1 \input texinfo @c -*-texinfo-*-
3 @setfilename ../info/standards.info
4 @settitle GNU Coding Standards
5 @c This date is automagically updated when you save this file:
6 @set lastupdate February 21, 2001
12 * Standards: (standards). GNU coding standards.
17 @c @setchapternewpage odd
18 @setchapternewpage off
20 @c Put everything in one index (arbitrarily chosen to be the concept index).
26 @c This is used by a cross ref in make-stds.texi
37 Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000 Free Software Foundation, Inc.
39 Permission is granted to make and distribute verbatim copies of
40 this manual provided the copyright notice and this permission notice
41 are preserved on all copies.
44 Permission is granted to process this file through TeX and print the
45 results, provided the printed document carries copying permission
46 notice identical to this one except for the removal of this paragraph
47 (this paragraph not being relevant to the printed manual).
50 Permission is granted to copy and distribute modified versions of this
51 manual under the conditions for verbatim copying, provided that the entire
52 resulting derived work is distributed under the terms of a permission
53 notice identical to this one.
55 Permission is granted to copy and distribute translations of this manual
56 into another language, under the above conditions for modified versions,
57 except that this permission notice may be stated in a translation approved
58 by the Free Software Foundation.
62 @title GNU Coding Standards
63 @author Richard Stallman
64 @author last updated @value{lastupdate}
67 @vskip 0pt plus 1filll
68 Copyright @copyright{} 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000 Free Software Foundation, Inc.
70 Permission is granted to make and distribute verbatim copies of
71 this manual provided the copyright notice and this permission notice
72 are preserved on all copies.
74 Permission is granted to copy and distribute modified versions of this
75 manual under the conditions for verbatim copying, provided that the entire
76 resulting derived work is distributed under the terms of a permission
77 notice identical to this one.
79 Permission is granted to copy and distribute translations of this manual
80 into another language, under the above conditions for modified versions,
81 except that this permission notice may be stated in a translation approved
82 by the Free Software Foundation.
86 @node Top, Preface, (dir), (dir)
89 Last updated @value{lastupdate}.
93 * Preface:: About the GNU Coding Standards
94 * Legal Issues:: Keeping Free Software Free
95 * Design Advice:: General Program Design
96 * Program Behavior:: Program Behavior for All Programs
97 * Writing C:: Making The Best Use of C
98 * Documentation:: Documenting Programs
99 * Managing Releases:: The Release Process
100 * References:: References to Non-Free Software or Documentation
105 @chapter About the GNU Coding Standards
107 The GNU Coding Standards were written by Richard Stallman and other GNU
108 Project volunteers. Their purpose is to make the GNU system clean,
109 consistent, and easy to install. This document can also be read as a
110 guide to writing portable, robust and reliable programs. It focuses on
111 programs written in C, but many of the rules and principles are useful
112 even if you write in another programming language. The rules often
113 state reasons for writing in a certain way.
115 Corrections or suggestions for this document should be sent to
116 @email{bug-standards@@gnu.org}. If you make a suggestion, please include a
117 suggested new wording for it; our time is limited. We prefer a context
118 diff to the @file{standards.texi} or @file{make-stds.texi} files, but if
119 you don't have those files, please mail your suggestion anyway.
121 This release of the GNU Coding Standards was last updated
124 @cindex where to obtain @code{standards.texi}
125 @cindex downloading this manual
126 If you did not obtain this file directly from the GNU project and
127 recently, please check for a newer version. You can ftp the GNU Coding
128 Standards from any GNU FTP host in the directory
129 @file{/pub/gnu/standards/}. The GNU Coding Standards are available
130 there in several different formats: @file{standards.text},
131 @file{standards.texi}, @file{standards.info}, and @file{standards.dvi}.
132 The GNU Coding Standards are also available on the GNU World Wide Web
133 server: @uref{http://www.gnu.org/prep/standards_toc.html}.
136 @chapter Keeping Free Software Free
137 @cindex legal aspects
139 This @value{CHAPTER} discusses how you can make sure that GNU software
140 avoids legal difficulties, and other related issues.
143 * Reading Non-Free Code:: Referring to Proprietary Programs
144 * Contributions:: Accepting Contributions
145 * Trademarks:: How We Deal with Trademark Issues
148 @node Reading Non-Free Code
149 @section Referring to Proprietary Programs
150 @cindex proprietary programs
151 @cindex avoiding proprietary code
153 Don't in any circumstances refer to Unix source code for or during
154 your work on GNU! (Or to any other proprietary programs.)
156 If you have a vague recollection of the internals of a Unix program,
157 this does not absolutely mean you can't write an imitation of it, but
158 do try to organize the imitation internally along different lines,
159 because this is likely to make the details of the Unix version
160 irrelevant and dissimilar to your results.
162 For example, Unix utilities were generally optimized to minimize
163 memory use; if you go for speed instead, your program will be very
164 different. You could keep the entire input file in core and scan it
165 there instead of using stdio. Use a smarter algorithm discovered more
166 recently than the Unix program. Eliminate use of temporary files. Do
167 it in one pass instead of two (we did this in the assembler).
169 Or, on the contrary, emphasize simplicity instead of speed. For some
170 applications, the speed of today's computers makes simpler algorithms
173 Or go for generality. For example, Unix programs often have static
174 tables or fixed-size strings, which make for arbitrary limits; use
175 dynamic allocation instead. Make sure your program handles NULs and
176 other funny characters in the input files. Add a programming language
177 for extensibility and write part of the program in that language.
179 Or turn some parts of the program into independently usable libraries.
180 Or use a simple garbage collector instead of tracking precisely when
181 to free memory, or use a new GNU facility such as obstacks.
184 @section Accepting Contributions
186 @cindex accepting contributions
188 If the program you are working on is copyrighted by the Free Software
189 Foundation, then when someone else sends you a piece of code to add to
190 the program, we need legal papers to use it---just as we asked you to
191 sign papers initially. @emph{Each} person who makes a nontrivial
192 contribution to a program must sign some sort of legal papers in order
193 for us to have clear title to the program; the main author alone is not
196 So, before adding in any contributions from other people, please tell
197 us, so we can arrange to get the papers. Then wait until we tell you
198 that we have received the signed papers, before you actually use the
201 This applies both before you release the program and afterward. If
202 you receive diffs to fix a bug, and they make significant changes, we
203 need legal papers for that change.
205 This also applies to comments and documentation files. For copyright
206 law, comments and code are just text. Copyright applies to all kinds of
207 text, so we need legal papers for all kinds.
209 We know it is frustrating to ask for legal papers; it's frustrating for
210 us as well. But if you don't wait, you are going out on a limb---for
211 example, what if the contributor's employer won't sign a disclaimer?
212 You might have to take that code out again!
214 You don't need papers for changes of a few lines here or there, since
215 they are not significant for copyright purposes. Also, you don't need
216 papers if all you get from the suggestion is some ideas, not actual code
217 which you use. For example, if someone send you one implementation, but
218 you write a different implementation of the same idea, you don't need to
221 The very worst thing is if you forget to tell us about the other
222 contributor. We could be very embarrassed in court some day as a
225 We have more detailed advice for maintainers of programs; if you have
226 reached the stage of actually maintaining a program for GNU (whether
227 released or not), please ask us for a copy.
233 Please do not include any trademark acknowledgements in GNU software
234 packages or documentation.
236 Trademark acknowledgements are the statements that such-and-such is a
237 trademark of so-and-so. The GNU Project has no objection to the basic
238 idea of trademarks, but these acknowledgements feel like kowtowing, so
239 we don't use them. There is no legal requirement for them.
241 What is legally required, as regards other people's trademarks, is to
242 avoid using them in ways which a reader might read as naming or labeling
243 our own programs or activities. For example, since ``Objective C'' is
244 (or at least was) a trademark, we made sure to say that we provide a
245 ``compiler for the Objective C language'' rather than an ``Objective C
246 compiler''. The latter is meant to be short for the former, but it does
247 not explicitly state the relationship, so it could be misinterpreted as
248 using ``Objective C'' as a label for the compiler rather than for the
252 @chapter General Program Design
253 @cindex program design
255 This @value{CHAPTER} discusses some of the issues you should take into
256 account when designing your program.
258 @c Standard or ANSI C
260 @c In 1989 the American National Standards Institute (ANSI) standardized
261 @c C as standard X3.159-1989. In December of that year the
262 @c International Standards Organization ISO adopted the ANSI C standard
263 @c making minor changes. In 1990 ANSI then re-adopted ISO standard
264 @c C. This version of C is known as either ANSI C or Standard C.
266 @c A major revision of the C Standard appeared in 1999.
269 * Source Language:: Which languges to use.
270 * Compatibility:: Compatibility with other implementations
271 * Using Extensions:: Using non-standard features
272 * Standard C:: Using Standard C features
275 @node Source Language
276 @section Which Languages to Use
277 @cindex programming languges
279 When you want to use a language that gets compiled and runs at high
280 speed, the best language to use is C. Using another language is like
281 using a non-standard feature: it will cause trouble for users. Even if
282 GCC supports the other language, users may find it inconvenient to have
283 to install the compiler for that other language in order to build your
284 program. For example, if you write your program in C++, people will
285 have to install the GNU C++ compiler in order to compile your program.
287 C has one other advantage over C++ and other compiled languages: more
288 people know C, so more people will find it easy to read and modify the
289 program if it is written in C.
291 So in general it is much better to use C, rather than the
292 comparable alternatives.
294 But there are two exceptions to that conclusion:
298 It is no problem to use another language to write a tool specifically
299 intended for use with that language. That is because the only people
300 who want to build the tool will be those who have installed the other
304 If an application is of interest only to a narrow part of the community,
305 then the question of which language it is written in has less effect on
306 other people, so you may as well please yourself.
309 Many programs are designed to be extensible: they include an interpreter
310 for a language that is higher level than C. Often much of the program
311 is written in that language, too. The Emacs editor pioneered this
315 The standard extensibility interpreter for GNU software is GUILE, which
316 implements the language Scheme (an especially clean and simple dialect
317 of Lisp). @uref{http://www.gnu.org/software/guile/}. We don't reject
318 programs written in other ``scripting languages'' such as Perl and
319 Python, but using GUILE is very important for the overall consistency of
323 @section Compatibility with Other Implementations
324 @cindex compatibility with C and @sc{posix} standards
325 @cindex @sc{posix} compatibility
327 With occasional exceptions, utility programs and libraries for GNU
328 should be upward compatible with those in Berkeley Unix, and upward
329 compatible with Standard C if Standard C specifies their
330 behavior, and upward compatible with @sc{posix} if @sc{posix} specifies
333 When these standards conflict, it is useful to offer compatibility
334 modes for each of them.
336 @cindex options for compatibility
337 Standard C and @sc{posix} prohibit many kinds of extensions. Feel
338 free to make the extensions anyway, and include a @samp{--ansi},
339 @samp{--posix}, or @samp{--compatible} option to turn them off.
340 However, if the extension has a significant chance of breaking any real
341 programs or scripts, then it is not really upward compatible. So you
342 should try to redesign its interface to make it upward compatible.
344 @cindex @code{POSIXLY_CORRECT}, environment variable
345 Many GNU programs suppress extensions that conflict with @sc{posix} if the
346 environment variable @code{POSIXLY_CORRECT} is defined (even if it is
347 defined with a null value). Please make your program recognize this
348 variable if appropriate.
350 When a feature is used only by users (not by programs or command
351 files), and it is done poorly in Unix, feel free to replace it
352 completely with something totally different and better. (For example,
353 @code{vi} is replaced with Emacs.) But it is nice to offer a compatible
354 feature as well. (There is a free @code{vi} clone, so we offer it.)
356 Additional useful features are welcome regardless of whether
357 there is any precedent for them.
359 @node Using Extensions
360 @section Using Non-standard Features
361 @cindex non-standard extensions
363 Many GNU facilities that already exist support a number of convenient
364 extensions over the comparable Unix facilities. Whether to use these
365 extensions in implementing your program is a difficult question.
367 On the one hand, using the extensions can make a cleaner program.
368 On the other hand, people will not be able to build the program
369 unless the other GNU tools are available. This might cause the
370 program to work on fewer kinds of machines.
372 With some extensions, it might be easy to provide both alternatives.
373 For example, you can define functions with a ``keyword'' @code{INLINE}
374 and define that as a macro to expand into either @code{inline} or
375 nothing, depending on the compiler.
377 In general, perhaps it is best not to use the extensions if you can
378 straightforwardly do without them, but to use the extensions if they
379 are a big improvement.
381 An exception to this rule are the large, established programs (such as
382 Emacs) which run on a great variety of systems. Using GNU extensions in
383 such programs would make many users unhappy, so we don't do that.
385 Another exception is for programs that are used as part of compilation:
386 anything that must be compiled with other compilers in order to
387 bootstrap the GNU compilation facilities. If these require the GNU
388 compiler, then no one can compile them without having them installed
389 already. That would be extremely troublesome in certain cases.
392 @section Standard C and Pre-Standard C
393 @cindex @sc{ansi} C standard
395 1989 Standard C is widespread enough now that it is ok to use its
396 features in new programs. There is one exception: do not ever use the
397 ``trigraph'' feature of Standard C.
399 1999 Standard C is not widespread yet, so please do not require its
400 features in programs. It is ok to use its features if they are present.
402 However, it is easy to support pre-standard compilers in most programs,
403 so if you know how to do that, feel free. If a program you are
404 maintaining has such support, you should try to keep it working.
406 @cindex function prototypes
407 To support pre-standard C, instead of writing function definitions in
408 standard prototype form,
417 write the definition in pre-standard style like this,
427 and use a separate declaration to specify the argument prototype:
433 You need such a declaration anyway, in a header file, to get the benefit
434 of prototypes in all the files where the function is called. And once
435 you have the declaration, you normally lose nothing by writing the
436 function definition in the pre-standard style.
438 This technique does not work for integer types narrower than @code{int}.
439 If you think of an argument as being of a type narrower than @code{int},
440 declare it as @code{int} instead.
442 There are a few special cases where this technique is hard to use. For
443 example, if a function argument needs to hold the system type
444 @code{dev_t}, you run into trouble, because @code{dev_t} is shorter than
445 @code{int} on some machines; but you cannot use @code{int} instead,
446 because @code{dev_t} is wider than @code{int} on some machines. There
447 is no type you can safely use on all machines in a non-standard
448 definition. The only way to support non-standard C and pass such an
449 argument is to check the width of @code{dev_t} using Autoconf and choose
450 the argument type accordingly. This may not be worth the trouble.
452 In order to support pre-standard compilers that do not recognize
453 prototypes, you may want to use a preprocessor macro like this:
456 /* Declare the prototype for a general external function. */
457 #if defined (__STDC__) || defined (WINDOWSNT)
458 #define P_(proto) proto
464 @node Program Behavior
465 @chapter Program Behavior for All Programs
467 This @value{CHAPTER} describes conventions for writing robust
468 software. It also describes general standards for error messages, the
469 command line interface, and how libraries should behave.
472 * Semantics:: Writing robust programs
473 * Libraries:: Library behavior
474 * Errors:: Formatting error messages
475 * User Interfaces:: Standards about interfaces generally
476 * Graphical Interfaces:: Standards for graphical interfaces
477 * Command-Line Interfaces:: Standards for command line interfaces
478 * Option Table:: Table of long options
479 * Memory Usage:: When and how to care about memory needs
480 * File Usage:: Which files to use, and where
484 @section Writing Robust Programs
486 @cindex arbitrary limits on data
487 Avoid arbitrary limits on the length or number of @emph{any} data
488 structure, including file names, lines, files, and symbols, by allocating
489 all data structures dynamically. In most Unix utilities, ``long lines
490 are silently truncated''. This is not acceptable in a GNU utility.
492 @cindex @code{NUL} characters
493 Utilities reading files should not drop NUL characters, or any other
494 nonprinting characters @emph{including those with codes above 0177}.
495 The only sensible exceptions would be utilities specifically intended
496 for interface to certain types of terminals or printers
497 that can't handle those characters.
498 Whenever possible, try to make programs work properly with
499 sequences of bytes that represent multibyte characters, using encodings
500 such as UTF-8 and others.
502 @cindex error messages
503 Check every system call for an error return, unless you know you wish to
504 ignore errors. Include the system error text (from @code{perror} or
505 equivalent) in @emph{every} error message resulting from a failing
506 system call, as well as the name of the file if any and the name of the
507 utility. Just ``cannot open foo.c'' or ``stat failed'' is not
510 @cindex @code{malloc} return value
511 @cindex memory allocation failure
512 Check every call to @code{malloc} or @code{realloc} to see if it
513 returned zero. Check @code{realloc} even if you are making the block
514 smaller; in a system that rounds block sizes to a power of 2,
515 @code{realloc} may get a different block if you ask for less space.
517 In Unix, @code{realloc} can destroy the storage block if it returns
518 zero. GNU @code{realloc} does not have this bug: if it fails, the
519 original block is unchanged. Feel free to assume the bug is fixed. If
520 you wish to run your program on Unix, and wish to avoid lossage in this
521 case, you can use the GNU @code{malloc}.
523 You must expect @code{free} to alter the contents of the block that was
524 freed. Anything you want to fetch from the block, you must fetch before
527 If @code{malloc} fails in a noninteractive program, make that a fatal
528 error. In an interactive program (one that reads commands from the
529 user), it is better to abort the command and return to the command
530 reader loop. This allows the user to kill other processes to free up
531 virtual memory, and then try the command again.
533 @cindex command-line arguments, decoding
534 Use @code{getopt_long} to decode arguments, unless the argument syntax
535 makes this unreasonable.
537 When static storage is to be written in during program execution, use
538 explicit C code to initialize it. Reserve C initialized declarations
539 for data that will not be changed.
542 Try to avoid low-level interfaces to obscure Unix data structures (such
543 as file directories, utmp, or the layout of kernel memory), since these
544 are less likely to work compatibly. If you need to find all the files
545 in a directory, use @code{readdir} or some other high-level interface.
546 These are supported compatibly by GNU.
548 @cindex signal handling
549 The preferred signal handling facilities are the BSD variant of
550 @code{signal}, and the @sc{posix} @code{sigaction} function; the
551 alternative USG @code{signal} interface is an inferior design.
553 Nowadays, using the @sc{posix} signal functions may be the easiest way
554 to make a program portable. If you use @code{signal}, then on GNU/Linux
555 systems running GNU libc version 1, you should include
556 @file{bsd/signal.h} instead of @file{signal.h}, so as to get BSD
557 behavior. It is up to you whether to support systems where
558 @code{signal} has only the USG behavior, or give up on them.
560 @cindex impossible conditions
561 In error checks that detect ``impossible'' conditions, just abort.
562 There is usually no point in printing any message. These checks
563 indicate the existence of bugs. Whoever wants to fix the bugs will have
564 to read the source code and run a debugger. So explain the problem with
565 comments in the source. The relevant data will be in variables, which
566 are easy to examine with the debugger, so there is no point moving them
569 Do not use a count of errors as the exit status for a program.
570 @emph{That does not work}, because exit status values are limited to 8
571 bits (0 through 255). A single run of the program might have 256
572 errors; if you try to return 256 as the exit status, the parent process
573 will see 0 as the status, and it will appear that the program succeeded.
575 @cindex temporary files
576 @cindex @code{TMPDIR} environment variable
577 If you make temporary files, check the @code{TMPDIR} environment
578 variable; if that variable is defined, use the specified directory
579 instead of @file{/tmp}.
581 In addition, be aware that there is a possible security problem when
582 creating temporary files in world-writable directories. In C, you can
583 avoid this problem by creating temporary files in this manner:
586 fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0600);
590 or by using the @code{mkstemps} function from libiberty.
592 In bash, use @code{set -C} to avoid this problem.
595 @section Library Behavior
598 Try to make library functions reentrant. If they need to do dynamic
599 storage allocation, at least try to avoid any nonreentrancy aside from
600 that of @code{malloc} itself.
602 Here are certain name conventions for libraries, to avoid name
605 Choose a name prefix for the library, more than two characters long.
606 All external function and variable names should start with this
607 prefix. In addition, there should only be one of these in any given
608 library member. This usually means putting each one in a separate
611 An exception can be made when two external symbols are always used
612 together, so that no reasonable program could use one without the
613 other; then they can both go in the same file.
615 External symbols that are not documented entry points for the user
616 should have names beginning with @samp{_}. The @samp{_} should be
617 followed by the chosen name prefix for the library, to prevent
618 collisions with other libraries. These can go in the same files with
619 user entry points if you like.
621 Static functions and variables can be used as you like and need not
622 fit any naming convention.
625 @section Formatting Error Messages
626 @cindex formatting error messages
627 @cindex error messages, formatting
629 Error messages from compilers should look like this:
632 @var{source-file-name}:@var{lineno}: @var{message}
636 If you want to mention the column number, use this format:
639 @var{source-file-name}:@var{lineno}:@var{column}: @var{message}
643 Line numbers should start from 1 at the beginning of the file, and
644 column numbers should start from 1 at the beginning of the line. (Both
645 of these conventions are chosen for compatibility.) Calculate column
646 numbers assuming that space and all ASCII printing characters have
647 equal width, and assuming tab stops every 8 columns.
649 Error messages from other noninteractive programs should look like this:
652 @var{program}:@var{source-file-name}:@var{lineno}: @var{message}
656 when there is an appropriate source file, or like this:
659 @var{program}: @var{message}
663 when there is no relevant source file.
665 If you want to mention the column number, use this format:
668 @var{program}:@var{source-file-name}:@var{lineno}:@var{column}: @var{message}
671 In an interactive program (one that is reading commands from a
672 terminal), it is better not to include the program name in an error
673 message. The place to indicate which program is running is in the
674 prompt or with the screen layout. (When the same program runs with
675 input from a source other than a terminal, it is not interactive and
676 would do best to print error messages using the noninteractive style.)
678 The string @var{message} should not begin with a capital letter when
679 it follows a program name and/or file name. Also, it should not end
682 Error messages from interactive programs, and other messages such as
683 usage messages, should start with a capital letter. But they should not
686 @node User Interfaces
687 @section Standards for Interfaces Generally
689 @cindex program name and its behavior
690 @cindex behavior, dependent on program's name
691 Please don't make the behavior of a utility depend on the name used
692 to invoke it. It is useful sometimes to make a link to a utility
693 with a different name, and that should not change what it does.
695 Instead, use a run time option or a compilation switch or both
696 to select among the alternate behaviors.
698 @cindex output device and program's behavior
699 Likewise, please don't make the behavior of the program depend on the
700 type of output device it is used with. Device independence is an
701 important principle of the system's design; do not compromise it merely
702 to save someone from typing an option now and then. (Variation in error
703 message syntax when using a terminal is ok, because that is a side issue
704 that people do not depend on.)
706 If you think one behavior is most useful when the output is to a
707 terminal, and another is most useful when the output is a file or a
708 pipe, then it is usually best to make the default behavior the one that
709 is useful with output to a terminal, and have an option for the other
712 Compatibility requires certain programs to depend on the type of output
713 device. It would be disastrous if @code{ls} or @code{sh} did not do so
714 in the way all users expect. In some of these cases, we supplement the
715 program with a preferred alternate version that does not depend on the
716 output device type. For example, we provide a @code{dir} program much
717 like @code{ls} except that its default output format is always
720 @node Graphical Interfaces
721 @section Standards for Graphical Interfaces
722 @cindex graphical user interface
725 When you write a program that provides a graphical user interface,
726 please make it work with X Windows and the GTK toolkit unless the
727 functionality specifically requires some alternative (for example,
728 ``displaying jpeg images while in console mode'').
730 In addition, please provide a command-line interface to control the
731 functionality. (In many cases, the graphical user interface can be a
732 separate program which invokes the command-line program.) This is
733 so that the same jobs can be done from scripts.
737 Please also consider providing a CORBA interface (for use from GNOME), a
738 library interface (for use from C), and perhaps a keyboard-driven
739 console interface (for use by users from console mode). Once you are
740 doing the work to provide the functionality and the graphical interface,
741 these won't be much extra work.
743 @node Command-Line Interfaces
744 @section Standards for Command Line Interfaces
745 @cindex command-line interface
748 It is a good idea to follow the @sc{posix} guidelines for the
749 command-line options of a program. The easiest way to do this is to use
750 @code{getopt} to parse them. Note that the GNU version of @code{getopt}
751 will normally permit options anywhere among the arguments unless the
752 special argument @samp{--} is used. This is not what @sc{posix}
753 specifies; it is a GNU extension.
755 @cindex long-named options
756 Please define long-named options that are equivalent to the
757 single-letter Unix-style options. We hope to make GNU more user
758 friendly this way. This is easy to do with the GNU function
761 One of the advantages of long-named options is that they can be
762 consistent from program to program. For example, users should be able
763 to expect the ``verbose'' option of any GNU program which has one, to be
764 spelled precisely @samp{--verbose}. To achieve this uniformity, look at
765 the table of common long-option names when you choose the option names
766 for your program (@pxref{Option Table}).
768 It is usually a good idea for file names given as ordinary arguments to
769 be input files only; any output files would be specified using options
770 (preferably @samp{-o} or @samp{--output}). Even if you allow an output
771 file name as an ordinary argument for compatibility, try to provide an
772 option as another way to specify it. This will lead to more consistency
773 among GNU utilities, and fewer idiosyncracies for users to remember.
775 @cindex standard command-line options
776 All programs should support two standard options: @samp{--version}
780 @cindex @samp{--version} option
782 This option should direct the program to print information about its name,
783 version, origin and legal status, all on standard output, and then exit
784 successfully. Other options and arguments should be ignored once this
785 is seen, and the program should not perform its normal function.
787 @cindex canonical name of a program
788 @cindex program's canonical name
789 The first line is meant to be easy for a program to parse; the version
790 number proper starts after the last space. In addition, it contains
791 the canonical name for this program, in this format:
798 The program's name should be a constant string; @emph{don't} compute it
799 from @code{argv[0]}. The idea is to state the standard or canonical
800 name for the program, not its file name. There are other ways to find
801 out the precise file name where a command is found in @code{PATH}.
803 If the program is a subsidiary part of a larger package, mention the
804 package name in parentheses, like this:
807 emacsserver (GNU Emacs) 19.30
811 If the package has a version number which is different from this
812 program's version number, you can mention the package version number
813 just before the close-parenthesis.
815 If you @strong{need} to mention the version numbers of libraries which
816 are distributed separately from the package which contains this program,
817 you can do so by printing an additional line of version info for each
818 library you want to mention. Use the same format for these lines as for
821 Please do not mention all of the libraries that the program uses ``just
822 for completeness''---that would produce a lot of unhelpful clutter.
823 Please mention library version numbers only if you find in practice that
824 they are very important to you in debugging.
826 The following line, after the version number line or lines, should be a
827 copyright notice. If more than one copyright notice is called for, put
828 each on a separate line.
830 Next should follow a brief statement that the program is free software,
831 and that users are free to copy and change it on certain conditions. If
832 the program is covered by the GNU GPL, say so here. Also mention that
833 there is no warranty, to the extent permitted by law.
835 It is ok to finish the output with a list of the major authors of the
836 program, as a way of giving credit.
838 Here's an example of output that follows these rules:
842 Copyright (C) 1996 Free Software Foundation, Inc.
843 GNU Emacs comes with NO WARRANTY,
844 to the extent permitted by law.
845 You may redistribute copies of GNU Emacs
846 under the terms of the GNU General Public License.
847 For more information about these matters,
848 see the files named COPYING.
851 You should adapt this to your program, of course, filling in the proper
852 year, copyright holder, name of program, and the references to
853 distribution terms, and changing the rest of the wording as necessary.
855 This copyright notice only needs to mention the most recent year in
856 which changes were made---there's no need to list the years for previous
857 versions' changes. You don't have to mention the name of the program in
858 these notices, if that is inconvenient, since it appeared in the first
861 @cindex @samp{--help} option
863 This option should output brief documentation for how to invoke the
864 program, on standard output, then exit successfully. Other options and
865 arguments should be ignored once this is seen, and the program should
866 not perform its normal function.
868 @cindex address for bug reports
870 Near the end of the @samp{--help} option's output there should be a line
871 that says where to mail bug reports. It should have this format:
874 Report bugs to @var{mailing-address}.
879 @section Table of Long Options
880 @cindex long option names
881 @cindex table of long options
883 Here is a table of long options used by GNU programs. It is surely
884 incomplete, but we aim to list all the options that a new program might
885 want to be compatible with. If you use names not already in the table,
886 please send @email{bug-standards@@gnu.org} a list of them, with their
887 meanings, so we can update the table.
889 @c Please leave newlines between items in this table; it's much easier
890 @c to update when it isn't completely squashed together and unreadable.
891 @c When there is more than one short option for a long option name, put
892 @c a semicolon between the lists of the programs that use them, not a
893 @c period. --friedman
897 @samp{-N} in @code{tar}.
900 @samp{-a} in @code{du}, @code{ls}, @code{nm}, @code{stty}, @code{uname},
904 @samp{-a} in @code{diff}.
907 @samp{-A} in @code{ls}.
910 @samp{-a} in @code{etags}, @code{tee}, @code{time};
911 @samp{-r} in @code{tar}.
914 @samp{-a} in @code{cp}.
917 @samp{-n} in @code{shar}.
920 @samp{-l} in @code{m4}.
923 @samp{-a} in @code{diff}.
926 @samp{-v} in @code{gawk}.
935 @samp{-a} in @code{recode}.
938 @samp{-a} in @code{wdiff}.
941 @samp{-A} in @code{ptx}.
944 @samp{-n} in @code{wdiff}.
947 For server programs, run in the background.
949 @item backward-search
950 @samp{-B} in @code{ctags}.
953 @samp{-f} in @code{shar}.
962 @samp{-b} in @code{tac}.
965 @samp{-b} in @code{cpio} and @code{diff}.
968 @samp{-b} in @code{shar}.
971 Used in @code{cpio} and @code{tar}.
974 @samp{-b} in @code{head} and @code{tail}.
977 @samp{-b} in @code{ptx}.
980 Used in various programs to make output shorter.
983 @samp{-c} in @code{head}, @code{split}, and @code{tail}.
986 @samp{-C} in @code{etags}.
989 @samp{-A} in @code{tar}.
992 Used in various programs to specify the directory to use.
995 @samp{-c} in @code{chgrp} and @code{chown}.
998 @samp{-F} in @code{ls}.
1001 @samp{-c} in @code{recode}.
1004 @samp{-c} in @code{su};
1008 @samp{-d} in @code{tar}.
1011 Used in @code{gawk}.
1014 @samp{-Z} in @code{tar} and @code{shar}.
1017 @samp{-A} in @code{tar}.
1020 @samp{-w} in @code{tar}.
1023 Used in @code{diff}.
1026 @samp{-W copyleft} in @code{gawk}.
1029 @samp{-C} in @code{ptx}, @code{recode}, and @code{wdiff};
1030 @samp{-W copyright} in @code{gawk}.
1036 @samp{-q} in @code{who}.
1039 @samp{-l} in @code{du}.
1042 Used in @code{tar} and @code{cpio}.
1045 @samp{-c} in @code{shar}.
1048 @samp{-x} in @code{ctags}.
1051 @samp{-d} in @code{touch}.
1054 @samp{-d} in Make and @code{m4};
1058 @samp{-D} in @code{m4}.
1061 @samp{-d} in Bison and @code{ctags}.
1064 @samp{-D} in @code{tar}.
1067 @samp{-L} in @code{chgrp}, @code{chown}, @code{cpio}, @code{du},
1068 @code{ls}, and @code{tar}.
1070 @item dereference-args
1071 @samp{-D} in @code{du}.
1074 Specify an I/O device (special file name).
1077 @samp{-d} in @code{recode}.
1079 @item dictionary-order
1080 @samp{-d} in @code{look}.
1083 @samp{-d} in @code{tar}.
1086 @samp{-n} in @code{csplit}.
1089 Specify the directory to use, in various programs. In @code{ls}, it
1090 means to show directories themselves rather than their contents. In
1091 @code{rm} and @code{ln}, it means to not treat links to directories
1095 @samp{-x} in @code{strip}.
1097 @item discard-locals
1098 @samp{-X} in @code{strip}.
1104 @samp{-e} in @code{diff}.
1106 @item elide-empty-files
1107 @samp{-z} in @code{csplit}.
1110 @samp{-x} in @code{wdiff}.
1113 @samp{-z} in @code{wdiff}.
1115 @item entire-new-file
1116 @samp{-N} in @code{diff}.
1118 @item environment-overrides
1122 @samp{-e} in @code{xargs}.
1128 Used in @code{makeinfo}.
1131 @samp{-o} in @code{m4}.
1134 @samp{-b} in @code{ls}.
1137 @samp{-X} in @code{tar}.
1143 @samp{-x} in @code{xargs}.
1146 @samp{-e} in @code{unshar}.
1149 @samp{-t} in @code{diff}.
1152 @samp{-e} in @code{sed}.
1155 @samp{-g} in @code{nm}.
1158 @samp{-i} in @code{cpio};
1159 @samp{-x} in @code{tar}.
1162 @samp{-f} in @code{finger}.
1165 @samp{-f} in @code{su}.
1167 @item fatal-warnings
1168 @samp{-E} in @code{m4}.
1171 @samp{-f} in @code{info}, @code{gawk}, Make, @code{mt}, and @code{tar};
1172 @samp{-n} in @code{sed};
1173 @samp{-r} in @code{touch}.
1175 @item field-separator
1176 @samp{-F} in @code{gawk}.
1182 @samp{-F} in @code{ls}.
1185 @samp{-T} in @code{tar}.
1188 Used in @code{makeinfo}.
1190 @item flag-truncation
1191 @samp{-F} in @code{ptx}.
1193 @item fixed-output-files
1197 @samp{-f} in @code{tail}.
1199 @item footnote-style
1200 Used in @code{makeinfo}.
1203 @samp{-f} in @code{cp}, @code{ln}, @code{mv}, and @code{rm}.
1206 @samp{-F} in @code{shar}.
1209 For server programs, run in the foreground;
1210 in other words, don't do anything special to run the server
1214 Used in @code{ls}, @code{time}, and @code{ptx}.
1217 @samp{-F} in @code{m4}.
1223 @samp{-g} in @code{ptx}.
1226 @samp{-x} in @code{tar}.
1229 @samp{-i} in @code{ul}.
1232 @samp{-g} in @code{recode}.
1235 @samp{-g} in @code{install}.
1238 @samp{-z} in @code{tar} and @code{shar}.
1241 @samp{-H} in @code{m4}.
1244 @samp{-h} in @code{objdump} and @code{recode}
1247 @samp{-H} in @code{who}.
1250 Used to ask for brief usage information.
1252 @item here-delimiter
1253 @samp{-d} in @code{shar}.
1255 @item hide-control-chars
1256 @samp{-q} in @code{ls}.
1259 In @code{makeinfo}, output HTML.
1262 @samp{-u} in @code{who}.
1265 @samp{-D} in @code{diff}.
1268 @samp{-I} in @code{ls};
1269 @samp{-x} in @code{recode}.
1271 @item ignore-all-space
1272 @samp{-w} in @code{diff}.
1274 @item ignore-backups
1275 @samp{-B} in @code{ls}.
1277 @item ignore-blank-lines
1278 @samp{-B} in @code{diff}.
1281 @samp{-f} in @code{look} and @code{ptx};
1282 @samp{-i} in @code{diff} and @code{wdiff}.
1288 @samp{-i} in @code{ptx}.
1290 @item ignore-indentation
1291 @samp{-I} in @code{etags}.
1293 @item ignore-init-file
1296 @item ignore-interrupts
1297 @samp{-i} in @code{tee}.
1299 @item ignore-matching-lines
1300 @samp{-I} in @code{diff}.
1302 @item ignore-space-change
1303 @samp{-b} in @code{diff}.
1306 @samp{-i} in @code{tar}.
1309 @samp{-i} in @code{etags};
1310 @samp{-I} in @code{m4}.
1316 @samp{-G} in @code{tar}.
1319 @samp{-i}, @samp{-l}, and @samp{-m} in Finger.
1322 In some programs, specify the name of the file to read as the user's
1326 @samp{-i} in @code{expand}.
1329 @samp{-T} in @code{diff}.
1332 @samp{-i} in @code{ls}.
1335 @samp{-i} in @code{cp}, @code{ln}, @code{mv}, @code{rm};
1336 @samp{-e} in @code{m4};
1337 @samp{-p} in @code{xargs};
1338 @samp{-w} in @code{tar}.
1341 @samp{-p} in @code{shar}.
1356 @samp{-k} in @code{csplit}.
1359 @samp{-k} in @code{du} and @code{ls}.
1362 @samp{-l} in @code{etags}.
1365 @samp{-l} in @code{wdiff}.
1367 @item level-for-gzip
1368 @samp{-g} in @code{shar}.
1371 @samp{-C} in @code{split}.
1374 Used in @code{split}, @code{head}, and @code{tail}.
1377 @samp{-l} in @code{cpio}.
1381 Used in @code{gawk}.
1384 @samp{-t} in @code{cpio};
1385 @samp{-l} in @code{recode}.
1388 @samp{-t} in @code{tar}.
1391 @samp{-N} in @code{ls}.
1400 No listing of which programs already use this;
1401 someone should check to
1402 see if any actually do, and tell @email{gnu@@gnu.org}.
1405 @samp{-M} in @code{ptx}.
1408 @samp{-m} in @code{hello} and @code{uname}.
1410 @item make-directories
1411 @samp{-d} in @code{cpio}.
1420 @samp{-n} in @code{xargs}.
1423 @samp{-n} in @code{xargs}.
1426 @samp{-l} in @code{xargs}.
1432 @samp{-P} in @code{xargs}.
1435 @samp{-T} in @code{who}.
1438 @samp{-T} in @code{who}.
1441 @samp{-d} in @code{diff}.
1443 @item mixed-uuencode
1444 @samp{-M} in @code{shar}.
1447 @samp{-m} in @code{install}, @code{mkdir}, and @code{mkfifo}.
1449 @item modification-time
1450 @samp{-m} in @code{tar}.
1453 @samp{-M} in @code{tar}.
1459 @samp{-L} in @code{m4}.
1462 @samp{-a} in @code{shar}.
1467 @item no-builtin-rules
1470 @item no-character-count
1471 @samp{-w} in @code{shar}.
1473 @item no-check-existing
1474 @samp{-x} in @code{shar}.
1477 @samp{-3} in @code{wdiff}.
1480 @samp{-c} in @code{touch}.
1483 @samp{-D} in @code{etags}.
1486 @samp{-1} in @code{wdiff}.
1488 @item no-dereference
1489 @samp{-d} in @code{cp}.
1492 @samp{-2} in @code{wdiff}.
1501 @samp{-P} in @code{shar}.
1504 @samp{-e} in @code{gprof}.
1507 @samp{-R} in @code{etags}.
1510 @samp{-p} in @code{nm}.
1513 Used in @code{makeinfo}.
1516 @samp{-a} in @code{gprof}.
1519 @samp{-E} in @code{gprof}.
1522 @samp{-m} in @code{shar}.
1525 Used in @code{makeinfo}.
1528 Used in @code{emacsclient}.
1531 Used in various programs to inhibit warnings.
1534 @samp{-n} in @code{info}.
1537 @samp{-n} in @code{uname}.
1540 @samp{-f} in @code{cpio}.
1543 @samp{-n} in @code{objdump}.
1546 @samp{-0} in @code{xargs}.
1549 @samp{-n} in @code{cat}.
1551 @item number-nonblank
1552 @samp{-b} in @code{cat}.
1555 @samp{-n} in @code{nm}.
1557 @item numeric-uid-gid
1558 @samp{-n} in @code{cpio} and @code{ls}.
1564 @samp{-o} in @code{tar}.
1569 @item one-file-system
1570 @samp{-l} in @code{tar}, @code{cp}, and @code{du}.
1573 @samp{-o} in @code{ptx}.
1576 @samp{-f} in @code{gprof}.
1579 @samp{-F} in @code{gprof}.
1582 @samp{-o} in @code{getopt}, @code{fdlist}, @code{fdmount},
1583 @code{fdmountd}, and @code{fdumount}.
1586 In various programs, specify the output file name.
1589 @samp{-o} in @code{shar}.
1592 @samp{-o} in @code{rm}.
1595 @samp{-c} in @code{unshar}.
1598 @samp{-o} in @code{install}.
1601 @samp{-l} in @code{diff}.
1603 @item paragraph-indent
1604 Used in @code{makeinfo}.
1607 @samp{-p} in @code{mkdir} and @code{rmdir}.
1610 @samp{-p} in @code{ul}.
1613 @samp{-p} in @code{cpio}.
1616 @samp{-P} in @code{finger}.
1619 @samp{-c} in @code{cpio} and @code{tar}.
1622 Used in @code{gawk}.
1624 @item prefix-builtins
1625 @samp{-P} in @code{m4}.
1628 @samp{-f} in @code{csplit}.
1631 Used in @code{tar} and @code{cp}.
1633 @item preserve-environment
1634 @samp{-p} in @code{su}.
1636 @item preserve-modification-time
1637 @samp{-m} in @code{cpio}.
1639 @item preserve-order
1640 @samp{-s} in @code{tar}.
1642 @item preserve-permissions
1643 @samp{-p} in @code{tar}.
1646 @samp{-l} in @code{diff}.
1649 @samp{-L} in @code{cmp}.
1651 @item print-data-base
1654 @item print-directory
1657 @item print-file-name
1658 @samp{-o} in @code{nm}.
1661 @samp{-s} in @code{nm}.
1664 @samp{-p} in @code{wdiff}.
1667 @samp{-p} in @code{ed}.
1670 Specify an HTTP proxy.
1673 @samp{-X} in @code{shar}.
1679 Used in many programs to inhibit the usual output. @strong{Note:} every
1680 program accepting @samp{--quiet} should accept @samp{--silent} as a
1684 @samp{-Q} in @code{shar}
1687 @samp{-Q} in @code{ls}.
1690 @samp{-n} in @code{diff}.
1693 Used in @code{gawk}.
1695 @item read-full-blocks
1696 @samp{-B} in @code{tar}.
1705 @samp{-R} in @code{tar}.
1708 Used in @code{chgrp}, @code{chown}, @code{cp}, @code{ls}, @code{diff},
1711 @item reference-limit
1712 Used in @code{makeinfo}.
1715 @samp{-r} in @code{ptx}.
1718 @samp{-r} in @code{tac} and @code{etags}.
1721 @samp{-r} in @code{uname}.
1724 @samp{-R} in @code{m4}.
1727 @samp{-r} in @code{objdump}.
1730 @samp{-r} in @code{cpio}.
1733 @samp{-i} in @code{xargs}.
1735 @item report-identical-files
1736 @samp{-s} in @code{diff}.
1738 @item reset-access-time
1739 @samp{-a} in @code{cpio}.
1742 @samp{-r} in @code{ls} and @code{nm}.
1745 @samp{-f} in @code{diff}.
1747 @item right-side-defs
1748 @samp{-R} in @code{ptx}.
1751 @samp{-s} in @code{tar}.
1753 @item same-permissions
1754 @samp{-p} in @code{tar}.
1757 @samp{-g} in @code{stty}.
1762 @item sentence-regexp
1763 @samp{-S} in @code{ptx}.
1766 @samp{-S} in @code{du}.
1769 @samp{-s} in @code{tac}.
1772 Used by @code{recode} to chose files or pipes for sequencing passes.
1775 @samp{-s} in @code{su}.
1778 @samp{-A} in @code{cat}.
1780 @item show-c-function
1781 @samp{-p} in @code{diff}.
1784 @samp{-E} in @code{cat}.
1786 @item show-function-line
1787 @samp{-F} in @code{diff}.
1790 @samp{-T} in @code{cat}.
1793 Used in many programs to inhibit the usual output.
1794 @strong{Note:} every program accepting
1795 @samp{--silent} should accept @samp{--quiet} as a synonym.
1798 @samp{-s} in @code{ls}.
1801 Specify a file descriptor for a network server to use for its socket,
1802 instead of opening and binding a new socket. This provides a way to
1803 run, in a nonpriveledged process, a server that normally needs a
1804 reserved port number.
1810 @samp{-W source} in @code{gawk}.
1813 @samp{-S} in @code{tar}.
1815 @item speed-large-files
1816 @samp{-H} in @code{diff}.
1819 @samp{-E} in @code{unshar}.
1821 @item split-size-limit
1822 @samp{-L} in @code{shar}.
1825 @samp{-s} in @code{cat}.
1828 @samp{-w} in @code{wdiff}.
1831 @samp{-y} in @code{wdiff}.
1834 Used in @code{tar} and @code{diff} to specify which file within
1835 a directory to start processing with.
1838 @samp{-s} in @code{wdiff}.
1840 @item stdin-file-list
1841 @samp{-S} in @code{shar}.
1847 @samp{-s} in @code{recode}.
1850 @samp{-s} in @code{install}.
1853 @samp{-s} in @code{strip}.
1856 @samp{-S} in @code{strip}.
1859 @samp{-s} in @code{shar}.
1862 @samp{-S} in @code{cp}, @code{ln}, @code{mv}.
1865 @samp{-b} in @code{csplit}.
1868 @samp{-s} in @code{gprof}.
1871 @samp{-s} in @code{du}.
1874 @samp{-s} in @code{ln}.
1877 Used in GDB and @code{objdump}.
1880 @samp{-s} in @code{m4}.
1883 @samp{-s} in @code{uname}.
1886 @samp{-t} in @code{expand} and @code{unexpand}.
1889 @samp{-T} in @code{ls}.
1892 @samp{-T} in @code{tput} and @code{ul}.
1893 @samp{-t} in @code{wdiff}.
1896 @samp{-a} in @code{diff}.
1899 @samp{-T} in @code{shar}.
1902 Used in @code{ls} and @code{touch}.
1905 Specify how long to wait before giving up on some operation.
1908 @samp{-O} in @code{tar}.
1911 @samp{-c} in @code{du}.
1914 @samp{-t} in Make, @code{ranlib}, and @code{recode}.
1917 @samp{-t} in @code{m4}.
1920 @samp{-t} in @code{hello};
1921 @samp{-W traditional} in @code{gawk};
1922 @samp{-G} in @code{ed}, @code{m4}, and @code{ptx}.
1928 @samp{-t} in @code{ctags}.
1930 @item typedefs-and-c++
1931 @samp{-T} in @code{ctags}.
1934 @samp{-t} in @code{ptx}.
1937 @samp{-z} in @code{tar}.
1940 @samp{-u} in @code{cpio}.
1943 @samp{-U} in @code{m4}.
1945 @item undefined-only
1946 @samp{-u} in @code{nm}.
1949 @samp{-u} in @code{cp}, @code{ctags}, @code{mv}, @code{tar}.
1952 Used in @code{gawk}; same as @samp{--help}.
1955 @samp{-B} in @code{shar}.
1957 @item vanilla-operation
1958 @samp{-V} in @code{shar}.
1961 Print more information about progress. Many programs support this.
1964 @samp{-W} in @code{tar}.
1967 Print the version number.
1969 @item version-control
1970 @samp{-V} in @code{cp}, @code{ln}, @code{mv}.
1973 @samp{-v} in @code{ctags}.
1976 @samp{-V} in @code{tar}.
1981 @item whole-size-limit
1982 @samp{-l} in @code{shar}.
1985 @samp{-w} in @code{ls} and @code{ptx}.
1988 @samp{-W} in @code{ptx}.
1991 @samp{-T} in @code{who}.
1994 @samp{-z} in @code{gprof}.
1998 @section Memory Usage
1999 @cindex memory usage
2001 If a program typically uses just a few meg of memory, don't bother making any
2002 effort to reduce memory usage. For example, if it is impractical for
2003 other reasons to operate on files more than a few meg long, it is
2004 reasonable to read entire input files into core to operate on them.
2006 However, for programs such as @code{cat} or @code{tail}, that can
2007 usefully operate on very large files, it is important to avoid using a
2008 technique that would artificially limit the size of files it can handle.
2009 If a program works by lines and could be applied to arbitrary
2010 user-supplied input files, it should keep only a line in memory, because
2011 this is not very hard and users will want to be able to operate on input
2012 files that are bigger than will fit in core all at once.
2014 If your program creates complicated data structures, just make them in
2015 core and give a fatal error if @code{malloc} returns zero.
2021 Programs should be prepared to operate when @file{/usr} and @file{/etc}
2022 are read-only file systems. Thus, if the program manages log files,
2023 lock files, backup files, score files, or any other files which are
2024 modified for internal purposes, these files should not be stored in
2025 @file{/usr} or @file{/etc}.
2027 There are two exceptions. @file{/etc} is used to store system
2028 configuration information; it is reasonable for a program to modify
2029 files in @file{/etc} when its job is to update the system configuration.
2030 Also, if the user explicitly asks to modify one file in a directory, it
2031 is reasonable for the program to store other files in the same
2035 @chapter Making The Best Use of C
2037 This @value{CHAPTER} provides advice on how best to use the C language
2038 when writing GNU software.
2041 * Formatting:: Formatting Your Source Code
2042 * Comments:: Commenting Your Work
2043 * Syntactic Conventions:: Clean Use of C Constructs
2044 * Names:: Naming Variables and Functions
2045 * System Portability:: Portability between different operating systems
2046 * CPU Portability:: Supporting the range of CPU types
2047 * System Functions:: Portability and ``standard'' library functions
2048 * Internationalization:: Techniques for internationalization
2049 * Mmap:: How you can safely use @code{mmap}.
2053 @section Formatting Your Source Code
2054 @cindex formatting source code
2057 @cindex braces, in C source
2058 It is important to put the open-brace that starts the body of a C
2059 function in column zero, and avoid putting any other open-brace or
2060 open-parenthesis or open-bracket in column zero. Several tools look
2061 for open-braces in column zero to find the beginnings of C functions.
2062 These tools will not work on code not formatted that way.
2064 It is also important for function definitions to start the name of the
2065 function in column zero. This helps people to search for function
2066 definitions, and may also help certain tools recognize them. Thus,
2067 the proper format is this:
2071 concat (s1, s2) /* Name starts in column zero here */
2073 @{ /* Open brace in column zero here */
2079 or, if you want to use Standard C syntax, format the definition like
2084 concat (char *s1, char *s2)
2090 In Standard C, if the arguments don't fit nicely on one line,
2095 lots_of_args (int an_integer, long a_long, short a_short,
2096 double a_double, float a_float)
2100 The rest of this section gives our recommendations for other aspects of
2101 C formatting style, which is also the default style of the @code{indent}
2102 program in version 1.2 and newer. It corresponds to the options
2105 -nbad -bap -nbc -bbo -bl -bli2 -bls -ncdb -nce -cp1 -cs -di2
2106 -ndj -nfc1 -nfca -hnl -i2 -ip5 -lp -pcs -psl -nsc -nsob
2109 We don't think of these recommendations as requirements, because it
2110 causes no problems for users if two different programs have different
2113 But whatever style you use, please use it consistently, since a mixture
2114 of styles within one program tends to look ugly. If you are
2115 contributing changes to an existing program, please follow the style of
2118 For the body of the function, our recommended style looks like this:
2130 return ++x + bar ();
2134 @cindex spaces before open-paren
2135 We find it easier to read a program when it has spaces before the
2136 open-parentheses and after the commas. Especially after the commas.
2138 When you split an expression into multiple lines, split it
2139 before an operator, not after one. Here is the right way:
2141 @cindex expressions, splitting
2143 if (foo_this_is_long && bar > win (x, y, z)
2144 && remaining_condition)
2147 Try to avoid having two operators of different precedence at the same
2148 level of indentation. For example, don't write this:
2151 mode = (inmode[j] == VOIDmode
2152 || GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j])
2153 ? outmode[j] : inmode[j]);
2156 Instead, use extra parentheses so that the indentation shows the nesting:
2159 mode = ((inmode[j] == VOIDmode
2160 || (GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j])))
2161 ? outmode[j] : inmode[j]);
2164 Insert extra parentheses so that Emacs will indent the code properly.
2165 For example, the following indentation looks nice if you do it by hand,
2168 v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
2169 + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000;
2173 but Emacs would alter it. Adding a set of parentheses produces
2174 something that looks equally nice, and which Emacs will preserve:
2177 v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
2178 + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000);
2181 Format do-while statements like this:
2193 Please use formfeed characters (control-L) to divide the program into
2194 pages at logical places (but not within a function). It does not matter
2195 just how long the pages are, since they do not have to fit on a printed
2196 page. The formfeeds should appear alone on lines by themselves.
2199 @section Commenting Your Work
2202 Every program should start with a comment saying briefly what it is for.
2203 Example: @samp{fmt - filter for simple filling of text}.
2205 Please write the comments in a GNU program in English, because English
2206 is the one language that nearly all programmers in all countries can
2207 read. If you do not write English well, please write comments in
2208 English as well as you can, then ask other people to help rewrite them.
2209 If you can't write comments in English, please find someone to work with
2210 you and translate your comments into English.
2212 Please put a comment on each function saying what the function does,
2213 what sorts of arguments it gets, and what the possible values of
2214 arguments mean and are used for. It is not necessary to duplicate in
2215 words the meaning of the C argument declarations, if a C type is being
2216 used in its customary fashion. If there is anything nonstandard about
2217 its use (such as an argument of type @code{char *} which is really the
2218 address of the second character of a string, not the first), or any
2219 possible values that would not work the way one would expect (such as,
2220 that strings containing newlines are not guaranteed to work), be sure
2223 Also explain the significance of the return value, if there is one.
2225 Please put two spaces after the end of a sentence in your comments, so
2226 that the Emacs sentence commands will work. Also, please write
2227 complete sentences and capitalize the first word. If a lower-case
2228 identifier comes at the beginning of a sentence, don't capitalize it!
2229 Changing the spelling makes it a different identifier. If you don't
2230 like starting a sentence with a lower case letter, write the sentence
2231 differently (e.g., ``The identifier lower-case is @dots{}'').
2233 The comment on a function is much clearer if you use the argument
2234 names to speak about the argument values. The variable name itself
2235 should be lower case, but write it in upper case when you are speaking
2236 about the value rather than the variable itself. Thus, ``the inode
2237 number NODE_NUM'' rather than ``an inode''.
2239 There is usually no purpose in restating the name of the function in
2240 the comment before it, because the reader can see that for himself.
2241 There might be an exception when the comment is so long that the function
2242 itself would be off the bottom of the screen.
2244 There should be a comment on each static variable as well, like this:
2247 /* Nonzero means truncate lines in the display;
2248 zero means continue them. */
2252 @cindex conditionals, comments for
2253 @cindex @code{#endif}, commenting
2254 Every @samp{#endif} should have a comment, except in the case of short
2255 conditionals (just a few lines) that are not nested. The comment should
2256 state the condition of the conditional that is ending, @emph{including
2257 its sense}. @samp{#else} should have a comment describing the condition
2258 @emph{and sense} of the code that follows. For example:
2266 #endif /* not foo */
2276 but, by contrast, write the comments this way for a @samp{#ifndef}:
2289 #endif /* not foo */
2293 @node Syntactic Conventions
2294 @section Clean Use of C Constructs
2295 @cindex syntactic conventions
2297 @cindex implicit @code{int}
2298 @cindex function argument, declaring
2299 Please explicitly declare the types of all objects. For example, you
2300 should explicitly declare all arguments to functions, and you should
2301 declare functions to return @code{int} rather than omitting the
2304 @cindex compiler warnings
2305 @cindex @samp{-Wall} compiler option
2306 Some programmers like to use the GCC @samp{-Wall} option, and change the
2307 code whenever it issues a warning. If you want to do this, then do.
2308 Other programmers prefer not to use @samp{-Wall}, because it gives
2309 warnings for valid and legitimate code which they do not want to change.
2310 If you want to do this, then do. The compiler should be your servant,
2313 Declarations of external functions and functions to appear later in the
2314 source file should all go in one place near the beginning of the file
2315 (somewhere before the first function definition in the file), or else
2316 should go in a header file. Don't put @code{extern} declarations inside
2319 @cindex temporary variables
2320 It used to be common practice to use the same local variables (with
2321 names like @code{tem}) over and over for different values within one
2322 function. Instead of doing this, it is better declare a separate local
2323 variable for each distinct purpose, and give it a name which is
2324 meaningful. This not only makes programs easier to understand, it also
2325 facilitates optimization by good compilers. You can also move the
2326 declaration of each local variable into the smallest scope that includes
2327 all its uses. This makes the program even cleaner.
2329 Don't use local variables or parameters that shadow global identifiers.
2331 @cindex multiple variables in a line
2332 Don't declare multiple variables in one declaration that spans lines.
2333 Start a new declaration on each line, instead. For example, instead
2359 (If they are global variables, each should have a comment preceding it
2362 When you have an @code{if}-@code{else} statement nested in another
2363 @code{if} statement, always put braces around the @code{if}-@code{else}.
2364 Thus, never write like this:
2387 If you have an @code{if} statement nested inside of an @code{else}
2388 statement, either write @code{else if} on one line, like this,
2398 with its @code{then}-part indented like the preceding @code{then}-part,
2399 or write the nested @code{if} within braces like this:
2411 Don't declare both a structure tag and variables or typedefs in the
2412 same declaration. Instead, declare the structure tag separately
2413 and then use it to declare the variables or typedefs.
2415 Try to avoid assignments inside @code{if}-conditions. For example,
2419 if ((foo = (char *) malloc (sizeof *foo)) == 0)
2420 fatal ("virtual memory exhausted");
2424 instead, write this:
2427 foo = (char *) malloc (sizeof *foo);
2429 fatal ("virtual memory exhausted");
2433 Don't make the program ugly to placate @code{lint}. Please don't insert any
2434 casts to @code{void}. Zero without a cast is perfectly fine as a null
2435 pointer constant, except when calling a varargs function.
2438 @section Naming Variables and Functions
2440 @cindex names of variables and functions
2441 The names of global variables and functions in a program serve as
2442 comments of a sort. So don't choose terse names---instead, look for
2443 names that give useful information about the meaning of the variable or
2444 function. In a GNU program, names should be English, like other
2447 Local variable names can be shorter, because they are used only within
2448 one context, where (presumably) comments explain their purpose.
2450 Try to limit your use of abbreviations in symbol names. It is ok to
2451 make a few abbreviations, explain what they mean, and then use them
2452 frequently, but don't use lots of obscure abbreviations.
2454 Please use underscores to separate words in a name, so that the Emacs
2455 word commands can be useful within them. Stick to lower case; reserve
2456 upper case for macros and @code{enum} constants, and for name-prefixes
2457 that follow a uniform convention.
2459 For example, you should use names like @code{ignore_space_change_flag};
2460 don't use names like @code{iCantReadThis}.
2462 Variables that indicate whether command-line options have been
2463 specified should be named after the meaning of the option, not after
2464 the option-letter. A comment should state both the exact meaning of
2465 the option and its letter. For example,
2469 /* Ignore changes in horizontal whitespace (-b). */
2470 int ignore_space_change_flag;
2474 When you want to define names with constant integer values, use
2475 @code{enum} rather than @samp{#define}. GDB knows about enumeration
2478 @cindex file-name limitations
2480 You might want to make sure that none of the file names would conflict
2481 the files were loaded onto an MS-DOS file system which shortens the
2482 names. You can use the program @code{doschk} to test for this.
2484 Some GNU programs were designed to limit themselves to file names of 14
2485 characters or less, to avoid file name conflicts if they are read into
2486 older System V systems. Please preserve this feature in the existing
2487 GNU programs that have it, but there is no need to do this in new GNU
2488 programs. @code{doschk} also reports file names longer than 14
2491 @node System Portability
2492 @section Portability between System Types
2493 @cindex portability, between system types
2495 In the Unix world, ``portability'' refers to porting to different Unix
2496 versions. For a GNU program, this kind of portability is desirable, but
2499 The primary purpose of GNU software is to run on top of the GNU kernel,
2500 compiled with the GNU C compiler, on various types of @sc{cpu}. So the
2501 kinds of portability that are absolutely necessary are quite limited.
2502 But it is important to support Linux-based GNU systems, since they
2503 are the form of GNU that is popular.
2505 Beyond that, it is good to support the other free operating systems
2506 (*BSD), and it is nice to support other Unix-like systems if you want
2507 to. Supporting a variety of Unix-like systems is desirable, although
2508 not paramount. It is usually not too hard, so you may as well do it.
2509 But you don't have to consider it an obligation, if it does turn out to
2513 The easiest way to achieve portability to most Unix-like systems is to
2514 use Autoconf. It's unlikely that your program needs to know more
2515 information about the host platform than Autoconf can provide, simply
2516 because most of the programs that need such knowledge have already been
2519 Avoid using the format of semi-internal data bases (e.g., directories)
2520 when there is a higher-level alternative (@code{readdir}).
2522 @cindex non-@sc{posix} systems, and portability
2523 As for systems that are not like Unix, such as MSDOS, Windows, the
2524 Macintosh, VMS, and MVS, supporting them is often a lot of work. When
2525 that is the case, it is better to spend your time adding features that
2526 will be useful on GNU and GNU/Linux, rather than on supporting other
2527 incompatible systems.
2529 It is a good idea to define the ``feature test macro''
2530 @code{_GNU_SOURCE} when compiling your C files. When you compile on GNU
2531 or GNU/Linux, this will enable the declarations of GNU library extension
2532 functions, and that will usually give you a compiler error message if
2533 you define the same function names in some other way in your program.
2534 (You don't have to actually @emph{use} these functions, if you prefer
2535 to make the program more portable to other systems.)
2537 But whether or not you use these GNU extensions, you should avoid
2538 using their names for any other meanings. Doing so would make it hard
2539 to move your code into other GNU programs.
2541 @node CPU Portability
2542 @section Portability between @sc{cpu}s
2544 @cindex data types, and portability
2545 @cindex portability, and data types
2546 Even GNU systems will differ because of differences among @sc{cpu}
2547 types---for example, difference in byte ordering and alignment
2548 requirements. It is absolutely essential to handle these differences.
2549 However, don't make any effort to cater to the possibility that an
2550 @code{int} will be less than 32 bits. We don't support 16-bit machines
2553 Similarly, don't make any effort to cater to the possibility that
2554 @code{long} will be smaller than predefined types like @code{size_t}.
2555 For example, the following code is ok:
2558 printf ("size = %lu\n", (unsigned long) sizeof array);
2559 printf ("diff = %ld\n", (long) (pointer2 - pointer1));
2562 1989 Standard C requires this to work, and we know of only one
2563 counterexample: 64-bit programs on Microsoft Windows IA-64. We will
2564 leave it to those who want to port GNU programs to that environment
2565 to figure out how to do it.
2567 Predefined file-size types like @code{off_t} are an exception: they are
2568 longer than @code{long} on many platforms, so code like the above won't
2569 work with them. One way to print an @code{off_t} value portably is to
2570 print its digits yourself, one by one.
2572 Don't assume that the address of an @code{int} object is also the
2573 address of its least-significant byte. This is false on big-endian
2574 machines. Thus, don't make the following mistake:
2579 while ((c = getchar()) != EOF)
2580 write(file_descriptor, &c, 1);
2583 When calling functions, you need not worry about the difference between
2584 pointers of various types, or between pointers and integers. On most
2585 machines, there's no difference anyway. As for the few machines where
2586 there is a difference, all of them support Standard C prototypes, so you can
2587 use prototypes (perhaps conditionalized to be active only in Standard C)
2588 to make the code work on those systems.
2590 In certain cases, it is ok to pass integer and pointer arguments
2591 indiscriminately to the same function, and use no prototype on any
2592 system. For example, many GNU programs have error-reporting functions
2593 that pass their arguments along to @code{printf} and friends:
2596 error (s, a1, a2, a3)
2600 fprintf (stderr, "error: ");
2601 fprintf (stderr, s, a1, a2, a3);
2606 In practice, this works on all machines, since a pointer is generally
2607 the widest possible kind of argument; it is much simpler than any
2608 ``correct'' alternative. Be sure @emph{not} to use a prototype for such
2611 If you have decided to use Standard C, then you can instead define
2612 @code{error} using @file{stdarg.h}, and pass the arguments along to
2615 @cindex casting pointers to integers
2616 Avoid casting pointers to integers if you can. Such casts greatly
2617 reduce portability, and in most programs they are easy to avoid. In the
2618 cases where casting pointers to integers is essential---such as, a Lisp
2619 interpreter which stores type information as well as an address in one
2620 word---you'll have to make explicit provisions to handle different word
2621 sizes. You will also need to make provision for systems in which the
2622 normal range of addresses you can get from @code{malloc} starts far away
2625 @node System Functions
2626 @section Calling System Functions
2627 @cindex library functions, and portability
2628 @cindex portability, and library functions
2630 C implementations differ substantially. Standard C reduces but does
2631 not eliminate the incompatibilities; meanwhile, many GNU packages still
2632 support pre-standard compilers because this is not hard to do. This
2633 chapter gives recommendations for how to use the more-or-less standard C
2634 library functions to avoid unnecessary loss of portability.
2638 Don't use the return value of @code{sprintf}. It returns the number of
2639 characters written on some systems, but not on all systems.
2642 Be aware that @code{vfprintf} is not always available.
2645 @code{main} should be declared to return type @code{int}. It should
2646 terminate either by calling @code{exit} or by returning the integer
2647 status code; make sure it cannot ever return an undefined value.
2649 @cindex declaration for system functions
2651 Don't declare system functions explicitly.
2653 Almost any declaration for a system function is wrong on some system.
2654 To minimize conflicts, leave it to the system header files to declare
2655 system functions. If the headers don't declare a function, let it
2658 While it may seem unclean to use a function without declaring it, in
2659 practice this works fine for most system library functions on the
2660 systems where this really happens; thus, the disadvantage is only
2661 theoretical. By contrast, actual declarations have frequently caused
2665 If you must declare a system function, don't specify the argument types.
2666 Use an old-style declaration, not a Standard C prototype. The more you
2667 specify about the function, the more likely a conflict.
2670 In particular, don't unconditionally declare @code{malloc} or
2673 Most GNU programs use those functions just once, in functions
2674 conventionally named @code{xmalloc} and @code{xrealloc}. These
2675 functions call @code{malloc} and @code{realloc}, respectively, and
2678 Because @code{xmalloc} and @code{xrealloc} are defined in your program,
2679 you can declare them in other files without any risk of type conflict.
2681 On most systems, @code{int} is the same length as a pointer; thus, the
2682 calls to @code{malloc} and @code{realloc} work fine. For the few
2683 exceptional systems (mostly 64-bit machines), you can use
2684 @strong{conditionalized} declarations of @code{malloc} and
2685 @code{realloc}---or put these declarations in configuration files
2686 specific to those systems.
2688 @cindex string library functions
2690 The string functions require special treatment. Some Unix systems have
2691 a header file @file{string.h}; others have @file{strings.h}. Neither
2692 file name is portable. There are two things you can do: use Autoconf to
2693 figure out which file to include, or don't include either file.
2696 If you don't include either strings file, you can't get declarations for
2697 the string functions from the header file in the usual way.
2699 That causes less of a problem than you might think. The newer standard
2700 string functions should be avoided anyway because many systems still
2701 don't support them. The string functions you can use are these:
2704 strcpy strncpy strcat strncat
2705 strlen strcmp strncmp
2709 The copy and concatenate functions work fine without a declaration as
2710 long as you don't use their values. Using their values without a
2711 declaration fails on systems where the width of a pointer differs from
2712 the width of @code{int}, and perhaps in other cases. It is trivial to
2713 avoid using their values, so do that.
2715 The compare functions and @code{strlen} work fine without a declaration
2716 on most systems, possibly all the ones that GNU software runs on.
2717 You may find it necessary to declare them @strong{conditionally} on a
2720 The search functions must be declared to return @code{char *}. Luckily,
2721 there is no variation in the data type they return. But there is
2722 variation in their names. Some systems give these functions the names
2723 @code{index} and @code{rindex}; other systems use the names
2724 @code{strchr} and @code{strrchr}. Some systems support both pairs of
2725 names, but neither pair works on all systems.
2727 You should pick a single pair of names and use it throughout your
2728 program. (Nowadays, it is better to choose @code{strchr} and
2729 @code{strrchr} for new programs, since those are the standard
2730 names.) Declare both of those names as functions returning @code{char
2731 *}. On systems which don't support those names, define them as macros
2732 in terms of the other pair. For example, here is what to put at the
2733 beginning of your file (or in a header) if you want to use the names
2734 @code{strchr} and @code{strrchr} throughout:
2738 #define strchr index
2740 #ifndef HAVE_STRRCHR
2741 #define strrchr rindex
2749 Here we assume that @code{HAVE_STRCHR} and @code{HAVE_STRRCHR} are
2750 macros defined in systems where the corresponding functions exist.
2751 One way to get them properly defined is to use Autoconf.
2753 @node Internationalization
2754 @section Internationalization
2755 @cindex internationalization
2758 GNU has a library called GNU gettext that makes it easy to translate the
2759 messages in a program into various languages. You should use this
2760 library in every program. Use English for the messages as they appear
2761 in the program, and let gettext provide the way to translate them into
2764 Using GNU gettext involves putting a call to the @code{gettext} macro
2765 around each string that might need translation---like this:
2768 printf (gettext ("Processing file `%s'..."));
2772 This permits GNU gettext to replace the string @code{"Processing file
2773 `%s'..."} with a translated version.
2775 Once a program uses gettext, please make a point of writing calls to
2776 @code{gettext} when you add new strings that call for translation.
2778 Using GNU gettext in a package involves specifying a @dfn{text domain
2779 name} for the package. The text domain name is used to separate the
2780 translations for this package from the translations for other packages.
2781 Normally, the text domain name should be the same as the name of the
2782 package---for example, @samp{fileutils} for the GNU file utilities.
2784 @cindex message text, and internationalization
2785 To enable gettext to work well, avoid writing code that makes
2786 assumptions about the structure of words or sentences. When you want
2787 the precise text of a sentence to vary depending on the data, use two or
2788 more alternative string constants each containing a complete sentences,
2789 rather than inserting conditionalized words or phrases into a single
2792 Here is an example of what not to do:
2795 printf ("%d file%s processed", nfiles,
2796 nfiles != 1 ? "s" : "");
2800 The problem with that example is that it assumes that plurals are made
2801 by adding `s'. If you apply gettext to the format string, like this,
2804 printf (gettext ("%d file%s processed"), nfiles,
2805 nfiles != 1 ? "s" : "");
2809 the message can use different words, but it will still be forced to use
2810 `s' for the plural. Here is a better way:
2813 printf ((nfiles != 1 ? "%d files processed"
2814 : "%d file processed"),
2819 This way, you can apply gettext to each of the two strings
2823 printf ((nfiles != 1 ? gettext ("%d files processed")
2824 : gettext ("%d file processed")),
2829 This can be any method of forming the plural of the word for ``file'', and
2830 also handles languages that require agreement in the word for
2833 A similar problem appears at the level of sentence structure with this
2837 printf ("# Implicit rule search has%s been done.\n",
2838 f->tried_implicit ? "" : " not");
2842 Adding @code{gettext} calls to this code cannot give correct results for
2843 all languages, because negation in some languages requires adding words
2844 at more than one place in the sentence. By contrast, adding
2845 @code{gettext} calls does the job straightfowardly if the code starts
2849 printf (f->tried_implicit
2850 ? "# Implicit rule search has been done.\n",
2851 : "# Implicit rule search has not been done.\n");
2858 Don't assume that @code{mmap} either works on all files or fails
2859 for all files. It may work on some files and fail on others.
2861 The proper way to use @code{mmap} is to try it on the specific file for
2862 which you want to use it---and if @code{mmap} doesn't work, fall back on
2863 doing the job in another way using @code{read} and @code{write}.
2865 The reason this precaution is needed is that the GNU kernel (the HURD)
2866 provides a user-extensible file system, in which there can be many
2867 different kinds of ``ordinary files.'' Many of them support
2868 @code{mmap}, but some do not. It is important to make programs handle
2869 all these kinds of files.
2872 @chapter Documenting Programs
2873 @cindex documentation
2875 A GNU program should ideally come with full free documentation, adequate
2876 for both reference and tutorial purposes. If the package can be
2877 programmed or extended, the documentation should cover programming or
2878 extending it, as well as just using it.
2881 * GNU Manuals:: Writing proper manuals.
2882 * Doc Strings and Manuals:: Compiling doc strings doesn't make a manual.
2883 * Manual Structure Details:: Specific structure conventions.
2884 * License for Manuals:: Writing the distribution terms for a manual.
2885 * Manual Credits:: Giving credit to documentation contributors.
2886 * Printed Manuals:: Mentioning the printed manual.
2887 * NEWS File:: NEWS files supplement manuals.
2888 * Change Logs:: Recording Changes
2889 * Man Pages:: Man pages are secondary.
2890 * Reading other Manuals:: How far you can go in learning
2895 @section GNU Manuals
2897 The preferred document format for the GNU system is the Texinfo
2898 formatting language. Every GNU package should (ideally) have
2899 documentation in Texinfo both for reference and for learners. Texinfo
2900 makes it possible to produce a good quality formatted book, using
2901 @TeX{}, and to generate an Info file. It is also possible to generate
2902 HTML output from Texinfo source. See the Texinfo manual, either the
2903 hardcopy, or the on-line version available through @code{info} or the
2904 Emacs Info subsystem (@kbd{C-h i}).
2906 Nowadays some other formats such as Docbook and Sgmltexi can be
2907 converted automatically into Texinfo. It is ok to produce the Texinfo
2908 documentation by conversion this way, as long as it gives good results.
2910 Programmers often find it most natural to structure the documentation
2911 following the structure of the implementation, which they know. But
2912 this structure is not necessarily good for explaining how to use the
2913 program; it may be irrelevant and confusing for a user.
2915 At every level, from the sentences in a paragraph to the grouping of
2916 topics into separate manuals, the right way to structure documentation
2917 is according to the concepts and questions that a user will have in mind
2918 when reading it. Sometimes this structure of ideas matches the
2919 structure of the implementation of the software being documented---but
2920 often they are different. Often the most important part of learning to
2921 write good documentation is learning to notice when you are structuring
2922 the documentation like the implementation, and think about better
2925 For example, each program in the GNU system probably ought to be
2926 documented in one manual; but this does not mean each program should
2927 have its own manual. That would be following the structure of the
2928 implementation, rather than the structure that helps the user
2931 Instead, each manual should cover a coherent @emph{topic}. For example,
2932 instead of a manual for @code{diff} and a manual for @code{diff3}, we
2933 have one manual for ``comparison of files'' which covers both of those
2934 programs, as well as @code{cmp}. By documenting these programs
2935 together, we can make the whole subject clearer.
2937 The manual which discusses a program should certainly document all of
2938 the program's command-line options and all of its commands. It should
2939 give examples of their use. But don't organize the manual as a list of
2940 features. Instead, organize it logically, by subtopics. Address the
2941 questions that a user will ask when thinking about the job that the
2944 In general, a GNU manual should serve both as tutorial and reference.
2945 It should be set up for convenient access to each topic through Info,
2946 and for reading straight through (appendixes aside). A GNU manual
2947 should give a good introduction to a beginner reading through from the
2948 start, and should also provide all the details that hackers want.
2949 The Bison manual is a good example of this---please take a look at it
2950 to see what we mean.
2952 That is not as hard as it first sounds. Arrange each chapter as a
2953 logical breakdown of its topic, but order the sections, and write their
2954 text, so that reading the chapter straight through makes sense. Do
2955 likewise when structuring the book into chapters, and when structuring a
2956 section into paragraphs. The watchword is, @emph{at each point, address
2957 the most fundamental and important issue raised by the preceding text.}
2959 If necessary, add extra chapters at the beginning of the manual which
2960 are purely tutorial and cover the basics of the subject. These provide
2961 the framework for a beginner to understand the rest of the manual. The
2962 Bison manual provides a good example of how to do this.
2964 To serve as a reference, a manual should have an Index that list all the
2965 functions, variables, options, and important concepts that are part of
2966 the program. One combined Index should do for a short manual, but
2967 sometimes for a complex package it is better to use multiple indices.
2968 The Texinfo manual includes advice on preparing good index entries, see
2969 @ref{Index Entries, , Making Index Entries, texinfo, The GNU Texinfo
2970 Manual}, and see @ref{Indexing Commands, , Defining the Entries of an
2971 Index, texinfo, The GNU Texinfo manual}.
2973 Don't use Unix man pages as a model for how to write GNU documentation;
2974 most of them are terse, badly structured, and give inadequate
2975 explanation of the underlying concepts. (There are, of course, some
2976 exceptions.) Also, Unix man pages use a particular format which is
2977 different from what we use in GNU manuals.
2979 Please include an email address in the manual for where to report
2980 bugs @emph{in the manual}.
2982 Please do not use the term ``pathname'' that is used in Unix
2983 documentation; use ``file name'' (two words) instead. We use the term
2984 ``path'' only for search paths, which are lists of directory names.
2986 Please do not use the term ``illegal'' to refer to erroneous input to a
2987 computer program. Please use ``invalid'' for this, and reserve the term
2988 ``illegal'' for activities punishable by law.
2990 @node Doc Strings and Manuals
2991 @section Doc Strings and Manuals
2993 Some programming systems, such as Emacs, provide a documentation string
2994 for each function, command or variable. You may be tempted to write a
2995 reference manual by compiling the documentation strings and writing a
2996 little additional text to go around them---but you must not do it. That
2997 approach is a fundamental mistake. The text of well-written
2998 documentation strings will be entirely wrong for a manual.
3000 A documentation string needs to stand alone---when it appears on the
3001 screen, there will be no other text to introduce or explain it.
3002 Meanwhile, it can be rather informal in style.
3004 The text describing a function or variable in a manual must not stand
3005 alone; it appears in the context of a section or subsection. Other text
3006 at the beginning of the section should explain some of the concepts, and
3007 should often make some general points that apply to several functions or
3008 variables. The previous descriptions of functions and variables in the
3009 section will also have given information about the topic. A description
3010 written to stand alone would repeat some of that information; this
3011 redundance looks bad. Meanwhile, the informality that is acceptable in
3012 a documentation string is totally unacceptable in a manual.
3014 The only good way to use documentation strings in writing a good manual
3015 is to use them as a source of information for writing good text.
3017 @node Manual Structure Details
3018 @section Manual Structure Details
3019 @cindex manual structure
3021 The title page of the manual should state the version of the programs or
3022 packages documented in the manual. The Top node of the manual should
3023 also contain this information. If the manual is changing more
3024 frequently than or independent of the program, also state a version
3025 number for the manual in both of these places.
3027 Each program documented in the manual should have a node named
3028 @samp{@var{program} Invocation} or @samp{Invoking @var{program}}. This
3029 node (together with its subnodes, if any) should describe the program's
3030 command line arguments and how to run it (the sort of information people
3031 would look in a man page for). Start with an @samp{@@example}
3032 containing a template for all the options and arguments that the program
3035 Alternatively, put a menu item in some menu whose item name fits one of
3036 the above patterns. This identifies the node which that item points to
3037 as the node for this purpose, regardless of the node's actual name.
3039 The @samp{--usage} feature of the Info reader looks for such a node
3040 or menu item in order to find the relevant text, so it is essential
3041 for every Texinfo file to have one.
3043 If one manual describes several programs, it should have such a node for
3044 each program described in the manual.
3046 @node License for Manuals
3047 @section License for Manuals
3048 @cindex license for manuals
3050 Please use the GNU Free Documentation License for all GNU manuals that
3051 are more than a few pages long. Likewise for a collection of short
3052 documents---you only need one copy of the GNU FDL for the whole
3053 collection. For a single short document, you can use a very permissive
3054 non-copyleft license, to avoid taking up space with a long license.
3056 See @uref{http://www.gnu.org/copyleft/fdl-howto.html} for more explanation
3057 of how to employ the GFDL.
3059 Note that it is not obligatory to include a copy of the GNU GPL or GNU
3060 LGPL in a manual whose license is neither the GPL nor the LGPL. It can
3061 be a good idea to include the program's license in a large manual; in a
3062 short manual, whose size would be increased considerably by including
3063 the program's license, it is probably better not to include it.
3065 @node Manual Credits
3066 @section Manual Credits
3067 @cindex credits for manuals
3069 Please credit the principal human writers of the manual as the authors,
3070 on the title page of the manual. If a company sponsored the work, thank
3071 the company in a suitable place in the manual, but do not cite the
3072 company as an author.
3074 @node Printed Manuals
3075 @section Printed Manuals
3077 The FSF publishes some GNU manuals in printed form. To encourage sales
3078 of these manuals, the on-line versions of the manual should mention at
3079 the very start that the printed manual is available and should point at
3080 information for getting it---for instance, with a link to the page
3081 @url{http://www.gnu.org/order/order.html}. This should not be included
3082 in the printed manual, though, because there it is redundant.
3084 It is also useful to explain in the on-line forms of the manual how the
3085 user can print out the manual from the sources.
3088 @section The NEWS File
3089 @cindex @file{NEWS} file
3091 In addition to its manual, the package should have a file named
3092 @file{NEWS} which contains a list of user-visible changes worth
3093 mentioning. In each new release, add items to the front of the file and
3094 identify the version they pertain to. Don't discard old items; leave
3095 them in the file after the newer items. This way, a user upgrading from
3096 any previous version can see what is new.
3098 If the @file{NEWS} file gets very long, move some of the older items
3099 into a file named @file{ONEWS} and put a note at the end referring the
3103 @section Change Logs
3106 Keep a change log to describe all the changes made to program source
3107 files. The purpose of this is so that people investigating bugs in the
3108 future will know about the changes that might have introduced the bug.
3109 Often a new bug can be found by looking at what was recently changed.
3110 More importantly, change logs can help you eliminate conceptual
3111 inconsistencies between different parts of a program, by giving you a
3112 history of how the conflicting concepts arose and who they came from.
3115 * Change Log Concepts::
3116 * Style of Change Logs::
3118 * Conditional Changes::
3119 * Indicating the Part Changed::
3122 @node Change Log Concepts
3123 @subsection Change Log Concepts
3125 You can think of the change log as a conceptual ``undo list'' which
3126 explains how earlier versions were different from the current version.
3127 People can see the current version; they don't need the change log
3128 to tell them what is in it. What they want from a change log is a
3129 clear explanation of how the earlier version differed.
3131 The change log file is normally called @file{ChangeLog} and covers an
3132 entire directory. Each directory can have its own change log, or a
3133 directory can use the change log of its parent directory--it's up to
3136 Another alternative is to record change log information with a version
3137 control system such as RCS or CVS. This can be converted automatically
3138 to a @file{ChangeLog} file using @code{rcs2log}; in Emacs, the command
3139 @kbd{C-x v a} (@code{vc-update-change-log}) does the job.
3141 There's no need to describe the full purpose of the changes or how they
3142 work together. If you think that a change calls for explanation, you're
3143 probably right. Please do explain it---but please put the explanation
3144 in comments in the code, where people will see it whenever they see the
3145 code. For example, ``New function'' is enough for the change log when
3146 you add a function, because there should be a comment before the
3147 function definition to explain what it does.
3149 However, sometimes it is useful to write one line to describe the
3150 overall purpose of a batch of changes.
3152 The easiest way to add an entry to @file{ChangeLog} is with the Emacs
3153 command @kbd{M-x add-change-log-entry}. An entry should have an
3154 asterisk, the name of the changed file, and then in parentheses the name
3155 of the changed functions, variables or whatever, followed by a colon.
3156 Then describe the changes you made to that function or variable.
3158 @node Style of Change Logs
3159 @subsection Style of Change Logs
3160 @cindex change logs, style
3162 Here are some simple examples of change log entries, starting with the
3163 header line that says who made the change and when, followed by
3164 descriptions of specific changes. (These examples are drawn from Emacs
3168 1998-08-17 Richard Stallman <rms@@gnu.org>
3170 * register.el (insert-register): Return nil.
3171 (jump-to-register): Likewise.
3173 * sort.el (sort-subr): Return nil.
3175 * tex-mode.el (tex-bibtex-file, tex-file, tex-region):
3176 Restart the tex shell if process is gone or stopped.
3177 (tex-shell-running): New function.
3179 * expr.c (store_one_arg): Round size up for move_block_to_reg.
3180 (expand_call): Round up when emitting USE insns.
3181 * stmt.c (assign_parms): Round size up for move_block_from_reg.
3184 It's important to name the changed function or variable in full. Don't
3185 abbreviate function or variable names, and don't combine them.
3186 Subsequent maintainers will often search for a function name to find all
3187 the change log entries that pertain to it; if you abbreviate the name,
3188 they won't find it when they search.
3190 For example, some people are tempted to abbreviate groups of function
3191 names by writing @samp{* register.el (@{insert,jump-to@}-register)};
3192 this is not a good idea, since searching for @code{jump-to-register} or
3193 @code{insert-register} would not find that entry.
3195 Separate unrelated change log entries with blank lines. When two
3196 entries represent parts of the same change, so that they work together,
3197 then don't put blank lines between them. Then you can omit the file
3198 name and the asterisk when successive entries are in the same file.
3200 Break long lists of function names by closing continued lines with
3201 @samp{)}, rather than @samp{,}, and opening the continuation with
3202 @samp{(} as in this example:
3205 * keyboard.c (menu_bar_items, tool_bar_items)
3206 (Fexecute_extended_command): Deal with `keymap' property.
3209 @node Simple Changes
3210 @subsection Simple Changes
3212 Certain simple kinds of changes don't need much detail in the change
3215 When you change the calling sequence of a function in a simple fashion,
3216 and you change all the callers of the function to use the new calling
3217 sequence, there is no need to make individual entries for all the
3218 callers that you changed. Just write in the entry for the function
3219 being called, ``All callers changed''---like this:
3222 * keyboard.c (Fcommand_execute): New arg SPECIAL.
3223 All callers changed.
3226 When you change just comments or doc strings, it is enough to write an
3227 entry for the file, without mentioning the functions. Just ``Doc
3228 fixes'' is enough for the change log.
3230 There's no need to make change log entries for documentation files.
3231 This is because documentation is not susceptible to bugs that are hard
3232 to fix. Documentation does not consist of parts that must interact in a
3233 precisely engineered fashion. To correct an error, you need not know
3234 the history of the erroneous passage; it is enough to compare what the
3235 documentation says with the way the program actually works.
3237 @node Conditional Changes
3238 @subsection Conditional Changes
3239 @cindex conditional changes, and change logs
3240 @cindex change logs, conditional changes
3242 C programs often contain compile-time @code{#if} conditionals. Many
3243 changes are conditional; sometimes you add a new definition which is
3244 entirely contained in a conditional. It is very useful to indicate in
3245 the change log the conditions for which the change applies.
3247 Our convention for indicating conditional changes is to use square
3248 brackets around the name of the condition.
3250 Here is a simple example, describing a change which is conditional but
3251 does not have a function or entity name associated with it:
3254 * xterm.c [SOLARIS2]: Include string.h.
3257 Here is an entry describing a new definition which is entirely
3258 conditional. This new definition for the macro @code{FRAME_WINDOW_P} is
3259 used only when @code{HAVE_X_WINDOWS} is defined:
3262 * frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined.
3265 Here is an entry for a change within the function @code{init_display},
3266 whose definition as a whole is unconditional, but the changes themselves
3267 are contained in a @samp{#ifdef HAVE_LIBNCURSES} conditional:
3270 * dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent.
3273 Here is an entry for a change that takes affect only when
3274 a certain macro is @emph{not} defined:
3277 (gethostname) [!HAVE_SOCKETS]: Replace with winsock version.
3280 @node Indicating the Part Changed
3281 @subsection Indicating the Part Changed
3283 Indicate the part of a function which changed by using angle brackets
3284 enclosing an indication of what the changed part does. Here is an entry
3285 for a change in the part of the function @code{sh-while-getopts} that
3286 deals with @code{sh} commands:
3289 * progmodes/sh-script.el (sh-while-getopts) <sh>: Handle case that
3290 user-specified option string is empty.
3298 In the GNU project, man pages are secondary. It is not necessary or
3299 expected for every GNU program to have a man page, but some of them do.
3300 It's your choice whether to include a man page in your program.
3302 When you make this decision, consider that supporting a man page
3303 requires continual effort each time the program is changed. The time
3304 you spend on the man page is time taken away from more useful work.
3306 For a simple program which changes little, updating the man page may be
3307 a small job. Then there is little reason not to include a man page, if
3310 For a large program that changes a great deal, updating a man page may
3311 be a substantial burden. If a user offers to donate a man page, you may
3312 find this gift costly to accept. It may be better to refuse the man
3313 page unless the same person agrees to take full responsibility for
3314 maintaining it---so that you can wash your hands of it entirely. If
3315 this volunteer later ceases to do the job, then don't feel obliged to
3316 pick it up yourself; it may be better to withdraw the man page from the
3317 distribution until someone else agrees to update it.
3319 When a program changes only a little, you may feel that the
3320 discrepancies are small enough that the man page remains useful without
3321 updating. If so, put a prominent note near the beginning of the man
3322 page explaining that you don't maintain it and that the Texinfo manual
3323 is more authoritative. The note should say how to access the Texinfo
3326 @node Reading other Manuals
3327 @section Reading other Manuals
3329 There may be non-free books or documentation files that describe the
3330 program you are documenting.
3332 It is ok to use these documents for reference, just as the author of a
3333 new algebra textbook can read other books on algebra. A large portion
3334 of any non-fiction book consists of facts, in this case facts about how
3335 a certain program works, and these facts are necessarily the same for
3336 everyone who writes about the subject. But be careful not to copy your
3337 outline structure, wording, tables or examples from preexisting non-free
3338 documentation. Copying from free documentation may be ok; please check
3339 with the FSF about the individual case.
3341 @node Managing Releases
3342 @chapter The Release Process
3345 Making a release is more than just bundling up your source files in a
3346 tar file and putting it up for FTP. You should set up your software so
3347 that it can be configured to run on a variety of systems. Your Makefile
3348 should conform to the GNU standards described below, and your directory
3349 layout should also conform to the standards discussed below. Doing so
3350 makes it easy to include your package into the larger framework of
3354 * Configuration:: How Configuration Should Work
3355 * Makefile Conventions:: Makefile Conventions
3356 * Releases:: Making Releases
3360 @section How Configuration Should Work
3361 @cindex program configuration
3364 Each GNU distribution should come with a shell script named
3365 @code{configure}. This script is given arguments which describe the
3366 kind of machine and system you want to compile the program for.
3368 The @code{configure} script must record the configuration options so
3369 that they affect compilation.
3371 One way to do this is to make a link from a standard name such as
3372 @file{config.h} to the proper configuration file for the chosen system.
3373 If you use this technique, the distribution should @emph{not} contain a
3374 file named @file{config.h}. This is so that people won't be able to
3375 build the program without configuring it first.
3377 Another thing that @code{configure} can do is to edit the Makefile. If
3378 you do this, the distribution should @emph{not} contain a file named
3379 @file{Makefile}. Instead, it should include a file @file{Makefile.in} which
3380 contains the input used for editing. Once again, this is so that people
3381 won't be able to build the program without configuring it first.
3383 If @code{configure} does write the @file{Makefile}, then @file{Makefile}
3384 should have a target named @file{Makefile} which causes @code{configure}
3385 to be rerun, setting up the same configuration that was set up last
3386 time. The files that @code{configure} reads should be listed as
3387 dependencies of @file{Makefile}.
3389 All the files which are output from the @code{configure} script should
3390 have comments at the beginning explaining that they were generated
3391 automatically using @code{configure}. This is so that users won't think
3392 of trying to edit them by hand.
3394 The @code{configure} script should write a file named @file{config.status}
3395 which describes which configuration options were specified when the
3396 program was last configured. This file should be a shell script which,
3397 if run, will recreate the same configuration.
3399 The @code{configure} script should accept an option of the form
3400 @samp{--srcdir=@var{dirname}} to specify the directory where sources are found
3401 (if it is not the current directory). This makes it possible to build
3402 the program in a separate directory, so that the actual source directory
3405 If the user does not specify @samp{--srcdir}, then @code{configure} should
3406 check both @file{.} and @file{..} to see if it can find the sources. If
3407 it finds the sources in one of these places, it should use them from
3408 there. Otherwise, it should report that it cannot find the sources, and
3409 should exit with nonzero status.
3411 Usually the easy way to support @samp{--srcdir} is by editing a
3412 definition of @code{VPATH} into the Makefile. Some rules may need to
3413 refer explicitly to the specified source directory. To make this
3414 possible, @code{configure} can add to the Makefile a variable named
3415 @code{srcdir} whose value is precisely the specified directory.
3417 The @code{configure} script should also take an argument which specifies the
3418 type of system to build the program for. This argument should look like
3422 @var{cpu}-@var{company}-@var{system}
3425 For example, a Sun 3 might be @samp{m68k-sun-sunos4.1}.
3427 The @code{configure} script needs to be able to decode all plausible
3428 alternatives for how to describe a machine. Thus, @samp{sun3-sunos4.1}
3429 would be a valid alias. For many programs, @samp{vax-dec-ultrix} would
3430 be an alias for @samp{vax-dec-bsd}, simply because the differences
3431 between Ultrix and @sc{bsd} are rarely noticeable, but a few programs
3432 might need to distinguish them.
3433 @c Real 4.4BSD now runs on some Suns.
3435 There is a shell script called @file{config.sub} that you can use
3436 as a subroutine to validate system types and canonicalize aliases.
3438 @cindex optional features, configure-time
3439 Other options are permitted to specify in more detail the software
3440 or hardware present on the machine, and include or exclude optional
3441 parts of the package:
3444 @item --enable-@var{feature}@r{[}=@var{parameter}@r{]}
3445 Configure the package to build and install an optional user-level
3446 facility called @var{feature}. This allows users to choose which
3447 optional features to include. Giving an optional @var{parameter} of
3448 @samp{no} should omit @var{feature}, if it is built by default.
3450 No @samp{--enable} option should @strong{ever} cause one feature to
3451 replace another. No @samp{--enable} option should ever substitute one
3452 useful behavior for another useful behavior. The only proper use for
3453 @samp{--enable} is for questions of whether to build part of the program
3456 @item --with-@var{package}
3457 @c @r{[}=@var{parameter}@r{]}
3458 The package @var{package} will be installed, so configure this package
3459 to work with @var{package}.
3461 @c Giving an optional @var{parameter} of
3462 @c @samp{no} should omit @var{package}, if it is used by default.
3464 Possible values of @var{package} include
3465 @samp{gnu-as} (or @samp{gas}), @samp{gnu-ld}, @samp{gnu-libc},
3471 Do not use a @samp{--with} option to specify the file name to use to
3472 find certain files. That is outside the scope of what @samp{--with}
3476 All @code{configure} scripts should accept all of these ``detail''
3477 options, whether or not they make any difference to the particular
3478 package at hand. In particular, they should accept any option that
3479 starts with @samp{--with-} or @samp{--enable-}. This is so users will
3480 be able to configure an entire GNU source tree at once with a single set
3483 You will note that the categories @samp{--with-} and @samp{--enable-}
3484 are narrow: they @strong{do not} provide a place for any sort of option
3485 you might think of. That is deliberate. We want to limit the possible
3486 configuration options in GNU software. We do not want GNU programs to
3487 have idiosyncratic configuration options.
3489 Packages that perform part of the compilation process may support
3490 cross-compilation. In such a case, the host and target machines for the
3491 program may be different.
3493 The @code{configure} script should normally treat the specified type of
3494 system as both the host and the target, thus producing a program which
3495 works for the same type of machine that it runs on.
3497 To configure a cross-compiler, cross-assembler, or what have you, you
3498 should specify a target different from the host, using the configure
3499 option @samp{--target=@var{targettype}}. The syntax for
3500 @var{targettype} is the same as for the host type. So the command would
3504 ./configure @var{hosttype} --target=@var{targettype}
3507 Programs for which cross-operation is not meaningful need not accept the
3508 @samp{--target} option, because configuring an entire operating system for
3509 cross-operation is not a meaningful operation.
3511 Bootstrapping a cross-compiler requires compiling it on a machine other
3512 than the host it will run on. Compilation packages accept a
3513 configuration option @samp{--build=@var{buildtype}} for specifying the
3514 configuration on which you will compile them, but the configure script
3515 should normally guess the build machine type (using
3516 @file{config.guess}), so this option is probably not necessary. The
3517 host and target types normally default from the build type, so in
3518 bootstrapping a cross-compiler you must specify them both explicitly.
3520 Some programs have ways of configuring themselves automatically. If
3521 your program is set up to do this, your @code{configure} script can simply
3522 ignore most of its arguments.
3524 @comment The makefile standards are in a separate file that is also
3525 @comment included by make.texinfo. Done by roland@gnu.ai.mit.edu on 1/6/93.
3526 @comment For this document, turn chapters into sections, etc.
3528 @include make-stds.texi
3532 @section Making Releases
3535 Package the distribution of @code{Foo version 69.96} up in a gzipped tar
3536 file with the name @file{foo-69.96.tar.gz}. It should unpack into a
3537 subdirectory named @file{foo-69.96}.
3539 Building and installing the program should never modify any of the files
3540 contained in the distribution. This means that all the files that form
3541 part of the program in any way must be classified into @dfn{source
3542 files} and @dfn{non-source files}. Source files are written by humans
3543 and never changed automatically; non-source files are produced from
3544 source files by programs under the control of the Makefile.
3546 @cindex @file{README} file
3547 The distribution should contain a file named @file{README} which gives
3548 the name of the package, and a general description of what it does. It
3549 is also good to explain the purpose of each of the first-level
3550 subdirectories in the package, if there are any. The @file{README} file
3551 should either state the version number of the package, or refer to where
3552 in the package it can be found.
3554 The @file{README} file should refer to the file @file{INSTALL}, which
3555 should contain an explanation of the installation procedure.
3557 The @file{README} file should also refer to the file which contains the
3558 copying conditions. The GNU GPL, if used, should be in a file called
3559 @file{COPYING}. If the GNU LGPL is used, it should be in a file called
3562 Naturally, all the source files must be in the distribution. It is okay
3563 to include non-source files in the distribution, provided they are
3564 up-to-date and machine-independent, so that building the distribution
3565 normally will never modify them. We commonly include non-source files
3566 produced by Bison, @code{lex}, @TeX{}, and @code{makeinfo}; this helps avoid
3567 unnecessary dependencies between our distributions, so that users can
3568 install whichever packages they want to install.
3570 Non-source files that might actually be modified by building and
3571 installing the program should @strong{never} be included in the
3572 distribution. So if you do distribute non-source files, always make
3573 sure they are up to date when you make a new distribution.
3575 Make sure that the directory into which the distribution unpacks (as
3576 well as any subdirectories) are all world-writable (octal mode 777).
3577 This is so that old versions of @code{tar} which preserve the
3578 ownership and permissions of the files from the tar archive will be
3579 able to extract all the files even if the user is unprivileged.
3581 Make sure that all the files in the distribution are world-readable.
3583 Make sure that no file name in the distribution is more than 14
3584 characters long. Likewise, no file created by building the program
3585 should have a name longer than 14 characters. The reason for this is
3586 that some systems adhere to a foolish interpretation of the @sc{posix}
3587 standard, and refuse to open a longer name, rather than truncating as
3588 they did in the past.
3590 Don't include any symbolic links in the distribution itself. If the tar
3591 file contains symbolic links, then people cannot even unpack it on
3592 systems that don't support symbolic links. Also, don't use multiple
3593 names for one file in different directories, because certain file
3594 systems cannot handle this and that prevents unpacking the
3597 Try to make sure that all the file names will be unique on MS-DOS. A
3598 name on MS-DOS consists of up to 8 characters, optionally followed by a
3599 period and up to three characters. MS-DOS will truncate extra
3600 characters both before and after the period. Thus,
3601 @file{foobarhacker.c} and @file{foobarhacker.o} are not ambiguous; they
3602 are truncated to @file{foobarha.c} and @file{foobarha.o}, which are
3605 @cindex @file{texinfo.tex}, in a distribution
3606 Include in your distribution a copy of the @file{texinfo.tex} you used
3607 to test print any @file{*.texinfo} or @file{*.texi} files.
3609 Likewise, if your program uses small GNU software packages like regex,
3610 getopt, obstack, or termcap, include them in the distribution file.
3611 Leaving them out would make the distribution file a little smaller at
3612 the expense of possible inconvenience to a user who doesn't know what
3616 @chapter References to Non-Free Software and Documentation
3617 @cindex references to non-free material
3619 A GNU program should not recommend use of any non-free program. We
3620 can't stop some people from writing proprietary programs, or stop other
3621 people from using them. But we can and should avoid helping to
3622 advertise them to new customers.
3624 Sometimes it is important to mention how to build your package on top of
3625 some non-free operating system or other non-free base package. In such
3626 cases, please mention the name of the non-free package or system in the
3627 briefest possible way. Don't include any references for where to find
3628 more information about the proprietary program. The goal should be that
3629 people already using the proprietary program will get the advice they
3630 need about how to use your free program, while people who don't already
3631 use the proprietary program will not see anything to encourage them to
3632 take an interest in it.
3634 Likewise, a GNU package should not refer the user to any non-free
3635 documentation for free software. The need for free documentation to go
3636 with free software is now a major focus of the GNU project; to show that
3637 we are serious about the need for free documentation, we must not
3638 undermine our position by recommending use of documentation that isn't
3649 update-date-leading-regexp: "@c This date is automagically updated when you save this file:\n@set lastupdate "
3650 update-date-trailing-regexp: ""
3651 eval: (load "/gd/gnuorg/update-date.el")
3652 eval: (add-hook 'write-file-hooks 'update-date)
3653 compile-command: "make just-standards"