diff options
Diffstat (limited to 'binutils-2.25/etc/standards.texi')
| -rw-r--r-- | binutils-2.25/etc/standards.texi | 4235 |
1 files changed, 0 insertions, 4235 deletions
diff --git a/binutils-2.25/etc/standards.texi b/binutils-2.25/etc/standards.texi deleted file mode 100644 index 4b1c03dd..00000000 --- a/binutils-2.25/etc/standards.texi +++ /dev/null @@ -1,4235 +0,0 @@ -\input texinfo @c -*-texinfo-*- -@c %**start of header -@setfilename standards.info -@settitle GNU Coding Standards -@c This date is automagically updated when you save this file: -@set lastupdate April 12, 2010 -@c %**end of header - -@dircategory GNU organization -@direntry -* Standards: (standards). GNU coding standards. -@end direntry - -@c @setchapternewpage odd -@setchapternewpage off - -@c Put everything in one index (arbitrarily chosen to be the concept index). -@syncodeindex fn cp -@syncodeindex ky cp -@syncodeindex pg cp -@syncodeindex vr cp - -@c This is used by a cross ref in make-stds.texi -@set CODESTD 1 - -@copying -The GNU coding standards, last updated @value{lastupdate}. - -Copyright @copyright{} 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, -2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software -Foundation, Inc. - -Permission is granted to copy, distribute and/or modify this document -under the terms of the GNU Free Documentation License, Version 1.3 or -any later version published by the Free Software Foundation; with no -Invariant Sections, with no Front-Cover Texts, and with no Back-Cover -Texts. A copy of the license is included in the section entitled -``GNU Free Documentation License''. -@end copying - -@titlepage -@title GNU Coding Standards -@author Richard Stallman, et al. -@author last updated @value{lastupdate} -@page -@vskip 0pt plus 1filll -@insertcopying -@end titlepage - -@contents - -@ifnottex -@node Top, Preface, (dir), (dir) -@top Version - -@insertcopying -@end ifnottex - -@menu -* Preface:: About the GNU Coding Standards. -* Legal Issues:: Keeping free software free. -* Design Advice:: General program design. -* Program Behavior:: Program behavior for all programs -* Writing C:: Making the best use of C. -* Documentation:: Documenting programs. -* Managing Releases:: The release process. -* References:: Mentioning non-free software or documentation. -* GNU Free Documentation License:: Copying and sharing this manual. -* Index:: - -@end menu - -@node Preface -@chapter About the GNU Coding Standards - -The GNU Coding Standards were written by Richard Stallman and other GNU -Project volunteers. Their purpose is to make the GNU system clean, -consistent, and easy to install. This document can also be read as a -guide to writing portable, robust and reliable programs. It focuses on -programs written in C, but many of the rules and principles are useful -even if you write in another programming language. The rules often -state reasons for writing in a certain way. - -@cindex where to obtain @code{standards.texi} -@cindex downloading this manual -If you did not obtain this file directly from the GNU project and -recently, please check for a newer version. You can get the GNU -Coding Standards from the GNU web server in many -different formats, including the Texinfo source, PDF, HTML, DVI, plain -text, and more, at: @uref{http://www.gnu.org/prep/standards/}. - -If you are maintaining an official GNU package, in addition to this -document, please read and follow the GNU maintainer information -(@pxref{Top, , Contents, maintain, Information for Maintainers of GNU -Software}). - -@cindex @code{gnustandards-commit@@gnu.org} mailing list -If you want to receive diffs for every change to these GNU documents, -join the mailing list @code{gnustandards-commit@@gnu.org}, via the web -interface at -@url{http://lists.gnu.org/mailman/listinfo/gnustandards-commit}. -Archives are also available there. - -@cindex @code{bug-standards@@gnu.org} email address -@cindex Savannah repository for gnustandards -@cindex gnustandards project repository -Please send corrections or suggestions for this document to -@email{bug-standards@@gnu.org}. If you make a suggestion, please -include a suggested new wording for it, to help us consider the -suggestion efficiently. We prefer a context diff to the Texinfo -source, but if that's difficult for you, you can make a context diff -for some other version of this document, or propose it in any way that -makes it clear. The source repository for this document can be found -at @url{http://savannah.gnu.org/projects/gnustandards}. - -These standards cover the minimum of what is important when writing a -GNU package. Likely, the need for additional standards will come up. -Sometimes, you might suggest that such standards be added to this -document. If you think your standards would be generally useful, please -do suggest them. - -You should also set standards for your package on many questions not -addressed or not firmly specified here. The most important point is to -be self-consistent---try to stick to the conventions you pick, and try -to document them as much as possible. That way, your program will be -more maintainable by others. - -The GNU Hello program serves as an example of how to follow the GNU -coding standards for a trivial program. -@uref{http://www.gnu.org/software/hello/hello.html}. - -This release of the GNU Coding Standards was last updated -@value{lastupdate}. - - -@node Legal Issues -@chapter Keeping Free Software Free -@cindex legal aspects - -This chapter discusses how you can make sure that GNU software -avoids legal difficulties, and other related issues. - -@menu -* Reading Non-Free Code:: Referring to proprietary programs. -* Contributions:: Accepting contributions. -* Trademarks:: How we deal with trademark issues. -@end menu - -@node Reading Non-Free Code -@section Referring to Proprietary Programs -@cindex proprietary programs -@cindex avoiding proprietary code - -Don't in any circumstances refer to Unix source code for or during -your work on GNU! (Or to any other proprietary programs.) - -If you have a vague recollection of the internals of a Unix program, -this does not absolutely mean you can't write an imitation of it, but -do try to organize the imitation internally along different lines, -because this is likely to make the details of the Unix version -irrelevant and dissimilar to your results. - -For example, Unix utilities were generally optimized to minimize -memory use; if you go for speed instead, your program will be very -different. You could keep the entire input file in memory and scan it -there instead of using stdio. Use a smarter algorithm discovered more -recently than the Unix program. Eliminate use of temporary files. Do -it in one pass instead of two (we did this in the assembler). - -Or, on the contrary, emphasize simplicity instead of speed. For some -applications, the speed of today's computers makes simpler algorithms -adequate. - -Or go for generality. For example, Unix programs often have static -tables or fixed-size strings, which make for arbitrary limits; use -dynamic allocation instead. Make sure your program handles NULs and -other funny characters in the input files. Add a programming language -for extensibility and write part of the program in that language. - -Or turn some parts of the program into independently usable libraries. -Or use a simple garbage collector instead of tracking precisely when -to free memory, or use a new GNU facility such as obstacks. - -@node Contributions -@section Accepting Contributions -@cindex legal papers -@cindex accepting contributions - -If the program you are working on is copyrighted by the Free Software -Foundation, then when someone else sends you a piece of code to add to -the program, we need legal papers to use it---just as we asked you to -sign papers initially. @emph{Each} person who makes a nontrivial -contribution to a program must sign some sort of legal papers in order -for us to have clear title to the program; the main author alone is not -enough. - -So, before adding in any contributions from other people, please tell -us, so we can arrange to get the papers. Then wait until we tell you -that we have received the signed papers, before you actually use the -contribution. - -This applies both before you release the program and afterward. If -you receive diffs to fix a bug, and they make significant changes, we -need legal papers for that change. - -This also applies to comments and documentation files. For copyright -law, comments and code are just text. Copyright applies to all kinds of -text, so we need legal papers for all kinds. - -We know it is frustrating to ask for legal papers; it's frustrating for -us as well. But if you don't wait, you are going out on a limb---for -example, what if the contributor's employer won't sign a disclaimer? -You might have to take that code out again! - -You don't need papers for changes of a few lines here or there, since -they are not significant for copyright purposes. Also, you don't need -papers if all you get from the suggestion is some ideas, not actual code -which you use. For example, if someone sent you one implementation, but -you write a different implementation of the same idea, you don't need to -get papers. - -The very worst thing is if you forget to tell us about the other -contributor. We could be very embarrassed in court some day as a -result. - -We have more detailed advice for maintainers of programs; if you have -reached the stage of actually maintaining a program for GNU (whether -released or not), please ask us for a copy. It is also available -online for your perusal: @uref{http://www.gnu.org/prep/maintain/}. - -@node Trademarks -@section Trademarks -@cindex trademarks - -Please do not include any trademark acknowledgements in GNU software -packages or documentation. - -Trademark acknowledgements are the statements that such-and-such is a -trademark of so-and-so. The GNU Project has no objection to the basic -idea of trademarks, but these acknowledgements feel like kowtowing, -and there is no legal requirement for them, so we don't use them. - -What is legally required, as regards other people's trademarks, is to -avoid using them in ways which a reader might reasonably understand as -naming or labeling our own programs or activities. For example, since -``Objective C'' is (or at least was) a trademark, we made sure to say -that we provide a ``compiler for the Objective C language'' rather -than an ``Objective C compiler''. The latter would have been meant as -a shorter way of saying the former, but it does not explicitly state -the relationship, so it could be misinterpreted as using ``Objective -C'' as a label for the compiler rather than for the language. - -Please don't use ``win'' as an abbreviation for Microsoft Windows in -GNU software or documentation. In hacker terminology, calling -something a ``win'' is a form of praise. If you wish to praise -Microsoft Windows when speaking on your own, by all means do so, but -not in GNU software. Usually we write the name ``Windows'' in full, -but when brevity is very important (as in file names and sometimes -symbol names), we abbreviate it to ``w''. For instance, the files and -functions in Emacs that deal with Windows start with @samp{w32}. - -@node Design Advice -@chapter General Program Design -@cindex program design - -This chapter discusses some of the issues you should take into -account when designing your program. - -@c Standard or ANSI C -@c -@c In 1989 the American National Standards Institute (ANSI) standardized -@c C as standard X3.159-1989. In December of that year the -@c International Standards Organization ISO adopted the ANSI C standard -@c making minor changes. In 1990 ANSI then re-adopted ISO standard -@c C. This version of C is known as either ANSI C or Standard C. - -@c A major revision of the C Standard appeared in 1999. - -@menu -* Source Language:: Which languages to use. -* Compatibility:: Compatibility with other implementations. -* Using Extensions:: Using non-standard features. -* Standard C:: Using standard C features. -* Conditional Compilation:: Compiling code only if a conditional is true. -@end menu - -@node Source Language -@section Which Languages to Use -@cindex programming languages - -When you want to use a language that gets compiled and runs at high -speed, the best language to use is C. Using another language is like -using a non-standard feature: it will cause trouble for users. Even if -GCC supports the other language, users may find it inconvenient to have -to install the compiler for that other language in order to build your -program. For example, if you write your program in C++, people will -have to install the GNU C++ compiler in order to compile your program. - -C has one other advantage over C++ and other compiled languages: more -people know C, so more people will find it easy to read and modify the -program if it is written in C. - -So in general it is much better to use C, rather than the -comparable alternatives. - -But there are two exceptions to that conclusion: - -@itemize @bullet -@item -It is no problem to use another language to write a tool specifically -intended for use with that language. That is because the only people -who want to build the tool will be those who have installed the other -language anyway. - -@item -If an application is of interest only to a narrow part of the community, -then the question of which language it is written in has less effect on -other people, so you may as well please yourself. -@end itemize - -Many programs are designed to be extensible: they include an interpreter -for a language that is higher level than C. Often much of the program -is written in that language, too. The Emacs editor pioneered this -technique. - -@cindex Guile -@cindex GNOME and Guile -The standard extensibility interpreter for GNU software is Guile -(@uref{http://www.gnu.org/@/software/@/guile/}), which implements the -language Scheme (an especially clean and simple dialect of Lisp). -Guile also includes bindings for GTK+/GNOME, making it practical to -write modern GUI functionality within Guile. We don't reject programs -written in other ``scripting languages'' such as Perl and Python, but -using Guile is very important for the overall consistency of the GNU -system. - - -@node Compatibility -@section Compatibility with Other Implementations -@cindex compatibility with C and @sc{posix} standards -@cindex @sc{posix} compatibility - -With occasional exceptions, utility programs and libraries for GNU -should be upward compatible with those in Berkeley Unix, and upward -compatible with Standard C if Standard C specifies their -behavior, and upward compatible with @sc{posix} if @sc{posix} specifies -their behavior. - -When these standards conflict, it is useful to offer compatibility -modes for each of them. - -@cindex options for compatibility -Standard C and @sc{posix} prohibit many kinds of extensions. Feel -free to make the extensions anyway, and include a @samp{--ansi}, -@samp{--posix}, or @samp{--compatible} option to turn them off. -However, if the extension has a significant chance of breaking any real -programs or scripts, then it is not really upward compatible. So you -should try to redesign its interface to make it upward compatible. - -@cindex @code{POSIXLY_CORRECT}, environment variable -Many GNU programs suppress extensions that conflict with @sc{posix} if the -environment variable @code{POSIXLY_CORRECT} is defined (even if it is -defined with a null value). Please make your program recognize this -variable if appropriate. - -When a feature is used only by users (not by programs or command -files), and it is done poorly in Unix, feel free to replace it -completely with something totally different and better. (For example, -@code{vi} is replaced with Emacs.) But it is nice to offer a compatible -feature as well. (There is a free @code{vi} clone, so we offer it.) - -Additional useful features are welcome regardless of whether -there is any precedent for them. - -@node Using Extensions -@section Using Non-standard Features -@cindex non-standard extensions - -Many GNU facilities that already exist support a number of convenient -extensions over the comparable Unix facilities. Whether to use these -extensions in implementing your program is a difficult question. - -On the one hand, using the extensions can make a cleaner program. -On the other hand, people will not be able to build the program -unless the other GNU tools are available. This might cause the -program to work on fewer kinds of machines. - -With some extensions, it might be easy to provide both alternatives. -For example, you can define functions with a ``keyword'' @code{INLINE} -and define that as a macro to expand into either @code{inline} or -nothing, depending on the compiler. - -In general, perhaps it is best not to use the extensions if you can -straightforwardly do without them, but to use the extensions if they -are a big improvement. - -An exception to this rule are the large, established programs (such as -Emacs) which run on a great variety of systems. Using GNU extensions in -such programs would make many users unhappy, so we don't do that. - -Another exception is for programs that are used as part of compilation: -anything that must be compiled with other compilers in order to -bootstrap the GNU compilation facilities. If these require the GNU -compiler, then no one can compile them without having them installed -already. That would be extremely troublesome in certain cases. - -@node Standard C -@section Standard C and Pre-Standard C -@cindex @sc{ansi} C standard - -1989 Standard C is widespread enough now that it is ok to use its -features in new programs. There is one exception: do not ever use the -``trigraph'' feature of Standard C. - -1999 Standard C is not widespread yet, so please do not require its -features in programs. It is ok to use its features if they are present. - -However, it is easy to support pre-standard compilers in most programs, -so if you know how to do that, feel free. If a program you are -maintaining has such support, you should try to keep it working. - -@cindex function prototypes -To support pre-standard C, instead of writing function definitions in -standard prototype form, - -@example -int -foo (int x, int y) -@dots{} -@end example - -@noindent -write the definition in pre-standard style like this, - -@example -int -foo (x, y) - int x, y; -@dots{} -@end example - -@noindent -and use a separate declaration to specify the argument prototype: - -@example -int foo (int, int); -@end example - -You need such a declaration anyway, in a header file, to get the benefit -of prototypes in all the files where the function is called. And once -you have the declaration, you normally lose nothing by writing the -function definition in the pre-standard style. - -This technique does not work for integer types narrower than @code{int}. -If you think of an argument as being of a type narrower than @code{int}, -declare it as @code{int} instead. - -There are a few special cases where this technique is hard to use. For -example, if a function argument needs to hold the system type -@code{dev_t}, you run into trouble, because @code{dev_t} is shorter than -@code{int} on some machines; but you cannot use @code{int} instead, -because @code{dev_t} is wider than @code{int} on some machines. There -is no type you can safely use on all machines in a non-standard -definition. The only way to support non-standard C and pass such an -argument is to check the width of @code{dev_t} using Autoconf and choose -the argument type accordingly. This may not be worth the trouble. - -In order to support pre-standard compilers that do not recognize -prototypes, you may want to use a preprocessor macro like this: - -@example -/* Declare the prototype for a general external function. */ -#if defined (__STDC__) || defined (WINDOWSNT) -#define P_(proto) proto -#else -#define P_(proto) () -#endif -@end example - -@node Conditional Compilation -@section Conditional Compilation - -When supporting configuration options already known when building your -program we prefer using @code{if (... )} over conditional compilation, -as in the former case the compiler is able to perform more extensive -checking of all possible code paths. - -For example, please write - -@smallexample - if (HAS_FOO) - ... - else - ... -@end smallexample - -@noindent -instead of: - -@smallexample - #ifdef HAS_FOO - ... - #else - ... - #endif -@end smallexample - -A modern compiler such as GCC will generate exactly the same code in -both cases, and we have been using similar techniques with good success -in several projects. Of course, the former method assumes that -@code{HAS_FOO} is defined as either 0 or 1. - -While this is not a silver bullet solving all portability problems, -and is not always appropriate, following this policy would have saved -GCC developers many hours, or even days, per year. - -In the case of function-like macros like @code{REVERSIBLE_CC_MODE} in -GCC which cannot be simply used in @code{if (...)} statements, there is -an easy workaround. Simply introduce another macro -@code{HAS_REVERSIBLE_CC_MODE} as in the following example: - -@smallexample - #ifdef REVERSIBLE_CC_MODE - #define HAS_REVERSIBLE_CC_MODE 1 - #else - #define HAS_REVERSIBLE_CC_MODE 0 - #endif -@end smallexample - -@node Program Behavior -@chapter Program Behavior for All Programs - -This chapter describes conventions for writing robust -software. It also describes general standards for error messages, the -command line interface, and how libraries should behave. - -@menu -* Non-GNU Standards:: We consider standards such as POSIX; - we don't "obey" them. -* Semantics:: Writing robust programs. -* Libraries:: Library behavior. -* Errors:: Formatting error messages. -* User Interfaces:: Standards about interfaces generally. -* Graphical Interfaces:: Standards for graphical interfaces. -* Command-Line Interfaces:: Standards for command line interfaces. -* Option Table:: Table of long options. -* OID Allocations:: Table of OID slots for GNU. -* Memory Usage:: When and how to care about memory needs. -* File Usage:: Which files to use, and where. -@end menu - -@node Non-GNU Standards -@section Non-GNU Standards - -The GNU Project regards standards published by other organizations as -suggestions, not orders. We consider those standards, but we do not -``obey'' them. In developing a GNU program, you should implement -an outside standard's specifications when that makes the GNU system -better overall in an objective sense. When it doesn't, you shouldn't. - -In most cases, following published standards is convenient for -users---it means that their programs or scripts will work more -portably. For instance, GCC implements nearly all the features of -Standard C as specified by that standard. C program developers would -be unhappy if it did not. And GNU utilities mostly follow -specifications of POSIX.2; shell script writers and users would be -unhappy if our programs were incompatible. - -But we do not follow either of these specifications rigidly, and there -are specific points on which we decided not to follow them, so as to -make the GNU system better for users. - -For instance, Standard C says that nearly all extensions to C are -prohibited. How silly! GCC implements many extensions, some of which -were later adopted as part of the standard. If you want these -constructs to give an error message as ``required'' by the standard, -you must specify @samp{--pedantic}, which was implemented only so that -we can say ``GCC is a 100% implementation of the standard,'' not -because there is any reason to actually use it. - -POSIX.2 specifies that @samp{df} and @samp{du} must output sizes by -default in units of 512 bytes. What users want is units of 1k, so -that is what we do by default. If you want the ridiculous behavior -``required'' by POSIX, you must set the environment variable -@samp{POSIXLY_CORRECT} (which was originally going to be named -@samp{POSIX_ME_HARDER}). - -GNU utilities also depart from the letter of the POSIX.2 specification -when they support long-named command-line options, and intermixing -options with ordinary arguments. This minor incompatibility with -POSIX is never a problem in practice, and it is very useful. - -In particular, don't reject a new feature, or remove an old one, -merely because a standard says it is ``forbidden'' or ``deprecated.'' - -@node Semantics -@section Writing Robust Programs - -@cindex arbitrary limits on data -Avoid arbitrary limits on the length or number of @emph{any} data -structure, including file names, lines, files, and symbols, by allocating -all data structures dynamically. In most Unix utilities, ``long lines -are silently truncated''. This is not acceptable in a GNU utility. - -@cindex @code{NUL} characters -Utilities reading files should not drop NUL characters, or any other -nonprinting characters @emph{including those with codes above 0177}. -The only sensible exceptions would be utilities specifically intended -for interface to certain types of terminals or printers -that can't handle those characters. -Whenever possible, try to make programs work properly with -sequences of bytes that represent multibyte characters, using encodings -such as UTF-8 and others. - -@cindex error messages -Check every system call for an error return, unless you know you wish to -ignore errors. Include the system error text (from @code{perror} or -equivalent) in @emph{every} error message resulting from a failing -system call, as well as the name of the file if any and the name of the -utility. Just ``cannot open foo.c'' or ``stat failed'' is not -sufficient. - -@cindex @code{malloc} return value -@cindex memory allocation failure -Check every call to @code{malloc} or @code{realloc} to see if it -returned zero. Check @code{realloc} even if you are making the block -smaller; in a system that rounds block sizes to a power of 2, -@code{realloc} may get a different block if you ask for less space. - -In Unix, @code{realloc} can destroy the storage block if it returns -zero. GNU @code{realloc} does not have this bug: if it fails, the -original block is unchanged. Feel free to assume the bug is fixed. If -you wish to run your program on Unix, and wish to avoid lossage in this -case, you can use the GNU @code{malloc}. - -You must expect @code{free} to alter the contents of the block that was -freed. Anything you want to fetch from the block, you must fetch before -calling @code{free}. - -If @code{malloc} fails in a noninteractive program, make that a fatal -error. In an interactive program (one that reads commands from the -user), it is better to abort the command and return to the command -reader loop. This allows the user to kill other processes to free up -virtual memory, and then try the command again. - -@cindex command-line arguments, decoding -Use @code{getopt_long} to decode arguments, unless the argument syntax -makes this unreasonable. - -When static storage is to be written in during program execution, use -explicit C code to initialize it. Reserve C initialized declarations -for data that will not be changed. -@c ADR: why? - -Try to avoid low-level interfaces to obscure Unix data structures (such -as file directories, utmp, or the layout of kernel memory), since these -are less likely to work compatibly. If you need to find all the files -in a directory, use @code{readdir} or some other high-level interface. -These are supported compatibly by GNU. - -@cindex signal handling -The preferred signal handling facilities are the BSD variant of -@code{signal}, and the @sc{posix} @code{sigaction} function; the -alternative USG @code{signal} interface is an inferior design. - -Nowadays, using the @sc{posix} signal functions may be the easiest way -to make a program portable. If you use @code{signal}, then on GNU/Linux -systems running GNU libc version 1, you should include -@file{bsd/signal.h} instead of @file{signal.h}, so as to get BSD -behavior. It is up to you whether to support systems where -@code{signal} has only the USG behavior, or give up on them. - -@cindex impossible conditions -In error checks that detect ``impossible'' conditions, just abort. -There is usually no point in printing any message. These checks -indicate the existence of bugs. Whoever wants to fix the bugs will have -to read the source code and run a debugger. So explain the problem with -comments in the source. The relevant data will be in variables, which -are easy to examine with the debugger, so there is no point moving them -elsewhere. - -Do not use a count of errors as the exit status for a program. -@emph{That does not work}, because exit status values are limited to 8 -bits (0 through 255). A single run of the program might have 256 -errors; if you try to return 256 as the exit status, the parent process -will see 0 as the status, and it will appear that the program succeeded. - -@cindex temporary files -@cindex @code{TMPDIR} environment variable -If you make temporary files, check the @code{TMPDIR} environment -variable; if that variable is defined, use the specified directory -instead of @file{/tmp}. - -In addition, be aware that there is a possible security problem when -creating temporary files in world-writable directories. In C, you can -avoid this problem by creating temporary files in this manner: - -@example -fd = open (filename, O_WRONLY | O_CREAT | O_EXCL, 0600); -@end example - -@noindent -or by using the @code{mkstemps} function from libiberty. - -In bash, use @code{set -C} to avoid this problem. - -@node Libraries -@section Library Behavior -@cindex libraries - -Try to make library functions reentrant. If they need to do dynamic -storage allocation, at least try to avoid any nonreentrancy aside from -that of @code{malloc} itself. - -Here are certain name conventions for libraries, to avoid name -conflicts. - -Choose a name prefix for the library, more than two characters long. -All external function and variable names should start with this -prefix. In addition, there should only be one of these in any given -library member. This usually means putting each one in a separate -source file. - -An exception can be made when two external symbols are always used -together, so that no reasonable program could use one without the -other; then they can both go in the same file. - -External symbols that are not documented entry points for the user -should have names beginning with @samp{_}. The @samp{_} should be -followed by the chosen name prefix for the library, to prevent -collisions with other libraries. These can go in the same files with -user entry points if you like. - -Static functions and variables can be used as you like and need not -fit any naming convention. - -@node Errors -@section Formatting Error Messages -@cindex formatting error messages -@cindex error messages, formatting - -Error messages from compilers should look like this: - -@example -@var{source-file-name}:@var{lineno}: @var{message} -@end example - -@noindent -If you want to mention the column number, use one of these formats: - -@example -@var{source-file-name}:@var{lineno}:@var{column}: @var{message} -@var{source-file-name}:@var{lineno}.@var{column}: @var{message} - -@end example - -@noindent -Line numbers should start from 1 at the beginning of the file, and -column numbers should start from 1 at the beginning of the line. (Both -of these conventions are chosen for compatibility.) Calculate column -numbers assuming that space and all ASCII printing characters have -equal width, and assuming tab stops every 8 columns. - -The error message can also give both the starting and ending positions -of the erroneous text. There are several formats so that you can -avoid redundant information such as a duplicate line number. -Here are the possible formats: - -@example -@var{source-file-name}:@var{lineno-1}.@var{column-1}-@var{lineno-2}.@var{column-2}: @var{message} -@var{source-file-name}:@var{lineno-1}.@var{column-1}-@var{column-2}: @var{message} -@var{source-file-name}:@var{lineno-1}-@var{lineno-2}: @var{message} -@end example - -@noindent -When an error is spread over several files, you can use this format: - -@example -@var{file-1}:@var{lineno-1}.@var{column-1}-@var{file-2}:@var{lineno-2}.@var{column-2}: @var{message} -@end example - -Error messages from other noninteractive programs should look like this: - -@example -@var{program}:@var{source-file-name}:@var{lineno}: @var{message} -@end example - -@noindent -when there is an appropriate source file, or like this: - -@example -@var{program}: @var{message} -@end example - -@noindent -when there is no relevant source file. - -If you want to mention the column number, use this format: - -@example -@var{program}:@var{source-file-name}:@var{lineno}:@var{column}: @var{message} -@end example - -In an interactive program (one that is reading commands from a -terminal), it is better not to include the program name in an error -message. The place to indicate which program is running is in the -prompt or with the screen layout. (When the same program runs with -input from a source other than a terminal, it is not interactive and -would do best to print error messages using the noninteractive style.) - -The string @var{message} should not begin with a capital letter when -it follows a program name and/or file name, because that isn't the -beginning of a sentence. (The sentence conceptually starts at the -beginning of the line.) Also, it should not end with a period. - -Error messages from interactive programs, and other messages such as -usage messages, should start with a capital letter. But they should not -end with a period. - -@node User Interfaces -@section Standards for Interfaces Generally - -@cindex program name and its behavior -@cindex behavior, dependent on program's name -Please don't make the behavior of a utility depend on the name used -to invoke it. It is useful sometimes to make a link to a utility -with a different name, and that should not change what it does. - -Instead, use a run time option or a compilation switch or both -to select among the alternate behaviors. - -@cindex output device and program's behavior -Likewise, please don't make the behavior of the program depend on the -type of output device it is used with. Device independence is an -important principle of the system's design; do not compromise it merely -to save someone from typing an option now and then. (Variation in error -message syntax when using a terminal is ok, because that is a side issue -that people do not depend on.) - -If you think one behavior is most useful when the output is to a -terminal, and another is most useful when the output is a file or a -pipe, then it is usually best to make the default behavior the one that -is useful with output to a terminal, and have an option for the other -behavior. - -Compatibility requires certain programs to depend on the type of output -device. It would be disastrous if @code{ls} or @code{sh} did not do so -in the way all users expect. In some of these cases, we supplement the -program with a preferred alternate version that does not depend on the -output device type. For example, we provide a @code{dir} program much -like @code{ls} except that its default output format is always -multi-column format. - - -@node Graphical Interfaces -@section Standards for Graphical Interfaces -@cindex graphical user interface -@cindex interface styles -@cindex user interface styles - -@cindex GTK+ -When you write a program that provides a graphical user interface, -please make it work with the X Window System and the GTK+ toolkit -unless the functionality specifically requires some alternative (for -example, ``displaying jpeg images while in console mode''). - -In addition, please provide a command-line interface to control the -functionality. (In many cases, the graphical user interface can be a -separate program which invokes the command-line program.) This is -so that the same jobs can be done from scripts. - -@cindex CORBA -@cindex GNOME -@cindex D-bus -@cindex keyboard interface -@cindex library interface -Please also consider providing a D-bus interface for use from other -running programs, such as within GNOME. (GNOME used to use CORBA -for this, but that is being phased out.) In addition, consider -providing a library interface (for use from C), and perhaps a -keyboard-driven console interface (for use by users from console -mode). Once you are doing the work to provide the functionality and -the graphical interface, these won't be much extra work. - - -@node Command-Line Interfaces -@section Standards for Command Line Interfaces -@cindex command-line interface - -@findex getopt -It is a good idea to follow the @sc{posix} guidelines for the -command-line options of a program. The easiest way to do this is to use -@code{getopt} to parse them. Note that the GNU version of @code{getopt} -will normally permit options anywhere among the arguments unless the -special argument @samp{--} is used. This is not what @sc{posix} -specifies; it is a GNU extension. - -@cindex long-named options -Please define long-named options that are equivalent to the -single-letter Unix-style options. We hope to make GNU more user -friendly this way. This is easy to do with the GNU function -@code{getopt_long}. - -One of the advantages of long-named options is that they can be -consistent from program to program. For example, users should be able -to expect the ``verbose'' option of any GNU program which has one, to be -spelled precisely @samp{--verbose}. To achieve this uniformity, look at -the table of common long-option names when you choose the option names -for your program (@pxref{Option Table}). - -It is usually a good idea for file names given as ordinary arguments to -be input files only; any output files would be specified using options -(preferably @samp{-o} or @samp{--output}). Even if you allow an output -file name as an ordinary argument for compatibility, try to provide an -option as another way to specify it. This will lead to more consistency -among GNU utilities, and fewer idiosyncrasies for users to remember. - -@cindex standard command-line options -@cindex options, standard command-line -@cindex CGI programs, standard options for -@cindex PATH_INFO, specifying standard options as -All programs should support two standard options: @samp{--version} -and @samp{--help}. CGI programs should accept these as command-line -options, and also if given as the @env{PATH_INFO}; for instance, -visiting @url{http://example.org/p.cgi/--help} in a browser should -output the same information as invoking @samp{p.cgi --help} from the -command line. - -@menu -* --version:: The standard output for --version. -* --help:: The standard output for --help. -@end menu - -@node --version -@subsection @option{--version} - -@cindex @samp{--version} output - -The standard @code{--version} option should direct the program to -print information about its name, version, origin and legal status, -all on standard output, and then exit successfully. Other options and -arguments should be ignored once this is seen, and the program should -not perform its normal function. - -@cindex canonical name of a program -@cindex program's canonical name -The first line is meant to be easy for a program to parse; the version -number proper starts after the last space. In addition, it contains -the canonical name for this program, in this format: - -@example -GNU Emacs 19.30 -@end example - -@noindent -The program's name should be a constant string; @emph{don't} compute it -from @code{argv[0]}. The idea is to state the standard or canonical -name for the program, not its file name. There are other ways to find -out the precise file name where a command is found in @code{PATH}. - -If the program is a subsidiary part of a larger package, mention the -package name in parentheses, like this: - -@example -emacsserver (GNU Emacs) 19.30 -@end example - -@noindent -If the package has a version number which is different from this -program's version number, you can mention the package version number -just before the close-parenthesis. - -If you @emph{need} to mention the version numbers of libraries which -are distributed separately from the package which contains this program, -you can do so by printing an additional line of version info for each -library you want to mention. Use the same format for these lines as for -the first line. - -Please do not mention all of the libraries that the program uses ``just -for completeness''---that would produce a lot of unhelpful clutter. -Please mention library version numbers only if you find in practice that -they are very important to you in debugging. - -The following line, after the version number line or lines, should be a -copyright notice. If more than one copyright notice is called for, put -each on a separate line. - -Next should follow a line stating the license, preferably using one of -abbrevations below, and a brief statement that the program is free -software, and that users are free to copy and change it. Also mention -that there is no warranty, to the extent permitted by law. See -recommended wording below. - -It is ok to finish the output with a list of the major authors of the -program, as a way of giving credit. - -Here's an example of output that follows these rules: - -@smallexample -GNU hello 2.3 -Copyright (C) 2007 Free Software Foundation, Inc. -License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> -This is free software: you are free to change and redistribute it. -There is NO WARRANTY, to the extent permitted by law. -@end smallexample - -You should adapt this to your program, of course, filling in the proper -year, copyright holder, name of program, and the references to -distribution terms, and changing the rest of the wording as necessary. - -This copyright notice only needs to mention the most recent year in -which changes were made---there's no need to list the years for previous -versions' changes. You don't have to mention the name of the program in -these notices, if that is inconvenient, since it appeared in the first -line. (The rules are different for copyright notices in source files; -@pxref{Copyright Notices,,,maintain,Information for GNU Maintainers}.) - -Translations of the above lines must preserve the validity of the -copyright notices (@pxref{Internationalization}). If the translation's -character set supports it, the @samp{(C)} should be replaced with the -copyright symbol, as follows: - -@ifinfo -(the official copyright symbol, which is the letter C in a circle); -@end ifinfo -@ifnotinfo -@copyright{} -@end ifnotinfo - -Write the word ``Copyright'' exactly like that, in English. Do not -translate it into another language. International treaties recognize -the English word ``Copyright''; translations into other languages do not -have legal significance. - -Finally, here is the table of our suggested license abbreviations. -Any abbreviation can be followed by @samp{v@var{version}[+]}, meaning -that particular version, or later versions with the @samp{+}, as shown -above. - -In the case of exceptions for extra permissions with the GPL, we use -@samp{/} for a separator; the version number can follow the license -abbreviation as usual, as in the examples below. - -@table @asis -@item GPL -GNU General Public License, @url{http://www.gnu.org/@/licenses/@/gpl.html}. - -@item LGPL -GNU Lesser General Public License, @url{http://www.gnu.org/@/licenses/@/lgpl.html}. - -@item GPL/Ada -GNU GPL with the exception for Ada. - -@item Apache -The Apache Software Foundation license, -@url{http://www.apache.org/@/licenses}. - -@item Artistic -The Artistic license used for Perl, @url{http://www.perlfoundation.org/@/legal}. - -@item Expat -The Expat license, @url{http://www.jclark.com/@/xml/@/copying.txt}. - -@item MPL -The Mozilla Public License, @url{http://www.mozilla.org/@/MPL/}. - -@item OBSD -The original (4-clause) BSD license, incompatible with the GNU GPL -@url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#6}. - -@item PHP -The license used for PHP, @url{http://www.php.net/@/license/}. - -@item public domain -The non-license that is being in the public domain, -@url{http://www.gnu.org/@/licenses/@/license-list.html#PublicDomain}. - -@item Python -The license for Python, @url{http://www.python.org/@/2.0.1/@/license.html}. - -@item RBSD -The revised (3-clause) BSD, compatible with the GNU GPL,@* -@url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#5}. - -@item X11 -The simple non-copyleft license used for most versions of the X Window -System, @url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#3}. - -@item Zlib -The license for Zlib, @url{http://www.gzip.org/@/zlib/@/zlib_license.html}. - -@end table - -More information about these licenses and many more are on the GNU -licensing web pages, -@url{http://www.gnu.org/@/licenses/@/license-list.html}. - - -@node --help -@subsection @option{--help} - -@cindex @samp{--help} output - -The standard @code{--help} option should output brief documentation -for how to invoke the program, on standard output, then exit -successfully. Other options and arguments should be ignored once this -is seen, and the program should not perform its normal function. - -@cindex address for bug reports -@cindex bug reports -Near the end of the @samp{--help} option's output, please place lines -giving the email address for bug reports, the package's home page -(normally @indicateurl{http://www.gnu.org/software/@var{pkg}}, and the -general page for help using GNU programs. The format should be like this: - -@example -Report bugs to: @var{mailing-address} -@var{pkg} home page: <http://www.gnu.org/software/@var{pkg}/> -General help using GNU software: <http://www.gnu.org/gethelp/> -@end example - -It is ok to mention other appropriate mailing lists and web pages. - - -@node Option Table -@section Table of Long Options -@cindex long option names -@cindex table of long options - -Here is a table of long options used by GNU programs. It is surely -incomplete, but we aim to list all the options that a new program might -want to be compatible with. If you use names not already in the table, -please send @email{bug-standards@@gnu.org} a list of them, with their -meanings, so we can update the table. - -@c Please leave newlines between items in this table; it's much easier -@c to update when it isn't completely squashed together and unreadable. -@c When there is more than one short option for a long option name, put -@c a semicolon between the lists of the programs that use them, not a -@c period. --friedman - -@table @samp -@item after-date -@samp{-N} in @code{tar}. - -@item all -@samp{-a} in @code{du}, @code{ls}, @code{nm}, @code{stty}, @code{uname}, -and @code{unexpand}. - -@item all-text -@samp{-a} in @code{diff}. - -@item almost-all -@samp{-A} in @code{ls}. - -@item append -@samp{-a} in @code{etags}, @code{tee}, @code{time}; -@samp{-r} in @code{tar}. - -@item archive -@samp{-a} in @code{cp}. - -@item archive-name -@samp{-n} in @code{shar}. - -@item arglength -@samp{-l} in @code{m4}. - -@item ascii -@samp{-a} in @code{diff}. - -@item assign -@samp{-v} in @code{gawk}. - -@item assume-new -@samp{-W} in @code{make}. - -@item assume-old -@samp{-o} in @code{make}. - -@item auto-check -@samp{-a} in @code{recode}. - -@item auto-pager -@samp{-a} in @code{wdiff}. - -@item auto-reference -@samp{-A} in @code{ptx}. - -@item avoid-wraps -@samp{-n} in @code{wdiff}. - -@item background -For server programs, run in the background. - -@item backward-search -@samp{-B} in @code{ctags}. - -@item basename -@samp{-f} in @code{shar}. - -@item batch -Used in GDB. - -@item baud -Used in GDB. - -@item before -@samp{-b} in @code{tac}. - -@item binary -@samp{-b} in @code{cpio} and @code{diff}. - -@item bits-per-code -@samp{-b} in @code{shar}. - -@item block-size -Used in @code{cpio} and @code{tar}. - -@item blocks -@samp{-b} in @code{head} and @code{tail}. - -@item break-file -@samp{-b} in @code{ptx}. - -@item brief -Used in various programs to make output shorter. - -@item bytes -@samp{-c} in @code{head}, @code{split}, and @code{tail}. - -@item c@t{++} -@samp{-C} in @code{etags}. - -@item catenate -@samp{-A} in @code{tar}. - -@item cd -Used in various programs to specify the directory to use. - -@item changes -@samp{-c} in @code{chgrp} and @code{chown}. - -@item classify -@samp{-F} in @code{ls}. - -@item colons -@samp{-c} in @code{recode}. - -@item command -@samp{-c} in @code{su}; -@samp{-x} in GDB. - -@item compare -@samp{-d} in @code{tar}. - -@item compat -Used in @code{gawk}. - -@item compress -@samp{-Z} in @code{tar} and @code{shar}. - -@item concatenate -@samp{-A} in @code{tar}. - -@item confirmation -@samp{-w} in @code{tar}. - -@item context -Used in @code{diff}. - -@item copyleft -@samp{-W copyleft} in @code{gawk}. - -@item copyright -@samp{-C} in @code{ptx}, @code{recode}, and @code{wdiff}; -@samp{-W copyright} in @code{gawk}. - -@item core -Used in GDB. - -@item count -@samp{-q} in @code{who}. - -@item count-links -@samp{-l} in @code{du}. - -@item create -Used in @code{tar} and @code{cpio}. - -@item cut-mark -@samp{-c} in @code{shar}. - -@item cxref -@samp{-x} in @code{ctags}. - -@item date -@samp{-d} in @code{touch}. - -@item debug -@samp{-d} in @code{make} and @code{m4}; -@samp{-t} in Bison. - -@item define -@samp{-D} in @code{m4}. - -@item defines -@samp{-d} in Bison and @code{ctags}. - -@item delete -@samp{-D} in @code{tar}. - -@item dereference -@samp{-L} in @code{chgrp}, @code{chown}, @code{cpio}, @code{du}, -@code{ls}, and @code{tar}. - -@item dereference-args -@samp{-D} in @code{du}. - -@item device -Specify an I/O device (special file name). - -@item diacritics -@samp{-d} in @code{recode}. - -@item dictionary-order -@samp{-d} in @code{look}. - -@item diff -@samp{-d} in @code{tar}. - -@item digits -@samp{-n} in @code{csplit}. - -@item directory -Specify the directory to use, in various programs. In @code{ls}, it -means to show directories themselves rather than their contents. In -@code{rm} and @code{ln}, it means to not treat links to directories -specially. - -@item discard-all -@samp{-x} in @code{strip}. - -@item discard-locals -@samp{-X} in @code{strip}. - -@item dry-run -@samp{-n} in @code{make}. - -@item ed -@samp{-e} in @code{diff}. - -@item elide-empty-files -@samp{-z} in @code{csplit}. - -@item end-delete -@samp{-x} in @code{wdiff}. - -@item end-insert -@samp{-z} in @code{wdiff}. - -@item entire-new-file -@samp{-N} in @code{diff}. - -@item environment-overrides -@samp{-e} in @code{make}. - -@item eof -@samp{-e} in @code{xargs}. - -@item epoch -Used in GDB. - -@item error-limit -Used in @code{makeinfo}. - -@item error-output -@samp{-o} in @code{m4}. - -@item escape -@samp{-b} in @code{ls}. - -@item exclude-from -@samp{-X} in @code{tar}. - -@item exec -Used in GDB. - -@item exit -@samp{-x} in @code{xargs}. - -@item exit-0 -@samp{-e} in @code{unshar}. - -@item expand-tabs -@samp{-t} in @code{diff}. - -@item expression -@samp{-e} in @code{sed}. - -@item extern-only -@samp{-g} in @code{nm}. - -@item extract -@samp{-i} in @code{cpio}; -@samp{-x} in @code{tar}. - -@item faces -@samp{-f} in @code{finger}. - -@item fast -@samp{-f} in @code{su}. - -@item fatal-warnings -@samp{-E} in @code{m4}. - -@item file -@samp{-f} in @code{gawk}, @code{info}, @code{make}, @code{mt}, -@code{sed}, and @code{tar}. - -@item field-separator -@samp{-F} in @code{gawk}. - -@item file-prefix -@samp{-b} in Bison. - -@item file-type -@samp{-F} in @code{ls}. - -@item files-from -@samp{-T} in @code{tar}. - -@item fill-column -Used in @code{makeinfo}. - -@item flag-truncation -@samp{-F} in @code{ptx}. - -@item fixed-output-files -@samp{-y} in Bison. - -@item follow -@samp{-f} in @code{tail}. - -@item footnote-style -Used in @code{makeinfo}. - -@item force -@samp{-f} in @code{cp}, @code{ln}, @code{mv}, and @code{rm}. - -@item force-prefix -@samp{-F} in @code{shar}. - -@item foreground -For server programs, run in the foreground; -in other words, don't do anything special to run the server -in the background. - -@item format -Used in @code{ls}, @code{time}, and @code{ptx}. - -@item freeze-state -@samp{-F} in @code{m4}. - -@item fullname -Used in GDB. - -@item gap-size -@samp{-g} in @code{ptx}. - -@item get -@samp{-x} in @code{tar}. - -@item graphic -@samp{-i} in @code{ul}. - -@item graphics -@samp{-g} in @code{recode}. - -@item group -@samp{-g} in @code{install}. - -@item gzip -@samp{-z} in @code{tar} and @code{shar}. - -@item hashsize -@samp{-H} in @code{m4}. - -@item header -@samp{-h} in @code{objdump} and @code{recode} - -@item heading -@samp{-H} in @code{who}. - -@item help -Used to ask for brief usage information. - -@item here-delimiter -@samp{-d} in @code{shar}. - -@item hide-control-chars -@samp{-q} in @code{ls}. - -@item html -In @code{makeinfo}, output HTML. - -@item idle -@samp{-u} in @code{who}. - -@item ifdef -@samp{-D} in @code{diff}. - -@item ignore -@samp{-I} in @code{ls}; -@samp{-x} in @code{recode}. - -@item ignore-all-space -@samp{-w} in @code{diff}. - -@item ignore-backups -@samp{-B} in @code{ls}. - -@item ignore-blank-lines -@samp{-B} in @code{diff}. - -@item ignore-case -@samp{-f} in @code{look} and @code{ptx}; -@samp{-i} in @code{diff} and @code{wdiff}. - -@item ignore-errors -@samp{-i} in @code{make}. - -@item ignore-file -@samp{-i} in @code{ptx}. - -@item ignore-indentation -@samp{-I} in @code{etags}. - -@item ignore-init-file -@samp{-f} in Oleo. - -@item ignore-interrupts -@samp{-i} in @code{tee}. - -@item ignore-matching-lines -@samp{-I} in @code{diff}. - -@item ignore-space-change -@samp{-b} in @code{diff}. - -@item ignore-zeros -@samp{-i} in @code{tar}. - -@item include -@samp{-i} in @code{etags}; -@samp{-I} in @code{m4}. - -@item include-dir -@samp{-I} in @code{make}. - -@item incremental -@samp{-G} in @code{tar}. - -@item info -@samp{-i}, @samp{-l}, and @samp{-m} in Finger. - -@item init-file -In some programs, specify the name of the file to read as the user's -init file. - -@item initial -@samp{-i} in @code{expand}. - -@item initial-tab -@samp{-T} in @code{diff}. - -@item inode -@samp{-i} in @code{ls}. - -@item interactive -@samp{-i} in @code{cp}, @code{ln}, @code{mv}, @code{rm}; -@samp{-e} in @code{m4}; -@samp{-p} in @code{xargs}; -@samp{-w} in @code{tar}. - -@item intermix-type -@samp{-p} in @code{shar}. - -@item iso-8601 -Used in @code{date} - -@item jobs -@samp{-j} in @code{make}. - -@item just-print -@samp{-n} in @code{make}. - -@item keep-going -@samp{-k} in @code{make}. - -@item keep-files -@samp{-k} in @code{csplit}. - -@item kilobytes -@samp{-k} in @code{du} and @code{ls}. - -@item language -@samp{-l} in @code{etags}. - -@item less-mode -@samp{-l} in @code{wdiff}. - -@item level-for-gzip -@samp{-g} in @code{shar}. - -@item line-bytes -@samp{-C} in @code{split}. - -@item lines -Used in @code{split}, @code{head}, and @code{tail}. - -@item link -@samp{-l} in @code{cpio}. - -@item lint -@itemx lint-old -Used in @code{gawk}. - -@item list -@samp{-t} in @code{cpio}; -@samp{-l} in @code{recode}. - -@item list -@samp{-t} in @code{tar}. - -@item literal -@samp{-N} in @code{ls}. - -@item load-average -@samp{-l} in @code{make}. - -@item login -Used in @code{su}. - -@item machine -Used in @code{uname}. - -@item macro-name -@samp{-M} in @code{ptx}. - -@item mail -@samp{-m} in @code{hello} and @code{uname}. - -@item make-directories -@samp{-d} in @code{cpio}. - -@item makefile -@samp{-f} in @code{make}. - -@item mapped -Used in GDB. - -@item max-args -@samp{-n} in @code{xargs}. - -@item max-chars -@samp{-n} in @code{xargs}. - -@item max-lines -@samp{-l} in @code{xargs}. - -@item max-load -@samp{-l} in @code{make}. - -@item max-procs -@samp{-P} in @code{xargs}. - -@item mesg -@samp{-T} in @code{who}. - -@item message -@samp{-T} in @code{who}. - -@item minimal -@samp{-d} in @code{diff}. - -@item mixed-uuencode -@samp{-M} in @code{shar}. - -@item mode -@samp{-m} in @code{install}, @code{mkdir}, and @code{mkfifo}. - -@item modification-time -@samp{-m} in @code{tar}. - -@item multi-volume -@samp{-M} in @code{tar}. - -@item name-prefix -@samp{-a} in Bison. - -@item nesting-limit -@samp{-L} in @code{m4}. - -@item net-headers -@samp{-a} in @code{shar}. - -@item new-file -@samp{-W} in @code{make}. - -@item no-builtin-rules -@samp{-r} in @code{make}. - -@item no-character-count -@samp{-w} in @code{shar}. - -@item no-check-existing -@samp{-x} in @code{shar}. - -@item no-common -@samp{-3} in @code{wdiff}. - -@item no-create -@samp{-c} in @code{touch}. - -@item no-defines -@samp{-D} in @code{etags}. - -@item no-deleted -@samp{-1} in @code{wdiff}. - -@item no-dereference -@samp{-d} in @code{cp}. - -@item no-inserted -@samp{-2} in @code{wdiff}. - -@item no-keep-going -@samp{-S} in @code{make}. - -@item no-lines -@samp{-l} in Bison. - -@item no-piping -@samp{-P} in @code{shar}. - -@item no-prof -@samp{-e} in @code{gprof}. - -@item no-regex -@samp{-R} in @code{etags}. - -@item no-sort -@samp{-p} in @code{nm}. - -@item no-splash -Don't print a startup splash screen. - -@item no-split -Used in @code{makeinfo}. - -@item no-static -@samp{-a} in @code{gprof}. - -@item no-time -@samp{-E} in @code{gprof}. - -@item no-timestamp -@samp{-m} in @code{shar}. - -@item no-validate -Used in @code{makeinfo}. - -@item no-wait -Used in @code{emacsclient}. - -@item no-warn -Used in various programs to inhibit warnings. - -@item node -@samp{-n} in @code{info}. - -@item nodename -@samp{-n} in @code{uname}. - -@item nonmatching -@samp{-f} in @code{cpio}. - -@item nstuff -@samp{-n} in @code{objdump}. - -@item null -@samp{-0} in @code{xargs}. - -@item number -@samp{-n} in @code{cat}. - -@item number-nonblank -@samp{-b} in @code{cat}. - -@item numeric-sort -@samp{-n} in @code{nm}. - -@item numeric-uid-gid -@samp{-n} in @code{cpio} and @code{ls}. - -@item nx -Used in GDB. - -@item old-archive -@samp{-o} in @code{tar}. - -@item old-file -@samp{-o} in @code{make}. - -@item one-file-system -@samp{-l} in @code{tar}, @code{cp}, and @code{du}. - -@item only-file -@samp{-o} in @code{ptx}. - -@item only-prof -@samp{-f} in @code{gprof}. - -@item only-time -@samp{-F} in @code{gprof}. - -@item options -@samp{-o} in @code{getopt}, @code{fdlist}, @code{fdmount}, -@code{fdmountd}, and @code{fdumount}. - -@item output -In various programs, specify the output file name. - -@item output-prefix -@samp{-o} in @code{shar}. - -@item override -@samp{-o} in @code{rm}. - -@item overwrite -@samp{-c} in @code{unshar}. - -@item owner -@samp{-o} in @code{install}. - -@item paginate -@samp{-l} in @code{diff}. - -@item paragraph-indent -Used in @code{makeinfo}. - -@item parents -@samp{-p} in @code{mkdir} and @code{rmdir}. - -@item pass-all -@samp{-p} in @code{ul}. - -@item pass-through -@samp{-p} in @code{cpio}. - -@item port -@samp{-P} in @code{finger}. - -@item portability -@samp{-c} in @code{cpio} and @code{tar}. - -@item posix -Used in @code{gawk}. - -@item prefix-builtins -@samp{-P} in @code{m4}. - -@item prefix -@samp{-f} in @code{csplit}. - -@item preserve -Used in @code{tar} and @code{cp}. - -@item preserve-environment -@samp{-p} in @code{su}. - -@item preserve-modification-time -@samp{-m} in @code{cpio}. - -@item preserve-order -@samp{-s} in @code{tar}. - -@item preserve-permissions -@samp{-p} in @code{tar}. - -@item print -@samp{-l} in @code{diff}. - -@item print-chars -@samp{-L} in @code{cmp}. - -@item print-data-base -@samp{-p} in @code{make}. - -@item print-directory -@samp{-w} in @code{make}. - -@item print-file-name -@samp{-o} in @code{nm}. - -@item print-symdefs -@samp{-s} in @code{nm}. - -@item printer -@samp{-p} in @code{wdiff}. - -@item prompt -@samp{-p} in @code{ed}. - -@item proxy -Specify an HTTP proxy. - -@item query-user -@samp{-X} in @code{shar}. - -@item question -@samp{-q} in @code{make}. - -@item quiet -Used in many programs to inhibit the usual output. Every -program accepting @samp{--quiet} should accept @samp{--silent} as a -synonym. - -@item quiet-unshar -@samp{-Q} in @code{shar} - -@item quote-name -@samp{-Q} in @code{ls}. - -@item rcs -@samp{-n} in @code{diff}. - -@item re-interval -Used in @code{gawk}. - -@item read-full-blocks -@samp{-B} in @code{tar}. - -@item readnow -Used in GDB. - -@item recon -@samp{-n} in @code{make}. - -@item record-number -@samp{-R} in @code{tar}. - -@item recursive -Used in @code{chgrp}, @code{chown}, @code{cp}, @code{ls}, @code{diff}, -and @code{rm}. - -@item reference -@samp{-r} in @code{touch}. - -@item references -@samp{-r} in @code{ptx}. - -@item regex -@samp{-r} in @code{tac} and @code{etags}. - -@item release -@samp{-r} in @code{uname}. - -@item reload-state -@samp{-R} in @code{m4}. - -@item relocation -@samp{-r} in @code{objdump}. - -@item rename -@samp{-r} in @code{cpio}. - -@item replace -@samp{-i} in @code{xargs}. - -@item report-identical-files -@samp{-s} in @code{diff}. - -@item reset-access-time -@samp{-a} in @code{cpio}. - -@item reverse -@samp{-r} in @code{ls} and @code{nm}. - -@item reversed-ed -@samp{-f} in @code{diff}. - -@item right-side-defs -@samp{-R} in @code{ptx}. - -@item same-order -@samp{-s} in @code{tar}. - -@item same-permissions -@samp{-p} in @code{tar}. - -@item save -@samp{-g} in @code{stty}. - -@item se -Used in GDB. - -@item sentence-regexp -@samp{-S} in @code{ptx}. - -@item separate-dirs -@samp{-S} in @code{du}. - -@item separator -@samp{-s} in @code{tac}. - -@item sequence -Used by @code{recode} to chose files or pipes for sequencing passes. - -@item shell -@samp{-s} in @code{su}. - -@item show-all -@samp{-A} in @code{cat}. - -@item show-c-function -@samp{-p} in @code{diff}. - -@item show-ends -@samp{-E} in @code{cat}. - -@item show-function-line -@samp{-F} in @code{diff}. - -@item show-tabs -@samp{-T} in @code{cat}. - -@item silent -Used in many programs to inhibit the usual output. -Every program accepting -@samp{--silent} should accept @samp{--quiet} as a synonym. - -@item size -@samp{-s} in @code{ls}. - -@item socket -Specify a file descriptor for a network server to use for its socket, -instead of opening and binding a new socket. This provides a way to -run, in a non-privileged process, a server that normally needs a -reserved port number. - -@item sort -Used in @code{ls}. - -@item source -@samp{-W source} in @code{gawk}. - -@item sparse -@samp{-S} in @code{tar}. - -@item speed-large-files -@samp{-H} in @code{diff}. - -@item split-at -@samp{-E} in @code{unshar}. - -@item split-size-limit -@samp{-L} in @code{shar}. - -@item squeeze-blank -@samp{-s} in @code{cat}. - -@item start-delete -@samp{-w} in @code{wdiff}. - -@item start-insert -@samp{-y} in @code{wdiff}. - -@item starting-file -Used in @code{tar} and @code{diff} to specify which file within -a directory to start processing with. - -@item statistics -@samp{-s} in @code{wdiff}. - -@item stdin-file-list -@samp{-S} in @code{shar}. - -@item stop -@samp{-S} in @code{make}. - -@item strict -@samp{-s} in @code{recode}. - -@item strip -@samp{-s} in @code{install}. - -@item strip-all -@samp{-s} in @code{strip}. - -@item strip-debug -@samp{-S} in @code{strip}. - -@item submitter -@samp{-s} in @code{shar}. - -@item suffix -@samp{-S} in @code{cp}, @code{ln}, @code{mv}. - -@item suffix-format -@samp{-b} in @code{csplit}. - -@item sum -@samp{-s} in @code{gprof}. - -@item summarize -@samp{-s} in @code{du}. - -@item symbolic -@samp{-s} in @code{ln}. - -@item symbols -Used in GDB and @code{objdump}. - -@item synclines -@samp{-s} in @code{m4}. - -@item sysname -@samp{-s} in @code{uname}. - -@item tabs -@samp{-t} in @code{expand} and @code{unexpand}. - -@item tabsize -@samp{-T} in @code{ls}. - -@item terminal -@samp{-T} in @code{tput} and @code{ul}. -@samp{-t} in @code{wdiff}. - -@item text -@samp{-a} in @code{diff}. - -@item text-files -@samp{-T} in @code{shar}. - -@item time -Used in @code{ls} and @code{touch}. - -@item timeout -Specify how long to wait before giving up on some operation. - -@item to-stdout -@samp{-O} in @code{tar}. - -@item total -@samp{-c} in @code{du}. - -@item touch -@samp{-t} in @code{make}, @code{ranlib}, and @code{recode}. - -@item trace -@samp{-t} in @code{m4}. - -@item traditional -@samp{-t} in @code{hello}; -@samp{-W traditional} in @code{gawk}; -@samp{-G} in @code{ed}, @code{m4}, and @code{ptx}. - -@item tty -Used in GDB. - -@item typedefs -@samp{-t} in @code{ctags}. - -@item typedefs-and-c++ -@samp{-T} in @code{ctags}. - -@item typeset-mode -@samp{-t} in @code{ptx}. - -@item uncompress -@samp{-z} in @code{tar}. - -@item unconditional -@samp{-u} in @code{cpio}. - -@item undefine -@samp{-U} in @code{m4}. - -@item undefined-only -@samp{-u} in @code{nm}. - -@item update -@samp{-u} in @code{cp}, @code{ctags}, @code{mv}, @code{tar}. - -@item usage -Used in @code{gawk}; same as @samp{--help}. - -@item uuencode -@samp{-B} in @code{shar}. - -@item vanilla-operation -@samp{-V} in @code{shar}. - -@item verbose -Print more information about progress. Many programs support this. - -@item verify -@samp{-W} in @code{tar}. - -@item version -Print the version number. - -@item version-control -@samp{-V} in @code{cp}, @code{ln}, @code{mv}. - -@item vgrind -@samp{-v} in @code{ctags}. - -@item volume -@samp{-V} in @code{tar}. - -@item what-if -@samp{-W} in @code{make}. - -@item whole-size-limit -@samp{-l} in @code{shar}. - -@item width -@samp{-w} in @code{ls} and @code{ptx}. - -@item word-regexp -@samp{-W} in @code{ptx}. - -@item writable -@samp{-T} in @code{who}. - -@item zeros -@samp{-z} in @code{gprof}. -@end table - -@node OID Allocations -@section OID Allocations -@cindex OID allocations for GNU -@cindex SNMP -@cindex LDAP -@cindex X.509 - -The OID (object identifier) 1.3.6.1.4.1.11591 has been assigned to the -GNU Project (thanks to Werner Koch). These are used for SNMP, LDAP, -X.509 certificates, and so on. The web site -@url{http://www.alvestrand.no/objectid} has a (voluntary) listing of -many OID assignments. - -If you need a new slot for your GNU package, write -@email{maintainers@@gnu.org}. Here is a list of arcs currently -assigned: - -@example -@include gnu-oids.texi -@end example - - -@node Memory Usage -@section Memory Usage -@cindex memory usage - -If a program typically uses just a few meg of memory, don't bother making any -effort to reduce memory usage. For example, if it is impractical for -other reasons to operate on files more than a few meg long, it is -reasonable to read entire input files into memory to operate on them. - -However, for programs such as @code{cat} or @code{tail}, that can -usefully operate on very large files, it is important to avoid using a -technique that would artificially limit the size of files it can handle. -If a program works by lines and could be applied to arbitrary -user-supplied input files, it should keep only a line in memory, because -this is not very hard and users will want to be able to operate on input -files that are bigger than will fit in memory all at once. - -If your program creates complicated data structures, just make them in -memory and give a fatal error if @code{malloc} returns zero. - -@node File Usage -@section File Usage -@cindex file usage - -Programs should be prepared to operate when @file{/usr} and @file{/etc} -are read-only file systems. Thus, if the program manages log files, -lock files, backup files, score files, or any other files which are -modified for internal purposes, these files should not be stored in -@file{/usr} or @file{/etc}. - -There are two exceptions. @file{/etc} is used to store system -configuration information; it is reasonable for a program to modify -files in @file{/etc} when its job is to update the system configuration. -Also, if the user explicitly asks to modify one file in a directory, it -is reasonable for the program to store other files in the same -directory. - -@node Writing C -@chapter Making The Best Use of C - -This chapter provides advice on how best to use the C language -when writing GNU software. - -@menu -* Formatting:: Formatting your source code. -* Comments:: Commenting your work. -* Syntactic Conventions:: Clean use of C constructs. -* Names:: Naming variables, functions, and files. -* System Portability:: Portability among different operating systems. -* CPU Portability:: Supporting the range of CPU types. -* System Functions:: Portability and ``standard'' library functions. -* Internationalization:: Techniques for internationalization. -* Character Set:: Use ASCII by default. -* Quote Characters:: Use `...' in the C locale. -* Mmap:: How you can safely use @code{mmap}. -@end menu - -@node Formatting -@section Formatting Your Source Code -@cindex formatting source code - -@cindex open brace -@cindex braces, in C source -It is important to put the open-brace that starts the body of a C -function in column one, so that they will start a defun. Several -tools look for open-braces in column one to find the beginnings of C -functions. These tools will not work on code not formatted that way. - -Avoid putting open-brace, open-parenthesis or open-bracket in column -one when they are inside a function, so that they won't start a defun. -The open-brace that starts a @code{struct} body can go in column one -if you find it useful to treat that definition as a defun. - -It is also important for function definitions to start the name of the -function in column one. This helps people to search for function -definitions, and may also help certain tools recognize them. Thus, -using Standard C syntax, the format is this: - -@example -static char * -concat (char *s1, char *s2) -@{ - @dots{} -@} -@end example - -@noindent -or, if you want to use traditional C syntax, format the definition like -this: - -@example -static char * -concat (s1, s2) /* Name starts in column one here */ - char *s1, *s2; -@{ /* Open brace in column one here */ - @dots{} -@} -@end example - -In Standard C, if the arguments don't fit nicely on one line, -split it like this: - -@example -int -lots_of_args (int an_integer, long a_long, short a_short, - double a_double, float a_float) -@dots{} -@end example - -The rest of this section gives our recommendations for other aspects of -C formatting style, which is also the default style of the @code{indent} -program in version 1.2 and newer. It corresponds to the options - -@smallexample --nbad -bap -nbc -bbo -bl -bli2 -bls -ncdb -nce -cp1 -cs -di2 --ndj -nfc1 -nfca -hnl -i2 -ip5 -lp -pcs -psl -nsc -nsob -@end smallexample - -We don't think of these recommendations as requirements, because it -causes no problems for users if two different programs have different -formatting styles. - -But whatever style you use, please use it consistently, since a mixture -of styles within one program tends to look ugly. If you are -contributing changes to an existing program, please follow the style of -that program. - -For the body of the function, our recommended style looks like this: - -@example -if (x < foo (y, z)) - haha = bar[4] + 5; -else - @{ - while (z) - @{ - haha += foo (z, z); - z--; - @} - return ++x + bar (); - @} -@end example - -@cindex spaces before open-paren -We find it easier to read a program when it has spaces before the -open-parentheses and after the commas. Especially after the commas. - -When you split an expression into multiple lines, split it -before an operator, not after one. Here is the right way: - -@cindex expressions, splitting -@example -if (foo_this_is_long && bar > win (x, y, z) - && remaining_condition) -@end example - -Try to avoid having two operators of different precedence at the same -level of indentation. For example, don't write this: - -@example -mode = (inmode[j] == VOIDmode - || GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j]) - ? outmode[j] : inmode[j]); -@end example - -Instead, use extra parentheses so that the indentation shows the nesting: - -@example -mode = ((inmode[j] == VOIDmode - || (GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j]))) - ? outmode[j] : inmode[j]); -@end example - -Insert extra parentheses so that Emacs will indent the code properly. -For example, the following indentation looks nice if you do it by hand, - -@example -v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000 - + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000; -@end example - -@noindent -but Emacs would alter it. Adding a set of parentheses produces -something that looks equally nice, and which Emacs will preserve: - -@example -v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000 - + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000); -@end example - -Format do-while statements like this: - -@example -do - @{ - a = foo (a); - @} -while (a > 0); -@end example - -@cindex formfeed -@cindex control-L -Please use formfeed characters (control-L) to divide the program into -pages at logical places (but not within a function). It does not matter -just how long the pages are, since they do not have to fit on a printed -page. The formfeeds should appear alone on lines by themselves. - -@node Comments -@section Commenting Your Work -@cindex commenting - -Every program should start with a comment saying briefly what it is for. -Example: @samp{fmt - filter for simple filling of text}. This comment -should be at the top of the source file containing the @samp{main} -function of the program. - -Also, please write a brief comment at the start of each source file, -with the file name and a line or two about the overall purpose of the -file. - -Please write the comments in a GNU program in English, because English -is the one language that nearly all programmers in all countries can -read. If you do not write English well, please write comments in -English as well as you can, then ask other people to help rewrite them. -If you can't write comments in English, please find someone to work with -you and translate your comments into English. - -Please put a comment on each function saying what the function does, -what sorts of arguments it gets, and what the possible values of -arguments mean and are used for. It is not necessary to duplicate in -words the meaning of the C argument declarations, if a C type is being -used in its customary fashion. If there is anything nonstandard about -its use (such as an argument of type @code{char *} which is really the -address of the second character of a string, not the first), or any -possible values that would not work the way one would expect (such as, -that strings containing newlines are not guaranteed to work), be sure -to say so. - -Also explain the significance of the return value, if there is one. - -Please put two spaces after the end of a sentence in your comments, so -that the Emacs sentence commands will work. Also, please write -complete sentences and capitalize the first word. If a lower-case -identifier comes at the beginning of a sentence, don't capitalize it! -Changing the spelling makes it a different identifier. If you don't -like starting a sentence with a lower case letter, write the sentence -differently (e.g., ``The identifier lower-case is @dots{}''). - -The comment on a function is much clearer if you use the argument -names to speak about the argument values. The variable name itself -should be lower case, but write it in upper case when you are speaking -about the value rather than the variable itself. Thus, ``the inode -number NODE_NUM'' rather than ``an inode''. - -There is usually no purpose in restating the name of the function in -the comment before it, because the reader can see that for himself. -There might be an exception when the comment is so long that the function -itself would be off the bottom of the screen. - -There should be a comment on each static variable as well, like this: - -@example -/* Nonzero means truncate lines in the display; - zero means continue them. */ -int truncate_lines; -@end example - -@cindex conditionals, comments for -@cindex @code{#endif}, commenting -Every @samp{#endif} should have a comment, except in the case of short -conditionals (just a few lines) that are not nested. The comment should -state the condition of the conditional that is ending, @emph{including -its sense}. @samp{#else} should have a comment describing the condition -@emph{and sense} of the code that follows. For example: - -@example -@group -#ifdef foo - @dots{} -#else /* not foo */ - @dots{} -#endif /* not foo */ -@end group -@group -#ifdef foo - @dots{} -#endif /* foo */ -@end group -@end example - -@noindent -but, by contrast, write the comments this way for a @samp{#ifndef}: - -@example -@group -#ifndef foo - @dots{} -#else /* foo */ - @dots{} -#endif /* foo */ -@end group -@group -#ifndef foo - @dots{} -#endif /* not foo */ -@end group -@end example - -@node Syntactic Conventions -@section Clean Use of C Constructs -@cindex syntactic conventions - -@cindex implicit @code{int} -@cindex function argument, declaring -Please explicitly declare the types of all objects. For example, you -should explicitly declare all arguments to functions, and you should -declare functions to return @code{int} rather than omitting the -@code{int}. - -@cindex compiler warnings -@cindex @samp{-Wall} compiler option -Some programmers like to use the GCC @samp{-Wall} option, and change the -code whenever it issues a warning. If you want to do this, then do. -Other programmers prefer not to use @samp{-Wall}, because it gives -warnings for valid and legitimate code which they do not want to change. -If you want to do this, then do. The compiler should be your servant, -not your master. - -Declarations of external functions and functions to appear later in the -source file should all go in one place near the beginning of the file -(somewhere before the first function definition in the file), or else -should go in a header file. Don't put @code{extern} declarations inside -functions. - -@cindex temporary variables -It used to be common practice to use the same local variables (with -names like @code{tem}) over and over for different values within one -function. Instead of doing this, it is better to declare a separate local -variable for each distinct purpose, and give it a name which is -meaningful. This not only makes programs easier to understand, it also -facilitates optimization by good compilers. You can also move the -declaration of each local variable into the smallest scope that includes -all its uses. This makes the program even cleaner. - -Don't use local variables or parameters that shadow global identifiers. - -@cindex multiple variables in a line -Don't declare multiple variables in one declaration that spans lines. -Start a new declaration on each line, instead. For example, instead -of this: - -@example -@group -int foo, - bar; -@end group -@end example - -@noindent -write either this: - -@example -int foo, bar; -@end example - -@noindent -or this: - -@example -int foo; -int bar; -@end example - -@noindent -(If they are global variables, each should have a comment preceding it -anyway.) - -When you have an @code{if}-@code{else} statement nested in another -@code{if} statement, always put braces around the @code{if}-@code{else}. -Thus, never write like this: - -@example -if (foo) - if (bar) - win (); - else - lose (); -@end example - -@noindent -always like this: - -@example -if (foo) - @{ - if (bar) - win (); - else - lose (); - @} -@end example - -If you have an @code{if} statement nested inside of an @code{else} -statement, either write @code{else if} on one line, like this, - -@example -if (foo) - @dots{} -else if (bar) - @dots{} -@end example - -@noindent -with its @code{then}-part indented like the preceding @code{then}-part, -or write the nested @code{if} within braces like this: - -@example -if (foo) - @dots{} -else - @{ - if (bar) - @dots{} - @} -@end example - -Don't declare both a structure tag and variables or typedefs in the -same declaration. Instead, declare the structure tag separately -and then use it to declare the variables or typedefs. - -Try to avoid assignments inside @code{if}-conditions (assignments -inside @code{while}-conditions are ok). For example, don't write -this: - -@example -if ((foo = (char *) malloc (sizeof *foo)) == 0) - fatal ("virtual memory exhausted"); -@end example - -@noindent -instead, write this: - -@example -foo = (char *) malloc (sizeof *foo); -if (foo == 0) - fatal ("virtual memory exhausted"); -@end example - -@pindex lint -Don't make the program ugly to placate @code{lint}. Please don't insert any -casts to @code{void}. Zero without a cast is perfectly fine as a null -pointer constant, except when calling a varargs function. - -@node Names -@section Naming Variables, Functions, and Files - -@cindex names of variables, functions, and files -The names of global variables and functions in a program serve as -comments of a sort. So don't choose terse names---instead, look for -names that give useful information about the meaning of the variable or -function. In a GNU program, names should be English, like other -comments. - -Local variable names can be shorter, because they are used only within -one context, where (presumably) comments explain their purpose. - -Try to limit your use of abbreviations in symbol names. It is ok to -make a few abbreviations, explain what they mean, and then use them -frequently, but don't use lots of obscure abbreviations. - -Please use underscores to separate words in a name, so that the Emacs -word commands can be useful within them. Stick to lower case; reserve -upper case for macros and @code{enum} constants, and for name-prefixes -that follow a uniform convention. - -For example, you should use names like @code{ignore_space_change_flag}; -don't use names like @code{iCantReadThis}. - -Variables that indicate whether command-line options have been -specified should be named after the meaning of the option, not after -the option-letter. A comment should state both the exact meaning of -the option and its letter. For example, - -@example -@group -/* Ignore changes in horizontal whitespace (-b). */ -int ignore_space_change_flag; -@end group -@end example - -When you want to define names with constant integer values, use -@code{enum} rather than @samp{#define}. GDB knows about enumeration -constants. - -@cindex file-name limitations -@pindex doschk -You might want to make sure that none of the file names would conflict -if the files were loaded onto an MS-DOS file system which shortens the -names. You can use the program @code{doschk} to test for this. - -Some GNU programs were designed to limit themselves to file names of 14 -characters or less, to avoid file name conflicts if they are read into -older System V systems. Please preserve this feature in the existing -GNU programs that have it, but there is no need to do this in new GNU -programs. @code{doschk} also reports file names longer than 14 -characters. - -@node System Portability -@section Portability between System Types -@cindex portability, between system types - -In the Unix world, ``portability'' refers to porting to different Unix -versions. For a GNU program, this kind of portability is desirable, but -not paramount. - -The primary purpose of GNU software is to run on top of the GNU kernel, -compiled with the GNU C compiler, on various types of @sc{cpu}. So the -kinds of portability that are absolutely necessary are quite limited. -But it is important to support Linux-based GNU systems, since they -are the form of GNU that is popular. - -Beyond that, it is good to support the other free operating systems -(*BSD), and it is nice to support other Unix-like systems if you want -to. Supporting a variety of Unix-like systems is desirable, although -not paramount. It is usually not too hard, so you may as well do it. -But you don't have to consider it an obligation, if it does turn out to -be hard. - -@pindex autoconf -The easiest way to achieve portability to most Unix-like systems is to -use Autoconf. It's unlikely that your program needs to know more -information about the host platform than Autoconf can provide, simply -because most of the programs that need such knowledge have already been -written. - -Avoid using the format of semi-internal data bases (e.g., directories) -when there is a higher-level alternative (@code{readdir}). - -@cindex non-@sc{posix} systems, and portability -As for systems that are not like Unix, such as MSDOS, Windows, VMS, MVS, -and older Macintosh systems, supporting them is often a lot of work. -When that is the case, it is better to spend your time adding features -that will be useful on GNU and GNU/Linux, rather than on supporting -other incompatible systems. - -If you do support Windows, please do not abbreviate it as ``win''. In -hacker terminology, calling something a ``win'' is a form of praise. -You're free to praise Microsoft Windows on your own if you want, but -please don't do this in GNU packages. Instead of abbreviating -``Windows'' to ``win'', you can write it in full or abbreviate it to -``woe'' or ``w''. In GNU Emacs, for instance, we use @samp{w32} in -file names of Windows-specific files, but the macro for Windows -conditionals is called @code{WINDOWSNT}. - -It is a good idea to define the ``feature test macro'' -@code{_GNU_SOURCE} when compiling your C files. When you compile on GNU -or GNU/Linux, this will enable the declarations of GNU library extension -functions, and that will usually give you a compiler error message if -you define the same function names in some other way in your program. -(You don't have to actually @emph{use} these functions, if you prefer -to make the program more portable to other systems.) - -But whether or not you use these GNU extensions, you should avoid -using their names for any other meanings. Doing so would make it hard -to move your code into other GNU programs. - -@node CPU Portability -@section Portability between @sc{cpu}s - -@cindex data types, and portability -@cindex portability, and data types -Even GNU systems will differ because of differences among @sc{cpu} -types---for example, difference in byte ordering and alignment -requirements. It is absolutely essential to handle these differences. -However, don't make any effort to cater to the possibility that an -@code{int} will be less than 32 bits. We don't support 16-bit machines -in GNU. - -Similarly, don't make any effort to cater to the possibility that -@code{long} will be smaller than predefined types like @code{size_t}. -For example, the following code is ok: - -@example -printf ("size = %lu\n", (unsigned long) sizeof array); -printf ("diff = %ld\n", (long) (pointer2 - pointer1)); -@end example - -1989 Standard C requires this to work, and we know of only one -counterexample: 64-bit programs on Microsoft Windows. We will -leave it to those who want to port GNU programs to that environment -to figure out how to do it. - -Predefined file-size types like @code{off_t} are an exception: they are -longer than @code{long} on many platforms, so code like the above won't -work with them. One way to print an @code{off_t} value portably is to -print its digits yourself, one by one. - -Don't assume that the address of an @code{int} object is also the -address of its least-significant byte. This is false on big-endian -machines. Thus, don't make the following mistake: - -@example -int c; -@dots{} -while ((c = getchar ()) != EOF) - write (file_descriptor, &c, 1); -@end example - -@noindent Instead, use @code{unsigned char} as follows. (The @code{unsigned} -is for portability to unusual systems where @code{char} is signed and -where there is integer overflow checking.) - -@example -int c; -while ((c = getchar ()) != EOF) - @{ - unsigned char u = c; - write (file_descriptor, &u, 1); - @} -@end example - -It used to be ok to not worry about the difference between pointers -and integers when passing arguments to functions. However, on most -modern 64-bit machines pointers are wider than @code{int}. -Conversely, integer types like @code{long long int} and @code{off_t} -are wider than pointers on most modern 32-bit machines. Hence it's -often better nowadays to use prototypes to define functions whose -argument types are not trivial. - -In particular, if functions accept varying argument counts or types -they should be declared using prototypes containing @samp{...} and -defined using @file{stdarg.h}. For an example of this, please see the -@uref{http://www.gnu.org/software/gnulib/, Gnulib} error module, which -declares and defines the following function: - -@example -/* Print a message with `fprintf (stderr, FORMAT, ...)'; - if ERRNUM is nonzero, follow it with ": " and strerror (ERRNUM). - If STATUS is nonzero, terminate the program with `exit (STATUS)'. */ - -void error (int status, int errnum, const char *format, ...); -@end example - -A simple way to use the Gnulib error module is to obtain the two -source files @file{error.c} and @file{error.h} from the Gnulib library -source code repository at -@uref{http://git.savannah.gnu.org/@/gitweb/@/?p=gnulib.git}. -Here's a sample use: - -@example -#include "error.h" -#include <errno.h> -#include <stdio.h> - -char *program_name = "myprogram"; - -FILE * -xfopen (char const *name) -@{ - FILE *fp = fopen (name, "r"); - if (! fp) - error (1, errno, "cannot read %s", name); - return fp; -@} -@end example - -@cindex casting pointers to integers -Avoid casting pointers to integers if you can. Such casts greatly -reduce portability, and in most programs they are easy to avoid. In the -cases where casting pointers to integers is essential---such as, a Lisp -interpreter which stores type information as well as an address in one -word---you'll have to make explicit provisions to handle different word -sizes. You will also need to make provision for systems in which the -normal range of addresses you can get from @code{malloc} starts far away -from zero. - -@node System Functions -@section Calling System Functions -@cindex library functions, and portability -@cindex portability, and library functions - -C implementations differ substantially. Standard C reduces but does -not eliminate the incompatibilities; meanwhile, many GNU packages still -support pre-standard compilers because this is not hard to do. This -chapter gives recommendations for how to use the more-or-less standard C -library functions to avoid unnecessary loss of portability. - -@itemize @bullet -@item -Don't use the return value of @code{sprintf}. It returns the number of -characters written on some systems, but not on all systems. - -@item -Be aware that @code{vfprintf} is not always available. - -@item -@code{main} should be declared to return type @code{int}. It should -terminate either by calling @code{exit} or by returning the integer -status code; make sure it cannot ever return an undefined value. - -@cindex declaration for system functions -@item -Don't declare system functions explicitly. - -Almost any declaration for a system function is wrong on some system. -To minimize conflicts, leave it to the system header files to declare -system functions. If the headers don't declare a function, let it -remain undeclared. - -While it may seem unclean to use a function without declaring it, in -practice this works fine for most system library functions on the -systems where this really happens; thus, the disadvantage is only -theoretical. By contrast, actual declarations have frequently caused -actual conflicts. - -@item -If you must declare a system function, don't specify the argument types. -Use an old-style declaration, not a Standard C prototype. The more you -specify about the function, the more likely a conflict. - -@item -In particular, don't unconditionally declare @code{malloc} or -@code{realloc}. - -Most GNU programs use those functions just once, in functions -conventionally named @code{xmalloc} and @code{xrealloc}. These -functions call @code{malloc} and @code{realloc}, respectively, and -check the results. - -Because @code{xmalloc} and @code{xrealloc} are defined in your program, -you can declare them in other files without any risk of type conflict. - -On most systems, @code{int} is the same length as a pointer; thus, the -calls to @code{malloc} and @code{realloc} work fine. For the few -exceptional systems (mostly 64-bit machines), you can use -@strong{conditionalized} declarations of @code{malloc} and -@code{realloc}---or put these declarations in configuration files -specific to those systems. - -@cindex string library functions -@item -The string functions require special treatment. Some Unix systems have -a header file @file{string.h}; others have @file{strings.h}. Neither -file name is portable. There are two things you can do: use Autoconf to -figure out which file to include, or don't include either file. - -@item -If you don't include either strings file, you can't get declarations for -the string functions from the header file in the usual way. - -That causes less of a problem than you might think. The newer standard -string functions should be avoided anyway because many systems still -don't support them. The string functions you can use are these: - -@example -strcpy strncpy strcat strncat -strlen strcmp strncmp -strchr strrchr -@end example - -The copy and concatenate functions work fine without a declaration as -long as you don't use their values. Using their values without a -declaration fails on systems where the width of a pointer differs from -the width of @code{int}, and perhaps in other cases. It is trivial to -avoid using their values, so do that. - -The compare functions and @code{strlen} work fine without a declaration -on most systems, possibly all the ones that GNU software runs on. -You may find it necessary to declare them @strong{conditionally} on a -few systems. - -The search functions must be declared to return @code{char *}. Luckily, -there is no variation in the data type they return. But there is -variation in their names. Some systems give these functions the names -@code{index} and @code{rindex}; other systems use the names -@code{strchr} and @code{strrchr}. Some systems support both pairs of -names, but neither pair works on all systems. - -You should pick a single pair of names and use it throughout your -program. (Nowadays, it is better to choose @code{strchr} and -@code{strrchr} for new programs, since those are the standard -names.) Declare both of those names as functions returning @code{char -*}. On systems which don't support those names, define them as macros -in terms of the other pair. For example, here is what to put at the -beginning of your file (or in a header) if you want to use the names -@code{strchr} and @code{strrchr} throughout: - -@example -#ifndef HAVE_STRCHR -#define strchr index -#endif -#ifndef HAVE_STRRCHR -#define strrchr rindex -#endif - -char *strchr (); -char *strrchr (); -@end example -@end itemize - -Here we assume that @code{HAVE_STRCHR} and @code{HAVE_STRRCHR} are -macros defined in systems where the corresponding functions exist. -One way to get them properly defined is to use Autoconf. - -@node Internationalization -@section Internationalization -@cindex internationalization - -@pindex gettext -GNU has a library called GNU gettext that makes it easy to translate the -messages in a program into various languages. You should use this -library in every program. Use English for the messages as they appear -in the program, and let gettext provide the way to translate them into -other languages. - -Using GNU gettext involves putting a call to the @code{gettext} macro -around each string that might need translation---like this: - -@example -printf (gettext ("Processing file `%s'...")); -@end example - -@noindent -This permits GNU gettext to replace the string @code{"Processing file -`%s'..."} with a translated version. - -Once a program uses gettext, please make a point of writing calls to -@code{gettext} when you add new strings that call for translation. - -Using GNU gettext in a package involves specifying a @dfn{text domain -name} for the package. The text domain name is used to separate the -translations for this package from the translations for other packages. -Normally, the text domain name should be the same as the name of the -package---for example, @samp{coreutils} for the GNU core utilities. - -@cindex message text, and internationalization -To enable gettext to work well, avoid writing code that makes -assumptions about the structure of words or sentences. When you want -the precise text of a sentence to vary depending on the data, use two or -more alternative string constants each containing a complete sentences, -rather than inserting conditionalized words or phrases into a single -sentence framework. - -Here is an example of what not to do: - -@smallexample -printf ("%s is full", capacity > 5000000 ? "disk" : "floppy disk"); -@end smallexample - -If you apply gettext to all strings, like this, - -@smallexample -printf (gettext ("%s is full"), - capacity > 5000000 ? gettext ("disk") : gettext ("floppy disk")); -@end smallexample - -@noindent -the translator will hardly know that "disk" and "floppy disk" are meant to -be substituted in the other string. Worse, in some languages (like French) -the construction will not work: the translation of the word "full" depends -on the gender of the first part of the sentence; it happens to be not the -same for "disk" as for "floppy disk". - -Complete sentences can be translated without problems: - -@example -printf (capacity > 5000000 ? gettext ("disk is full") - : gettext ("floppy disk is full")); -@end example - -A similar problem appears at the level of sentence structure with this -code: - -@example -printf ("# Implicit rule search has%s been done.\n", - f->tried_implicit ? "" : " not"); -@end example - -@noindent -Adding @code{gettext} calls to this code cannot give correct results for -all languages, because negation in some languages requires adding words -at more than one place in the sentence. By contrast, adding -@code{gettext} calls does the job straightforwardly if the code starts -out like this: - -@example -printf (f->tried_implicit - ? "# Implicit rule search has been done.\n", - : "# Implicit rule search has not been done.\n"); -@end example - -Another example is this one: - -@example -printf ("%d file%s processed", nfiles, - nfiles != 1 ? "s" : ""); -@end example - -@noindent -The problem with this example is that it assumes that plurals are made -by adding `s'. If you apply gettext to the format string, like this, - -@example -printf (gettext ("%d file%s processed"), nfiles, - nfiles != 1 ? "s" : ""); -@end example - -@noindent -the message can use different words, but it will still be forced to use -`s' for the plural. Here is a better way, with gettext being applied to -the two strings independently: - -@example -printf ((nfiles != 1 ? gettext ("%d files processed") - : gettext ("%d file processed")), - nfiles); -@end example - -@noindent -But this still doesn't work for languages like Polish, which has three -plural forms: one for nfiles == 1, one for nfiles == 2, 3, 4, 22, 23, 24, ... -and one for the rest. The GNU @code{ngettext} function solves this problem: - -@example -printf (ngettext ("%d files processed", "%d file processed", nfiles), - nfiles); -@end example - - -@node Character Set -@section Character Set -@cindex character set -@cindex encodings -@cindex ASCII characters -@cindex non-ASCII characters - -Sticking to the ASCII character set (plain text, 7-bit characters) is -preferred in GNU source code comments, text documents, and other -contexts, unless there is good reason to do something else because of -the application domain. For example, if source code deals with the -French Revolutionary calendar, it is OK if its literal strings contain -accented characters in month names like ``Flor@'eal''. Also, it is OK -to use non-ASCII characters to represent proper names of contributors in -change logs (@pxref{Change Logs}). - -If you need to use non-ASCII characters, you should normally stick with -one encoding, as one cannot in general mix encodings reliably. - - -@node Quote Characters -@section Quote Characters -@cindex quote characters -@cindex locale-specific quote characters -@cindex left quote -@cindex grave accent - -In the C locale, GNU programs should stick to plain ASCII for quotation -characters in messages to users: preferably 0x60 (@samp{`}) for left -quotes and 0x27 (@samp{'}) for right quotes. It is ok, but not -required, to use locale-specific quotes in other locales. - -The @uref{http://www.gnu.org/software/gnulib/, Gnulib} @code{quote} and -@code{quotearg} modules provide a reasonably straightforward way to -support locale-specific quote characters, as well as taking care of -other issues, such as quoting a filename that itself contains a quote -character. See the Gnulib documentation for usage details. - -In any case, the documentation for your program should clearly specify -how it does quoting, if different than the preferred method of @samp{`} -and @samp{'}. This is especially important if the output of your -program is ever likely to be parsed by another program. - -Quotation characters are a difficult area in the computing world at -this time: there are no true left or right quote characters in Latin1; -the @samp{`} character we use was standardized there as a grave -accent. Moreover, Latin1 is still not universally usable. - -Unicode contains the unambiguous quote characters required, and its -common encoding UTF-8 is upward compatible with Latin1. However, -Unicode and UTF-8 are not universally well-supported, either. - -This may change over the next few years, and then we will revisit -this. - - -@node Mmap -@section Mmap -@findex mmap - -Don't assume that @code{mmap} either works on all files or fails -for all files. It may work on some files and fail on others. - -The proper way to use @code{mmap} is to try it on the specific file for -which you want to use it---and if @code{mmap} doesn't work, fall back on -doing the job in another way using @code{read} and @code{write}. - -The reason this precaution is needed is that the GNU kernel (the HURD) -provides a user-extensible file system, in which there can be many -different kinds of ``ordinary files.'' Many of them support -@code{mmap}, but some do not. It is important to make programs handle -all these kinds of files. - -@node Documentation -@chapter Documenting Programs -@cindex documentation - -A GNU program should ideally come with full free documentation, adequate -for both reference and tutorial purposes. If the package can be -programmed or extended, the documentation should cover programming or -extending it, as well as just using it. - -@menu -* GNU Manuals:: Writing proper manuals. -* Doc Strings and Manuals:: Compiling doc strings doesn't make a manual. -* Manual Structure Details:: Specific structure conventions. -* License for Manuals:: Writing the distribution terms for a manual. -* Manual Credits:: Giving credit to documentation contributors. -* Printed Manuals:: Mentioning the printed manual. -* NEWS File:: NEWS files supplement manuals. -* Change Logs:: Recording changes. -* Man Pages:: Man pages are secondary. -* Reading other Manuals:: How far you can go in learning - from other manuals. -@end menu - -@node GNU Manuals -@section GNU Manuals - -The preferred document format for the GNU system is the Texinfo -formatting language. Every GNU package should (ideally) have -documentation in Texinfo both for reference and for learners. Texinfo -makes it possible to produce a good quality formatted book, using -@TeX{}, and to generate an Info file. It is also possible to generate -HTML output from Texinfo source. See the Texinfo manual, either the -hardcopy, or the on-line version available through @code{info} or the -Emacs Info subsystem (@kbd{C-h i}). - -Nowadays some other formats such as Docbook and Sgmltexi can be -converted automatically into Texinfo. It is ok to produce the Texinfo -documentation by conversion this way, as long as it gives good results. - -Make sure your manual is clear to a reader who knows nothing about the -topic and reads it straight through. This means covering basic topics -at the beginning, and advanced topics only later. This also means -defining every specialized term when it is first used. - -Programmers tend to carry over the structure of the program as the -structure for its documentation. But this structure is not -necessarily good for explaining how to use the program; it may be -irrelevant and confusing for a user. - -Instead, the right way to structure documentation is according to the -concepts and questions that a user will have in mind when reading it. -This principle applies at every level, from the lowest (ordering -sentences in a paragraph) to the highest (ordering of chapter topics -within the manual). Sometimes this structure of ideas matches the -structure of the implementation of the software being documented---but -often they are different. An important part of learning to write good -documentation is to learn to notice when you have unthinkingly -structured the documentation like the implementation, stop yourself, -and look for better alternatives. - -For example, each program in the GNU system probably ought to be -documented in one manual; but this does not mean each program should -have its own manual. That would be following the structure of the -implementation, rather than the structure that helps the user -understand. - -Instead, each manual should cover a coherent @emph{topic}. For example, -instead of a manual for @code{diff} and a manual for @code{diff3}, we -have one manual for ``comparison of files'' which covers both of those -programs, as well as @code{cmp}. By documenting these programs -together, we can make the whole subject clearer. - -The manual which discusses a program should certainly document all of -the program's command-line options and all of its commands. It should -give examples of their use. But don't organize the manual as a list -of features. Instead, organize it logically, by subtopics. Address -the questions that a user will ask when thinking about the job that -the program does. Don't just tell the reader what each feature can -do---say what jobs it is good for, and show how to use it for those -jobs. Explain what is recommended usage, and what kinds of usage -users should avoid. - -In general, a GNU manual should serve both as tutorial and reference. -It should be set up for convenient access to each topic through Info, -and for reading straight through (appendixes aside). A GNU manual -should give a good introduction to a beginner reading through from the -start, and should also provide all the details that hackers want. -The Bison manual is a good example of this---please take a look at it -to see what we mean. - -That is not as hard as it first sounds. Arrange each chapter as a -logical breakdown of its topic, but order the sections, and write their -text, so that reading the chapter straight through makes sense. Do -likewise when structuring the book into chapters, and when structuring a -section into paragraphs. The watchword is, @emph{at each point, address -the most fundamental and important issue raised by the preceding text.} - -If necessary, add extra chapters at the beginning of the manual which -are purely tutorial and cover the basics of the subject. These provide -the framework for a beginner to understand the rest of the manual. The -Bison manual provides a good example of how to do this. - -To serve as a reference, a manual should have an Index that list all the -functions, variables, options, and important concepts that are part of -the program. One combined Index should do for a short manual, but -sometimes for a complex package it is better to use multiple indices. -The Texinfo manual includes advice on preparing good index entries, see -@ref{Index Entries, , Making Index Entries, texinfo, GNU Texinfo}, and -see @ref{Indexing Commands, , Defining the Entries of an -Index, texinfo, GNU Texinfo}. - -Don't use Unix man pages as a model for how to write GNU documentation; -most of them are terse, badly structured, and give inadequate -explanation of the underlying concepts. (There are, of course, some -exceptions.) Also, Unix man pages use a particular format which is -different from what we use in GNU manuals. - -Please include an email address in the manual for where to report -bugs @emph{in the text of the manual}. - -Please do not use the term ``pathname'' that is used in Unix -documentation; use ``file name'' (two words) instead. We use the term -``path'' only for search paths, which are lists of directory names. - -Please do not use the term ``illegal'' to refer to erroneous input to -a computer program. Please use ``invalid'' for this, and reserve the -term ``illegal'' for activities prohibited by law. - -Please do not write @samp{()} after a function name just to indicate -it is a function. @code{foo ()} is not a function, it is a function -call with no arguments. - -@node Doc Strings and Manuals -@section Doc Strings and Manuals - -Some programming systems, such as Emacs, provide a documentation string -for each function, command or variable. You may be tempted to write a -reference manual by compiling the documentation strings and writing a -little additional text to go around them---but you must not do it. That -approach is a fundamental mistake. The text of well-written -documentation strings will be entirely wrong for a manual. - -A documentation string needs to stand alone---when it appears on the -screen, there will be no other text to introduce or explain it. -Meanwhile, it can be rather informal in style. - -The text describing a function or variable in a manual must not stand -alone; it appears in the context of a section or subsection. Other text -at the beginning of the section should explain some of the concepts, and -should often make some general points that apply to several functions or -variables. The previous descriptions of functions and variables in the -section will also have given information about the topic. A description -written to stand alone would repeat some of that information; this -redundancy looks bad. Meanwhile, the informality that is acceptable in -a documentation string is totally unacceptable in a manual. - -The only good way to use documentation strings in writing a good manual -is to use them as a source of information for writing good text. - -@node Manual Structure Details -@section Manual Structure Details -@cindex manual structure - -The title page of the manual should state the version of the programs or -packages documented in the manual. The Top node of the manual should -also contain this information. If the manual is changing more -frequently than or independent of the program, also state a version -number for the manual in both of these places. - -Each program documented in the manual should have a node named -@samp{@var{program} Invocation} or @samp{Invoking @var{program}}. This -node (together with its subnodes, if any) should describe the program's -command line arguments and how to run it (the sort of information people -would look for in a man page). Start with an @samp{@@example} -containing a template for all the options and arguments that the program -uses. - -Alternatively, put a menu item in some menu whose item name fits one of -the above patterns. This identifies the node which that item points to -as the node for this purpose, regardless of the node's actual name. - -The @samp{--usage} feature of the Info reader looks for such a node -or menu item in order to find the relevant text, so it is essential -for every Texinfo file to have one. - -If one manual describes several programs, it should have such a node for -each program described in the manual. - -@node License for Manuals -@section License for Manuals -@cindex license for manuals - -Please use the GNU Free Documentation License for all GNU manuals that -are more than a few pages long. Likewise for a collection of short -documents---you only need one copy of the GNU FDL for the whole -collection. For a single short document, you can use a very permissive -non-copyleft license, to avoid taking up space with a long license. - -See @uref{http://www.gnu.org/copyleft/fdl-howto.html} for more explanation -of how to employ the GFDL. - -Note that it is not obligatory to include a copy of the GNU GPL or GNU -LGPL in a manual whose license is neither the GPL nor the LGPL. It can -be a good idea to include the program's license in a large manual; in a -short manual, whose size would be increased considerably by including -the program's license, it is probably better not to include it. - -@node Manual Credits -@section Manual Credits -@cindex credits for manuals - -Please credit the principal human writers of the manual as the authors, -on the title page of the manual. If a company sponsored the work, thank -the company in a suitable place in the manual, but do not cite the -company as an author. - -@node Printed Manuals -@section Printed Manuals - -The FSF publishes some GNU manuals in printed form. To encourage sales -of these manuals, the on-line versions of the manual should mention at -the very start that the printed manual is available and should point at -information for getting it---for instance, with a link to the page -@url{http://www.gnu.org/order/order.html}. This should not be included -in the printed manual, though, because there it is redundant. - -It is also useful to explain in the on-line forms of the manual how the -user can print out the manual from the sources. - -@node NEWS File -@section The NEWS File -@cindex @file{NEWS} file - -In addition to its manual, the package should have a file named -@file{NEWS} which contains a list of user-visible changes worth -mentioning. In each new release, add items to the front of the file and -identify the version they pertain to. Don't discard old items; leave -them in the file after the newer items. This way, a user upgrading from -any previous version can see what is new. - -If the @file{NEWS} file gets very long, move some of the older items -into a file named @file{ONEWS} and put a note at the end referring the -user to that file. - -@node Change Logs -@section Change Logs -@cindex change logs - -Keep a change log to describe all the changes made to program source -files. The purpose of this is so that people investigating bugs in the -future will know about the changes that might have introduced the bug. -Often a new bug can be found by looking at what was recently changed. -More importantly, change logs can help you eliminate conceptual -inconsistencies between different parts of a program, by giving you a -history of how the conflicting concepts arose and who they came from. - -@menu -* Change Log Concepts:: -* Style of Change Logs:: -* Simple Changes:: -* Conditional Changes:: -* Indicating the Part Changed:: -@end menu - -@node Change Log Concepts -@subsection Change Log Concepts - -You can think of the change log as a conceptual ``undo list'' which -explains how earlier versions were different from the current version. -People can see the current version; they don't need the change log -to tell them what is in it. What they want from a change log is a -clear explanation of how the earlier version differed. - -The change log file is normally called @file{ChangeLog} and covers an -entire directory. Each directory can have its own change log, or a -directory can use the change log of its parent directory---it's up to -you. - -Another alternative is to record change log information with a version -control system such as RCS or CVS. This can be converted automatically -to a @file{ChangeLog} file using @code{rcs2log}; in Emacs, the command -@kbd{C-x v a} (@code{vc-update-change-log}) does the job. - -There's no need to describe the full purpose of the changes or how -they work together. However, sometimes it is useful to write one line -to describe the overall purpose of a change or a batch of changes. If -you think that a change calls for explanation, you're probably right. -Please do explain it---but please put the full explanation in comments -in the code, where people will see it whenever they see the code. For -example, ``New function'' is enough for the change log when you add a -function, because there should be a comment before the function -definition to explain what it does. - -In the past, we recommended not mentioning changes in non-software -files (manuals, help files, etc.) in change logs. However, we've been -advised that it is a good idea to include them, for the sake of -copyright records. - -The easiest way to add an entry to @file{ChangeLog} is with the Emacs -command @kbd{M-x add-change-log-entry}. An entry should have an -asterisk, the name of the changed file, and then in parentheses the name -of the changed functions, variables or whatever, followed by a colon. -Then describe the changes you made to that function or variable. - -@node Style of Change Logs -@subsection Style of Change Logs -@cindex change logs, style - -Here are some simple examples of change log entries, starting with the -header line that says who made the change and when it was installed, -followed by descriptions of specific changes. (These examples are -drawn from Emacs and GCC.) - -@example -1998-08-17 Richard Stallman <rms@@gnu.org> - -* register.el (insert-register): Return nil. -(jump-to-register): Likewise. - -* sort.el (sort-subr): Return nil. - -* tex-mode.el (tex-bibtex-file, tex-file, tex-region): -Restart the tex shell if process is gone or stopped. -(tex-shell-running): New function. - -* expr.c (store_one_arg): Round size up for move_block_to_reg. -(expand_call): Round up when emitting USE insns. -* stmt.c (assign_parms): Round size up for move_block_from_reg. -@end example - -It's important to name the changed function or variable in full. Don't -abbreviate function or variable names, and don't combine them. -Subsequent maintainers will often search for a function name to find all -the change log entries that pertain to it; if you abbreviate the name, -they won't find it when they search. - -For example, some people are tempted to abbreviate groups of function -names by writing @samp{* register.el (@{insert,jump-to@}-register)}; -this is not a good idea, since searching for @code{jump-to-register} or -@code{insert-register} would not find that entry. - -Separate unrelated change log entries with blank lines. When two -entries represent parts of the same change, so that they work together, -then don't put blank lines between them. Then you can omit the file -name and the asterisk when successive entries are in the same file. - -Break long lists of function names by closing continued lines with -@samp{)}, rather than @samp{,}, and opening the continuation with -@samp{(} as in this example: - -@example -* keyboard.c (menu_bar_items, tool_bar_items) -(Fexecute_extended_command): Deal with `keymap' property. -@end example - -When you install someone else's changes, put the contributor's name in -the change log entry rather than in the text of the entry. In other -words, write this: - -@example -2002-07-14 John Doe <jdoe@@gnu.org> - - * sewing.c: Make it sew. -@end example - -@noindent -rather than this: - -@example -2002-07-14 Usual Maintainer <usual@@gnu.org> - - * sewing.c: Make it sew. Patch by jdoe@@gnu.org. -@end example - -As for the date, that should be the date you applied the change. - -@node Simple Changes -@subsection Simple Changes - -Certain simple kinds of changes don't need much detail in the change -log. - -When you change the calling sequence of a function in a simple fashion, -and you change all the callers of the function to use the new calling -sequence, there is no need to make individual entries for all the -callers that you changed. Just write in the entry for the function -being called, ``All callers changed''---like this: - -@example -* keyboard.c (Fcommand_execute): New arg SPECIAL. -All callers changed. -@end example - -When you change just comments or doc strings, it is enough to write an -entry for the file, without mentioning the functions. Just ``Doc -fixes'' is enough for the change log. - -There's no technical need to make change log entries for documentation -files. This is because documentation is not susceptible to bugs that -are hard to fix. Documentation does not consist of parts that must -interact in a precisely engineered fashion. To correct an error, you -need not know the history of the erroneous passage; it is enough to -compare what the documentation says with the way the program actually -works. - -However, you should keep change logs for documentation files when the -project gets copyright assignments from its contributors, so as to -make the records of authorship more accurate. - -@node Conditional Changes -@subsection Conditional Changes -@cindex conditional changes, and change logs -@cindex change logs, conditional changes - -C programs often contain compile-time @code{#if} conditionals. Many -changes are conditional; sometimes you add a new definition which is -entirely contained in a conditional. It is very useful to indicate in -the change log the conditions for which the change applies. - -Our convention for indicating conditional changes is to use square -brackets around the name of the condition. - -Here is a simple example, describing a change which is conditional but -does not have a function or entity name associated with it: - -@example -* xterm.c [SOLARIS2]: Include string.h. -@end example - -Here is an entry describing a new definition which is entirely -conditional. This new definition for the macro @code{FRAME_WINDOW_P} is -used only when @code{HAVE_X_WINDOWS} is defined: - -@example -* frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined. -@end example - -Here is an entry for a change within the function @code{init_display}, -whose definition as a whole is unconditional, but the changes themselves -are contained in a @samp{#ifdef HAVE_LIBNCURSES} conditional: - -@example -* dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent. -@end example - -Here is an entry for a change that takes affect only when -a certain macro is @emph{not} defined: - -@example -(gethostname) [!HAVE_SOCKETS]: Replace with winsock version. -@end example - -@node Indicating the Part Changed -@subsection Indicating the Part Changed - -Indicate the part of a function which changed by using angle brackets -enclosing an indication of what the changed part does. Here is an entry -for a change in the part of the function @code{sh-while-getopts} that -deals with @code{sh} commands: - -@example -* progmodes/sh-script.el (sh-while-getopts) <sh>: Handle case that -user-specified option string is empty. -@end example - - -@node Man Pages -@section Man Pages -@cindex man pages - -In the GNU project, man pages are secondary. It is not necessary or -expected for every GNU program to have a man page, but some of them do. -It's your choice whether to include a man page in your program. - -When you make this decision, consider that supporting a man page -requires continual effort each time the program is changed. The time -you spend on the man page is time taken away from more useful work. - -For a simple program which changes little, updating the man page may be -a small job. Then there is little reason not to include a man page, if -you have one. - -For a large program that changes a great deal, updating a man page may -be a substantial burden. If a user offers to donate a man page, you may -find this gift costly to accept. It may be better to refuse the man -page unless the same person agrees to take full responsibility for -maintaining it---so that you can wash your hands of it entirely. If -this volunteer later ceases to do the job, then don't feel obliged to -pick it up yourself; it may be better to withdraw the man page from the -distribution until someone else agrees to update it. - -When a program changes only a little, you may feel that the -discrepancies are small enough that the man page remains useful without -updating. If so, put a prominent note near the beginning of the man -page explaining that you don't maintain it and that the Texinfo manual -is more authoritative. The note should say how to access the Texinfo -documentation. - -Be sure that man pages include a copyright statement and free license. -The simple all-permissive license is appropriate for simple man pages -(@pxref{License Notices for Other Files,,,maintain,Information for GNU -Maintainers}). - -For long man pages, with enough explanation and documentation that -they can be considered true manuals, use the GFDL (@pxref{License for -Manuals}). - -Finally, the GNU help2man program -(@uref{http://www.gnu.org/software/help2man/}) is one way to automate -generation of a man page, in this case from @option{--help} output. -This is sufficient in many cases. - -@node Reading other Manuals -@section Reading other Manuals - -There may be non-free books or documentation files that describe the -program you are documenting. - -It is ok to use these documents for reference, just as the author of a -new algebra textbook can read other books on algebra. A large portion -of any non-fiction book consists of facts, in this case facts about how -a certain program works, and these facts are necessarily the same for -everyone who writes about the subject. But be careful not to copy your -outline structure, wording, tables or examples from preexisting non-free -documentation. Copying from free documentation may be ok; please check -with the FSF about the individual case. - -@node Managing Releases -@chapter The Release Process -@cindex releasing - -Making a release is more than just bundling up your source files in a -tar file and putting it up for FTP. You should set up your software so -that it can be configured to run on a variety of systems. Your Makefile -should conform to the GNU standards described below, and your directory -layout should also conform to the standards discussed below. Doing so -makes it easy to include your package into the larger framework of -all GNU software. - -@menu -* Configuration:: How configuration of GNU packages should work. -* Makefile Conventions:: Makefile conventions. -* Releases:: Making releases -@end menu - -@node Configuration -@section How Configuration Should Work -@cindex program configuration - -@pindex configure -Each GNU distribution should come with a shell script named -@code{configure}. This script is given arguments which describe the -kind of machine and system you want to compile the program for. -The @code{configure} script must record the configuration options so -that they affect compilation. - -The description here is the specification of the interface for the -@code{configure} script in GNU packages. Many packages implement it -using GNU Autoconf (@pxref{Top,, Introduction, autoconf, Autoconf}) -and/or GNU Automake (@pxref{Top,, Introduction, automake, Automake}), -but you do not have to use these tools. You can implement it any way -you like; for instance, by making @code{configure} be a wrapper around -a completely different configuration system. - -Another way for the @code{configure} script to operate is to make a -link from a standard name such as @file{config.h} to the proper -configuration file for the chosen system. If you use this technique, -the distribution should @emph{not} contain a file named -@file{config.h}. This is so that people won't be able to build the -program without configuring it first. - -Another thing that @code{configure} can do is to edit the Makefile. If -you do this, the distribution should @emph{not} contain a file named -@file{Makefile}. Instead, it should include a file @file{Makefile.in} which -contains the input used for editing. Once again, this is so that people -won't be able to build the program without configuring it first. - -If @code{configure} does write the @file{Makefile}, then @file{Makefile} -should have a target named @file{Makefile} which causes @code{configure} -to be rerun, setting up the same configuration that was set up last -time. The files that @code{configure} reads should be listed as -dependencies of @file{Makefile}. - -All the files which are output from the @code{configure} script should -have comments at the beginning explaining that they were generated -automatically using @code{configure}. This is so that users won't think -of trying to edit them by hand. - -The @code{configure} script should write a file named @file{config.status} -which describes which configuration options were specified when the -program was last configured. This file should be a shell script which, -if run, will recreate the same configuration. - -The @code{configure} script should accept an option of the form -@samp{--srcdir=@var{dirname}} to specify the directory where sources are found -(if it is not the current directory). This makes it possible to build -the program in a separate directory, so that the actual source directory -is not modified. - -If the user does not specify @samp{--srcdir}, then @code{configure} should -check both @file{.} and @file{..} to see if it can find the sources. If -it finds the sources in one of these places, it should use them from -there. Otherwise, it should report that it cannot find the sources, and -should exit with nonzero status. - -Usually the easy way to support @samp{--srcdir} is by editing a -definition of @code{VPATH} into the Makefile. Some rules may need to -refer explicitly to the specified source directory. To make this -possible, @code{configure} can add to the Makefile a variable named -@code{srcdir} whose value is precisely the specified directory. - -In addition, the @samp{configure} script should take options -corresponding to most of the standard directory variables -(@pxref{Directory Variables}). Here is the list: - -@example ---prefix --exec-prefix --bindir --sbindir --libexecdir --sysconfdir ---sharedstatedir --localstatedir --libdir --includedir --oldincludedir ---datarootdir --datadir --infodir --localedir --mandir --docdir ---htmldir --dvidir --pdfdir --psdir -@end example - -The @code{configure} script should also take an argument which specifies the -type of system to build the program for. This argument should look like -this: - -@example -@var{cpu}-@var{company}-@var{system} -@end example - -For example, an Athlon-based GNU/Linux system might be -@samp{i686-pc-linux-gnu}. - -The @code{configure} script needs to be able to decode all plausible -alternatives for how to describe a machine. Thus, -@samp{athlon-pc-gnu/linux} would be a valid alias. There is a shell -script called -@uref{http://git.savannah.gnu.org/@/gitweb/@/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD, -@file{config.sub}} that you can use as a subroutine to validate system -types and canonicalize aliases. - -The @code{configure} script should also take the option -@option{--build=@var{buildtype}}, which should be equivalent to a -plain @var{buildtype} argument. For example, @samp{configure ---build=i686-pc-linux-gnu} is equivalent to @samp{configure -i686-pc-linux-gnu}. When the build type is not specified by an option -or argument, the @code{configure} script should normally guess it using -the shell script -@uref{http://git.savannah.gnu.org/@/gitweb/@/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD, -@file{config.guess}}. - -@cindex optional features, configure-time -Other options are permitted to specify in more detail the software -or hardware present on the machine, to include or exclude optional parts -of the package, or to adjust the name of some tools or arguments to them: - -@table @samp -@item --enable-@var{feature}@r{[}=@var{parameter}@r{]} -Configure the package to build and install an optional user-level -facility called @var{feature}. This allows users to choose which -optional features to include. Giving an optional @var{parameter} of -@samp{no} should omit @var{feature}, if it is built by default. - -No @samp{--enable} option should @strong{ever} cause one feature to -replace another. No @samp{--enable} option should ever substitute one -useful behavior for another useful behavior. The only proper use for -@samp{--enable} is for questions of whether to build part of the program -or exclude it. - -@item --with-@var{package} -@c @r{[}=@var{parameter}@r{]} -The package @var{package} will be installed, so configure this package -to work with @var{package}. - -@c Giving an optional @var{parameter} of -@c @samp{no} should omit @var{package}, if it is used by default. - -Possible values of @var{package} include -@samp{gnu-as} (or @samp{gas}), @samp{gnu-ld}, @samp{gnu-libc}, -@samp{gdb}, -@samp{x}, -and -@samp{x-toolkit}. - -Do not use a @samp{--with} option to specify the file name to use to -find certain files. That is outside the scope of what @samp{--with} -options are for. - -@item @var{variable}=@var{value} -Set the value of the variable @var{variable} to @var{value}. This is -used to override the default values of commands or arguments in the -build process. For example, the user could issue @samp{configure -CFLAGS=-g CXXFLAGS=-g} to build with debugging information and without -the default optimization. - -Specifying variables as arguments to @code{configure}, like this: -@example -./configure CC=gcc -@end example -is preferable to setting them in environment variables: -@example -CC=gcc ./configure -@end example -as it helps to recreate the same configuration later with -@file{config.status}. However, both methods should be supported. -@end table - -All @code{configure} scripts should accept all of the ``detail'' -options and the variable settings, whether or not they make any -difference to the particular package at hand. In particular, they -should accept any option that starts with @samp{--with-} or -@samp{--enable-}. This is so users will be able to configure an -entire GNU source tree at once with a single set of options. - -You will note that the categories @samp{--with-} and @samp{--enable-} -are narrow: they @strong{do not} provide a place for any sort of option -you might think of. That is deliberate. We want to limit the possible -configuration options in GNU software. We do not want GNU programs to -have idiosyncratic configuration options. - -Packages that perform part of the compilation process may support -cross-compilation. In such a case, the host and target machines for the -program may be different. - -The @code{configure} script should normally treat the specified type of -system as both the host and the target, thus producing a program which -works for the same type of machine that it runs on. - -To compile a program to run on a host type that differs from the build -type, use the configure option @option{--host=@var{hosttype}}, where -@var{hosttype} uses the same syntax as @var{buildtype}. The host type -normally defaults to the build type. - -To configure a cross-compiler, cross-assembler, or what have you, you -should specify a target different from the host, using the configure -option @samp{--target=@var{targettype}}. The syntax for -@var{targettype} is the same as for the host type. So the command would -look like this: - -@example -./configure --host=@var{hosttype} --target=@var{targettype} -@end example - -The target type normally defaults to the host type. -Programs for which cross-operation is not meaningful need not accept the -@samp{--target} option, because configuring an entire operating system for -cross-operation is not a meaningful operation. - -Some programs have ways of configuring themselves automatically. If -your program is set up to do this, your @code{configure} script can simply -ignore most of its arguments. - -@comment The makefile standards are in a separate file that is also -@comment included by make.texinfo. Done by roland@gnu.ai.mit.edu on 1/6/93. -@comment For this document, turn chapters into sections, etc. -@lowersections -@include make-stds.texi -@raisesections - -@node Releases -@section Making Releases -@cindex packaging - -You should identify each release with a pair of version numbers, a -major version and a minor. We have no objection to using more than -two numbers, but it is very unlikely that you really need them. - -Package the distribution of @code{Foo version 69.96} up in a gzipped tar -file with the name @file{foo-69.96.tar.gz}. It should unpack into a -subdirectory named @file{foo-69.96}. - -Building and installing the program should never modify any of the files -contained in the distribution. This means that all the files that form -part of the program in any way must be classified into @dfn{source -files} and @dfn{non-source files}. Source files are written by humans -and never changed automatically; non-source files are produced from -source files by programs under the control of the Makefile. - -@cindex @file{README} file -The distribution should contain a file named @file{README} which gives -the name of the package, and a general description of what it does. It -is also good to explain the purpose of each of the first-level -subdirectories in the package, if there are any. The @file{README} file -should either state the version number of the package, or refer to where -in the package it can be found. - -The @file{README} file should refer to the file @file{INSTALL}, which -should contain an explanation of the installation procedure. - -The @file{README} file should also refer to the file which contains the -copying conditions. The GNU GPL, if used, should be in a file called -@file{COPYING}. If the GNU LGPL is used, it should be in a file called -@file{COPYING.LESSER}. - -Naturally, all the source files must be in the distribution. It is okay -to include non-source files in the distribution, provided they are -up-to-date and machine-independent, so that building the distribution -normally will never modify them. We commonly include non-source files -produced by Bison, @code{lex}, @TeX{}, and @code{makeinfo}; this helps avoid -unnecessary dependencies between our distributions, so that users can -install whichever packages they want to install. - -Non-source files that might actually be modified by building and -installing the program should @strong{never} be included in the -distribution. So if you do distribute non-source files, always make -sure they are up to date when you make a new distribution. - -Make sure that all the files in the distribution are world-readable, and -that directories are world-readable and world-searchable (octal mode 755). -We used to recommend that all directories in the distribution also be -world-writable (octal mode 777), because ancient versions of @code{tar} -would otherwise not cope when extracting the archive as an unprivileged -user. That can easily lead to security issues when creating the archive, -however, so now we recommend against that. - -Don't include any symbolic links in the distribution itself. If the tar -file contains symbolic links, then people cannot even unpack it on -systems that don't support symbolic links. Also, don't use multiple -names for one file in different directories, because certain file -systems cannot handle this and that prevents unpacking the -distribution. - -Try to make sure that all the file names will be unique on MS-DOS. A -name on MS-DOS consists of up to 8 characters, optionally followed by a -period and up to three characters. MS-DOS will truncate extra -characters both before and after the period. Thus, -@file{foobarhacker.c} and @file{foobarhacker.o} are not ambiguous; they -are truncated to @file{foobarha.c} and @file{foobarha.o}, which are -distinct. - -@cindex @file{texinfo.tex}, in a distribution -Include in your distribution a copy of the @file{texinfo.tex} you used -to test print any @file{*.texinfo} or @file{*.texi} files. - -Likewise, if your program uses small GNU software packages like regex, -getopt, obstack, or termcap, include them in the distribution file. -Leaving them out would make the distribution file a little smaller at -the expense of possible inconvenience to a user who doesn't know what -other files to get. - -@node References -@chapter References to Non-Free Software and Documentation -@cindex references to non-free material - -A GNU program should not recommend, promote, or grant legitimacy to -the use of any non-free program. Proprietary software is a social and -ethical problem, and our aim is to put an end to that problem. We -can't stop some people from writing proprietary programs, or stop -other people from using them, but we can and should refuse to -advertise them to new potential customers, or to give the public the -idea that their existence is ethical. - -The GNU definition of free software is found on the GNU web site at -@url{http://www.gnu.org/@/philosophy/@/free-sw.html}, and the definition -of free documentation is found at -@url{http://www.gnu.org/@/philosophy/@/free-doc.html}. The terms ``free'' -and ``non-free'', used in this document, refer to those definitions. - -A list of important licenses and whether they qualify as free is in -@url{http://www.gnu.org/@/licenses/@/license-list.html}. If it is not -clear whether a license qualifies as free, please ask the GNU Project -by writing to @email{licensing@@gnu.org}. We will answer, and if the -license is an important one, we will add it to the list. - -When a non-free program or system is well known, you can mention it in -passing---that is harmless, since users who might want to use it -probably already know about it. For instance, it is fine to explain -how to build your package on top of some widely used non-free -operating system, or how to use it together with some widely used -non-free program. - -However, you should give only the necessary information to help those -who already use the non-free program to use your program with -it---don't give, or refer to, any further information about the -proprietary program, and don't imply that the proprietary program -enhances your program, or that its existence is in any way a good -thing. The goal should be that people already using the proprietary -program will get the advice they need about how to use your free -program with it, while people who don't already use the proprietary -program will not see anything likely to lead them to take an interest -in it. - -If a non-free program or system is obscure in your program's domain, -your program should not mention or support it at all, since doing so -would tend to popularize the non-free program more than it popularizes -your program. (You cannot hope to find many additional users for your -program among the users of Foobar, if the existence of Foobar is not -generally known among people who might want to use your program.) - -Sometimes a program is free software in itself but depends on a -non-free platform in order to run. For instance, many Java programs -depend on some non-free Java libraries. To recommend or promote such -a program is to promote the other programs it needs. This is why we -are careful about listing Java programs in the Free Software -Directory: we don't want to promote the non-free Java libraries. - -We hope this particular problem with Java will be gone by and by, as -we replace the remaining non-free standard Java libraries with free -software, but the general principle will remain the same: don't -recommend, promote or legitimize programs that depend on non-free -software to run. - -Some free programs strongly encourage the use of non-free software. A -typical example is @command{mplayer}. It is free software in itself, -and the free code can handle some kinds of files. However, -@command{mplayer} recommends use of non-free codecs for other kinds of -files, and users that install @command{mplayer} are very likely to -install those codecs along with it. To recommend @command{mplayer} -is, in effect, to promote use of the non-free codecs. - -Thus, you should not recommend programs that strongly encourage the -use of non-free software. This is why we do not list -@command{mplayer} in the Free Software Directory. - -A GNU package should not refer the user to any non-free documentation -for free software. Free documentation that can be included in free -operating systems is essential for completing the GNU system, or any -free operating system, so encouraging it is a priority; to recommend -use of documentation that we are not allowed to include undermines the -impetus for the community to produce documentation that we can -include. So GNU packages should never recommend non-free -documentation. - -By contrast, it is ok to refer to journal articles and textbooks in -the comments of a program for explanation of how it functions, even -though they are non-free. This is because we don't include such -things in the GNU system even they are free---they are outside the -scope of what a software distribution needs to include. - -Referring to a web site that describes or recommends a non-free -program is promoting that program, so please do not make links (or -mention by name) web sites that contain such material. This policy is -relevant particularly for the web pages for a GNU package. - -Following links from nearly any web site can lead eventually to -non-free software; this is inherent in the nature of the web. So it -makes no sense to criticize a site for having such links. As long as -the site does not itself recommend a non-free program, there is no -need to consider the question of the sites that it links to for other -reasons. - -Thus, for example, you should not refer to AT&T's web site if that -recommends AT&T's non-free software packages; you should not refer to -a site that links to AT&T's site presenting it as a place to get some -non-free program, because that link recommends and legitimizes the -non-free program. However, that a site contains a link to AT&T's web -site for some other purpose (such as long-distance telephone service) -is not an objection against it. - -@node GNU Free Documentation License -@appendix GNU Free Documentation License - -@cindex FDL, GNU Free Documentation License -@include fdl.texi - -@node Index -@unnumbered Index -@printindex cp - -@bye - -Local variables: -eval: (add-hook 'write-file-hooks 'time-stamp) -time-stamp-start: "@set lastupdate " -time-stamp-end: "$" -time-stamp-format: "%:b %:d, %:y" -compile-command: "cd work.s && make" -End: |