word commands can be useful within them. Stick to lower case; reserve
upper case for macros and @code{enum} constants, and for name-prefixes
@ -2198,14 +2367,22 @@ Avoid using the format of semi-internal data bases (e.g., directories)
when there is a higher-level alternative (@code{readdir}).
As for systems that are not like Unix, such as MSDOS, Windows, the
Macintosh, VMS, and MVS, supporting them is usually so much work that it
is better if you don't.
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.
The planned GNU kernel is not finished yet, but you can tell which
facilities it will provide by looking at the GNU C Library Manual. The
GNU kernel is based on Mach, so the features of Mach will also be
available. However, if you use Mach features, you'll probably have
trouble debugging your program today.
It is a good idea to define the ``feature test macro''
@code{_GNU_SOURCE} when compiling your C files. When you compile on GNU
or GNU/Linux, this will enable the declarations of GNU library extension
functions, and that will usually give you a compiler error message if
you define the same function names in some other way in your program.
(You don't have to actually @emph{use} these functions, if you prefer
to make the program more portable to other systems.)
But whether or not you use these GNU extensions, you should avoid
using their names for any other meanings. Doing so would make it hard
to move your code into other GNU programs.
@node CPU Portability
@section Portability between @sc{cpu}s
@ -2231,9 +2408,9 @@ while ((c = getchar()) != EOF)
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 @sc{ansi} C, so you can use
prototypes (conditionalized to be active only in @sc{ansi} C) to make
the code work on those systems.
there is a difference, all of them support 1989 Standard C, so you can
use prototypes (perhaps conditionalized to be active only in Standard C)
to make the code work on those systems.
In certain cases, it is ok to pass integer and pointer arguments
indiscriminately to the same function, and use no prototype on any
@ -2243,7 +2420,7 @@ that pass their arguments along to @code{printf} and friends:
@example
error (s, a1, a2, a3)
char *s;
int a1, a2, a3;
char *a1, *a2, *a3;
@{
fprintf (stderr, "error: ");
fprintf (stderr, s, a1, a2, a3);
@ -2251,31 +2428,41 @@ error (s, a1, a2, a3)
@end example
@noindent
In practice, this works on all machines, and it is much simpler than any
``correct'' alternative. Be sure @emph{not} to use a prototype
for such functions.
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.
However, avoid casting pointers to integers unless you really need to.
These assumptions really reduce portability, and in most programs they
are easy to avoid. In the cases where casting pointers to integers is
essential---such as, a Lisp interpreter which stores type information as
well as an address in one word---it is ok to do so, but you'll have to
make explicit provisions to handle different word sizes.
If you have decided to use 1989 Standard C, then you can instead define
@code{error} using @file{stdarg.h}, and pass the arguments along to
@code{vfprintf}.
Avoid casting pointers to integers if you can. Such casts greatly
reduce portability, and in most programs they are easy to avoid. In the
cases where casting pointers to integers is essential---such as, a Lisp
interpreter which stores type information as well as an address in one
word---you'll have to make explicit provisions to handle different word
sizes. You will also need to make provision for systems in which the
normal range of addresses you can get from @code{malloc} starts far away
from zero.
@node System Functions
@section Calling System Functions
C implementations differ substantially. @sc{ansi} C reduces but does not
eliminate the incompatibilities; meanwhile, many users wish to compile
GNU software with pre-@sc{ansi} compilers. This chapter gives
recommendations for how to use the more or less standard C library
functions to avoid unnecessary loss of portability.
C implementations differ substantially. 1989 Standard C reduces but does
not eliminate the incompatibilities; meanwhile, many GNU packages still
support pre-standard compilers because this is not hard to do. This
chapter gives recommendations for how to use the more-or-less standard C
library functions to avoid unnecessary loss of portability.
@itemize @bullet
@item
Don't use the value of @code{sprintf}. It returns the number of
Don't use the return value of @code{sprintf}. It returns the number of
characters written on some systems, but not on all systems.
@item
Be aware that @code{vfprintf} is not always available.
@item
@code{main} should be declared to return type @code{int}. It should
terminate either by calling @code{exit} or by returning the integer
@ -2297,7 +2484,7 @@ actual conflicts.
@item
If you must declare a system function, don't specify the argument types.
Use an old-style declaration, not an @sc{ansi} prototype. The more you
Use an old-style declaration, not a Standard C prototype. The more you
specify about the function, the more likely a conflict.
@item
@ -2329,7 +2516,7 @@ figure out which file to include, or don't include either file.
If you don't include either strings file, you can't get declarations for
the string functions from the header file in the usual way.
That causes less of a problem than you might think. The newer @sc{ansi}
That causes less of a problem than you might think. The newer standard
string functions should be avoided anyway because many systems still
don't support them. The string functions you can use are these:
@ -2359,7 +2546,7 @@ names, but neither pair works on all systems.
You should pick a single pair of names and use it throughout your
program. (Nowadays, it is better to choose @code{strchr} and
@code{strrchr} for new programs, since those are the standard @sc{ansi}
@code{strrchr} for new programs, since those are the standard
names.) Declare both of those names as functions returning @code{char
*}. On systems which don't support those names, define them as macros
in terms of the other pair. For example, here is what to put at the
@ -2503,6 +2690,7 @@ all these kinds of files.
@menu
* GNU Manuals:: Writing proper manuals.
* Manual Structure Details:: Specific structure conventions.
* License for Manuals:: Writing the distribution terms for a manual.
* NEWS File:: NEWS files supplement manuals.
* Change Logs:: Recording Changes
* Man Pages:: Man pages are secondary.
@ -2514,9 +2702,12 @@ all these kinds of files.
@section GNU Manuals
The preferred way to document part of the GNU system is to write a
manual in the Texinfo formatting language. See the Texinfo manual,
either the hardcopy, or the on-line version available through
@code{info} or the Emacs Info subsystem (@kbd{C-h i}).
manual in the Texinfo formatting language. This makes it possible to
produce a good quality formatted book, using @TeX{}, and to generate an
Info file. It is also possible to generate HTML output from Texinfo
source. See the Texinfo manual, either the hardcopy, or the on-line
version available through @code{info} or the Emacs Info subsystem
(@kbd{C-h i}).
Programmers often find it most natural to structure the documentation
following the structure of the implementation, which they know. But
@ -2557,6 +2748,8 @@ It should be set up for convenient access to each topic through Info,
and for reading straight through (appendixes aside). A GNU manual
should give a good introduction to a beginner reading through from the
start, and should also provide all the details that hackers want.
The Bison manual is a good example of this---please take a look at it
to see what we mean.
That is not as hard as it first sounds. Arrange each chapter as a
logical breakdown of its topic, but order the sections, and write their
@ -2576,9 +2769,12 @@ explanation of the underlying concepts. (There are, of course
exceptions.) Also Unix man pages use a particular format which is
different from what we use in GNU manuals.
Please include an email address in the manual for where to report
bugs @emph{in the manual}.
Please do not use the term ``pathname'' that is used in Unix
documentation; use ``file name'' (two words) instead. We use the term
``path'' only for search paths, which are lists of file names.
``path'' only for search paths, which are lists of directory names.
Please do not use the term ``illegal'' to refer to erroneous input to a
computer program. Please use ``invalid'' for this, and reserve the term
@ -2611,6 +2807,18 @@ quickly reading just this part of its manual.
If one manual describes several programs, it should have such a node for
each program described.
@node License for Manuals
@section License for Manuals
If the manual contains a copy of the GNU GPL or GNU LGPL, or if it
contains chapters that make political or personal statements, please
copy the distribution terms of the GNU Emacs Manual, and adapt it by
modifying appropriately the list of special chapters that may not be
modified or deleted.
If the manual does not contain any such chapters, then imitate the
simpler distribution terms of the Texinfo manual.
@node NEWS File
@section The NEWS File
@ -2659,7 +2867,8 @@ you.
Another alternative is to record change log information with a version
control system such as RCS or CVS. This can be converted automatically
to a @file{ChangeLog} file.
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
@ -3030,6 +3239,21 @@ files} and @dfn{non-source files}. Source files are written by humans
and never changed automatically; non-source files are produced from
source files by programs under the control of the Makefile.
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
@file{COPYING.LIB}.
Naturally, all the source files must be in the distribution. It is okay
to include non-source files in the distribution, provided they are
up-to-date and machine-independent, so that building the distribution
@ -3054,7 +3278,7 @@ Make sure that all the files in the distribution are world-readable.
Make sure that no file name in the distribution is more than 14
characters long. Likewise, no file created by building the program
should have a name longer than 14 characters. The reason for this is
that some systems adhere to a foolish interpretation of the POSIX
that some systems adhere to a foolish interpretation of the @sc{posix}
standard, and refuse to open a longer name, rather than truncating as
they did in the past.
@ -3082,6 +3306,31 @@ Leaving them out would make the distribution file a little smaller at
the expense of possible inconvenience to a user who doesn't know what
other files to get.
@node References
@chapter References to Non-Free Software and Documentation
A GNU program should not recommend use of any non-free program. We
can't stop some people from writing proprietary programs, or stop other
people from using them. But we can and should avoid helping to
advertise them to new customers.
Sometimes it is important to mention how to build your package on top of
some non-free operating system or other non-free base package. In such
cases, please mention the name of the non-free package or system in the
briefest possible way. Don't include any references for where to find
more information about the proprietary program. The goal should be that
people already using the proprietary program will get the advice they
need about how to use your free program, while people who don't already
use the proprietary program will not see anything to encourage them to
take an interest in it.
Likewise, a GNU package should not refer the user to any non-free
documentation for free software. The need for free documentation to go
with free software is now a major focus of the GNU project; to show that
we are serious about the need for free documentation, we must not
undermine our position by recommending use of documentation that isn't
free.
@contents
@bye