| 1 | \input texinfo @c -*-texinfo-*- |
| 2 | @c %**start of header |
| 3 | @setfilename standards.info |
| 4 | @settitle GNU Coding Standards |
| 5 | @c This date is automagically updated when you save this file: |
| 6 | @set lastupdate April 12, 2010 |
| 7 | @c %**end of header |
| 8 | |
| 9 | @dircategory GNU organization |
| 10 | @direntry |
| 11 | * Standards: (standards). GNU coding standards. |
| 12 | @end direntry |
| 13 | |
| 14 | @c @setchapternewpage odd |
| 15 | @setchapternewpage off |
| 16 | |
| 17 | @c Put everything in one index (arbitrarily chosen to be the concept index). |
| 18 | @syncodeindex fn cp |
| 19 | @syncodeindex ky cp |
| 20 | @syncodeindex pg cp |
| 21 | @syncodeindex vr cp |
| 22 | |
| 23 | @c This is used by a cross ref in make-stds.texi |
| 24 | @set CODESTD 1 |
| 25 | |
| 26 | @copying |
| 27 | The GNU coding standards, last updated @value{lastupdate}. |
| 28 | |
| 29 | Copyright @copyright{} 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, |
| 30 | 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software |
| 31 | Foundation, Inc. |
| 32 | |
| 33 | Permission is granted to copy, distribute and/or modify this document |
| 34 | under the terms of the GNU Free Documentation License, Version 1.3 or |
| 35 | any later version published by the Free Software Foundation; with no |
| 36 | Invariant Sections, with no Front-Cover Texts, and with no Back-Cover |
| 37 | Texts. A copy of the license is included in the section entitled |
| 38 | ``GNU Free Documentation License''. |
| 39 | @end copying |
| 40 | |
| 41 | @titlepage |
| 42 | @title GNU Coding Standards |
| 43 | @author Richard Stallman, et al. |
| 44 | @author last updated @value{lastupdate} |
| 45 | @page |
| 46 | @vskip 0pt plus 1filll |
| 47 | @insertcopying |
| 48 | @end titlepage |
| 49 | |
| 50 | @contents |
| 51 | |
| 52 | @ifnottex |
| 53 | @node Top, Preface, (dir), (dir) |
| 54 | @top Version |
| 55 | |
| 56 | @insertcopying |
| 57 | @end ifnottex |
| 58 | |
| 59 | @menu |
| 60 | * Preface:: About the GNU Coding Standards. |
| 61 | * Legal Issues:: Keeping free software free. |
| 62 | * Design Advice:: General program design. |
| 63 | * Program Behavior:: Program behavior for all programs |
| 64 | * Writing C:: Making the best use of C. |
| 65 | * Documentation:: Documenting programs. |
| 66 | * Managing Releases:: The release process. |
| 67 | * References:: Mentioning non-free software or documentation. |
| 68 | * GNU Free Documentation License:: Copying and sharing this manual. |
| 69 | * Index:: |
| 70 | |
| 71 | @end menu |
| 72 | |
| 73 | @node Preface |
| 74 | @chapter About the GNU Coding Standards |
| 75 | |
| 76 | The GNU Coding Standards were written by Richard Stallman and other GNU |
| 77 | Project volunteers. Their purpose is to make the GNU system clean, |
| 78 | consistent, and easy to install. This document can also be read as a |
| 79 | guide to writing portable, robust and reliable programs. It focuses on |
| 80 | programs written in C, but many of the rules and principles are useful |
| 81 | even if you write in another programming language. The rules often |
| 82 | state reasons for writing in a certain way. |
| 83 | |
| 84 | @cindex where to obtain @code{standards.texi} |
| 85 | @cindex downloading this manual |
| 86 | If you did not obtain this file directly from the GNU project and |
| 87 | recently, please check for a newer version. You can get the GNU |
| 88 | Coding Standards from the GNU web server in many |
| 89 | different formats, including the Texinfo source, PDF, HTML, DVI, plain |
| 90 | text, and more, at: @uref{http://www.gnu.org/prep/standards/}. |
| 91 | |
| 92 | If you are maintaining an official GNU package, in addition to this |
| 93 | document, please read and follow the GNU maintainer information |
| 94 | (@pxref{Top, , Contents, maintain, Information for Maintainers of GNU |
| 95 | Software}). |
| 96 | |
| 97 | @cindex @code{gnustandards-commit@@gnu.org} mailing list |
| 98 | If you want to receive diffs for every change to these GNU documents, |
| 99 | join the mailing list @code{gnustandards-commit@@gnu.org}, via the web |
| 100 | interface at |
| 101 | @url{http://lists.gnu.org/mailman/listinfo/gnustandards-commit}. |
| 102 | Archives are also available there. |
| 103 | |
| 104 | @cindex @code{bug-standards@@gnu.org} email address |
| 105 | @cindex Savannah repository for gnustandards |
| 106 | @cindex gnustandards project repository |
| 107 | Please send corrections or suggestions for this document to |
| 108 | @email{bug-standards@@gnu.org}. If you make a suggestion, please |
| 109 | include a suggested new wording for it, to help us consider the |
| 110 | suggestion efficiently. We prefer a context diff to the Texinfo |
| 111 | source, but if that's difficult for you, you can make a context diff |
| 112 | for some other version of this document, or propose it in any way that |
| 113 | makes it clear. The source repository for this document can be found |
| 114 | at @url{http://savannah.gnu.org/projects/gnustandards}. |
| 115 | |
| 116 | These standards cover the minimum of what is important when writing a |
| 117 | GNU package. Likely, the need for additional standards will come up. |
| 118 | Sometimes, you might suggest that such standards be added to this |
| 119 | document. If you think your standards would be generally useful, please |
| 120 | do suggest them. |
| 121 | |
| 122 | You should also set standards for your package on many questions not |
| 123 | addressed or not firmly specified here. The most important point is to |
| 124 | be self-consistent---try to stick to the conventions you pick, and try |
| 125 | to document them as much as possible. That way, your program will be |
| 126 | more maintainable by others. |
| 127 | |
| 128 | The GNU Hello program serves as an example of how to follow the GNU |
| 129 | coding standards for a trivial program. |
| 130 | @uref{http://www.gnu.org/software/hello/hello.html}. |
| 131 | |
| 132 | This release of the GNU Coding Standards was last updated |
| 133 | @value{lastupdate}. |
| 134 | |
| 135 | |
| 136 | @node Legal Issues |
| 137 | @chapter Keeping Free Software Free |
| 138 | @cindex legal aspects |
| 139 | |
| 140 | This chapter discusses how you can make sure that GNU software |
| 141 | avoids legal difficulties, and other related issues. |
| 142 | |
| 143 | @menu |
| 144 | * Reading Non-Free Code:: Referring to proprietary programs. |
| 145 | * Contributions:: Accepting contributions. |
| 146 | * Trademarks:: How we deal with trademark issues. |
| 147 | @end menu |
| 148 | |
| 149 | @node Reading Non-Free Code |
| 150 | @section Referring to Proprietary Programs |
| 151 | @cindex proprietary programs |
| 152 | @cindex avoiding proprietary code |
| 153 | |
| 154 | Don't in any circumstances refer to Unix source code for or during |
| 155 | your work on GNU! (Or to any other proprietary programs.) |
| 156 | |
| 157 | If you have a vague recollection of the internals of a Unix program, |
| 158 | this does not absolutely mean you can't write an imitation of it, but |
| 159 | do try to organize the imitation internally along different lines, |
| 160 | because this is likely to make the details of the Unix version |
| 161 | irrelevant and dissimilar to your results. |
| 162 | |
| 163 | For example, Unix utilities were generally optimized to minimize |
| 164 | memory use; if you go for speed instead, your program will be very |
| 165 | different. You could keep the entire input file in memory and scan it |
| 166 | there instead of using stdio. Use a smarter algorithm discovered more |
| 167 | recently than the Unix program. Eliminate use of temporary files. Do |
| 168 | it in one pass instead of two (we did this in the assembler). |
| 169 | |
| 170 | Or, on the contrary, emphasize simplicity instead of speed. For some |
| 171 | applications, the speed of today's computers makes simpler algorithms |
| 172 | adequate. |
| 173 | |
| 174 | Or go for generality. For example, Unix programs often have static |
| 175 | tables or fixed-size strings, which make for arbitrary limits; use |
| 176 | dynamic allocation instead. Make sure your program handles NULs and |
| 177 | other funny characters in the input files. Add a programming language |
| 178 | for extensibility and write part of the program in that language. |
| 179 | |
| 180 | Or turn some parts of the program into independently usable libraries. |
| 181 | Or use a simple garbage collector instead of tracking precisely when |
| 182 | to free memory, or use a new GNU facility such as obstacks. |
| 183 | |
| 184 | @node Contributions |
| 185 | @section Accepting Contributions |
| 186 | @cindex legal papers |
| 187 | @cindex accepting contributions |
| 188 | |
| 189 | If the program you are working on is copyrighted by the Free Software |
| 190 | Foundation, then when someone else sends you a piece of code to add to |
| 191 | the program, we need legal papers to use it---just as we asked you to |
| 192 | sign papers initially. @emph{Each} person who makes a nontrivial |
| 193 | contribution to a program must sign some sort of legal papers in order |
| 194 | for us to have clear title to the program; the main author alone is not |
| 195 | enough. |
| 196 | |
| 197 | So, before adding in any contributions from other people, please tell |
| 198 | us, so we can arrange to get the papers. Then wait until we tell you |
| 199 | that we have received the signed papers, before you actually use the |
| 200 | contribution. |
| 201 | |
| 202 | This applies both before you release the program and afterward. If |
| 203 | you receive diffs to fix a bug, and they make significant changes, we |
| 204 | need legal papers for that change. |
| 205 | |
| 206 | This also applies to comments and documentation files. For copyright |
| 207 | law, comments and code are just text. Copyright applies to all kinds of |
| 208 | text, so we need legal papers for all kinds. |
| 209 | |
| 210 | We know it is frustrating to ask for legal papers; it's frustrating for |
| 211 | us as well. But if you don't wait, you are going out on a limb---for |
| 212 | example, what if the contributor's employer won't sign a disclaimer? |
| 213 | You might have to take that code out again! |
| 214 | |
| 215 | You don't need papers for changes of a few lines here or there, since |
| 216 | they are not significant for copyright purposes. Also, you don't need |
| 217 | papers if all you get from the suggestion is some ideas, not actual code |
| 218 | which you use. For example, if someone sent you one implementation, but |
| 219 | you write a different implementation of the same idea, you don't need to |
| 220 | get papers. |
| 221 | |
| 222 | The very worst thing is if you forget to tell us about the other |
| 223 | contributor. We could be very embarrassed in court some day as a |
| 224 | result. |
| 225 | |
| 226 | We have more detailed advice for maintainers of programs; if you have |
| 227 | reached the stage of actually maintaining a program for GNU (whether |
| 228 | released or not), please ask us for a copy. It is also available |
| 229 | online for your perusal: @uref{http://www.gnu.org/prep/maintain/}. |
| 230 | |
| 231 | @node Trademarks |
| 232 | @section Trademarks |
| 233 | @cindex trademarks |
| 234 | |
| 235 | Please do not include any trademark acknowledgements in GNU software |
| 236 | packages or documentation. |
| 237 | |
| 238 | Trademark acknowledgements are the statements that such-and-such is a |
| 239 | trademark of so-and-so. The GNU Project has no objection to the basic |
| 240 | idea of trademarks, but these acknowledgements feel like kowtowing, |
| 241 | and there is no legal requirement for them, so we don't use them. |
| 242 | |
| 243 | What is legally required, as regards other people's trademarks, is to |
| 244 | avoid using them in ways which a reader might reasonably understand as |
| 245 | naming or labeling our own programs or activities. For example, since |
| 246 | ``Objective C'' is (or at least was) a trademark, we made sure to say |
| 247 | that we provide a ``compiler for the Objective C language'' rather |
| 248 | than an ``Objective C compiler''. The latter would have been meant as |
| 249 | a shorter way of saying the former, but it does not explicitly state |
| 250 | the relationship, so it could be misinterpreted as using ``Objective |
| 251 | C'' as a label for the compiler rather than for the language. |
| 252 | |
| 253 | Please don't use ``win'' as an abbreviation for Microsoft Windows in |
| 254 | GNU software or documentation. In hacker terminology, calling |
| 255 | something a ``win'' is a form of praise. If you wish to praise |
| 256 | Microsoft Windows when speaking on your own, by all means do so, but |
| 257 | not in GNU software. Usually we write the name ``Windows'' in full, |
| 258 | but when brevity is very important (as in file names and sometimes |
| 259 | symbol names), we abbreviate it to ``w''. For instance, the files and |
| 260 | functions in Emacs that deal with Windows start with @samp{w32}. |
| 261 | |
| 262 | @node Design Advice |
| 263 | @chapter General Program Design |
| 264 | @cindex program design |
| 265 | |
| 266 | This chapter discusses some of the issues you should take into |
| 267 | account when designing your program. |
| 268 | |
| 269 | @c Standard or ANSI C |
| 270 | @c |
| 271 | @c In 1989 the American National Standards Institute (ANSI) standardized |
| 272 | @c C as standard X3.159-1989. In December of that year the |
| 273 | @c International Standards Organization ISO adopted the ANSI C standard |
| 274 | @c making minor changes. In 1990 ANSI then re-adopted ISO standard |
| 275 | @c C. This version of C is known as either ANSI C or Standard C. |
| 276 | |
| 277 | @c A major revision of the C Standard appeared in 1999. |
| 278 | |
| 279 | @menu |
| 280 | * Source Language:: Which languages to use. |
| 281 | * Compatibility:: Compatibility with other implementations. |
| 282 | * Using Extensions:: Using non-standard features. |
| 283 | * Standard C:: Using standard C features. |
| 284 | * Conditional Compilation:: Compiling code only if a conditional is true. |
| 285 | @end menu |
| 286 | |
| 287 | @node Source Language |
| 288 | @section Which Languages to Use |
| 289 | @cindex programming languages |
| 290 | |
| 291 | When you want to use a language that gets compiled and runs at high |
| 292 | speed, the best language to use is C. Using another language is like |
| 293 | using a non-standard feature: it will cause trouble for users. Even if |
| 294 | GCC supports the other language, users may find it inconvenient to have |
| 295 | to install the compiler for that other language in order to build your |
| 296 | program. For example, if you write your program in C++, people will |
| 297 | have to install the GNU C++ compiler in order to compile your program. |
| 298 | |
| 299 | C has one other advantage over C++ and other compiled languages: more |
| 300 | people know C, so more people will find it easy to read and modify the |
| 301 | program if it is written in C. |
| 302 | |
| 303 | So in general it is much better to use C, rather than the |
| 304 | comparable alternatives. |
| 305 | |
| 306 | But there are two exceptions to that conclusion: |
| 307 | |
| 308 | @itemize @bullet |
| 309 | @item |
| 310 | It is no problem to use another language to write a tool specifically |
| 311 | intended for use with that language. That is because the only people |
| 312 | who want to build the tool will be those who have installed the other |
| 313 | language anyway. |
| 314 | |
| 315 | @item |
| 316 | If an application is of interest only to a narrow part of the community, |
| 317 | then the question of which language it is written in has less effect on |
| 318 | other people, so you may as well please yourself. |
| 319 | @end itemize |
| 320 | |
| 321 | Many programs are designed to be extensible: they include an interpreter |
| 322 | for a language that is higher level than C. Often much of the program |
| 323 | is written in that language, too. The Emacs editor pioneered this |
| 324 | technique. |
| 325 | |
| 326 | @cindex Guile |
| 327 | @cindex GNOME and Guile |
| 328 | The standard extensibility interpreter for GNU software is Guile |
| 329 | (@uref{http://www.gnu.org/@/software/@/guile/}), which implements the |
| 330 | language Scheme (an especially clean and simple dialect of Lisp). |
| 331 | Guile also includes bindings for GTK+/GNOME, making it practical to |
| 332 | write modern GUI functionality within Guile. We don't reject programs |
| 333 | written in other ``scripting languages'' such as Perl and Python, but |
| 334 | using Guile is very important for the overall consistency of the GNU |
| 335 | system. |
| 336 | |
| 337 | |
| 338 | @node Compatibility |
| 339 | @section Compatibility with Other Implementations |
| 340 | @cindex compatibility with C and @sc{posix} standards |
| 341 | @cindex @sc{posix} compatibility |
| 342 | |
| 343 | With occasional exceptions, utility programs and libraries for GNU |
| 344 | should be upward compatible with those in Berkeley Unix, and upward |
| 345 | compatible with Standard C if Standard C specifies their |
| 346 | behavior, and upward compatible with @sc{posix} if @sc{posix} specifies |
| 347 | their behavior. |
| 348 | |
| 349 | When these standards conflict, it is useful to offer compatibility |
| 350 | modes for each of them. |
| 351 | |
| 352 | @cindex options for compatibility |
| 353 | Standard C and @sc{posix} prohibit many kinds of extensions. Feel |
| 354 | free to make the extensions anyway, and include a @samp{--ansi}, |
| 355 | @samp{--posix}, or @samp{--compatible} option to turn them off. |
| 356 | However, if the extension has a significant chance of breaking any real |
| 357 | programs or scripts, then it is not really upward compatible. So you |
| 358 | should try to redesign its interface to make it upward compatible. |
| 359 | |
| 360 | @cindex @code{POSIXLY_CORRECT}, environment variable |
| 361 | Many GNU programs suppress extensions that conflict with @sc{posix} if the |
| 362 | environment variable @code{POSIXLY_CORRECT} is defined (even if it is |
| 363 | defined with a null value). Please make your program recognize this |
| 364 | variable if appropriate. |
| 365 | |
| 366 | When a feature is used only by users (not by programs or command |
| 367 | files), and it is done poorly in Unix, feel free to replace it |
| 368 | completely with something totally different and better. (For example, |
| 369 | @code{vi} is replaced with Emacs.) But it is nice to offer a compatible |
| 370 | feature as well. (There is a free @code{vi} clone, so we offer it.) |
| 371 | |
| 372 | Additional useful features are welcome regardless of whether |
| 373 | there is any precedent for them. |
| 374 | |
| 375 | @node Using Extensions |
| 376 | @section Using Non-standard Features |
| 377 | @cindex non-standard extensions |
| 378 | |
| 379 | Many GNU facilities that already exist support a number of convenient |
| 380 | extensions over the comparable Unix facilities. Whether to use these |
| 381 | extensions in implementing your program is a difficult question. |
| 382 | |
| 383 | On the one hand, using the extensions can make a cleaner program. |
| 384 | On the other hand, people will not be able to build the program |
| 385 | unless the other GNU tools are available. This might cause the |
| 386 | program to work on fewer kinds of machines. |
| 387 | |
| 388 | With some extensions, it might be easy to provide both alternatives. |
| 389 | For example, you can define functions with a ``keyword'' @code{INLINE} |
| 390 | and define that as a macro to expand into either @code{inline} or |
| 391 | nothing, depending on the compiler. |
| 392 | |
| 393 | In general, perhaps it is best not to use the extensions if you can |
| 394 | straightforwardly do without them, but to use the extensions if they |
| 395 | are a big improvement. |
| 396 | |
| 397 | An exception to this rule are the large, established programs (such as |
| 398 | Emacs) which run on a great variety of systems. Using GNU extensions in |
| 399 | such programs would make many users unhappy, so we don't do that. |
| 400 | |
| 401 | Another exception is for programs that are used as part of compilation: |
| 402 | anything that must be compiled with other compilers in order to |
| 403 | bootstrap the GNU compilation facilities. If these require the GNU |
| 404 | compiler, then no one can compile them without having them installed |
| 405 | already. That would be extremely troublesome in certain cases. |
| 406 | |
| 407 | @node Standard C |
| 408 | @section Standard C and Pre-Standard C |
| 409 | @cindex @sc{ansi} C standard |
| 410 | |
| 411 | 1989 Standard C is widespread enough now that it is ok to use its |
| 412 | features in new programs. There is one exception: do not ever use the |
| 413 | ``trigraph'' feature of Standard C. |
| 414 | |
| 415 | 1999 Standard C is not widespread yet, so please do not require its |
| 416 | features in programs. It is ok to use its features if they are present. |
| 417 | |
| 418 | However, it is easy to support pre-standard compilers in most programs, |
| 419 | so if you know how to do that, feel free. If a program you are |
| 420 | maintaining has such support, you should try to keep it working. |
| 421 | |
| 422 | @cindex function prototypes |
| 423 | To support pre-standard C, instead of writing function definitions in |
| 424 | standard prototype form, |
| 425 | |
| 426 | @example |
| 427 | int |
| 428 | foo (int x, int y) |
| 429 | @dots{} |
| 430 | @end example |
| 431 | |
| 432 | @noindent |
| 433 | write the definition in pre-standard style like this, |
| 434 | |
| 435 | @example |
| 436 | int |
| 437 | foo (x, y) |
| 438 | int x, y; |
| 439 | @dots{} |
| 440 | @end example |
| 441 | |
| 442 | @noindent |
| 443 | and use a separate declaration to specify the argument prototype: |
| 444 | |
| 445 | @example |
| 446 | int foo (int, int); |
| 447 | @end example |
| 448 | |
| 449 | You need such a declaration anyway, in a header file, to get the benefit |
| 450 | of prototypes in all the files where the function is called. And once |
| 451 | you have the declaration, you normally lose nothing by writing the |
| 452 | function definition in the pre-standard style. |
| 453 | |
| 454 | This technique does not work for integer types narrower than @code{int}. |
| 455 | If you think of an argument as being of a type narrower than @code{int}, |
| 456 | declare it as @code{int} instead. |
| 457 | |
| 458 | There are a few special cases where this technique is hard to use. For |
| 459 | example, if a function argument needs to hold the system type |
| 460 | @code{dev_t}, you run into trouble, because @code{dev_t} is shorter than |
| 461 | @code{int} on some machines; but you cannot use @code{int} instead, |
| 462 | because @code{dev_t} is wider than @code{int} on some machines. There |
| 463 | is no type you can safely use on all machines in a non-standard |
| 464 | definition. The only way to support non-standard C and pass such an |
| 465 | argument is to check the width of @code{dev_t} using Autoconf and choose |
| 466 | the argument type accordingly. This may not be worth the trouble. |
| 467 | |
| 468 | In order to support pre-standard compilers that do not recognize |
| 469 | prototypes, you may want to use a preprocessor macro like this: |
| 470 | |
| 471 | @example |
| 472 | /* Declare the prototype for a general external function. */ |
| 473 | #if defined (__STDC__) || defined (WINDOWSNT) |
| 474 | #define P_(proto) proto |
| 475 | #else |
| 476 | #define P_(proto) () |
| 477 | #endif |
| 478 | @end example |
| 479 | |
| 480 | @node Conditional Compilation |
| 481 | @section Conditional Compilation |
| 482 | |
| 483 | When supporting configuration options already known when building your |
| 484 | program we prefer using @code{if (... )} over conditional compilation, |
| 485 | as in the former case the compiler is able to perform more extensive |
| 486 | checking of all possible code paths. |
| 487 | |
| 488 | For example, please write |
| 489 | |
| 490 | @smallexample |
| 491 | if (HAS_FOO) |
| 492 | ... |
| 493 | else |
| 494 | ... |
| 495 | @end smallexample |
| 496 | |
| 497 | @noindent |
| 498 | instead of: |
| 499 | |
| 500 | @smallexample |
| 501 | #ifdef HAS_FOO |
| 502 | ... |
| 503 | #else |
| 504 | ... |
| 505 | #endif |
| 506 | @end smallexample |
| 507 | |
| 508 | A modern compiler such as GCC will generate exactly the same code in |
| 509 | both cases, and we have been using similar techniques with good success |
| 510 | in several projects. Of course, the former method assumes that |
| 511 | @code{HAS_FOO} is defined as either 0 or 1. |
| 512 | |
| 513 | While this is not a silver bullet solving all portability problems, |
| 514 | and is not always appropriate, following this policy would have saved |
| 515 | GCC developers many hours, or even days, per year. |
| 516 | |
| 517 | In the case of function-like macros like @code{REVERSIBLE_CC_MODE} in |
| 518 | GCC which cannot be simply used in @code{if (...)} statements, there is |
| 519 | an easy workaround. Simply introduce another macro |
| 520 | @code{HAS_REVERSIBLE_CC_MODE} as in the following example: |
| 521 | |
| 522 | @smallexample |
| 523 | #ifdef REVERSIBLE_CC_MODE |
| 524 | #define HAS_REVERSIBLE_CC_MODE 1 |
| 525 | #else |
| 526 | #define HAS_REVERSIBLE_CC_MODE 0 |
| 527 | #endif |
| 528 | @end smallexample |
| 529 | |
| 530 | @node Program Behavior |
| 531 | @chapter Program Behavior for All Programs |
| 532 | |
| 533 | This chapter describes conventions for writing robust |
| 534 | software. It also describes general standards for error messages, the |
| 535 | command line interface, and how libraries should behave. |
| 536 | |
| 537 | @menu |
| 538 | * Non-GNU Standards:: We consider standards such as POSIX; |
| 539 | we don't "obey" them. |
| 540 | * Semantics:: Writing robust programs. |
| 541 | * Libraries:: Library behavior. |
| 542 | * Errors:: Formatting error messages. |
| 543 | * User Interfaces:: Standards about interfaces generally. |
| 544 | * Graphical Interfaces:: Standards for graphical interfaces. |
| 545 | * Command-Line Interfaces:: Standards for command line interfaces. |
| 546 | * Option Table:: Table of long options. |
| 547 | * OID Allocations:: Table of OID slots for GNU. |
| 548 | * Memory Usage:: When and how to care about memory needs. |
| 549 | * File Usage:: Which files to use, and where. |
| 550 | @end menu |
| 551 | |
| 552 | @node Non-GNU Standards |
| 553 | @section Non-GNU Standards |
| 554 | |
| 555 | The GNU Project regards standards published by other organizations as |
| 556 | suggestions, not orders. We consider those standards, but we do not |
| 557 | ``obey'' them. In developing a GNU program, you should implement |
| 558 | an outside standard's specifications when that makes the GNU system |
| 559 | better overall in an objective sense. When it doesn't, you shouldn't. |
| 560 | |
| 561 | In most cases, following published standards is convenient for |
| 562 | users---it means that their programs or scripts will work more |
| 563 | portably. For instance, GCC implements nearly all the features of |
| 564 | Standard C as specified by that standard. C program developers would |
| 565 | be unhappy if it did not. And GNU utilities mostly follow |
| 566 | specifications of POSIX.2; shell script writers and users would be |
| 567 | unhappy if our programs were incompatible. |
| 568 | |
| 569 | But we do not follow either of these specifications rigidly, and there |
| 570 | are specific points on which we decided not to follow them, so as to |
| 571 | make the GNU system better for users. |
| 572 | |
| 573 | For instance, Standard C says that nearly all extensions to C are |
| 574 | prohibited. How silly! GCC implements many extensions, some of which |
| 575 | were later adopted as part of the standard. If you want these |
| 576 | constructs to give an error message as ``required'' by the standard, |
| 577 | you must specify @samp{--pedantic}, which was implemented only so that |
| 578 | we can say ``GCC is a 100% implementation of the standard,'' not |
| 579 | because there is any reason to actually use it. |
| 580 | |
| 581 | POSIX.2 specifies that @samp{df} and @samp{du} must output sizes by |
| 582 | default in units of 512 bytes. What users want is units of 1k, so |
| 583 | that is what we do by default. If you want the ridiculous behavior |
| 584 | ``required'' by POSIX, you must set the environment variable |
| 585 | @samp{POSIXLY_CORRECT} (which was originally going to be named |
| 586 | @samp{POSIX_ME_HARDER}). |
| 587 | |
| 588 | GNU utilities also depart from the letter of the POSIX.2 specification |
| 589 | when they support long-named command-line options, and intermixing |
| 590 | options with ordinary arguments. This minor incompatibility with |
| 591 | POSIX is never a problem in practice, and it is very useful. |
| 592 | |
| 593 | In particular, don't reject a new feature, or remove an old one, |
| 594 | merely because a standard says it is ``forbidden'' or ``deprecated.'' |
| 595 | |
| 596 | @node Semantics |
| 597 | @section Writing Robust Programs |
| 598 | |
| 599 | @cindex arbitrary limits on data |
| 600 | Avoid arbitrary limits on the length or number of @emph{any} data |
| 601 | structure, including file names, lines, files, and symbols, by allocating |
| 602 | all data structures dynamically. In most Unix utilities, ``long lines |
| 603 | are silently truncated''. This is not acceptable in a GNU utility. |
| 604 | |
| 605 | @cindex @code{NUL} characters |
| 606 | Utilities reading files should not drop NUL characters, or any other |
| 607 | nonprinting characters @emph{including those with codes above 0177}. |
| 608 | The only sensible exceptions would be utilities specifically intended |
| 609 | for interface to certain types of terminals or printers |
| 610 | that can't handle those characters. |
| 611 | Whenever possible, try to make programs work properly with |
| 612 | sequences of bytes that represent multibyte characters, using encodings |
| 613 | such as UTF-8 and others. |
| 614 | |
| 615 | @cindex error messages |
| 616 | Check every system call for an error return, unless you know you wish to |
| 617 | ignore errors. Include the system error text (from @code{perror} or |
| 618 | equivalent) in @emph{every} error message resulting from a failing |
| 619 | system call, as well as the name of the file if any and the name of the |
| 620 | utility. Just ``cannot open foo.c'' or ``stat failed'' is not |
| 621 | sufficient. |
| 622 | |
| 623 | @cindex @code{malloc} return value |
| 624 | @cindex memory allocation failure |
| 625 | Check every call to @code{malloc} or @code{realloc} to see if it |
| 626 | returned zero. Check @code{realloc} even if you are making the block |
| 627 | smaller; in a system that rounds block sizes to a power of 2, |
| 628 | @code{realloc} may get a different block if you ask for less space. |
| 629 | |
| 630 | In Unix, @code{realloc} can destroy the storage block if it returns |
| 631 | zero. GNU @code{realloc} does not have this bug: if it fails, the |
| 632 | original block is unchanged. Feel free to assume the bug is fixed. If |
| 633 | you wish to run your program on Unix, and wish to avoid lossage in this |
| 634 | case, you can use the GNU @code{malloc}. |
| 635 | |
| 636 | You must expect @code{free} to alter the contents of the block that was |
| 637 | freed. Anything you want to fetch from the block, you must fetch before |
| 638 | calling @code{free}. |
| 639 | |
| 640 | If @code{malloc} fails in a noninteractive program, make that a fatal |
| 641 | error. In an interactive program (one that reads commands from the |
| 642 | user), it is better to abort the command and return to the command |
| 643 | reader loop. This allows the user to kill other processes to free up |
| 644 | virtual memory, and then try the command again. |
| 645 | |
| 646 | @cindex command-line arguments, decoding |
| 647 | Use @code{getopt_long} to decode arguments, unless the argument syntax |
| 648 | makes this unreasonable. |
| 649 | |
| 650 | When static storage is to be written in during program execution, use |
| 651 | explicit C code to initialize it. Reserve C initialized declarations |
| 652 | for data that will not be changed. |
| 653 | @c ADR: why? |
| 654 | |
| 655 | Try to avoid low-level interfaces to obscure Unix data structures (such |
| 656 | as file directories, utmp, or the layout of kernel memory), since these |
| 657 | are less likely to work compatibly. If you need to find all the files |
| 658 | in a directory, use @code{readdir} or some other high-level interface. |
| 659 | These are supported compatibly by GNU. |
| 660 | |
| 661 | @cindex signal handling |
| 662 | The preferred signal handling facilities are the BSD variant of |
| 663 | @code{signal}, and the @sc{posix} @code{sigaction} function; the |
| 664 | alternative USG @code{signal} interface is an inferior design. |
| 665 | |
| 666 | Nowadays, using the @sc{posix} signal functions may be the easiest way |
| 667 | to make a program portable. If you use @code{signal}, then on GNU/Linux |
| 668 | systems running GNU libc version 1, you should include |
| 669 | @file{bsd/signal.h} instead of @file{signal.h}, so as to get BSD |
| 670 | behavior. It is up to you whether to support systems where |
| 671 | @code{signal} has only the USG behavior, or give up on them. |
| 672 | |
| 673 | @cindex impossible conditions |
| 674 | In error checks that detect ``impossible'' conditions, just abort. |
| 675 | There is usually no point in printing any message. These checks |
| 676 | indicate the existence of bugs. Whoever wants to fix the bugs will have |
| 677 | to read the source code and run a debugger. So explain the problem with |
| 678 | comments in the source. The relevant data will be in variables, which |
| 679 | are easy to examine with the debugger, so there is no point moving them |
| 680 | elsewhere. |
| 681 | |
| 682 | Do not use a count of errors as the exit status for a program. |
| 683 | @emph{That does not work}, because exit status values are limited to 8 |
| 684 | bits (0 through 255). A single run of the program might have 256 |
| 685 | errors; if you try to return 256 as the exit status, the parent process |
| 686 | will see 0 as the status, and it will appear that the program succeeded. |
| 687 | |
| 688 | @cindex temporary files |
| 689 | @cindex @code{TMPDIR} environment variable |
| 690 | If you make temporary files, check the @code{TMPDIR} environment |
| 691 | variable; if that variable is defined, use the specified directory |
| 692 | instead of @file{/tmp}. |
| 693 | |
| 694 | In addition, be aware that there is a possible security problem when |
| 695 | creating temporary files in world-writable directories. In C, you can |
| 696 | avoid this problem by creating temporary files in this manner: |
| 697 | |
| 698 | @example |
| 699 | fd = open (filename, O_WRONLY | O_CREAT | O_EXCL, 0600); |
| 700 | @end example |
| 701 | |
| 702 | @noindent |
| 703 | or by using the @code{mkstemps} function from libiberty. |
| 704 | |
| 705 | In bash, use @code{set -C} to avoid this problem. |
| 706 | |
| 707 | @node Libraries |
| 708 | @section Library Behavior |
| 709 | @cindex libraries |
| 710 | |
| 711 | Try to make library functions reentrant. If they need to do dynamic |
| 712 | storage allocation, at least try to avoid any nonreentrancy aside from |
| 713 | that of @code{malloc} itself. |
| 714 | |
| 715 | Here are certain name conventions for libraries, to avoid name |
| 716 | conflicts. |
| 717 | |
| 718 | Choose a name prefix for the library, more than two characters long. |
| 719 | All external function and variable names should start with this |
| 720 | prefix. In addition, there should only be one of these in any given |
| 721 | library member. This usually means putting each one in a separate |
| 722 | source file. |
| 723 | |
| 724 | An exception can be made when two external symbols are always used |
| 725 | together, so that no reasonable program could use one without the |
| 726 | other; then they can both go in the same file. |
| 727 | |
| 728 | External symbols that are not documented entry points for the user |
| 729 | should have names beginning with @samp{_}. The @samp{_} should be |
| 730 | followed by the chosen name prefix for the library, to prevent |
| 731 | collisions with other libraries. These can go in the same files with |
| 732 | user entry points if you like. |
| 733 | |
| 734 | Static functions and variables can be used as you like and need not |
| 735 | fit any naming convention. |
| 736 | |
| 737 | @node Errors |
| 738 | @section Formatting Error Messages |
| 739 | @cindex formatting error messages |
| 740 | @cindex error messages, formatting |
| 741 | |
| 742 | Error messages from compilers should look like this: |
| 743 | |
| 744 | @example |
| 745 | @var{source-file-name}:@var{lineno}: @var{message} |
| 746 | @end example |
| 747 | |
| 748 | @noindent |
| 749 | If you want to mention the column number, use one of these formats: |
| 750 | |
| 751 | @example |
| 752 | @var{source-file-name}:@var{lineno}:@var{column}: @var{message} |
| 753 | @var{source-file-name}:@var{lineno}.@var{column}: @var{message} |
| 754 | |
| 755 | @end example |
| 756 | |
| 757 | @noindent |
| 758 | Line numbers should start from 1 at the beginning of the file, and |
| 759 | column numbers should start from 1 at the beginning of the line. (Both |
| 760 | of these conventions are chosen for compatibility.) Calculate column |
| 761 | numbers assuming that space and all ASCII printing characters have |
| 762 | equal width, and assuming tab stops every 8 columns. |
| 763 | |
| 764 | The error message can also give both the starting and ending positions |
| 765 | of the erroneous text. There are several formats so that you can |
| 766 | avoid redundant information such as a duplicate line number. |
| 767 | Here are the possible formats: |
| 768 | |
| 769 | @example |
| 770 | @var{source-file-name}:@var{lineno-1}.@var{column-1}-@var{lineno-2}.@var{column-2}: @var{message} |
| 771 | @var{source-file-name}:@var{lineno-1}.@var{column-1}-@var{column-2}: @var{message} |
| 772 | @var{source-file-name}:@var{lineno-1}-@var{lineno-2}: @var{message} |
| 773 | @end example |
| 774 | |
| 775 | @noindent |
| 776 | When an error is spread over several files, you can use this format: |
| 777 | |
| 778 | @example |
| 779 | @var{file-1}:@var{lineno-1}.@var{column-1}-@var{file-2}:@var{lineno-2}.@var{column-2}: @var{message} |
| 780 | @end example |
| 781 | |
| 782 | Error messages from other noninteractive programs should look like this: |
| 783 | |
| 784 | @example |
| 785 | @var{program}:@var{source-file-name}:@var{lineno}: @var{message} |
| 786 | @end example |
| 787 | |
| 788 | @noindent |
| 789 | when there is an appropriate source file, or like this: |
| 790 | |
| 791 | @example |
| 792 | @var{program}: @var{message} |
| 793 | @end example |
| 794 | |
| 795 | @noindent |
| 796 | when there is no relevant source file. |
| 797 | |
| 798 | If you want to mention the column number, use this format: |
| 799 | |
| 800 | @example |
| 801 | @var{program}:@var{source-file-name}:@var{lineno}:@var{column}: @var{message} |
| 802 | @end example |
| 803 | |
| 804 | In an interactive program (one that is reading commands from a |
| 805 | terminal), it is better not to include the program name in an error |
| 806 | message. The place to indicate which program is running is in the |
| 807 | prompt or with the screen layout. (When the same program runs with |
| 808 | input from a source other than a terminal, it is not interactive and |
| 809 | would do best to print error messages using the noninteractive style.) |
| 810 | |
| 811 | The string @var{message} should not begin with a capital letter when |
| 812 | it follows a program name and/or file name, because that isn't the |
| 813 | beginning of a sentence. (The sentence conceptually starts at the |
| 814 | beginning of the line.) Also, it should not end with a period. |
| 815 | |
| 816 | Error messages from interactive programs, and other messages such as |
| 817 | usage messages, should start with a capital letter. But they should not |
| 818 | end with a period. |
| 819 | |
| 820 | @node User Interfaces |
| 821 | @section Standards for Interfaces Generally |
| 822 | |
| 823 | @cindex program name and its behavior |
| 824 | @cindex behavior, dependent on program's name |
| 825 | Please don't make the behavior of a utility depend on the name used |
| 826 | to invoke it. It is useful sometimes to make a link to a utility |
| 827 | with a different name, and that should not change what it does. |
| 828 | |
| 829 | Instead, use a run time option or a compilation switch or both |
| 830 | to select among the alternate behaviors. |
| 831 | |
| 832 | @cindex output device and program's behavior |
| 833 | Likewise, please don't make the behavior of the program depend on the |
| 834 | type of output device it is used with. Device independence is an |
| 835 | important principle of the system's design; do not compromise it merely |
| 836 | to save someone from typing an option now and then. (Variation in error |
| 837 | message syntax when using a terminal is ok, because that is a side issue |
| 838 | that people do not depend on.) |
| 839 | |
| 840 | If you think one behavior is most useful when the output is to a |
| 841 | terminal, and another is most useful when the output is a file or a |
| 842 | pipe, then it is usually best to make the default behavior the one that |
| 843 | is useful with output to a terminal, and have an option for the other |
| 844 | behavior. |
| 845 | |
| 846 | Compatibility requires certain programs to depend on the type of output |
| 847 | device. It would be disastrous if @code{ls} or @code{sh} did not do so |
| 848 | in the way all users expect. In some of these cases, we supplement the |
| 849 | program with a preferred alternate version that does not depend on the |
| 850 | output device type. For example, we provide a @code{dir} program much |
| 851 | like @code{ls} except that its default output format is always |
| 852 | multi-column format. |
| 853 | |
| 854 | |
| 855 | @node Graphical Interfaces |
| 856 | @section Standards for Graphical Interfaces |
| 857 | @cindex graphical user interface |
| 858 | @cindex interface styles |
| 859 | @cindex user interface styles |
| 860 | |
| 861 | @cindex GTK+ |
| 862 | When you write a program that provides a graphical user interface, |
| 863 | please make it work with the X Window System and the GTK+ toolkit |
| 864 | unless the functionality specifically requires some alternative (for |
| 865 | example, ``displaying jpeg images while in console mode''). |
| 866 | |
| 867 | In addition, please provide a command-line interface to control the |
| 868 | functionality. (In many cases, the graphical user interface can be a |
| 869 | separate program which invokes the command-line program.) This is |
| 870 | so that the same jobs can be done from scripts. |
| 871 | |
| 872 | @cindex CORBA |
| 873 | @cindex GNOME |
| 874 | @cindex D-bus |
| 875 | @cindex keyboard interface |
| 876 | @cindex library interface |
| 877 | Please also consider providing a D-bus interface for use from other |
| 878 | running programs, such as within GNOME. (GNOME used to use CORBA |
| 879 | for this, but that is being phased out.) In addition, consider |
| 880 | providing a library interface (for use from C), and perhaps a |
| 881 | keyboard-driven console interface (for use by users from console |
| 882 | mode). Once you are doing the work to provide the functionality and |
| 883 | the graphical interface, these won't be much extra work. |
| 884 | |
| 885 | |
| 886 | @node Command-Line Interfaces |
| 887 | @section Standards for Command Line Interfaces |
| 888 | @cindex command-line interface |
| 889 | |
| 890 | @findex getopt |
| 891 | It is a good idea to follow the @sc{posix} guidelines for the |
| 892 | command-line options of a program. The easiest way to do this is to use |
| 893 | @code{getopt} to parse them. Note that the GNU version of @code{getopt} |
| 894 | will normally permit options anywhere among the arguments unless the |
| 895 | special argument @samp{--} is used. This is not what @sc{posix} |
| 896 | specifies; it is a GNU extension. |
| 897 | |
| 898 | @cindex long-named options |
| 899 | Please define long-named options that are equivalent to the |
| 900 | single-letter Unix-style options. We hope to make GNU more user |
| 901 | friendly this way. This is easy to do with the GNU function |
| 902 | @code{getopt_long}. |
| 903 | |
| 904 | One of the advantages of long-named options is that they can be |
| 905 | consistent from program to program. For example, users should be able |
| 906 | to expect the ``verbose'' option of any GNU program which has one, to be |
| 907 | spelled precisely @samp{--verbose}. To achieve this uniformity, look at |
| 908 | the table of common long-option names when you choose the option names |
| 909 | for your program (@pxref{Option Table}). |
| 910 | |
| 911 | It is usually a good idea for file names given as ordinary arguments to |
| 912 | be input files only; any output files would be specified using options |
| 913 | (preferably @samp{-o} or @samp{--output}). Even if you allow an output |
| 914 | file name as an ordinary argument for compatibility, try to provide an |
| 915 | option as another way to specify it. This will lead to more consistency |
| 916 | among GNU utilities, and fewer idiosyncrasies for users to remember. |
| 917 | |
| 918 | @cindex standard command-line options |
| 919 | @cindex options, standard command-line |
| 920 | @cindex CGI programs, standard options for |
| 921 | @cindex PATH_INFO, specifying standard options as |
| 922 | All programs should support two standard options: @samp{--version} |
| 923 | and @samp{--help}. CGI programs should accept these as command-line |
| 924 | options, and also if given as the @env{PATH_INFO}; for instance, |
| 925 | visiting @url{http://example.org/p.cgi/--help} in a browser should |
| 926 | output the same information as invoking @samp{p.cgi --help} from the |
| 927 | command line. |
| 928 | |
| 929 | @menu |
| 930 | * --version:: The standard output for --version. |
| 931 | * --help:: The standard output for --help. |
| 932 | @end menu |
| 933 | |
| 934 | @node --version |
| 935 | @subsection @option{--version} |
| 936 | |
| 937 | @cindex @samp{--version} output |
| 938 | |
| 939 | The standard @code{--version} option should direct the program to |
| 940 | print information about its name, version, origin and legal status, |
| 941 | all on standard output, and then exit successfully. Other options and |
| 942 | arguments should be ignored once this is seen, and the program should |
| 943 | not perform its normal function. |
| 944 | |
| 945 | @cindex canonical name of a program |
| 946 | @cindex program's canonical name |
| 947 | The first line is meant to be easy for a program to parse; the version |
| 948 | number proper starts after the last space. In addition, it contains |
| 949 | the canonical name for this program, in this format: |
| 950 | |
| 951 | @example |
| 952 | GNU Emacs 19.30 |
| 953 | @end example |
| 954 | |
| 955 | @noindent |
| 956 | The program's name should be a constant string; @emph{don't} compute it |
| 957 | from @code{argv[0]}. The idea is to state the standard or canonical |
| 958 | name for the program, not its file name. There are other ways to find |
| 959 | out the precise file name where a command is found in @code{PATH}. |
| 960 | |
| 961 | If the program is a subsidiary part of a larger package, mention the |
| 962 | package name in parentheses, like this: |
| 963 | |
| 964 | @example |
| 965 | emacsserver (GNU Emacs) 19.30 |
| 966 | @end example |
| 967 | |
| 968 | @noindent |
| 969 | If the package has a version number which is different from this |
| 970 | program's version number, you can mention the package version number |
| 971 | just before the close-parenthesis. |
| 972 | |
| 973 | If you @emph{need} to mention the version numbers of libraries which |
| 974 | are distributed separately from the package which contains this program, |
| 975 | you can do so by printing an additional line of version info for each |
| 976 | library you want to mention. Use the same format for these lines as for |
| 977 | the first line. |
| 978 | |
| 979 | Please do not mention all of the libraries that the program uses ``just |
| 980 | for completeness''---that would produce a lot of unhelpful clutter. |
| 981 | Please mention library version numbers only if you find in practice that |
| 982 | they are very important to you in debugging. |
| 983 | |
| 984 | The following line, after the version number line or lines, should be a |
| 985 | copyright notice. If more than one copyright notice is called for, put |
| 986 | each on a separate line. |
| 987 | |
| 988 | Next should follow a line stating the license, preferably using one of |
| 989 | abbrevations below, and a brief statement that the program is free |
| 990 | software, and that users are free to copy and change it. Also mention |
| 991 | that there is no warranty, to the extent permitted by law. See |
| 992 | recommended wording below. |
| 993 | |
| 994 | It is ok to finish the output with a list of the major authors of the |
| 995 | program, as a way of giving credit. |
| 996 | |
| 997 | Here's an example of output that follows these rules: |
| 998 | |
| 999 | @smallexample |
| 1000 | GNU hello 2.3 |
| 1001 | Copyright (C) 2007 Free Software Foundation, Inc. |
| 1002 | License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> |
| 1003 | This is free software: you are free to change and redistribute it. |
| 1004 | There is NO WARRANTY, to the extent permitted by law. |
| 1005 | @end smallexample |
| 1006 | |
| 1007 | You should adapt this to your program, of course, filling in the proper |
| 1008 | year, copyright holder, name of program, and the references to |
| 1009 | distribution terms, and changing the rest of the wording as necessary. |
| 1010 | |
| 1011 | This copyright notice only needs to mention the most recent year in |
| 1012 | which changes were made---there's no need to list the years for previous |
| 1013 | versions' changes. You don't have to mention the name of the program in |
| 1014 | these notices, if that is inconvenient, since it appeared in the first |
| 1015 | line. (The rules are different for copyright notices in source files; |
| 1016 | @pxref{Copyright Notices,,,maintain,Information for GNU Maintainers}.) |
| 1017 | |
| 1018 | Translations of the above lines must preserve the validity of the |
| 1019 | copyright notices (@pxref{Internationalization}). If the translation's |
| 1020 | character set supports it, the @samp{(C)} should be replaced with the |
| 1021 | copyright symbol, as follows: |
| 1022 | |
| 1023 | @ifinfo |
| 1024 | (the official copyright symbol, which is the letter C in a circle); |
| 1025 | @end ifinfo |
| 1026 | @ifnotinfo |
| 1027 | @copyright{} |
| 1028 | @end ifnotinfo |
| 1029 | |
| 1030 | Write the word ``Copyright'' exactly like that, in English. Do not |
| 1031 | translate it into another language. International treaties recognize |
| 1032 | the English word ``Copyright''; translations into other languages do not |
| 1033 | have legal significance. |
| 1034 | |
| 1035 | Finally, here is the table of our suggested license abbreviations. |
| 1036 | Any abbreviation can be followed by @samp{v@var{version}[+]}, meaning |
| 1037 | that particular version, or later versions with the @samp{+}, as shown |
| 1038 | above. |
| 1039 | |
| 1040 | In the case of exceptions for extra permissions with the GPL, we use |
| 1041 | @samp{/} for a separator; the version number can follow the license |
| 1042 | abbreviation as usual, as in the examples below. |
| 1043 | |
| 1044 | @table @asis |
| 1045 | @item GPL |
| 1046 | GNU General Public License, @url{http://www.gnu.org/@/licenses/@/gpl.html}. |
| 1047 | |
| 1048 | @item LGPL |
| 1049 | GNU Lesser General Public License, @url{http://www.gnu.org/@/licenses/@/lgpl.html}. |
| 1050 | |
| 1051 | @item GPL/Ada |
| 1052 | GNU GPL with the exception for Ada. |
| 1053 | |
| 1054 | @item Apache |
| 1055 | The Apache Software Foundation license, |
| 1056 | @url{http://www.apache.org/@/licenses}. |
| 1057 | |
| 1058 | @item Artistic |
| 1059 | The Artistic license used for Perl, @url{http://www.perlfoundation.org/@/legal}. |
| 1060 | |
| 1061 | @item Expat |
| 1062 | The Expat license, @url{http://www.jclark.com/@/xml/@/copying.txt}. |
| 1063 | |
| 1064 | @item MPL |
| 1065 | The Mozilla Public License, @url{http://www.mozilla.org/@/MPL/}. |
| 1066 | |
| 1067 | @item OBSD |
| 1068 | The original (4-clause) BSD license, incompatible with the GNU GPL |
| 1069 | @url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#6}. |
| 1070 | |
| 1071 | @item PHP |
| 1072 | The license used for PHP, @url{http://www.php.net/@/license/}. |
| 1073 | |
| 1074 | @item public domain |
| 1075 | The non-license that is being in the public domain, |
| 1076 | @url{http://www.gnu.org/@/licenses/@/license-list.html#PublicDomain}. |
| 1077 | |
| 1078 | @item Python |
| 1079 | The license for Python, @url{http://www.python.org/@/2.0.1/@/license.html}. |
| 1080 | |
| 1081 | @item RBSD |
| 1082 | The revised (3-clause) BSD, compatible with the GNU GPL,@* |
| 1083 | @url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#5}. |
| 1084 | |
| 1085 | @item X11 |
| 1086 | The simple non-copyleft license used for most versions of the X Window |
| 1087 | System, @url{http://www.xfree86.org/@/3.3.6/@/COPYRIGHT2.html#3}. |
| 1088 | |
| 1089 | @item Zlib |
| 1090 | The license for Zlib, @url{http://www.gzip.org/@/zlib/@/zlib_license.html}. |
| 1091 | |
| 1092 | @end table |
| 1093 | |
| 1094 | More information about these licenses and many more are on the GNU |
| 1095 | licensing web pages, |
| 1096 | @url{http://www.gnu.org/@/licenses/@/license-list.html}. |
| 1097 | |
| 1098 | |
| 1099 | @node --help |
| 1100 | @subsection @option{--help} |
| 1101 | |
| 1102 | @cindex @samp{--help} output |
| 1103 | |
| 1104 | The standard @code{--help} option should output brief documentation |
| 1105 | for how to invoke the program, on standard output, then exit |
| 1106 | successfully. Other options and arguments should be ignored once this |
| 1107 | is seen, and the program should not perform its normal function. |
| 1108 | |
| 1109 | @cindex address for bug reports |
| 1110 | @cindex bug reports |
| 1111 | Near the end of the @samp{--help} option's output, please place lines |
| 1112 | giving the email address for bug reports, the package's home page |
| 1113 | (normally @indicateurl{http://www.gnu.org/software/@var{pkg}}, and the |
| 1114 | general page for help using GNU programs. The format should be like this: |
| 1115 | |
| 1116 | @example |
| 1117 | Report bugs to: @var{mailing-address} |
| 1118 | @var{pkg} home page: <http://www.gnu.org/software/@var{pkg}/> |
| 1119 | General help using GNU software: <http://www.gnu.org/gethelp/> |
| 1120 | @end example |
| 1121 | |
| 1122 | It is ok to mention other appropriate mailing lists and web pages. |
| 1123 | |
| 1124 | |
| 1125 | @node Option Table |
| 1126 | @section Table of Long Options |
| 1127 | @cindex long option names |
| 1128 | @cindex table of long options |
| 1129 | |
| 1130 | Here is a table of long options used by GNU programs. It is surely |
| 1131 | incomplete, but we aim to list all the options that a new program might |
| 1132 | want to be compatible with. If you use names not already in the table, |
| 1133 | please send @email{bug-standards@@gnu.org} a list of them, with their |
| 1134 | meanings, so we can update the table. |
| 1135 | |
| 1136 | @c Please leave newlines between items in this table; it's much easier |
| 1137 | @c to update when it isn't completely squashed together and unreadable. |
| 1138 | @c When there is more than one short option for a long option name, put |
| 1139 | @c a semicolon between the lists of the programs that use them, not a |
| 1140 | @c period. --friedman |
| 1141 | |
| 1142 | @table @samp |
| 1143 | @item after-date |
| 1144 | @samp{-N} in @code{tar}. |
| 1145 | |
| 1146 | @item all |
| 1147 | @samp{-a} in @code{du}, @code{ls}, @code{nm}, @code{stty}, @code{uname}, |
| 1148 | and @code{unexpand}. |
| 1149 | |
| 1150 | @item all-text |
| 1151 | @samp{-a} in @code{diff}. |
| 1152 | |
| 1153 | @item almost-all |
| 1154 | @samp{-A} in @code{ls}. |
| 1155 | |
| 1156 | @item append |
| 1157 | @samp{-a} in @code{etags}, @code{tee}, @code{time}; |
| 1158 | @samp{-r} in @code{tar}. |
| 1159 | |
| 1160 | @item archive |
| 1161 | @samp{-a} in @code{cp}. |
| 1162 | |
| 1163 | @item archive-name |
| 1164 | @samp{-n} in @code{shar}. |
| 1165 | |
| 1166 | @item arglength |
| 1167 | @samp{-l} in @code{m4}. |
| 1168 | |
| 1169 | @item ascii |
| 1170 | @samp{-a} in @code{diff}. |
| 1171 | |
| 1172 | @item assign |
| 1173 | @samp{-v} in @code{gawk}. |
| 1174 | |
| 1175 | @item assume-new |
| 1176 | @samp{-W} in @code{make}. |
| 1177 | |
| 1178 | @item assume-old |
| 1179 | @samp{-o} in @code{make}. |
| 1180 | |
| 1181 | @item auto-check |
| 1182 | @samp{-a} in @code{recode}. |
| 1183 | |
| 1184 | @item auto-pager |
| 1185 | @samp{-a} in @code{wdiff}. |
| 1186 | |
| 1187 | @item auto-reference |
| 1188 | @samp{-A} in @code{ptx}. |
| 1189 | |
| 1190 | @item avoid-wraps |
| 1191 | @samp{-n} in @code{wdiff}. |
| 1192 | |
| 1193 | @item background |
| 1194 | For server programs, run in the background. |
| 1195 | |
| 1196 | @item backward-search |
| 1197 | @samp{-B} in @code{ctags}. |
| 1198 | |
| 1199 | @item basename |
| 1200 | @samp{-f} in @code{shar}. |
| 1201 | |
| 1202 | @item batch |
| 1203 | Used in GDB. |
| 1204 | |
| 1205 | @item baud |
| 1206 | Used in GDB. |
| 1207 | |
| 1208 | @item before |
| 1209 | @samp{-b} in @code{tac}. |
| 1210 | |
| 1211 | @item binary |
| 1212 | @samp{-b} in @code{cpio} and @code{diff}. |
| 1213 | |
| 1214 | @item bits-per-code |
| 1215 | @samp{-b} in @code{shar}. |
| 1216 | |
| 1217 | @item block-size |
| 1218 | Used in @code{cpio} and @code{tar}. |
| 1219 | |
| 1220 | @item blocks |
| 1221 | @samp{-b} in @code{head} and @code{tail}. |
| 1222 | |
| 1223 | @item break-file |
| 1224 | @samp{-b} in @code{ptx}. |
| 1225 | |
| 1226 | @item brief |
| 1227 | Used in various programs to make output shorter. |
| 1228 | |
| 1229 | @item bytes |
| 1230 | @samp{-c} in @code{head}, @code{split}, and @code{tail}. |
| 1231 | |
| 1232 | @item c@t{++} |
| 1233 | @samp{-C} in @code{etags}. |
| 1234 | |
| 1235 | @item catenate |
| 1236 | @samp{-A} in @code{tar}. |
| 1237 | |
| 1238 | @item cd |
| 1239 | Used in various programs to specify the directory to use. |
| 1240 | |
| 1241 | @item changes |
| 1242 | @samp{-c} in @code{chgrp} and @code{chown}. |
| 1243 | |
| 1244 | @item classify |
| 1245 | @samp{-F} in @code{ls}. |
| 1246 | |
| 1247 | @item colons |
| 1248 | @samp{-c} in @code{recode}. |
| 1249 | |
| 1250 | @item command |
| 1251 | @samp{-c} in @code{su}; |
| 1252 | @samp{-x} in GDB. |
| 1253 | |
| 1254 | @item compare |
| 1255 | @samp{-d} in @code{tar}. |
| 1256 | |
| 1257 | @item compat |
| 1258 | Used in @code{gawk}. |
| 1259 | |
| 1260 | @item compress |
| 1261 | @samp{-Z} in @code{tar} and @code{shar}. |
| 1262 | |
| 1263 | @item concatenate |
| 1264 | @samp{-A} in @code{tar}. |
| 1265 | |
| 1266 | @item confirmation |
| 1267 | @samp{-w} in @code{tar}. |
| 1268 | |
| 1269 | @item context |
| 1270 | Used in @code{diff}. |
| 1271 | |
| 1272 | @item copyleft |
| 1273 | @samp{-W copyleft} in @code{gawk}. |
| 1274 | |
| 1275 | @item copyright |
| 1276 | @samp{-C} in @code{ptx}, @code{recode}, and @code{wdiff}; |
| 1277 | @samp{-W copyright} in @code{gawk}. |
| 1278 | |
| 1279 | @item core |
| 1280 | Used in GDB. |
| 1281 | |
| 1282 | @item count |
| 1283 | @samp{-q} in @code{who}. |
| 1284 | |
| 1285 | @item count-links |
| 1286 | @samp{-l} in @code{du}. |
| 1287 | |
| 1288 | @item create |
| 1289 | Used in @code{tar} and @code{cpio}. |
| 1290 | |
| 1291 | @item cut-mark |
| 1292 | @samp{-c} in @code{shar}. |
| 1293 | |
| 1294 | @item cxref |
| 1295 | @samp{-x} in @code{ctags}. |
| 1296 | |
| 1297 | @item date |
| 1298 | @samp{-d} in @code{touch}. |
| 1299 | |
| 1300 | @item debug |
| 1301 | @samp{-d} in @code{make} and @code{m4}; |
| 1302 | @samp{-t} in Bison. |
| 1303 | |
| 1304 | @item define |
| 1305 | @samp{-D} in @code{m4}. |
| 1306 | |
| 1307 | @item defines |
| 1308 | @samp{-d} in Bison and @code{ctags}. |
| 1309 | |
| 1310 | @item delete |
| 1311 | @samp{-D} in @code{tar}. |
| 1312 | |
| 1313 | @item dereference |
| 1314 | @samp{-L} in @code{chgrp}, @code{chown}, @code{cpio}, @code{du}, |
| 1315 | @code{ls}, and @code{tar}. |
| 1316 | |
| 1317 | @item dereference-args |
| 1318 | @samp{-D} in @code{du}. |
| 1319 | |
| 1320 | @item device |
| 1321 | Specify an I/O device (special file name). |
| 1322 | |
| 1323 | @item diacritics |
| 1324 | @samp{-d} in @code{recode}. |
| 1325 | |
| 1326 | @item dictionary-order |
| 1327 | @samp{-d} in @code{look}. |
| 1328 | |
| 1329 | @item diff |
| 1330 | @samp{-d} in @code{tar}. |
| 1331 | |
| 1332 | @item digits |
| 1333 | @samp{-n} in @code{csplit}. |
| 1334 | |
| 1335 | @item directory |
| 1336 | Specify the directory to use, in various programs. In @code{ls}, it |
| 1337 | means to show directories themselves rather than their contents. In |
| 1338 | @code{rm} and @code{ln}, it means to not treat links to directories |
| 1339 | specially. |
| 1340 | |
| 1341 | @item discard-all |
| 1342 | @samp{-x} in @code{strip}. |
| 1343 | |
| 1344 | @item discard-locals |
| 1345 | @samp{-X} in @code{strip}. |
| 1346 | |
| 1347 | @item dry-run |
| 1348 | @samp{-n} in @code{make}. |
| 1349 | |
| 1350 | @item ed |
| 1351 | @samp{-e} in @code{diff}. |
| 1352 | |
| 1353 | @item elide-empty-files |
| 1354 | @samp{-z} in @code{csplit}. |
| 1355 | |
| 1356 | @item end-delete |
| 1357 | @samp{-x} in @code{wdiff}. |
| 1358 | |
| 1359 | @item end-insert |
| 1360 | @samp{-z} in @code{wdiff}. |
| 1361 | |
| 1362 | @item entire-new-file |
| 1363 | @samp{-N} in @code{diff}. |
| 1364 | |
| 1365 | @item environment-overrides |
| 1366 | @samp{-e} in @code{make}. |
| 1367 | |
| 1368 | @item eof |
| 1369 | @samp{-e} in @code{xargs}. |
| 1370 | |
| 1371 | @item epoch |
| 1372 | Used in GDB. |
| 1373 | |
| 1374 | @item error-limit |
| 1375 | Used in @code{makeinfo}. |
| 1376 | |
| 1377 | @item error-output |
| 1378 | @samp{-o} in @code{m4}. |
| 1379 | |
| 1380 | @item escape |
| 1381 | @samp{-b} in @code{ls}. |
| 1382 | |
| 1383 | @item exclude-from |
| 1384 | @samp{-X} in @code{tar}. |
| 1385 | |
| 1386 | @item exec |
| 1387 | Used in GDB. |
| 1388 | |
| 1389 | @item exit |
| 1390 | @samp{-x} in @code{xargs}. |
| 1391 | |
| 1392 | @item exit-0 |
| 1393 | @samp{-e} in @code{unshar}. |
| 1394 | |
| 1395 | @item expand-tabs |
| 1396 | @samp{-t} in @code{diff}. |
| 1397 | |
| 1398 | @item expression |
| 1399 | @samp{-e} in @code{sed}. |
| 1400 | |
| 1401 | @item extern-only |
| 1402 | @samp{-g} in @code{nm}. |
| 1403 | |
| 1404 | @item extract |
| 1405 | @samp{-i} in @code{cpio}; |
| 1406 | @samp{-x} in @code{tar}. |
| 1407 | |
| 1408 | @item faces |
| 1409 | @samp{-f} in @code{finger}. |
| 1410 | |
| 1411 | @item fast |
| 1412 | @samp{-f} in @code{su}. |
| 1413 | |
| 1414 | @item fatal-warnings |
| 1415 | @samp{-E} in @code{m4}. |
| 1416 | |
| 1417 | @item file |
| 1418 | @samp{-f} in @code{gawk}, @code{info}, @code{make}, @code{mt}, |
| 1419 | @code{sed}, and @code{tar}. |
| 1420 | |
| 1421 | @item field-separator |
| 1422 | @samp{-F} in @code{gawk}. |
| 1423 | |
| 1424 | @item file-prefix |
| 1425 | @samp{-b} in Bison. |
| 1426 | |
| 1427 | @item file-type |
| 1428 | @samp{-F} in @code{ls}. |
| 1429 | |
| 1430 | @item files-from |
| 1431 | @samp{-T} in @code{tar}. |
| 1432 | |
| 1433 | @item fill-column |
| 1434 | Used in @code{makeinfo}. |
| 1435 | |
| 1436 | @item flag-truncation |
| 1437 | @samp{-F} in @code{ptx}. |
| 1438 | |
| 1439 | @item fixed-output-files |
| 1440 | @samp{-y} in Bison. |
| 1441 | |
| 1442 | @item follow |
| 1443 | @samp{-f} in @code{tail}. |
| 1444 | |
| 1445 | @item footnote-style |
| 1446 | Used in @code{makeinfo}. |
| 1447 | |
| 1448 | @item force |
| 1449 | @samp{-f} in @code{cp}, @code{ln}, @code{mv}, and @code{rm}. |
| 1450 | |
| 1451 | @item force-prefix |
| 1452 | @samp{-F} in @code{shar}. |
| 1453 | |
| 1454 | @item foreground |
| 1455 | For server programs, run in the foreground; |
| 1456 | in other words, don't do anything special to run the server |
| 1457 | in the background. |
| 1458 | |
| 1459 | @item format |
| 1460 | Used in @code{ls}, @code{time}, and @code{ptx}. |
| 1461 | |
| 1462 | @item freeze-state |
| 1463 | @samp{-F} in @code{m4}. |
| 1464 | |
| 1465 | @item fullname |
| 1466 | Used in GDB. |
| 1467 | |
| 1468 | @item gap-size |
| 1469 | @samp{-g} in @code{ptx}. |
| 1470 | |
| 1471 | @item get |
| 1472 | @samp{-x} in @code{tar}. |
| 1473 | |
| 1474 | @item graphic |
| 1475 | @samp{-i} in @code{ul}. |
| 1476 | |
| 1477 | @item graphics |
| 1478 | @samp{-g} in @code{recode}. |
| 1479 | |
| 1480 | @item group |
| 1481 | @samp{-g} in @code{install}. |
| 1482 | |
| 1483 | @item gzip |
| 1484 | @samp{-z} in @code{tar} and @code{shar}. |
| 1485 | |
| 1486 | @item hashsize |
| 1487 | @samp{-H} in @code{m4}. |
| 1488 | |
| 1489 | @item header |
| 1490 | @samp{-h} in @code{objdump} and @code{recode} |
| 1491 | |
| 1492 | @item heading |
| 1493 | @samp{-H} in @code{who}. |
| 1494 | |
| 1495 | @item help |
| 1496 | Used to ask for brief usage information. |
| 1497 | |
| 1498 | @item here-delimiter |
| 1499 | @samp{-d} in @code{shar}. |
| 1500 | |
| 1501 | @item hide-control-chars |
| 1502 | @samp{-q} in @code{ls}. |
| 1503 | |
| 1504 | @item html |
| 1505 | In @code{makeinfo}, output HTML. |
| 1506 | |
| 1507 | @item idle |
| 1508 | @samp{-u} in @code{who}. |
| 1509 | |
| 1510 | @item ifdef |
| 1511 | @samp{-D} in @code{diff}. |
| 1512 | |
| 1513 | @item ignore |
| 1514 | @samp{-I} in @code{ls}; |
| 1515 | @samp{-x} in @code{recode}. |
| 1516 | |
| 1517 | @item ignore-all-space |
| 1518 | @samp{-w} in @code{diff}. |
| 1519 | |
| 1520 | @item ignore-backups |
| 1521 | @samp{-B} in @code{ls}. |
| 1522 | |
| 1523 | @item ignore-blank-lines |
| 1524 | @samp{-B} in @code{diff}. |
| 1525 | |
| 1526 | @item ignore-case |
| 1527 | @samp{-f} in @code{look} and @code{ptx}; |
| 1528 | @samp{-i} in @code{diff} and @code{wdiff}. |
| 1529 | |
| 1530 | @item ignore-errors |
| 1531 | @samp{-i} in @code{make}. |
| 1532 | |
| 1533 | @item ignore-file |
| 1534 | @samp{-i} in @code{ptx}. |
| 1535 | |
| 1536 | @item ignore-indentation |
| 1537 | @samp{-I} in @code{etags}. |
| 1538 | |
| 1539 | @item ignore-init-file |
| 1540 | @samp{-f} in Oleo. |
| 1541 | |
| 1542 | @item ignore-interrupts |
| 1543 | @samp{-i} in @code{tee}. |
| 1544 | |
| 1545 | @item ignore-matching-lines |
| 1546 | @samp{-I} in @code{diff}. |
| 1547 | |
| 1548 | @item ignore-space-change |
| 1549 | @samp{-b} in @code{diff}. |
| 1550 | |
| 1551 | @item ignore-zeros |
| 1552 | @samp{-i} in @code{tar}. |
| 1553 | |
| 1554 | @item include |
| 1555 | @samp{-i} in @code{etags}; |
| 1556 | @samp{-I} in @code{m4}. |
| 1557 | |
| 1558 | @item include-dir |
| 1559 | @samp{-I} in @code{make}. |
| 1560 | |
| 1561 | @item incremental |
| 1562 | @samp{-G} in @code{tar}. |
| 1563 | |
| 1564 | @item info |
| 1565 | @samp{-i}, @samp{-l}, and @samp{-m} in Finger. |
| 1566 | |
| 1567 | @item init-file |
| 1568 | In some programs, specify the name of the file to read as the user's |
| 1569 | init file. |
| 1570 | |
| 1571 | @item initial |
| 1572 | @samp{-i} in @code{expand}. |
| 1573 | |
| 1574 | @item initial-tab |
| 1575 | @samp{-T} in @code{diff}. |
| 1576 | |
| 1577 | @item inode |
| 1578 | @samp{-i} in @code{ls}. |
| 1579 | |
| 1580 | @item interactive |
| 1581 | @samp{-i} in @code{cp}, @code{ln}, @code{mv}, @code{rm}; |
| 1582 | @samp{-e} in @code{m4}; |
| 1583 | @samp{-p} in @code{xargs}; |
| 1584 | @samp{-w} in @code{tar}. |
| 1585 | |
| 1586 | @item intermix-type |
| 1587 | @samp{-p} in @code{shar}. |
| 1588 | |
| 1589 | @item iso-8601 |
| 1590 | Used in @code{date} |
| 1591 | |
| 1592 | @item jobs |
| 1593 | @samp{-j} in @code{make}. |
| 1594 | |
| 1595 | @item just-print |
| 1596 | @samp{-n} in @code{make}. |
| 1597 | |
| 1598 | @item keep-going |
| 1599 | @samp{-k} in @code{make}. |
| 1600 | |
| 1601 | @item keep-files |
| 1602 | @samp{-k} in @code{csplit}. |
| 1603 | |
| 1604 | @item kilobytes |
| 1605 | @samp{-k} in @code{du} and @code{ls}. |
| 1606 | |
| 1607 | @item language |
| 1608 | @samp{-l} in @code{etags}. |
| 1609 | |
| 1610 | @item less-mode |
| 1611 | @samp{-l} in @code{wdiff}. |
| 1612 | |
| 1613 | @item level-for-gzip |
| 1614 | @samp{-g} in @code{shar}. |
| 1615 | |
| 1616 | @item line-bytes |
| 1617 | @samp{-C} in @code{split}. |
| 1618 | |
| 1619 | @item lines |
| 1620 | Used in @code{split}, @code{head}, and @code{tail}. |
| 1621 | |
| 1622 | @item link |
| 1623 | @samp{-l} in @code{cpio}. |
| 1624 | |
| 1625 | @item lint |
| 1626 | @itemx lint-old |
| 1627 | Used in @code{gawk}. |
| 1628 | |
| 1629 | @item list |
| 1630 | @samp{-t} in @code{cpio}; |
| 1631 | @samp{-l} in @code{recode}. |
| 1632 | |
| 1633 | @item list |
| 1634 | @samp{-t} in @code{tar}. |
| 1635 | |
| 1636 | @item literal |
| 1637 | @samp{-N} in @code{ls}. |
| 1638 | |
| 1639 | @item load-average |
| 1640 | @samp{-l} in @code{make}. |
| 1641 | |
| 1642 | @item login |
| 1643 | Used in @code{su}. |
| 1644 | |
| 1645 | @item machine |
| 1646 | Used in @code{uname}. |
| 1647 | |
| 1648 | @item macro-name |
| 1649 | @samp{-M} in @code{ptx}. |
| 1650 | |
| 1651 | @item mail |
| 1652 | @samp{-m} in @code{hello} and @code{uname}. |
| 1653 | |
| 1654 | @item make-directories |
| 1655 | @samp{-d} in @code{cpio}. |
| 1656 | |
| 1657 | @item makefile |
| 1658 | @samp{-f} in @code{make}. |
| 1659 | |
| 1660 | @item mapped |
| 1661 | Used in GDB. |
| 1662 | |
| 1663 | @item max-args |
| 1664 | @samp{-n} in @code{xargs}. |
| 1665 | |
| 1666 | @item max-chars |
| 1667 | @samp{-n} in @code{xargs}. |
| 1668 | |
| 1669 | @item max-lines |
| 1670 | @samp{-l} in @code{xargs}. |
| 1671 | |
| 1672 | @item max-load |
| 1673 | @samp{-l} in @code{make}. |
| 1674 | |
| 1675 | @item max-procs |
| 1676 | @samp{-P} in @code{xargs}. |
| 1677 | |
| 1678 | @item mesg |
| 1679 | @samp{-T} in @code{who}. |
| 1680 | |
| 1681 | @item message |
| 1682 | @samp{-T} in @code{who}. |
| 1683 | |
| 1684 | @item minimal |
| 1685 | @samp{-d} in @code{diff}. |
| 1686 | |
| 1687 | @item mixed-uuencode |
| 1688 | @samp{-M} in @code{shar}. |
| 1689 | |
| 1690 | @item mode |
| 1691 | @samp{-m} in @code{install}, @code{mkdir}, and @code{mkfifo}. |
| 1692 | |
| 1693 | @item modification-time |
| 1694 | @samp{-m} in @code{tar}. |
| 1695 | |
| 1696 | @item multi-volume |
| 1697 | @samp{-M} in @code{tar}. |
| 1698 | |
| 1699 | @item name-prefix |
| 1700 | @samp{-a} in Bison. |
| 1701 | |
| 1702 | @item nesting-limit |
| 1703 | @samp{-L} in @code{m4}. |
| 1704 | |
| 1705 | @item net-headers |
| 1706 | @samp{-a} in @code{shar}. |
| 1707 | |
| 1708 | @item new-file |
| 1709 | @samp{-W} in @code{make}. |
| 1710 | |
| 1711 | @item no-builtin-rules |
| 1712 | @samp{-r} in @code{make}. |
| 1713 | |
| 1714 | @item no-character-count |
| 1715 | @samp{-w} in @code{shar}. |
| 1716 | |
| 1717 | @item no-check-existing |
| 1718 | @samp{-x} in @code{shar}. |
| 1719 | |
| 1720 | @item no-common |
| 1721 | @samp{-3} in @code{wdiff}. |
| 1722 | |
| 1723 | @item no-create |
| 1724 | @samp{-c} in @code{touch}. |
| 1725 | |
| 1726 | @item no-defines |
| 1727 | @samp{-D} in @code{etags}. |
| 1728 | |
| 1729 | @item no-deleted |
| 1730 | @samp{-1} in @code{wdiff}. |
| 1731 | |
| 1732 | @item no-dereference |
| 1733 | @samp{-d} in @code{cp}. |
| 1734 | |
| 1735 | @item no-inserted |
| 1736 | @samp{-2} in @code{wdiff}. |
| 1737 | |
| 1738 | @item no-keep-going |
| 1739 | @samp{-S} in @code{make}. |
| 1740 | |
| 1741 | @item no-lines |
| 1742 | @samp{-l} in Bison. |
| 1743 | |
| 1744 | @item no-piping |
| 1745 | @samp{-P} in @code{shar}. |
| 1746 | |
| 1747 | @item no-prof |
| 1748 | @samp{-e} in @code{gprof}. |
| 1749 | |
| 1750 | @item no-regex |
| 1751 | @samp{-R} in @code{etags}. |
| 1752 | |
| 1753 | @item no-sort |
| 1754 | @samp{-p} in @code{nm}. |
| 1755 | |
| 1756 | @item no-splash |
| 1757 | Don't print a startup splash screen. |
| 1758 | |
| 1759 | @item no-split |
| 1760 | Used in @code{makeinfo}. |
| 1761 | |
| 1762 | @item no-static |
| 1763 | @samp{-a} in @code{gprof}. |
| 1764 | |
| 1765 | @item no-time |
| 1766 | @samp{-E} in @code{gprof}. |
| 1767 | |
| 1768 | @item no-timestamp |
| 1769 | @samp{-m} in @code{shar}. |
| 1770 | |
| 1771 | @item no-validate |
| 1772 | Used in @code{makeinfo}. |
| 1773 | |
| 1774 | @item no-wait |
| 1775 | Used in @code{emacsclient}. |
| 1776 | |
| 1777 | @item no-warn |
| 1778 | Used in various programs to inhibit warnings. |
| 1779 | |
| 1780 | @item node |
| 1781 | @samp{-n} in @code{info}. |
| 1782 | |
| 1783 | @item nodename |
| 1784 | @samp{-n} in @code{uname}. |
| 1785 | |
| 1786 | @item nonmatching |
| 1787 | @samp{-f} in @code{cpio}. |
| 1788 | |
| 1789 | @item nstuff |
| 1790 | @samp{-n} in @code{objdump}. |
| 1791 | |
| 1792 | @item null |
| 1793 | @samp{-0} in @code{xargs}. |
| 1794 | |
| 1795 | @item number |
| 1796 | @samp{-n} in @code{cat}. |
| 1797 | |
| 1798 | @item number-nonblank |
| 1799 | @samp{-b} in @code{cat}. |
| 1800 | |
| 1801 | @item numeric-sort |
| 1802 | @samp{-n} in @code{nm}. |
| 1803 | |
| 1804 | @item numeric-uid-gid |
| 1805 | @samp{-n} in @code{cpio} and @code{ls}. |
| 1806 | |
| 1807 | @item nx |
| 1808 | Used in GDB. |
| 1809 | |
| 1810 | @item old-archive |
| 1811 | @samp{-o} in @code{tar}. |
| 1812 | |
| 1813 | @item old-file |
| 1814 | @samp{-o} in @code{make}. |
| 1815 | |
| 1816 | @item one-file-system |
| 1817 | @samp{-l} in @code{tar}, @code{cp}, and @code{du}. |
| 1818 | |
| 1819 | @item only-file |
| 1820 | @samp{-o} in @code{ptx}. |
| 1821 | |
| 1822 | @item only-prof |
| 1823 | @samp{-f} in @code{gprof}. |
| 1824 | |
| 1825 | @item only-time |
| 1826 | @samp{-F} in @code{gprof}. |
| 1827 | |
| 1828 | @item options |
| 1829 | @samp{-o} in @code{getopt}, @code{fdlist}, @code{fdmount}, |
| 1830 | @code{fdmountd}, and @code{fdumount}. |
| 1831 | |
| 1832 | @item output |
| 1833 | In various programs, specify the output file name. |
| 1834 | |
| 1835 | @item output-prefix |
| 1836 | @samp{-o} in @code{shar}. |
| 1837 | |
| 1838 | @item override |
| 1839 | @samp{-o} in @code{rm}. |
| 1840 | |
| 1841 | @item overwrite |
| 1842 | @samp{-c} in @code{unshar}. |
| 1843 | |
| 1844 | @item owner |
| 1845 | @samp{-o} in @code{install}. |
| 1846 | |
| 1847 | @item paginate |
| 1848 | @samp{-l} in @code{diff}. |
| 1849 | |
| 1850 | @item paragraph-indent |
| 1851 | Used in @code{makeinfo}. |
| 1852 | |
| 1853 | @item parents |
| 1854 | @samp{-p} in @code{mkdir} and @code{rmdir}. |
| 1855 | |
| 1856 | @item pass-all |
| 1857 | @samp{-p} in @code{ul}. |
| 1858 | |
| 1859 | @item pass-through |
| 1860 | @samp{-p} in @code{cpio}. |
| 1861 | |
| 1862 | @item port |
| 1863 | @samp{-P} in @code{finger}. |
| 1864 | |
| 1865 | @item portability |
| 1866 | @samp{-c} in @code{cpio} and @code{tar}. |
| 1867 | |
| 1868 | @item posix |
| 1869 | Used in @code{gawk}. |
| 1870 | |
| 1871 | @item prefix-builtins |
| 1872 | @samp{-P} in @code{m4}. |
| 1873 | |
| 1874 | @item prefix |
| 1875 | @samp{-f} in @code{csplit}. |
| 1876 | |
| 1877 | @item preserve |
| 1878 | Used in @code{tar} and @code{cp}. |
| 1879 | |
| 1880 | @item preserve-environment |
| 1881 | @samp{-p} in @code{su}. |
| 1882 | |
| 1883 | @item preserve-modification-time |
| 1884 | @samp{-m} in @code{cpio}. |
| 1885 | |
| 1886 | @item preserve-order |
| 1887 | @samp{-s} in @code{tar}. |
| 1888 | |
| 1889 | @item preserve-permissions |
| 1890 | @samp{-p} in @code{tar}. |
| 1891 | |
| 1892 | @item print |
| 1893 | @samp{-l} in @code{diff}. |
| 1894 | |
| 1895 | @item print-chars |
| 1896 | @samp{-L} in @code{cmp}. |
| 1897 | |
| 1898 | @item print-data-base |
| 1899 | @samp{-p} in @code{make}. |
| 1900 | |
| 1901 | @item print-directory |
| 1902 | @samp{-w} in @code{make}. |
| 1903 | |
| 1904 | @item print-file-name |
| 1905 | @samp{-o} in @code{nm}. |
| 1906 | |
| 1907 | @item print-symdefs |
| 1908 | @samp{-s} in @code{nm}. |
| 1909 | |
| 1910 | @item printer |
| 1911 | @samp{-p} in @code{wdiff}. |
| 1912 | |
| 1913 | @item prompt |
| 1914 | @samp{-p} in @code{ed}. |
| 1915 | |
| 1916 | @item proxy |
| 1917 | Specify an HTTP proxy. |
| 1918 | |
| 1919 | @item query-user |
| 1920 | @samp{-X} in @code{shar}. |
| 1921 | |
| 1922 | @item question |
| 1923 | @samp{-q} in @code{make}. |
| 1924 | |
| 1925 | @item quiet |
| 1926 | Used in many programs to inhibit the usual output. Every |
| 1927 | program accepting @samp{--quiet} should accept @samp{--silent} as a |
| 1928 | synonym. |
| 1929 | |
| 1930 | @item quiet-unshar |
| 1931 | @samp{-Q} in @code{shar} |
| 1932 | |
| 1933 | @item quote-name |
| 1934 | @samp{-Q} in @code{ls}. |
| 1935 | |
| 1936 | @item rcs |
| 1937 | @samp{-n} in @code{diff}. |
| 1938 | |
| 1939 | @item re-interval |
| 1940 | Used in @code{gawk}. |
| 1941 | |
| 1942 | @item read-full-blocks |
| 1943 | @samp{-B} in @code{tar}. |
| 1944 | |
| 1945 | @item readnow |
| 1946 | Used in GDB. |
| 1947 | |
| 1948 | @item recon |
| 1949 | @samp{-n} in @code{make}. |
| 1950 | |
| 1951 | @item record-number |
| 1952 | @samp{-R} in @code{tar}. |
| 1953 | |
| 1954 | @item recursive |
| 1955 | Used in @code{chgrp}, @code{chown}, @code{cp}, @code{ls}, @code{diff}, |
| 1956 | and @code{rm}. |
| 1957 | |
| 1958 | @item reference |
| 1959 | @samp{-r} in @code{touch}. |
| 1960 | |
| 1961 | @item references |
| 1962 | @samp{-r} in @code{ptx}. |
| 1963 | |
| 1964 | @item regex |
| 1965 | @samp{-r} in @code{tac} and @code{etags}. |
| 1966 | |
| 1967 | @item release |
| 1968 | @samp{-r} in @code{uname}. |
| 1969 | |
| 1970 | @item reload-state |
| 1971 | @samp{-R} in @code{m4}. |
| 1972 | |
| 1973 | @item relocation |
| 1974 | @samp{-r} in @code{objdump}. |
| 1975 | |
| 1976 | @item rename |
| 1977 | @samp{-r} in @code{cpio}. |
| 1978 | |
| 1979 | @item replace |
| 1980 | @samp{-i} in @code{xargs}. |
| 1981 | |
| 1982 | @item report-identical-files |
| 1983 | @samp{-s} in @code{diff}. |
| 1984 | |
| 1985 | @item reset-access-time |
| 1986 | @samp{-a} in @code{cpio}. |
| 1987 | |
| 1988 | @item reverse |
| 1989 | @samp{-r} in @code{ls} and @code{nm}. |
| 1990 | |
| 1991 | @item reversed-ed |
| 1992 | @samp{-f} in @code{diff}. |
| 1993 | |
| 1994 | @item right-side-defs |
| 1995 | @samp{-R} in @code{ptx}. |
| 1996 | |
| 1997 | @item same-order |
| 1998 | @samp{-s} in @code{tar}. |
| 1999 | |
| 2000 | @item same-permissions |
| 2001 | @samp{-p} in @code{tar}. |
| 2002 | |
| 2003 | @item save |
| 2004 | @samp{-g} in @code{stty}. |
| 2005 | |
| 2006 | @item se |
| 2007 | Used in GDB. |
| 2008 | |
| 2009 | @item sentence-regexp |
| 2010 | @samp{-S} in @code{ptx}. |
| 2011 | |
| 2012 | @item separate-dirs |
| 2013 | @samp{-S} in @code{du}. |
| 2014 | |
| 2015 | @item separator |
| 2016 | @samp{-s} in @code{tac}. |
| 2017 | |
| 2018 | @item sequence |
| 2019 | Used by @code{recode} to chose files or pipes for sequencing passes. |
| 2020 | |
| 2021 | @item shell |
| 2022 | @samp{-s} in @code{su}. |
| 2023 | |
| 2024 | @item show-all |
| 2025 | @samp{-A} in @code{cat}. |
| 2026 | |
| 2027 | @item show-c-function |
| 2028 | @samp{-p} in @code{diff}. |
| 2029 | |
| 2030 | @item show-ends |
| 2031 | @samp{-E} in @code{cat}. |
| 2032 | |
| 2033 | @item show-function-line |
| 2034 | @samp{-F} in @code{diff}. |
| 2035 | |
| 2036 | @item show-tabs |
| 2037 | @samp{-T} in @code{cat}. |
| 2038 | |
| 2039 | @item silent |
| 2040 | Used in many programs to inhibit the usual output. |
| 2041 | Every program accepting |
| 2042 | @samp{--silent} should accept @samp{--quiet} as a synonym. |
| 2043 | |
| 2044 | @item size |
| 2045 | @samp{-s} in @code{ls}. |
| 2046 | |
| 2047 | @item socket |
| 2048 | Specify a file descriptor for a network server to use for its socket, |
| 2049 | instead of opening and binding a new socket. This provides a way to |
| 2050 | run, in a non-privileged process, a server that normally needs a |
| 2051 | reserved port number. |
| 2052 | |
| 2053 | @item sort |
| 2054 | Used in @code{ls}. |
| 2055 | |
| 2056 | @item source |
| 2057 | @samp{-W source} in @code{gawk}. |
| 2058 | |
| 2059 | @item sparse |
| 2060 | @samp{-S} in @code{tar}. |
| 2061 | |
| 2062 | @item speed-large-files |
| 2063 | @samp{-H} in @code{diff}. |
| 2064 | |
| 2065 | @item split-at |
| 2066 | @samp{-E} in @code{unshar}. |
| 2067 | |
| 2068 | @item split-size-limit |
| 2069 | @samp{-L} in @code{shar}. |
| 2070 | |
| 2071 | @item squeeze-blank |
| 2072 | @samp{-s} in @code{cat}. |
| 2073 | |
| 2074 | @item start-delete |
| 2075 | @samp{-w} in @code{wdiff}. |
| 2076 | |
| 2077 | @item start-insert |
| 2078 | @samp{-y} in @code{wdiff}. |
| 2079 | |
| 2080 | @item starting-file |
| 2081 | Used in @code{tar} and @code{diff} to specify which file within |
| 2082 | a directory to start processing with. |
| 2083 | |
| 2084 | @item statistics |
| 2085 | @samp{-s} in @code{wdiff}. |
| 2086 | |
| 2087 | @item stdin-file-list |
| 2088 | @samp{-S} in @code{shar}. |
| 2089 | |
| 2090 | @item stop |
| 2091 | @samp{-S} in @code{make}. |
| 2092 | |
| 2093 | @item strict |
| 2094 | @samp{-s} in @code{recode}. |
| 2095 | |
| 2096 | @item strip |
| 2097 | @samp{-s} in @code{install}. |
| 2098 | |
| 2099 | @item strip-all |
| 2100 | @samp{-s} in @code{strip}. |
| 2101 | |
| 2102 | @item strip-debug |
| 2103 | @samp{-S} in @code{strip}. |
| 2104 | |
| 2105 | @item submitter |
| 2106 | @samp{-s} in @code{shar}. |
| 2107 | |
| 2108 | @item suffix |
| 2109 | @samp{-S} in @code{cp}, @code{ln}, @code{mv}. |
| 2110 | |
| 2111 | @item suffix-format |
| 2112 | @samp{-b} in @code{csplit}. |
| 2113 | |
| 2114 | @item sum |
| 2115 | @samp{-s} in @code{gprof}. |
| 2116 | |
| 2117 | @item summarize |
| 2118 | @samp{-s} in @code{du}. |
| 2119 | |
| 2120 | @item symbolic |
| 2121 | @samp{-s} in @code{ln}. |
| 2122 | |
| 2123 | @item symbols |
| 2124 | Used in GDB and @code{objdump}. |
| 2125 | |
| 2126 | @item synclines |
| 2127 | @samp{-s} in @code{m4}. |
| 2128 | |
| 2129 | @item sysname |
| 2130 | @samp{-s} in @code{uname}. |
| 2131 | |
| 2132 | @item tabs |
| 2133 | @samp{-t} in @code{expand} and @code{unexpand}. |
| 2134 | |
| 2135 | @item tabsize |
| 2136 | @samp{-T} in @code{ls}. |
| 2137 | |
| 2138 | @item terminal |
| 2139 | @samp{-T} in @code{tput} and @code{ul}. |
| 2140 | @samp{-t} in @code{wdiff}. |
| 2141 | |
| 2142 | @item text |
| 2143 | @samp{-a} in @code{diff}. |
| 2144 | |
| 2145 | @item text-files |
| 2146 | @samp{-T} in @code{shar}. |
| 2147 | |
| 2148 | @item time |
| 2149 | Used in @code{ls} and @code{touch}. |
| 2150 | |
| 2151 | @item timeout |
| 2152 | Specify how long to wait before giving up on some operation. |
| 2153 | |
| 2154 | @item to-stdout |
| 2155 | @samp{-O} in @code{tar}. |
| 2156 | |
| 2157 | @item total |
| 2158 | @samp{-c} in @code{du}. |
| 2159 | |
| 2160 | @item touch |
| 2161 | @samp{-t} in @code{make}, @code{ranlib}, and @code{recode}. |
| 2162 | |
| 2163 | @item trace |
| 2164 | @samp{-t} in @code{m4}. |
| 2165 | |
| 2166 | @item traditional |
| 2167 | @samp{-t} in @code{hello}; |
| 2168 | @samp{-W traditional} in @code{gawk}; |
| 2169 | @samp{-G} in @code{ed}, @code{m4}, and @code{ptx}. |
| 2170 | |
| 2171 | @item tty |
| 2172 | Used in GDB. |
| 2173 | |
| 2174 | @item typedefs |
| 2175 | @samp{-t} in @code{ctags}. |
| 2176 | |
| 2177 | @item typedefs-and-c++ |
| 2178 | @samp{-T} in @code{ctags}. |
| 2179 | |
| 2180 | @item typeset-mode |
| 2181 | @samp{-t} in @code{ptx}. |
| 2182 | |
| 2183 | @item uncompress |
| 2184 | @samp{-z} in @code{tar}. |
| 2185 | |
| 2186 | @item unconditional |
| 2187 | @samp{-u} in @code{cpio}. |
| 2188 | |
| 2189 | @item undefine |
| 2190 | @samp{-U} in @code{m4}. |
| 2191 | |
| 2192 | @item undefined-only |
| 2193 | @samp{-u} in @code{nm}. |
| 2194 | |
| 2195 | @item update |
| 2196 | @samp{-u} in @code{cp}, @code{ctags}, @code{mv}, @code{tar}. |
| 2197 | |
| 2198 | @item usage |
| 2199 | Used in @code{gawk}; same as @samp{--help}. |
| 2200 | |
| 2201 | @item uuencode |
| 2202 | @samp{-B} in @code{shar}. |
| 2203 | |
| 2204 | @item vanilla-operation |
| 2205 | @samp{-V} in @code{shar}. |
| 2206 | |
| 2207 | @item verbose |
| 2208 | Print more information about progress. Many programs support this. |
| 2209 | |
| 2210 | @item verify |
| 2211 | @samp{-W} in @code{tar}. |
| 2212 | |
| 2213 | @item version |
| 2214 | Print the version number. |
| 2215 | |
| 2216 | @item version-control |
| 2217 | @samp{-V} in @code{cp}, @code{ln}, @code{mv}. |
| 2218 | |
| 2219 | @item vgrind |
| 2220 | @samp{-v} in @code{ctags}. |
| 2221 | |
| 2222 | @item volume |
| 2223 | @samp{-V} in @code{tar}. |
| 2224 | |
| 2225 | @item what-if |
| 2226 | @samp{-W} in @code{make}. |
| 2227 | |
| 2228 | @item whole-size-limit |
| 2229 | @samp{-l} in @code{shar}. |
| 2230 | |
| 2231 | @item width |
| 2232 | @samp{-w} in @code{ls} and @code{ptx}. |
| 2233 | |
| 2234 | @item word-regexp |
| 2235 | @samp{-W} in @code{ptx}. |
| 2236 | |
| 2237 | @item writable |
| 2238 | @samp{-T} in @code{who}. |
| 2239 | |
| 2240 | @item zeros |
| 2241 | @samp{-z} in @code{gprof}. |
| 2242 | @end table |
| 2243 | |
| 2244 | @node OID Allocations |
| 2245 | @section OID Allocations |
| 2246 | @cindex OID allocations for GNU |
| 2247 | @cindex SNMP |
| 2248 | @cindex LDAP |
| 2249 | @cindex X.509 |
| 2250 | |
| 2251 | The OID (object identifier) 1.3.6.1.4.1.11591 has been assigned to the |
| 2252 | GNU Project (thanks to Werner Koch). These are used for SNMP, LDAP, |
| 2253 | X.509 certificates, and so on. The web site |
| 2254 | @url{http://www.alvestrand.no/objectid} has a (voluntary) listing of |
| 2255 | many OID assignments. |
| 2256 | |
| 2257 | If you need a new slot for your GNU package, write |
| 2258 | @email{maintainers@@gnu.org}. Here is a list of arcs currently |
| 2259 | assigned: |
| 2260 | |
| 2261 | @example |
| 2262 | @include gnu-oids.texi |
| 2263 | @end example |
| 2264 | |
| 2265 | |
| 2266 | @node Memory Usage |
| 2267 | @section Memory Usage |
| 2268 | @cindex memory usage |
| 2269 | |
| 2270 | If a program typically uses just a few meg of memory, don't bother making any |
| 2271 | effort to reduce memory usage. For example, if it is impractical for |
| 2272 | other reasons to operate on files more than a few meg long, it is |
| 2273 | reasonable to read entire input files into memory to operate on them. |
| 2274 | |
| 2275 | However, for programs such as @code{cat} or @code{tail}, that can |
| 2276 | usefully operate on very large files, it is important to avoid using a |
| 2277 | technique that would artificially limit the size of files it can handle. |
| 2278 | If a program works by lines and could be applied to arbitrary |
| 2279 | user-supplied input files, it should keep only a line in memory, because |
| 2280 | this is not very hard and users will want to be able to operate on input |
| 2281 | files that are bigger than will fit in memory all at once. |
| 2282 | |
| 2283 | If your program creates complicated data structures, just make them in |
| 2284 | memory and give a fatal error if @code{malloc} returns zero. |
| 2285 | |
| 2286 | @node File Usage |
| 2287 | @section File Usage |
| 2288 | @cindex file usage |
| 2289 | |
| 2290 | Programs should be prepared to operate when @file{/usr} and @file{/etc} |
| 2291 | are read-only file systems. Thus, if the program manages log files, |
| 2292 | lock files, backup files, score files, or any other files which are |
| 2293 | modified for internal purposes, these files should not be stored in |
| 2294 | @file{/usr} or @file{/etc}. |
| 2295 | |
| 2296 | There are two exceptions. @file{/etc} is used to store system |
| 2297 | configuration information; it is reasonable for a program to modify |
| 2298 | files in @file{/etc} when its job is to update the system configuration. |
| 2299 | Also, if the user explicitly asks to modify one file in a directory, it |
| 2300 | is reasonable for the program to store other files in the same |
| 2301 | directory. |
| 2302 | |
| 2303 | @node Writing C |
| 2304 | @chapter Making The Best Use of C |
| 2305 | |
| 2306 | This chapter provides advice on how best to use the C language |
| 2307 | when writing GNU software. |
| 2308 | |
| 2309 | @menu |
| 2310 | * Formatting:: Formatting your source code. |
| 2311 | * Comments:: Commenting your work. |
| 2312 | * Syntactic Conventions:: Clean use of C constructs. |
| 2313 | * Names:: Naming variables, functions, and files. |
| 2314 | * System Portability:: Portability among different operating systems. |
| 2315 | * CPU Portability:: Supporting the range of CPU types. |
| 2316 | * System Functions:: Portability and ``standard'' library functions. |
| 2317 | * Internationalization:: Techniques for internationalization. |
| 2318 | * Character Set:: Use ASCII by default. |
| 2319 | * Quote Characters:: Use `...' in the C locale. |
| 2320 | * Mmap:: How you can safely use @code{mmap}. |
| 2321 | @end menu |
| 2322 | |
| 2323 | @node Formatting |
| 2324 | @section Formatting Your Source Code |
| 2325 | @cindex formatting source code |
| 2326 | |
| 2327 | @cindex open brace |
| 2328 | @cindex braces, in C source |
| 2329 | It is important to put the open-brace that starts the body of a C |
| 2330 | function in column one, so that they will start a defun. Several |
| 2331 | tools look for open-braces in column one to find the beginnings of C |
| 2332 | functions. These tools will not work on code not formatted that way. |
| 2333 | |
| 2334 | Avoid putting open-brace, open-parenthesis or open-bracket in column |
| 2335 | one when they are inside a function, so that they won't start a defun. |
| 2336 | The open-brace that starts a @code{struct} body can go in column one |
| 2337 | if you find it useful to treat that definition as a defun. |
| 2338 | |
| 2339 | It is also important for function definitions to start the name of the |
| 2340 | function in column one. This helps people to search for function |
| 2341 | definitions, and may also help certain tools recognize them. Thus, |
| 2342 | using Standard C syntax, the format is this: |
| 2343 | |
| 2344 | @example |
| 2345 | static char * |
| 2346 | concat (char *s1, char *s2) |
| 2347 | @{ |
| 2348 | @dots{} |
| 2349 | @} |
| 2350 | @end example |
| 2351 | |
| 2352 | @noindent |
| 2353 | or, if you want to use traditional C syntax, format the definition like |
| 2354 | this: |
| 2355 | |
| 2356 | @example |
| 2357 | static char * |
| 2358 | concat (s1, s2) /* Name starts in column one here */ |
| 2359 | char *s1, *s2; |
| 2360 | @{ /* Open brace in column one here */ |
| 2361 | @dots{} |
| 2362 | @} |
| 2363 | @end example |
| 2364 | |
| 2365 | In Standard C, if the arguments don't fit nicely on one line, |
| 2366 | split it like this: |
| 2367 | |
| 2368 | @example |
| 2369 | int |
| 2370 | lots_of_args (int an_integer, long a_long, short a_short, |
| 2371 | double a_double, float a_float) |
| 2372 | @dots{} |
| 2373 | @end example |
| 2374 | |
| 2375 | The rest of this section gives our recommendations for other aspects of |
| 2376 | C formatting style, which is also the default style of the @code{indent} |
| 2377 | program in version 1.2 and newer. It corresponds to the options |
| 2378 | |
| 2379 | @smallexample |
| 2380 | -nbad -bap -nbc -bbo -bl -bli2 -bls -ncdb -nce -cp1 -cs -di2 |
| 2381 | -ndj -nfc1 -nfca -hnl -i2 -ip5 -lp -pcs -psl -nsc -nsob |
| 2382 | @end smallexample |
| 2383 | |
| 2384 | We don't think of these recommendations as requirements, because it |
| 2385 | causes no problems for users if two different programs have different |
| 2386 | formatting styles. |
| 2387 | |
| 2388 | But whatever style you use, please use it consistently, since a mixture |
| 2389 | of styles within one program tends to look ugly. If you are |
| 2390 | contributing changes to an existing program, please follow the style of |
| 2391 | that program. |
| 2392 | |
| 2393 | For the body of the function, our recommended style looks like this: |
| 2394 | |
| 2395 | @example |
| 2396 | if (x < foo (y, z)) |
| 2397 | haha = bar[4] + 5; |
| 2398 | else |
| 2399 | @{ |
| 2400 | while (z) |
| 2401 | @{ |
| 2402 | haha += foo (z, z); |
| 2403 | z--; |
| 2404 | @} |
| 2405 | return ++x + bar (); |
| 2406 | @} |
| 2407 | @end example |
| 2408 | |
| 2409 | @cindex spaces before open-paren |
| 2410 | We find it easier to read a program when it has spaces before the |
| 2411 | open-parentheses and after the commas. Especially after the commas. |
| 2412 | |
| 2413 | When you split an expression into multiple lines, split it |
| 2414 | before an operator, not after one. Here is the right way: |
| 2415 | |
| 2416 | @cindex expressions, splitting |
| 2417 | @example |
| 2418 | if (foo_this_is_long && bar > win (x, y, z) |
| 2419 | && remaining_condition) |
| 2420 | @end example |
| 2421 | |
| 2422 | Try to avoid having two operators of different precedence at the same |
| 2423 | level of indentation. For example, don't write this: |
| 2424 | |
| 2425 | @example |
| 2426 | mode = (inmode[j] == VOIDmode |
| 2427 | || GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j]) |
| 2428 | ? outmode[j] : inmode[j]); |
| 2429 | @end example |
| 2430 | |
| 2431 | Instead, use extra parentheses so that the indentation shows the nesting: |
| 2432 | |
| 2433 | @example |
| 2434 | mode = ((inmode[j] == VOIDmode |
| 2435 | || (GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j]))) |
| 2436 | ? outmode[j] : inmode[j]); |
| 2437 | @end example |
| 2438 | |
| 2439 | Insert extra parentheses so that Emacs will indent the code properly. |
| 2440 | For example, the following indentation looks nice if you do it by hand, |
| 2441 | |
| 2442 | @example |
| 2443 | v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000 |
| 2444 | + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000; |
| 2445 | @end example |
| 2446 | |
| 2447 | @noindent |
| 2448 | but Emacs would alter it. Adding a set of parentheses produces |
| 2449 | something that looks equally nice, and which Emacs will preserve: |
| 2450 | |
| 2451 | @example |
| 2452 | v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000 |
| 2453 | + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000); |
| 2454 | @end example |
| 2455 | |
| 2456 | Format do-while statements like this: |
| 2457 | |
| 2458 | @example |
| 2459 | do |
| 2460 | @{ |
| 2461 | a = foo (a); |
| 2462 | @} |
| 2463 | while (a > 0); |
| 2464 | @end example |
| 2465 | |
| 2466 | @cindex formfeed |
| 2467 | @cindex control-L |
| 2468 | Please use formfeed characters (control-L) to divide the program into |
| 2469 | pages at logical places (but not within a function). It does not matter |
| 2470 | just how long the pages are, since they do not have to fit on a printed |
| 2471 | page. The formfeeds should appear alone on lines by themselves. |
| 2472 | |
| 2473 | @node Comments |
| 2474 | @section Commenting Your Work |
| 2475 | @cindex commenting |
| 2476 | |
| 2477 | Every program should start with a comment saying briefly what it is for. |
| 2478 | Example: @samp{fmt - filter for simple filling of text}. This comment |
| 2479 | should be at the top of the source file containing the @samp{main} |
| 2480 | function of the program. |
| 2481 | |
| 2482 | Also, please write a brief comment at the start of each source file, |
| 2483 | with the file name and a line or two about the overall purpose of the |
| 2484 | file. |
| 2485 | |
| 2486 | Please write the comments in a GNU program in English, because English |
| 2487 | is the one language that nearly all programmers in all countries can |
| 2488 | read. If you do not write English well, please write comments in |
| 2489 | English as well as you can, then ask other people to help rewrite them. |
| 2490 | If you can't write comments in English, please find someone to work with |
| 2491 | you and translate your comments into English. |
| 2492 | |
| 2493 | Please put a comment on each function saying what the function does, |
| 2494 | what sorts of arguments it gets, and what the possible values of |
| 2495 | arguments mean and are used for. It is not necessary to duplicate in |
| 2496 | words the meaning of the C argument declarations, if a C type is being |
| 2497 | used in its customary fashion. If there is anything nonstandard about |
| 2498 | its use (such as an argument of type @code{char *} which is really the |
| 2499 | address of the second character of a string, not the first), or any |
| 2500 | possible values that would not work the way one would expect (such as, |
| 2501 | that strings containing newlines are not guaranteed to work), be sure |
| 2502 | to say so. |
| 2503 | |
| 2504 | Also explain the significance of the return value, if there is one. |
| 2505 | |
| 2506 | Please put two spaces after the end of a sentence in your comments, so |
| 2507 | that the Emacs sentence commands will work. Also, please write |
| 2508 | complete sentences and capitalize the first word. If a lower-case |
| 2509 | identifier comes at the beginning of a sentence, don't capitalize it! |
| 2510 | Changing the spelling makes it a different identifier. If you don't |
| 2511 | like starting a sentence with a lower case letter, write the sentence |
| 2512 | differently (e.g., ``The identifier lower-case is @dots{}''). |
| 2513 | |
| 2514 | The comment on a function is much clearer if you use the argument |
| 2515 | names to speak about the argument values. The variable name itself |
| 2516 | should be lower case, but write it in upper case when you are speaking |
| 2517 | about the value rather than the variable itself. Thus, ``the inode |
| 2518 | number NODE_NUM'' rather than ``an inode''. |
| 2519 | |
| 2520 | There is usually no purpose in restating the name of the function in |
| 2521 | the comment before it, because the reader can see that for himself. |
| 2522 | There might be an exception when the comment is so long that the function |
| 2523 | itself would be off the bottom of the screen. |
| 2524 | |
| 2525 | There should be a comment on each static variable as well, like this: |
| 2526 | |
| 2527 | @example |
| 2528 | /* Nonzero means truncate lines in the display; |
| 2529 | zero means continue them. */ |
| 2530 | int truncate_lines; |
| 2531 | @end example |
| 2532 | |
| 2533 | @cindex conditionals, comments for |
| 2534 | @cindex @code{#endif}, commenting |
| 2535 | Every @samp{#endif} should have a comment, except in the case of short |
| 2536 | conditionals (just a few lines) that are not nested. The comment should |
| 2537 | state the condition of the conditional that is ending, @emph{including |
| 2538 | its sense}. @samp{#else} should have a comment describing the condition |
| 2539 | @emph{and sense} of the code that follows. For example: |
| 2540 | |
| 2541 | @example |
| 2542 | @group |
| 2543 | #ifdef foo |
| 2544 | @dots{} |
| 2545 | #else /* not foo */ |
| 2546 | @dots{} |
| 2547 | #endif /* not foo */ |
| 2548 | @end group |
| 2549 | @group |
| 2550 | #ifdef foo |
| 2551 | @dots{} |
| 2552 | #endif /* foo */ |
| 2553 | @end group |
| 2554 | @end example |
| 2555 | |
| 2556 | @noindent |
| 2557 | but, by contrast, write the comments this way for a @samp{#ifndef}: |
| 2558 | |
| 2559 | @example |
| 2560 | @group |
| 2561 | #ifndef foo |
| 2562 | @dots{} |
| 2563 | #else /* foo */ |
| 2564 | @dots{} |
| 2565 | #endif /* foo */ |
| 2566 | @end group |
| 2567 | @group |
| 2568 | #ifndef foo |
| 2569 | @dots{} |
| 2570 | #endif /* not foo */ |
| 2571 | @end group |
| 2572 | @end example |
| 2573 | |
| 2574 | @node Syntactic Conventions |
| 2575 | @section Clean Use of C Constructs |
| 2576 | @cindex syntactic conventions |
| 2577 | |
| 2578 | @cindex implicit @code{int} |
| 2579 | @cindex function argument, declaring |
| 2580 | Please explicitly declare the types of all objects. For example, you |
| 2581 | should explicitly declare all arguments to functions, and you should |
| 2582 | declare functions to return @code{int} rather than omitting the |
| 2583 | @code{int}. |
| 2584 | |
| 2585 | @cindex compiler warnings |
| 2586 | @cindex @samp{-Wall} compiler option |
| 2587 | Some programmers like to use the GCC @samp{-Wall} option, and change the |
| 2588 | code whenever it issues a warning. If you want to do this, then do. |
| 2589 | Other programmers prefer not to use @samp{-Wall}, because it gives |
| 2590 | warnings for valid and legitimate code which they do not want to change. |
| 2591 | If you want to do this, then do. The compiler should be your servant, |
| 2592 | not your master. |
| 2593 | |
| 2594 | Declarations of external functions and functions to appear later in the |
| 2595 | source file should all go in one place near the beginning of the file |
| 2596 | (somewhere before the first function definition in the file), or else |
| 2597 | should go in a header file. Don't put @code{extern} declarations inside |
| 2598 | functions. |
| 2599 | |
| 2600 | @cindex temporary variables |
| 2601 | It used to be common practice to use the same local variables (with |
| 2602 | names like @code{tem}) over and over for different values within one |
| 2603 | function. Instead of doing this, it is better to declare a separate local |
| 2604 | variable for each distinct purpose, and give it a name which is |
| 2605 | meaningful. This not only makes programs easier to understand, it also |
| 2606 | facilitates optimization by good compilers. You can also move the |
| 2607 | declaration of each local variable into the smallest scope that includes |
| 2608 | all its uses. This makes the program even cleaner. |
| 2609 | |
| 2610 | Don't use local variables or parameters that shadow global identifiers. |
| 2611 | |
| 2612 | @cindex multiple variables in a line |
| 2613 | Don't declare multiple variables in one declaration that spans lines. |
| 2614 | Start a new declaration on each line, instead. For example, instead |
| 2615 | of this: |
| 2616 | |
| 2617 | @example |
| 2618 | @group |
| 2619 | int foo, |
| 2620 | bar; |
| 2621 | @end group |
| 2622 | @end example |
| 2623 | |
| 2624 | @noindent |
| 2625 | write either this: |
| 2626 | |
| 2627 | @example |
| 2628 | int foo, bar; |
| 2629 | @end example |
| 2630 | |
| 2631 | @noindent |
| 2632 | or this: |
| 2633 | |
| 2634 | @example |
| 2635 | int foo; |
| 2636 | int bar; |
| 2637 | @end example |
| 2638 | |
| 2639 | @noindent |
| 2640 | (If they are global variables, each should have a comment preceding it |
| 2641 | anyway.) |
| 2642 | |
| 2643 | When you have an @code{if}-@code{else} statement nested in another |
| 2644 | @code{if} statement, always put braces around the @code{if}-@code{else}. |
| 2645 | Thus, never write like this: |
| 2646 | |
| 2647 | @example |
| 2648 | if (foo) |
| 2649 | if (bar) |
| 2650 | win (); |
| 2651 | else |
| 2652 | lose (); |
| 2653 | @end example |
| 2654 | |
| 2655 | @noindent |
| 2656 | always like this: |
| 2657 | |
| 2658 | @example |
| 2659 | if (foo) |
| 2660 | @{ |
| 2661 | if (bar) |
| 2662 | win (); |
| 2663 | else |
| 2664 | lose (); |
| 2665 | @} |
| 2666 | @end example |
| 2667 | |
| 2668 | If you have an @code{if} statement nested inside of an @code{else} |
| 2669 | statement, either write @code{else if} on one line, like this, |
| 2670 | |
| 2671 | @example |
| 2672 | if (foo) |
| 2673 | @dots{} |
| 2674 | else if (bar) |
| 2675 | @dots{} |
| 2676 | @end example |
| 2677 | |
| 2678 | @noindent |
| 2679 | with its @code{then}-part indented like the preceding @code{then}-part, |
| 2680 | or write the nested @code{if} within braces like this: |
| 2681 | |
| 2682 | @example |
| 2683 | if (foo) |
| 2684 | @dots{} |
| 2685 | else |
| 2686 | @{ |
| 2687 | if (bar) |
| 2688 | @dots{} |
| 2689 | @} |
| 2690 | @end example |
| 2691 | |
| 2692 | Don't declare both a structure tag and variables or typedefs in the |
| 2693 | same declaration. Instead, declare the structure tag separately |
| 2694 | and then use it to declare the variables or typedefs. |
| 2695 | |
| 2696 | Try to avoid assignments inside @code{if}-conditions (assignments |
| 2697 | inside @code{while}-conditions are ok). For example, don't write |
| 2698 | this: |
| 2699 | |
| 2700 | @example |
| 2701 | if ((foo = (char *) malloc (sizeof *foo)) == 0) |
| 2702 | fatal ("virtual memory exhausted"); |
| 2703 | @end example |
| 2704 | |
| 2705 | @noindent |
| 2706 | instead, write this: |
| 2707 | |
| 2708 | @example |
| 2709 | foo = (char *) malloc (sizeof *foo); |
| 2710 | if (foo == 0) |
| 2711 | fatal ("virtual memory exhausted"); |
| 2712 | @end example |
| 2713 | |
| 2714 | @pindex lint |
| 2715 | Don't make the program ugly to placate @code{lint}. Please don't insert any |
| 2716 | casts to @code{void}. Zero without a cast is perfectly fine as a null |
| 2717 | pointer constant, except when calling a varargs function. |
| 2718 | |
| 2719 | @node Names |
| 2720 | @section Naming Variables, Functions, and Files |
| 2721 | |
| 2722 | @cindex names of variables, functions, and files |
| 2723 | The names of global variables and functions in a program serve as |
| 2724 | comments of a sort. So don't choose terse names---instead, look for |
| 2725 | names that give useful information about the meaning of the variable or |
| 2726 | function. In a GNU program, names should be English, like other |
| 2727 | comments. |
| 2728 | |
| 2729 | Local variable names can be shorter, because they are used only within |
| 2730 | one context, where (presumably) comments explain their purpose. |
| 2731 | |
| 2732 | Try to limit your use of abbreviations in symbol names. It is ok to |
| 2733 | make a few abbreviations, explain what they mean, and then use them |
| 2734 | frequently, but don't use lots of obscure abbreviations. |
| 2735 | |
| 2736 | Please use underscores to separate words in a name, so that the Emacs |
| 2737 | word commands can be useful within them. Stick to lower case; reserve |
| 2738 | upper case for macros and @code{enum} constants, and for name-prefixes |
| 2739 | that follow a uniform convention. |
| 2740 | |
| 2741 | For example, you should use names like @code{ignore_space_change_flag}; |
| 2742 | don't use names like @code{iCantReadThis}. |
| 2743 | |
| 2744 | Variables that indicate whether command-line options have been |
| 2745 | specified should be named after the meaning of the option, not after |
| 2746 | the option-letter. A comment should state both the exact meaning of |
| 2747 | the option and its letter. For example, |
| 2748 | |
| 2749 | @example |
| 2750 | @group |
| 2751 | /* Ignore changes in horizontal whitespace (-b). */ |
| 2752 | int ignore_space_change_flag; |
| 2753 | @end group |
| 2754 | @end example |
| 2755 | |
| 2756 | When you want to define names with constant integer values, use |
| 2757 | @code{enum} rather than @samp{#define}. GDB knows about enumeration |
| 2758 | constants. |
| 2759 | |
| 2760 | @cindex file-name limitations |
| 2761 | @pindex doschk |
| 2762 | You might want to make sure that none of the file names would conflict |
| 2763 | if the files were loaded onto an MS-DOS file system which shortens the |
| 2764 | names. You can use the program @code{doschk} to test for this. |
| 2765 | |
| 2766 | Some GNU programs were designed to limit themselves to file names of 14 |
| 2767 | characters or less, to avoid file name conflicts if they are read into |
| 2768 | older System V systems. Please preserve this feature in the existing |
| 2769 | GNU programs that have it, but there is no need to do this in new GNU |
| 2770 | programs. @code{doschk} also reports file names longer than 14 |
| 2771 | characters. |
| 2772 | |
| 2773 | @node System Portability |
| 2774 | @section Portability between System Types |
| 2775 | @cindex portability, between system types |
| 2776 | |
| 2777 | In the Unix world, ``portability'' refers to porting to different Unix |
| 2778 | versions. For a GNU program, this kind of portability is desirable, but |
| 2779 | not paramount. |
| 2780 | |
| 2781 | The primary purpose of GNU software is to run on top of the GNU kernel, |
| 2782 | compiled with the GNU C compiler, on various types of @sc{cpu}. So the |
| 2783 | kinds of portability that are absolutely necessary are quite limited. |
| 2784 | But it is important to support Linux-based GNU systems, since they |
| 2785 | are the form of GNU that is popular. |
| 2786 | |
| 2787 | Beyond that, it is good to support the other free operating systems |
| 2788 | (*BSD), and it is nice to support other Unix-like systems if you want |
| 2789 | to. Supporting a variety of Unix-like systems is desirable, although |
| 2790 | not paramount. It is usually not too hard, so you may as well do it. |
| 2791 | But you don't have to consider it an obligation, if it does turn out to |
| 2792 | be hard. |
| 2793 | |
| 2794 | @pindex autoconf |
| 2795 | The easiest way to achieve portability to most Unix-like systems is to |
| 2796 | use Autoconf. It's unlikely that your program needs to know more |
| 2797 | information about the host platform than Autoconf can provide, simply |
| 2798 | because most of the programs that need such knowledge have already been |
| 2799 | written. |
| 2800 | |
| 2801 | Avoid using the format of semi-internal data bases (e.g., directories) |
| 2802 | when there is a higher-level alternative (@code{readdir}). |
| 2803 | |
| 2804 | @cindex non-@sc{posix} systems, and portability |
| 2805 | As for systems that are not like Unix, such as MSDOS, Windows, VMS, MVS, |
| 2806 | and older Macintosh systems, supporting them is often a lot of work. |
| 2807 | When that is the case, it is better to spend your time adding features |
| 2808 | that will be useful on GNU and GNU/Linux, rather than on supporting |
| 2809 | other incompatible systems. |
| 2810 | |
| 2811 | If you do support Windows, please do not abbreviate it as ``win''. In |
| 2812 | hacker terminology, calling something a ``win'' is a form of praise. |
| 2813 | You're free to praise Microsoft Windows on your own if you want, but |
| 2814 | please don't do this in GNU packages. Instead of abbreviating |
| 2815 | ``Windows'' to ``win'', you can write it in full or abbreviate it to |
| 2816 | ``woe'' or ``w''. In GNU Emacs, for instance, we use @samp{w32} in |
| 2817 | file names of Windows-specific files, but the macro for Windows |
| 2818 | conditionals is called @code{WINDOWSNT}. |
| 2819 | |
| 2820 | It is a good idea to define the ``feature test macro'' |
| 2821 | @code{_GNU_SOURCE} when compiling your C files. When you compile on GNU |
| 2822 | or GNU/Linux, this will enable the declarations of GNU library extension |
| 2823 | functions, and that will usually give you a compiler error message if |
| 2824 | you define the same function names in some other way in your program. |
| 2825 | (You don't have to actually @emph{use} these functions, if you prefer |
| 2826 | to make the program more portable to other systems.) |
| 2827 | |
| 2828 | But whether or not you use these GNU extensions, you should avoid |
| 2829 | using their names for any other meanings. Doing so would make it hard |
| 2830 | to move your code into other GNU programs. |
| 2831 | |
| 2832 | @node CPU Portability |
| 2833 | @section Portability between @sc{cpu}s |
| 2834 | |
| 2835 | @cindex data types, and portability |
| 2836 | @cindex portability, and data types |
| 2837 | Even GNU systems will differ because of differences among @sc{cpu} |
| 2838 | types---for example, difference in byte ordering and alignment |
| 2839 | requirements. It is absolutely essential to handle these differences. |
| 2840 | However, don't make any effort to cater to the possibility that an |
| 2841 | @code{int} will be less than 32 bits. We don't support 16-bit machines |
| 2842 | in GNU. |
| 2843 | |
| 2844 | Similarly, don't make any effort to cater to the possibility that |
| 2845 | @code{long} will be smaller than predefined types like @code{size_t}. |
| 2846 | For example, the following code is ok: |
| 2847 | |
| 2848 | @example |
| 2849 | printf ("size = %lu\n", (unsigned long) sizeof array); |
| 2850 | printf ("diff = %ld\n", (long) (pointer2 - pointer1)); |
| 2851 | @end example |
| 2852 | |
| 2853 | 1989 Standard C requires this to work, and we know of only one |
| 2854 | counterexample: 64-bit programs on Microsoft Windows. We will |
| 2855 | leave it to those who want to port GNU programs to that environment |
| 2856 | to figure out how to do it. |
| 2857 | |
| 2858 | Predefined file-size types like @code{off_t} are an exception: they are |
| 2859 | longer than @code{long} on many platforms, so code like the above won't |
| 2860 | work with them. One way to print an @code{off_t} value portably is to |
| 2861 | print its digits yourself, one by one. |
| 2862 | |
| 2863 | Don't assume that the address of an @code{int} object is also the |
| 2864 | address of its least-significant byte. This is false on big-endian |
| 2865 | machines. Thus, don't make the following mistake: |
| 2866 | |
| 2867 | @example |
| 2868 | int c; |
| 2869 | @dots{} |
| 2870 | while ((c = getchar ()) != EOF) |
| 2871 | write (file_descriptor, &c, 1); |
| 2872 | @end example |
| 2873 | |
| 2874 | @noindent Instead, use @code{unsigned char} as follows. (The @code{unsigned} |
| 2875 | is for portability to unusual systems where @code{char} is signed and |
| 2876 | where there is integer overflow checking.) |
| 2877 | |
| 2878 | @example |
| 2879 | int c; |
| 2880 | while ((c = getchar ()) != EOF) |
| 2881 | @{ |
| 2882 | unsigned char u = c; |
| 2883 | write (file_descriptor, &u, 1); |
| 2884 | @} |
| 2885 | @end example |
| 2886 | |
| 2887 | It used to be ok to not worry about the difference between pointers |
| 2888 | and integers when passing arguments to functions. However, on most |
| 2889 | modern 64-bit machines pointers are wider than @code{int}. |
| 2890 | Conversely, integer types like @code{long long int} and @code{off_t} |
| 2891 | are wider than pointers on most modern 32-bit machines. Hence it's |
| 2892 | often better nowadays to use prototypes to define functions whose |
| 2893 | argument types are not trivial. |
| 2894 | |
| 2895 | In particular, if functions accept varying argument counts or types |
| 2896 | they should be declared using prototypes containing @samp{...} and |
| 2897 | defined using @file{stdarg.h}. For an example of this, please see the |
| 2898 | @uref{http://www.gnu.org/software/gnulib/, Gnulib} error module, which |
| 2899 | declares and defines the following function: |
| 2900 | |
| 2901 | @example |
| 2902 | /* Print a message with `fprintf (stderr, FORMAT, ...)'; |
| 2903 | if ERRNUM is nonzero, follow it with ": " and strerror (ERRNUM). |
| 2904 | If STATUS is nonzero, terminate the program with `exit (STATUS)'. */ |
| 2905 | |
| 2906 | void error (int status, int errnum, const char *format, ...); |
| 2907 | @end example |
| 2908 | |
| 2909 | A simple way to use the Gnulib error module is to obtain the two |
| 2910 | source files @file{error.c} and @file{error.h} from the Gnulib library |
| 2911 | source code repository at |
| 2912 | @uref{http://git.savannah.gnu.org/@/gitweb/@/?p=gnulib.git}. |
| 2913 | Here's a sample use: |
| 2914 | |
| 2915 | @example |
| 2916 | #include "error.h" |
| 2917 | #include <errno.h> |
| 2918 | #include <stdio.h> |
| 2919 | |
| 2920 | char *program_name = "myprogram"; |
| 2921 | |
| 2922 | FILE * |
| 2923 | xfopen (char const *name) |
| 2924 | @{ |
| 2925 | FILE *fp = fopen (name, "r"); |
| 2926 | if (! fp) |
| 2927 | error (1, errno, "cannot read %s", name); |
| 2928 | return fp; |
| 2929 | @} |
| 2930 | @end example |
| 2931 | |
| 2932 | @cindex casting pointers to integers |
| 2933 | Avoid casting pointers to integers if you can. Such casts greatly |
| 2934 | reduce portability, and in most programs they are easy to avoid. In the |
| 2935 | cases where casting pointers to integers is essential---such as, a Lisp |
| 2936 | interpreter which stores type information as well as an address in one |
| 2937 | word---you'll have to make explicit provisions to handle different word |
| 2938 | sizes. You will also need to make provision for systems in which the |
| 2939 | normal range of addresses you can get from @code{malloc} starts far away |
| 2940 | from zero. |
| 2941 | |
| 2942 | @node System Functions |
| 2943 | @section Calling System Functions |
| 2944 | @cindex library functions, and portability |
| 2945 | @cindex portability, and library functions |
| 2946 | |
| 2947 | C implementations differ substantially. Standard C reduces but does |
| 2948 | not eliminate the incompatibilities; meanwhile, many GNU packages still |
| 2949 | support pre-standard compilers because this is not hard to do. This |
| 2950 | chapter gives recommendations for how to use the more-or-less standard C |
| 2951 | library functions to avoid unnecessary loss of portability. |
| 2952 | |
| 2953 | @itemize @bullet |
| 2954 | @item |
| 2955 | Don't use the return value of @code{sprintf}. It returns the number of |
| 2956 | characters written on some systems, but not on all systems. |
| 2957 | |
| 2958 | @item |
| 2959 | Be aware that @code{vfprintf} is not always available. |
| 2960 | |
| 2961 | @item |
| 2962 | @code{main} should be declared to return type @code{int}. It should |
| 2963 | terminate either by calling @code{exit} or by returning the integer |
| 2964 | status code; make sure it cannot ever return an undefined value. |
| 2965 | |
| 2966 | @cindex declaration for system functions |
| 2967 | @item |
| 2968 | Don't declare system functions explicitly. |
| 2969 | |
| 2970 | Almost any declaration for a system function is wrong on some system. |
| 2971 | To minimize conflicts, leave it to the system header files to declare |
| 2972 | system functions. If the headers don't declare a function, let it |
| 2973 | remain undeclared. |
| 2974 | |
| 2975 | While it may seem unclean to use a function without declaring it, in |
| 2976 | practice this works fine for most system library functions on the |
| 2977 | systems where this really happens; thus, the disadvantage is only |
| 2978 | theoretical. By contrast, actual declarations have frequently caused |
| 2979 | actual conflicts. |
| 2980 | |
| 2981 | @item |
| 2982 | If you must declare a system function, don't specify the argument types. |
| 2983 | Use an old-style declaration, not a Standard C prototype. The more you |
| 2984 | specify about the function, the more likely a conflict. |
| 2985 | |
| 2986 | @item |
| 2987 | In particular, don't unconditionally declare @code{malloc} or |
| 2988 | @code{realloc}. |
| 2989 | |
| 2990 | Most GNU programs use those functions just once, in functions |
| 2991 | conventionally named @code{xmalloc} and @code{xrealloc}. These |
| 2992 | functions call @code{malloc} and @code{realloc}, respectively, and |
| 2993 | check the results. |
| 2994 | |
| 2995 | Because @code{xmalloc} and @code{xrealloc} are defined in your program, |
| 2996 | you can declare them in other files without any risk of type conflict. |
| 2997 | |
| 2998 | On most systems, @code{int} is the same length as a pointer; thus, the |
| 2999 | calls to @code{malloc} and @code{realloc} work fine. For the few |
| 3000 | exceptional systems (mostly 64-bit machines), you can use |
| 3001 | @strong{conditionalized} declarations of @code{malloc} and |
| 3002 | @code{realloc}---or put these declarations in configuration files |
| 3003 | specific to those systems. |
| 3004 | |
| 3005 | @cindex string library functions |
| 3006 | @item |
| 3007 | The string functions require special treatment. Some Unix systems have |
| 3008 | a header file @file{string.h}; others have @file{strings.h}. Neither |
| 3009 | file name is portable. There are two things you can do: use Autoconf to |
| 3010 | figure out which file to include, or don't include either file. |
| 3011 | |
| 3012 | @item |
| 3013 | If you don't include either strings file, you can't get declarations for |
| 3014 | the string functions from the header file in the usual way. |
| 3015 | |
| 3016 | That causes less of a problem than you might think. The newer standard |
| 3017 | string functions should be avoided anyway because many systems still |
| 3018 | don't support them. The string functions you can use are these: |
| 3019 | |
| 3020 | @example |
| 3021 | strcpy strncpy strcat strncat |
| 3022 | strlen strcmp strncmp |
| 3023 | strchr strrchr |
| 3024 | @end example |
| 3025 | |
| 3026 | The copy and concatenate functions work fine without a declaration as |
| 3027 | long as you don't use their values. Using their values without a |
| 3028 | declaration fails on systems where the width of a pointer differs from |
| 3029 | the width of @code{int}, and perhaps in other cases. It is trivial to |
| 3030 | avoid using their values, so do that. |
| 3031 | |
| 3032 | The compare functions and @code{strlen} work fine without a declaration |
| 3033 | on most systems, possibly all the ones that GNU software runs on. |
| 3034 | You may find it necessary to declare them @strong{conditionally} on a |
| 3035 | few systems. |
| 3036 | |
| 3037 | The search functions must be declared to return @code{char *}. Luckily, |
| 3038 | there is no variation in the data type they return. But there is |
| 3039 | variation in their names. Some systems give these functions the names |
| 3040 | @code{index} and @code{rindex}; other systems use the names |
| 3041 | @code{strchr} and @code{strrchr}. Some systems support both pairs of |
| 3042 | names, but neither pair works on all systems. |
| 3043 | |
| 3044 | You should pick a single pair of names and use it throughout your |
| 3045 | program. (Nowadays, it is better to choose @code{strchr} and |
| 3046 | @code{strrchr} for new programs, since those are the standard |
| 3047 | names.) Declare both of those names as functions returning @code{char |
| 3048 | *}. On systems which don't support those names, define them as macros |
| 3049 | in terms of the other pair. For example, here is what to put at the |
| 3050 | beginning of your file (or in a header) if you want to use the names |
| 3051 | @code{strchr} and @code{strrchr} throughout: |
| 3052 | |
| 3053 | @example |
| 3054 | #ifndef HAVE_STRCHR |
| 3055 | #define strchr index |
| 3056 | #endif |
| 3057 | #ifndef HAVE_STRRCHR |
| 3058 | #define strrchr rindex |
| 3059 | #endif |
| 3060 | |
| 3061 | char *strchr (); |
| 3062 | char *strrchr (); |
| 3063 | @end example |
| 3064 | @end itemize |
| 3065 | |
| 3066 | Here we assume that @code{HAVE_STRCHR} and @code{HAVE_STRRCHR} are |
| 3067 | macros defined in systems where the corresponding functions exist. |
| 3068 | One way to get them properly defined is to use Autoconf. |
| 3069 | |
| 3070 | @node Internationalization |
| 3071 | @section Internationalization |
| 3072 | @cindex internationalization |
| 3073 | |
| 3074 | @pindex gettext |
| 3075 | GNU has a library called GNU gettext that makes it easy to translate the |
| 3076 | messages in a program into various languages. You should use this |
| 3077 | library in every program. Use English for the messages as they appear |
| 3078 | in the program, and let gettext provide the way to translate them into |
| 3079 | other languages. |
| 3080 | |
| 3081 | Using GNU gettext involves putting a call to the @code{gettext} macro |
| 3082 | around each string that might need translation---like this: |
| 3083 | |
| 3084 | @example |
| 3085 | printf (gettext ("Processing file `%s'...")); |
| 3086 | @end example |
| 3087 | |
| 3088 | @noindent |
| 3089 | This permits GNU gettext to replace the string @code{"Processing file |
| 3090 | `%s'..."} with a translated version. |
| 3091 | |
| 3092 | Once a program uses gettext, please make a point of writing calls to |
| 3093 | @code{gettext} when you add new strings that call for translation. |
| 3094 | |
| 3095 | Using GNU gettext in a package involves specifying a @dfn{text domain |
| 3096 | name} for the package. The text domain name is used to separate the |
| 3097 | translations for this package from the translations for other packages. |
| 3098 | Normally, the text domain name should be the same as the name of the |
| 3099 | package---for example, @samp{coreutils} for the GNU core utilities. |
| 3100 | |
| 3101 | @cindex message text, and internationalization |
| 3102 | To enable gettext to work well, avoid writing code that makes |
| 3103 | assumptions about the structure of words or sentences. When you want |
| 3104 | the precise text of a sentence to vary depending on the data, use two or |
| 3105 | more alternative string constants each containing a complete sentences, |
| 3106 | rather than inserting conditionalized words or phrases into a single |
| 3107 | sentence framework. |
| 3108 | |
| 3109 | Here is an example of what not to do: |
| 3110 | |
| 3111 | @smallexample |
| 3112 | printf ("%s is full", capacity > 5000000 ? "disk" : "floppy disk"); |
| 3113 | @end smallexample |
| 3114 | |
| 3115 | If you apply gettext to all strings, like this, |
| 3116 | |
| 3117 | @smallexample |
| 3118 | printf (gettext ("%s is full"), |
| 3119 | capacity > 5000000 ? gettext ("disk") : gettext ("floppy disk")); |
| 3120 | @end smallexample |
| 3121 | |
| 3122 | @noindent |
| 3123 | the translator will hardly know that "disk" and "floppy disk" are meant to |
| 3124 | be substituted in the other string. Worse, in some languages (like French) |
| 3125 | the construction will not work: the translation of the word "full" depends |
| 3126 | on the gender of the first part of the sentence; it happens to be not the |
| 3127 | same for "disk" as for "floppy disk". |
| 3128 | |
| 3129 | Complete sentences can be translated without problems: |
| 3130 | |
| 3131 | @example |
| 3132 | printf (capacity > 5000000 ? gettext ("disk is full") |
| 3133 | : gettext ("floppy disk is full")); |
| 3134 | @end example |
| 3135 | |
| 3136 | A similar problem appears at the level of sentence structure with this |
| 3137 | code: |
| 3138 | |
| 3139 | @example |
| 3140 | printf ("# Implicit rule search has%s been done.\n", |
| 3141 | f->tried_implicit ? "" : " not"); |
| 3142 | @end example |
| 3143 | |
| 3144 | @noindent |
| 3145 | Adding @code{gettext} calls to this code cannot give correct results for |
| 3146 | all languages, because negation in some languages requires adding words |
| 3147 | at more than one place in the sentence. By contrast, adding |
| 3148 | @code{gettext} calls does the job straightforwardly if the code starts |
| 3149 | out like this: |
| 3150 | |
| 3151 | @example |
| 3152 | printf (f->tried_implicit |
| 3153 | ? "# Implicit rule search has been done.\n", |
| 3154 | : "# Implicit rule search has not been done.\n"); |
| 3155 | @end example |
| 3156 | |
| 3157 | Another example is this one: |
| 3158 | |
| 3159 | @example |
| 3160 | printf ("%d file%s processed", nfiles, |
| 3161 | nfiles != 1 ? "s" : ""); |
| 3162 | @end example |
| 3163 | |
| 3164 | @noindent |
| 3165 | The problem with this example is that it assumes that plurals are made |
| 3166 | by adding `s'. If you apply gettext to the format string, like this, |
| 3167 | |
| 3168 | @example |
| 3169 | printf (gettext ("%d file%s processed"), nfiles, |
| 3170 | nfiles != 1 ? "s" : ""); |
| 3171 | @end example |
| 3172 | |
| 3173 | @noindent |
| 3174 | the message can use different words, but it will still be forced to use |
| 3175 | `s' for the plural. Here is a better way, with gettext being applied to |
| 3176 | the two strings independently: |
| 3177 | |
| 3178 | @example |
| 3179 | printf ((nfiles != 1 ? gettext ("%d files processed") |
| 3180 | : gettext ("%d file processed")), |
| 3181 | nfiles); |
| 3182 | @end example |
| 3183 | |
| 3184 | @noindent |
| 3185 | But this still doesn't work for languages like Polish, which has three |
| 3186 | plural forms: one for nfiles == 1, one for nfiles == 2, 3, 4, 22, 23, 24, ... |
| 3187 | and one for the rest. The GNU @code{ngettext} function solves this problem: |
| 3188 | |
| 3189 | @example |
| 3190 | printf (ngettext ("%d files processed", "%d file processed", nfiles), |
| 3191 | nfiles); |
| 3192 | @end example |
| 3193 | |
| 3194 | |
| 3195 | @node Character Set |
| 3196 | @section Character Set |
| 3197 | @cindex character set |
| 3198 | @cindex encodings |
| 3199 | @cindex ASCII characters |
| 3200 | @cindex non-ASCII characters |
| 3201 | |
| 3202 | Sticking to the ASCII character set (plain text, 7-bit characters) is |
| 3203 | preferred in GNU source code comments, text documents, and other |
| 3204 | contexts, unless there is good reason to do something else because of |
| 3205 | the application domain. For example, if source code deals with the |
| 3206 | French Revolutionary calendar, it is OK if its literal strings contain |
| 3207 | accented characters in month names like ``Flor@'eal''. Also, it is OK |
| 3208 | to use non-ASCII characters to represent proper names of contributors in |
| 3209 | change logs (@pxref{Change Logs}). |
| 3210 | |
| 3211 | If you need to use non-ASCII characters, you should normally stick with |
| 3212 | one encoding, as one cannot in general mix encodings reliably. |
| 3213 | |
| 3214 | |
| 3215 | @node Quote Characters |
| 3216 | @section Quote Characters |
| 3217 | @cindex quote characters |
| 3218 | @cindex locale-specific quote characters |
| 3219 | @cindex left quote |
| 3220 | @cindex grave accent |
| 3221 | |
| 3222 | In the C locale, GNU programs should stick to plain ASCII for quotation |
| 3223 | characters in messages to users: preferably 0x60 (@samp{`}) for left |
| 3224 | quotes and 0x27 (@samp{'}) for right quotes. It is ok, but not |
| 3225 | required, to use locale-specific quotes in other locales. |
| 3226 | |
| 3227 | The @uref{http://www.gnu.org/software/gnulib/, Gnulib} @code{quote} and |
| 3228 | @code{quotearg} modules provide a reasonably straightforward way to |
| 3229 | support locale-specific quote characters, as well as taking care of |
| 3230 | other issues, such as quoting a filename that itself contains a quote |
| 3231 | character. See the Gnulib documentation for usage details. |
| 3232 | |
| 3233 | In any case, the documentation for your program should clearly specify |
| 3234 | how it does quoting, if different than the preferred method of @samp{`} |
| 3235 | and @samp{'}. This is especially important if the output of your |
| 3236 | program is ever likely to be parsed by another program. |
| 3237 | |
| 3238 | Quotation characters are a difficult area in the computing world at |
| 3239 | this time: there are no true left or right quote characters in Latin1; |
| 3240 | the @samp{`} character we use was standardized there as a grave |
| 3241 | accent. Moreover, Latin1 is still not universally usable. |
| 3242 | |
| 3243 | Unicode contains the unambiguous quote characters required, and its |
| 3244 | common encoding UTF-8 is upward compatible with Latin1. However, |
| 3245 | Unicode and UTF-8 are not universally well-supported, either. |
| 3246 | |
| 3247 | This may change over the next few years, and then we will revisit |
| 3248 | this. |
| 3249 | |
| 3250 | |
| 3251 | @node Mmap |
| 3252 | @section Mmap |
| 3253 | @findex mmap |
| 3254 | |
| 3255 | Don't assume that @code{mmap} either works on all files or fails |
| 3256 | for all files. It may work on some files and fail on others. |
| 3257 | |
| 3258 | The proper way to use @code{mmap} is to try it on the specific file for |
| 3259 | which you want to use it---and if @code{mmap} doesn't work, fall back on |
| 3260 | doing the job in another way using @code{read} and @code{write}. |
| 3261 | |
| 3262 | The reason this precaution is needed is that the GNU kernel (the HURD) |
| 3263 | provides a user-extensible file system, in which there can be many |
| 3264 | different kinds of ``ordinary files.'' Many of them support |
| 3265 | @code{mmap}, but some do not. It is important to make programs handle |
| 3266 | all these kinds of files. |
| 3267 | |
| 3268 | @node Documentation |
| 3269 | @chapter Documenting Programs |
| 3270 | @cindex documentation |
| 3271 | |
| 3272 | A GNU program should ideally come with full free documentation, adequate |
| 3273 | for both reference and tutorial purposes. If the package can be |
| 3274 | programmed or extended, the documentation should cover programming or |
| 3275 | extending it, as well as just using it. |
| 3276 | |
| 3277 | @menu |
| 3278 | * GNU Manuals:: Writing proper manuals. |
| 3279 | * Doc Strings and Manuals:: Compiling doc strings doesn't make a manual. |
| 3280 | * Manual Structure Details:: Specific structure conventions. |
| 3281 | * License for Manuals:: Writing the distribution terms for a manual. |
| 3282 | * Manual Credits:: Giving credit to documentation contributors. |
| 3283 | * Printed Manuals:: Mentioning the printed manual. |
| 3284 | * NEWS File:: NEWS files supplement manuals. |
| 3285 | * Change Logs:: Recording changes. |
| 3286 | * Man Pages:: Man pages are secondary. |
| 3287 | * Reading other Manuals:: How far you can go in learning |
| 3288 | from other manuals. |
| 3289 | @end menu |
| 3290 | |
| 3291 | @node GNU Manuals |
| 3292 | @section GNU Manuals |
| 3293 | |
| 3294 | The preferred document format for the GNU system is the Texinfo |
| 3295 | formatting language. Every GNU package should (ideally) have |
| 3296 | documentation in Texinfo both for reference and for learners. Texinfo |
| 3297 | makes it possible to produce a good quality formatted book, using |
| 3298 | @TeX{}, and to generate an Info file. It is also possible to generate |
| 3299 | HTML output from Texinfo source. See the Texinfo manual, either the |
| 3300 | hardcopy, or the on-line version available through @code{info} or the |
| 3301 | Emacs Info subsystem (@kbd{C-h i}). |
| 3302 | |
| 3303 | Nowadays some other formats such as Docbook and Sgmltexi can be |
| 3304 | converted automatically into Texinfo. It is ok to produce the Texinfo |
| 3305 | documentation by conversion this way, as long as it gives good results. |
| 3306 | |
| 3307 | Make sure your manual is clear to a reader who knows nothing about the |
| 3308 | topic and reads it straight through. This means covering basic topics |
| 3309 | at the beginning, and advanced topics only later. This also means |
| 3310 | defining every specialized term when it is first used. |
| 3311 | |
| 3312 | Programmers tend to carry over the structure of the program as the |
| 3313 | structure for its documentation. But this structure is not |
| 3314 | necessarily good for explaining how to use the program; it may be |
| 3315 | irrelevant and confusing for a user. |
| 3316 | |
| 3317 | Instead, the right way to structure documentation is according to the |
| 3318 | concepts and questions that a user will have in mind when reading it. |
| 3319 | This principle applies at every level, from the lowest (ordering |
| 3320 | sentences in a paragraph) to the highest (ordering of chapter topics |
| 3321 | within the manual). Sometimes this structure of ideas matches the |
| 3322 | structure of the implementation of the software being documented---but |
| 3323 | often they are different. An important part of learning to write good |
| 3324 | documentation is to learn to notice when you have unthinkingly |
| 3325 | structured the documentation like the implementation, stop yourself, |
| 3326 | and look for better alternatives. |
| 3327 | |
| 3328 | For example, each program in the GNU system probably ought to be |
| 3329 | documented in one manual; but this does not mean each program should |
| 3330 | have its own manual. That would be following the structure of the |
| 3331 | implementation, rather than the structure that helps the user |
| 3332 | understand. |
| 3333 | |
| 3334 | Instead, each manual should cover a coherent @emph{topic}. For example, |
| 3335 | instead of a manual for @code{diff} and a manual for @code{diff3}, we |
| 3336 | have one manual for ``comparison of files'' which covers both of those |
| 3337 | programs, as well as @code{cmp}. By documenting these programs |
| 3338 | together, we can make the whole subject clearer. |
| 3339 | |
| 3340 | The manual which discusses a program should certainly document all of |
| 3341 | the program's command-line options and all of its commands. It should |
| 3342 | give examples of their use. But don't organize the manual as a list |
| 3343 | of features. Instead, organize it logically, by subtopics. Address |
| 3344 | the questions that a user will ask when thinking about the job that |
| 3345 | the program does. Don't just tell the reader what each feature can |
| 3346 | do---say what jobs it is good for, and show how to use it for those |
| 3347 | jobs. Explain what is recommended usage, and what kinds of usage |
| 3348 | users should avoid. |
| 3349 | |
| 3350 | In general, a GNU manual should serve both as tutorial and reference. |
| 3351 | It should be set up for convenient access to each topic through Info, |
| 3352 | and for reading straight through (appendixes aside). A GNU manual |
| 3353 | should give a good introduction to a beginner reading through from the |
| 3354 | start, and should also provide all the details that hackers want. |
| 3355 | The Bison manual is a good example of this---please take a look at it |
| 3356 | to see what we mean. |
| 3357 | |
| 3358 | That is not as hard as it first sounds. Arrange each chapter as a |
| 3359 | logical breakdown of its topic, but order the sections, and write their |
| 3360 | text, so that reading the chapter straight through makes sense. Do |
| 3361 | likewise when structuring the book into chapters, and when structuring a |
| 3362 | section into paragraphs. The watchword is, @emph{at each point, address |
| 3363 | the most fundamental and important issue raised by the preceding text.} |
| 3364 | |
| 3365 | If necessary, add extra chapters at the beginning of the manual which |
| 3366 | are purely tutorial and cover the basics of the subject. These provide |
| 3367 | the framework for a beginner to understand the rest of the manual. The |
| 3368 | Bison manual provides a good example of how to do this. |
| 3369 | |
| 3370 | To serve as a reference, a manual should have an Index that list all the |
| 3371 | functions, variables, options, and important concepts that are part of |
| 3372 | the program. One combined Index should do for a short manual, but |
| 3373 | sometimes for a complex package it is better to use multiple indices. |
| 3374 | The Texinfo manual includes advice on preparing good index entries, see |
| 3375 | @ref{Index Entries, , Making Index Entries, texinfo, GNU Texinfo}, and |
| 3376 | see @ref{Indexing Commands, , Defining the Entries of an |
| 3377 | Index, texinfo, GNU Texinfo}. |
| 3378 | |
| 3379 | Don't use Unix man pages as a model for how to write GNU documentation; |
| 3380 | most of them are terse, badly structured, and give inadequate |
| 3381 | explanation of the underlying concepts. (There are, of course, some |
| 3382 | exceptions.) Also, Unix man pages use a particular format which is |
| 3383 | different from what we use in GNU manuals. |
| 3384 | |
| 3385 | Please include an email address in the manual for where to report |
| 3386 | bugs @emph{in the text of the manual}. |
| 3387 | |
| 3388 | Please do not use the term ``pathname'' that is used in Unix |
| 3389 | documentation; use ``file name'' (two words) instead. We use the term |
| 3390 | ``path'' only for search paths, which are lists of directory names. |
| 3391 | |
| 3392 | Please do not use the term ``illegal'' to refer to erroneous input to |
| 3393 | a computer program. Please use ``invalid'' for this, and reserve the |
| 3394 | term ``illegal'' for activities prohibited by law. |
| 3395 | |
| 3396 | Please do not write @samp{()} after a function name just to indicate |
| 3397 | it is a function. @code{foo ()} is not a function, it is a function |
| 3398 | call with no arguments. |
| 3399 | |
| 3400 | @node Doc Strings and Manuals |
| 3401 | @section Doc Strings and Manuals |
| 3402 | |
| 3403 | Some programming systems, such as Emacs, provide a documentation string |
| 3404 | for each function, command or variable. You may be tempted to write a |
| 3405 | reference manual by compiling the documentation strings and writing a |
| 3406 | little additional text to go around them---but you must not do it. That |
| 3407 | approach is a fundamental mistake. The text of well-written |
| 3408 | documentation strings will be entirely wrong for a manual. |
| 3409 | |
| 3410 | A documentation string needs to stand alone---when it appears on the |
| 3411 | screen, there will be no other text to introduce or explain it. |
| 3412 | Meanwhile, it can be rather informal in style. |
| 3413 | |
| 3414 | The text describing a function or variable in a manual must not stand |
| 3415 | alone; it appears in the context of a section or subsection. Other text |
| 3416 | at the beginning of the section should explain some of the concepts, and |
| 3417 | should often make some general points that apply to several functions or |
| 3418 | variables. The previous descriptions of functions and variables in the |
| 3419 | section will also have given information about the topic. A description |
| 3420 | written to stand alone would repeat some of that information; this |
| 3421 | redundancy looks bad. Meanwhile, the informality that is acceptable in |
| 3422 | a documentation string is totally unacceptable in a manual. |
| 3423 | |
| 3424 | The only good way to use documentation strings in writing a good manual |
| 3425 | is to use them as a source of information for writing good text. |
| 3426 | |
| 3427 | @node Manual Structure Details |
| 3428 | @section Manual Structure Details |
| 3429 | @cindex manual structure |
| 3430 | |
| 3431 | The title page of the manual should state the version of the programs or |
| 3432 | packages documented in the manual. The Top node of the manual should |
| 3433 | also contain this information. If the manual is changing more |
| 3434 | frequently than or independent of the program, also state a version |
| 3435 | number for the manual in both of these places. |
| 3436 | |
| 3437 | Each program documented in the manual should have a node named |
| 3438 | @samp{@var{program} Invocation} or @samp{Invoking @var{program}}. This |
| 3439 | node (together with its subnodes, if any) should describe the program's |
| 3440 | command line arguments and how to run it (the sort of information people |
| 3441 | would look for in a man page). Start with an @samp{@@example} |
| 3442 | containing a template for all the options and arguments that the program |
| 3443 | uses. |
| 3444 | |
| 3445 | Alternatively, put a menu item in some menu whose item name fits one of |
| 3446 | the above patterns. This identifies the node which that item points to |
| 3447 | as the node for this purpose, regardless of the node's actual name. |
| 3448 | |
| 3449 | The @samp{--usage} feature of the Info reader looks for such a node |
| 3450 | or menu item in order to find the relevant text, so it is essential |
| 3451 | for every Texinfo file to have one. |
| 3452 | |
| 3453 | If one manual describes several programs, it should have such a node for |
| 3454 | each program described in the manual. |
| 3455 | |
| 3456 | @node License for Manuals |
| 3457 | @section License for Manuals |
| 3458 | @cindex license for manuals |
| 3459 | |
| 3460 | Please use the GNU Free Documentation License for all GNU manuals that |
| 3461 | are more than a few pages long. Likewise for a collection of short |
| 3462 | documents---you only need one copy of the GNU FDL for the whole |
| 3463 | collection. For a single short document, you can use a very permissive |
| 3464 | non-copyleft license, to avoid taking up space with a long license. |
| 3465 | |
| 3466 | See @uref{http://www.gnu.org/copyleft/fdl-howto.html} for more explanation |
| 3467 | of how to employ the GFDL. |
| 3468 | |
| 3469 | Note that it is not obligatory to include a copy of the GNU GPL or GNU |
| 3470 | LGPL in a manual whose license is neither the GPL nor the LGPL. It can |
| 3471 | be a good idea to include the program's license in a large manual; in a |
| 3472 | short manual, whose size would be increased considerably by including |
| 3473 | the program's license, it is probably better not to include it. |
| 3474 | |
| 3475 | @node Manual Credits |
| 3476 | @section Manual Credits |
| 3477 | @cindex credits for manuals |
| 3478 | |
| 3479 | Please credit the principal human writers of the manual as the authors, |
| 3480 | on the title page of the manual. If a company sponsored the work, thank |
| 3481 | the company in a suitable place in the manual, but do not cite the |
| 3482 | company as an author. |
| 3483 | |
| 3484 | @node Printed Manuals |
| 3485 | @section Printed Manuals |
| 3486 | |
| 3487 | The FSF publishes some GNU manuals in printed form. To encourage sales |
| 3488 | of these manuals, the on-line versions of the manual should mention at |
| 3489 | the very start that the printed manual is available and should point at |
| 3490 | information for getting it---for instance, with a link to the page |
| 3491 | @url{http://www.gnu.org/order/order.html}. This should not be included |
| 3492 | in the printed manual, though, because there it is redundant. |
| 3493 | |
| 3494 | It is also useful to explain in the on-line forms of the manual how the |
| 3495 | user can print out the manual from the sources. |
| 3496 | |
| 3497 | @node NEWS File |
| 3498 | @section The NEWS File |
| 3499 | @cindex @file{NEWS} file |
| 3500 | |
| 3501 | In addition to its manual, the package should have a file named |
| 3502 | @file{NEWS} which contains a list of user-visible changes worth |
| 3503 | mentioning. In each new release, add items to the front of the file and |
| 3504 | identify the version they pertain to. Don't discard old items; leave |
| 3505 | them in the file after the newer items. This way, a user upgrading from |
| 3506 | any previous version can see what is new. |
| 3507 | |
| 3508 | If the @file{NEWS} file gets very long, move some of the older items |
| 3509 | into a file named @file{ONEWS} and put a note at the end referring the |
| 3510 | user to that file. |
| 3511 | |
| 3512 | @node Change Logs |
| 3513 | @section Change Logs |
| 3514 | @cindex change logs |
| 3515 | |
| 3516 | Keep a change log to describe all the changes made to program source |
| 3517 | files. The purpose of this is so that people investigating bugs in the |
| 3518 | future will know about the changes that might have introduced the bug. |
| 3519 | Often a new bug can be found by looking at what was recently changed. |
| 3520 | More importantly, change logs can help you eliminate conceptual |
| 3521 | inconsistencies between different parts of a program, by giving you a |
| 3522 | history of how the conflicting concepts arose and who they came from. |
| 3523 | |
| 3524 | @menu |
| 3525 | * Change Log Concepts:: |
| 3526 | * Style of Change Logs:: |
| 3527 | * Simple Changes:: |
| 3528 | * Conditional Changes:: |
| 3529 | * Indicating the Part Changed:: |
| 3530 | @end menu |
| 3531 | |
| 3532 | @node Change Log Concepts |
| 3533 | @subsection Change Log Concepts |
| 3534 | |
| 3535 | You can think of the change log as a conceptual ``undo list'' which |
| 3536 | explains how earlier versions were different from the current version. |
| 3537 | People can see the current version; they don't need the change log |
| 3538 | to tell them what is in it. What they want from a change log is a |
| 3539 | clear explanation of how the earlier version differed. |
| 3540 | |
| 3541 | The change log file is normally called @file{ChangeLog} and covers an |
| 3542 | entire directory. Each directory can have its own change log, or a |
| 3543 | directory can use the change log of its parent directory---it's up to |
| 3544 | you. |
| 3545 | |
| 3546 | Another alternative is to record change log information with a version |
| 3547 | control system such as RCS or CVS. This can be converted automatically |
| 3548 | to a @file{ChangeLog} file using @code{rcs2log}; in Emacs, the command |
| 3549 | @kbd{C-x v a} (@code{vc-update-change-log}) does the job. |
| 3550 | |
| 3551 | There's no need to describe the full purpose of the changes or how |
| 3552 | they work together. However, sometimes it is useful to write one line |
| 3553 | to describe the overall purpose of a change or a batch of changes. If |
| 3554 | you think that a change calls for explanation, you're probably right. |
| 3555 | Please do explain it---but please put the full explanation in comments |
| 3556 | in the code, where people will see it whenever they see the code. For |
| 3557 | example, ``New function'' is enough for the change log when you add a |
| 3558 | function, because there should be a comment before the function |
| 3559 | definition to explain what it does. |
| 3560 | |
| 3561 | In the past, we recommended not mentioning changes in non-software |
| 3562 | files (manuals, help files, etc.) in change logs. However, we've been |
| 3563 | advised that it is a good idea to include them, for the sake of |
| 3564 | copyright records. |
| 3565 | |
| 3566 | The easiest way to add an entry to @file{ChangeLog} is with the Emacs |
| 3567 | command @kbd{M-x add-change-log-entry}. An entry should have an |
| 3568 | asterisk, the name of the changed file, and then in parentheses the name |
| 3569 | of the changed functions, variables or whatever, followed by a colon. |
| 3570 | Then describe the changes you made to that function or variable. |
| 3571 | |
| 3572 | @node Style of Change Logs |
| 3573 | @subsection Style of Change Logs |
| 3574 | @cindex change logs, style |
| 3575 | |
| 3576 | Here are some simple examples of change log entries, starting with the |
| 3577 | header line that says who made the change and when it was installed, |
| 3578 | followed by descriptions of specific changes. (These examples are |
| 3579 | drawn from Emacs and GCC.) |
| 3580 | |
| 3581 | @example |
| 3582 | 1998-08-17 Richard Stallman <rms@@gnu.org> |
| 3583 | |
| 3584 | * register.el (insert-register): Return nil. |
| 3585 | (jump-to-register): Likewise. |
| 3586 | |
| 3587 | * sort.el (sort-subr): Return nil. |
| 3588 | |
| 3589 | * tex-mode.el (tex-bibtex-file, tex-file, tex-region): |
| 3590 | Restart the tex shell if process is gone or stopped. |
| 3591 | (tex-shell-running): New function. |
| 3592 | |
| 3593 | * expr.c (store_one_arg): Round size up for move_block_to_reg. |
| 3594 | (expand_call): Round up when emitting USE insns. |
| 3595 | * stmt.c (assign_parms): Round size up for move_block_from_reg. |
| 3596 | @end example |
| 3597 | |
| 3598 | It's important to name the changed function or variable in full. Don't |
| 3599 | abbreviate function or variable names, and don't combine them. |
| 3600 | Subsequent maintainers will often search for a function name to find all |
| 3601 | the change log entries that pertain to it; if you abbreviate the name, |
| 3602 | they won't find it when they search. |
| 3603 | |
| 3604 | For example, some people are tempted to abbreviate groups of function |
| 3605 | names by writing @samp{* register.el (@{insert,jump-to@}-register)}; |
| 3606 | this is not a good idea, since searching for @code{jump-to-register} or |
| 3607 | @code{insert-register} would not find that entry. |
| 3608 | |
| 3609 | Separate unrelated change log entries with blank lines. When two |
| 3610 | entries represent parts of the same change, so that they work together, |
| 3611 | then don't put blank lines between them. Then you can omit the file |
| 3612 | name and the asterisk when successive entries are in the same file. |
| 3613 | |
| 3614 | Break long lists of function names by closing continued lines with |
| 3615 | @samp{)}, rather than @samp{,}, and opening the continuation with |
| 3616 | @samp{(} as in this example: |
| 3617 | |
| 3618 | @example |
| 3619 | * keyboard.c (menu_bar_items, tool_bar_items) |
| 3620 | (Fexecute_extended_command): Deal with `keymap' property. |
| 3621 | @end example |
| 3622 | |
| 3623 | When you install someone else's changes, put the contributor's name in |
| 3624 | the change log entry rather than in the text of the entry. In other |
| 3625 | words, write this: |
| 3626 | |
| 3627 | @example |
| 3628 | 2002-07-14 John Doe <jdoe@@gnu.org> |
| 3629 | |
| 3630 | * sewing.c: Make it sew. |
| 3631 | @end example |
| 3632 | |
| 3633 | @noindent |
| 3634 | rather than this: |
| 3635 | |
| 3636 | @example |
| 3637 | 2002-07-14 Usual Maintainer <usual@@gnu.org> |
| 3638 | |
| 3639 | * sewing.c: Make it sew. Patch by jdoe@@gnu.org. |
| 3640 | @end example |
| 3641 | |
| 3642 | As for the date, that should be the date you applied the change. |
| 3643 | |
| 3644 | @node Simple Changes |
| 3645 | @subsection Simple Changes |
| 3646 | |
| 3647 | Certain simple kinds of changes don't need much detail in the change |
| 3648 | log. |
| 3649 | |
| 3650 | When you change the calling sequence of a function in a simple fashion, |
| 3651 | and you change all the callers of the function to use the new calling |
| 3652 | sequence, there is no need to make individual entries for all the |
| 3653 | callers that you changed. Just write in the entry for the function |
| 3654 | being called, ``All callers changed''---like this: |
| 3655 | |
| 3656 | @example |
| 3657 | * keyboard.c (Fcommand_execute): New arg SPECIAL. |
| 3658 | All callers changed. |
| 3659 | @end example |
| 3660 | |
| 3661 | When you change just comments or doc strings, it is enough to write an |
| 3662 | entry for the file, without mentioning the functions. Just ``Doc |
| 3663 | fixes'' is enough for the change log. |
| 3664 | |
| 3665 | There's no technical need to make change log entries for documentation |
| 3666 | files. This is because documentation is not susceptible to bugs that |
| 3667 | are hard to fix. Documentation does not consist of parts that must |
| 3668 | interact in a precisely engineered fashion. To correct an error, you |
| 3669 | need not know the history of the erroneous passage; it is enough to |
| 3670 | compare what the documentation says with the way the program actually |
| 3671 | works. |
| 3672 | |
| 3673 | However, you should keep change logs for documentation files when the |
| 3674 | project gets copyright assignments from its contributors, so as to |
| 3675 | make the records of authorship more accurate. |
| 3676 | |
| 3677 | @node Conditional Changes |
| 3678 | @subsection Conditional Changes |
| 3679 | @cindex conditional changes, and change logs |
| 3680 | @cindex change logs, conditional changes |
| 3681 | |
| 3682 | C programs often contain compile-time @code{#if} conditionals. Many |
| 3683 | changes are conditional; sometimes you add a new definition which is |
| 3684 | entirely contained in a conditional. It is very useful to indicate in |
| 3685 | the change log the conditions for which the change applies. |
| 3686 | |
| 3687 | Our convention for indicating conditional changes is to use square |
| 3688 | brackets around the name of the condition. |
| 3689 | |
| 3690 | Here is a simple example, describing a change which is conditional but |
| 3691 | does not have a function or entity name associated with it: |
| 3692 | |
| 3693 | @example |
| 3694 | * xterm.c [SOLARIS2]: Include string.h. |
| 3695 | @end example |
| 3696 | |
| 3697 | Here is an entry describing a new definition which is entirely |
| 3698 | conditional. This new definition for the macro @code{FRAME_WINDOW_P} is |
| 3699 | used only when @code{HAVE_X_WINDOWS} is defined: |
| 3700 | |
| 3701 | @example |
| 3702 | * frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined. |
| 3703 | @end example |
| 3704 | |
| 3705 | Here is an entry for a change within the function @code{init_display}, |
| 3706 | whose definition as a whole is unconditional, but the changes themselves |
| 3707 | are contained in a @samp{#ifdef HAVE_LIBNCURSES} conditional: |
| 3708 | |
| 3709 | @example |
| 3710 | * dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent. |
| 3711 | @end example |
| 3712 | |
| 3713 | Here is an entry for a change that takes affect only when |
| 3714 | a certain macro is @emph{not} defined: |
| 3715 | |
| 3716 | @example |
| 3717 | (gethostname) [!HAVE_SOCKETS]: Replace with winsock version. |
| 3718 | @end example |
| 3719 | |
| 3720 | @node Indicating the Part Changed |
| 3721 | @subsection Indicating the Part Changed |
| 3722 | |
| 3723 | Indicate the part of a function which changed by using angle brackets |
| 3724 | enclosing an indication of what the changed part does. Here is an entry |
| 3725 | for a change in the part of the function @code{sh-while-getopts} that |
| 3726 | deals with @code{sh} commands: |
| 3727 | |
| 3728 | @example |
| 3729 | * progmodes/sh-script.el (sh-while-getopts) <sh>: Handle case that |
| 3730 | user-specified option string is empty. |
| 3731 | @end example |
| 3732 | |
| 3733 | |
| 3734 | @node Man Pages |
| 3735 | @section Man Pages |
| 3736 | @cindex man pages |
| 3737 | |
| 3738 | In the GNU project, man pages are secondary. It is not necessary or |
| 3739 | expected for every GNU program to have a man page, but some of them do. |
| 3740 | It's your choice whether to include a man page in your program. |
| 3741 | |
| 3742 | When you make this decision, consider that supporting a man page |
| 3743 | requires continual effort each time the program is changed. The time |
| 3744 | you spend on the man page is time taken away from more useful work. |
| 3745 | |
| 3746 | For a simple program which changes little, updating the man page may be |
| 3747 | a small job. Then there is little reason not to include a man page, if |
| 3748 | you have one. |
| 3749 | |
| 3750 | For a large program that changes a great deal, updating a man page may |
| 3751 | be a substantial burden. If a user offers to donate a man page, you may |
| 3752 | find this gift costly to accept. It may be better to refuse the man |
| 3753 | page unless the same person agrees to take full responsibility for |
| 3754 | maintaining it---so that you can wash your hands of it entirely. If |
| 3755 | this volunteer later ceases to do the job, then don't feel obliged to |
| 3756 | pick it up yourself; it may be better to withdraw the man page from the |
| 3757 | distribution until someone else agrees to update it. |
| 3758 | |
| 3759 | When a program changes only a little, you may feel that the |
| 3760 | discrepancies are small enough that the man page remains useful without |
| 3761 | updating. If so, put a prominent note near the beginning of the man |
| 3762 | page explaining that you don't maintain it and that the Texinfo manual |
| 3763 | is more authoritative. The note should say how to access the Texinfo |
| 3764 | documentation. |
| 3765 | |
| 3766 | Be sure that man pages include a copyright statement and free license. |
| 3767 | The simple all-permissive license is appropriate for simple man pages |
| 3768 | (@pxref{License Notices for Other Files,,,maintain,Information for GNU |
| 3769 | Maintainers}). |
| 3770 | |
| 3771 | For long man pages, with enough explanation and documentation that |
| 3772 | they can be considered true manuals, use the GFDL (@pxref{License for |
| 3773 | Manuals}). |
| 3774 | |
| 3775 | Finally, the GNU help2man program |
| 3776 | (@uref{http://www.gnu.org/software/help2man/}) is one way to automate |
| 3777 | generation of a man page, in this case from @option{--help} output. |
| 3778 | This is sufficient in many cases. |
| 3779 | |
| 3780 | @node Reading other Manuals |
| 3781 | @section Reading other Manuals |
| 3782 | |
| 3783 | There may be non-free books or documentation files that describe the |
| 3784 | program you are documenting. |
| 3785 | |
| 3786 | It is ok to use these documents for reference, just as the author of a |
| 3787 | new algebra textbook can read other books on algebra. A large portion |
| 3788 | of any non-fiction book consists of facts, in this case facts about how |
| 3789 | a certain program works, and these facts are necessarily the same for |
| 3790 | everyone who writes about the subject. But be careful not to copy your |
| 3791 | outline structure, wording, tables or examples from preexisting non-free |
| 3792 | documentation. Copying from free documentation may be ok; please check |
| 3793 | with the FSF about the individual case. |
| 3794 | |
| 3795 | @node Managing Releases |
| 3796 | @chapter The Release Process |
| 3797 | @cindex releasing |
| 3798 | |
| 3799 | Making a release is more than just bundling up your source files in a |
| 3800 | tar file and putting it up for FTP. You should set up your software so |
| 3801 | that it can be configured to run on a variety of systems. Your Makefile |
| 3802 | should conform to the GNU standards described below, and your directory |
| 3803 | layout should also conform to the standards discussed below. Doing so |
| 3804 | makes it easy to include your package into the larger framework of |
| 3805 | all GNU software. |
| 3806 | |
| 3807 | @menu |
| 3808 | * Configuration:: How configuration of GNU packages should work. |
| 3809 | * Makefile Conventions:: Makefile conventions. |
| 3810 | * Releases:: Making releases |
| 3811 | @end menu |
| 3812 | |
| 3813 | @node Configuration |
| 3814 | @section How Configuration Should Work |
| 3815 | @cindex program configuration |
| 3816 | |
| 3817 | @pindex configure |
| 3818 | Each GNU distribution should come with a shell script named |
| 3819 | @code{configure}. This script is given arguments which describe the |
| 3820 | kind of machine and system you want to compile the program for. |
| 3821 | The @code{configure} script must record the configuration options so |
| 3822 | that they affect compilation. |
| 3823 | |
| 3824 | The description here is the specification of the interface for the |
| 3825 | @code{configure} script in GNU packages. Many packages implement it |
| 3826 | using GNU Autoconf (@pxref{Top,, Introduction, autoconf, Autoconf}) |
| 3827 | and/or GNU Automake (@pxref{Top,, Introduction, automake, Automake}), |
| 3828 | but you do not have to use these tools. You can implement it any way |
| 3829 | you like; for instance, by making @code{configure} be a wrapper around |
| 3830 | a completely different configuration system. |
| 3831 | |
| 3832 | Another way for the @code{configure} script to operate is to make a |
| 3833 | link from a standard name such as @file{config.h} to the proper |
| 3834 | configuration file for the chosen system. If you use this technique, |
| 3835 | the distribution should @emph{not} contain a file named |
| 3836 | @file{config.h}. This is so that people won't be able to build the |
| 3837 | program without configuring it first. |
| 3838 | |
| 3839 | Another thing that @code{configure} can do is to edit the Makefile. If |
| 3840 | you do this, the distribution should @emph{not} contain a file named |
| 3841 | @file{Makefile}. Instead, it should include a file @file{Makefile.in} which |
| 3842 | contains the input used for editing. Once again, this is so that people |
| 3843 | won't be able to build the program without configuring it first. |
| 3844 | |
| 3845 | If @code{configure} does write the @file{Makefile}, then @file{Makefile} |
| 3846 | should have a target named @file{Makefile} which causes @code{configure} |
| 3847 | to be rerun, setting up the same configuration that was set up last |
| 3848 | time. The files that @code{configure} reads should be listed as |
| 3849 | dependencies of @file{Makefile}. |
| 3850 | |
| 3851 | All the files which are output from the @code{configure} script should |
| 3852 | have comments at the beginning explaining that they were generated |
| 3853 | automatically using @code{configure}. This is so that users won't think |
| 3854 | of trying to edit them by hand. |
| 3855 | |
| 3856 | The @code{configure} script should write a file named @file{config.status} |
| 3857 | which describes which configuration options were specified when the |
| 3858 | program was last configured. This file should be a shell script which, |
| 3859 | if run, will recreate the same configuration. |
| 3860 | |
| 3861 | The @code{configure} script should accept an option of the form |
| 3862 | @samp{--srcdir=@var{dirname}} to specify the directory where sources are found |
| 3863 | (if it is not the current directory). This makes it possible to build |
| 3864 | the program in a separate directory, so that the actual source directory |
| 3865 | is not modified. |
| 3866 | |
| 3867 | If the user does not specify @samp{--srcdir}, then @code{configure} should |
| 3868 | check both @file{.} and @file{..} to see if it can find the sources. If |
| 3869 | it finds the sources in one of these places, it should use them from |
| 3870 | there. Otherwise, it should report that it cannot find the sources, and |
| 3871 | should exit with nonzero status. |
| 3872 | |
| 3873 | Usually the easy way to support @samp{--srcdir} is by editing a |
| 3874 | definition of @code{VPATH} into the Makefile. Some rules may need to |
| 3875 | refer explicitly to the specified source directory. To make this |
| 3876 | possible, @code{configure} can add to the Makefile a variable named |
| 3877 | @code{srcdir} whose value is precisely the specified directory. |
| 3878 | |
| 3879 | In addition, the @samp{configure} script should take options |
| 3880 | corresponding to most of the standard directory variables |
| 3881 | (@pxref{Directory Variables}). Here is the list: |
| 3882 | |
| 3883 | @example |
| 3884 | --prefix --exec-prefix --bindir --sbindir --libexecdir --sysconfdir |
| 3885 | --sharedstatedir --localstatedir --libdir --includedir --oldincludedir |
| 3886 | --datarootdir --datadir --infodir --localedir --mandir --docdir |
| 3887 | --htmldir --dvidir --pdfdir --psdir |
| 3888 | @end example |
| 3889 | |
| 3890 | The @code{configure} script should also take an argument which specifies the |
| 3891 | type of system to build the program for. This argument should look like |
| 3892 | this: |
| 3893 | |
| 3894 | @example |
| 3895 | @var{cpu}-@var{company}-@var{system} |
| 3896 | @end example |
| 3897 | |
| 3898 | For example, an Athlon-based GNU/Linux system might be |
| 3899 | @samp{i686-pc-linux-gnu}. |
| 3900 | |
| 3901 | The @code{configure} script needs to be able to decode all plausible |
| 3902 | alternatives for how to describe a machine. Thus, |
| 3903 | @samp{athlon-pc-gnu/linux} would be a valid alias. There is a shell |
| 3904 | script called |
| 3905 | @uref{http://git.savannah.gnu.org/@/gitweb/@/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD, |
| 3906 | @file{config.sub}} that you can use as a subroutine to validate system |
| 3907 | types and canonicalize aliases. |
| 3908 | |
| 3909 | The @code{configure} script should also take the option |
| 3910 | @option{--build=@var{buildtype}}, which should be equivalent to a |
| 3911 | plain @var{buildtype} argument. For example, @samp{configure |
| 3912 | --build=i686-pc-linux-gnu} is equivalent to @samp{configure |
| 3913 | i686-pc-linux-gnu}. When the build type is not specified by an option |
| 3914 | or argument, the @code{configure} script should normally guess it using |
| 3915 | the shell script |
| 3916 | @uref{http://git.savannah.gnu.org/@/gitweb/@/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD, |
| 3917 | @file{config.guess}}. |
| 3918 | |
| 3919 | @cindex optional features, configure-time |
| 3920 | Other options are permitted to specify in more detail the software |
| 3921 | or hardware present on the machine, to include or exclude optional parts |
| 3922 | of the package, or to adjust the name of some tools or arguments to them: |
| 3923 | |
| 3924 | @table @samp |
| 3925 | @item --enable-@var{feature}@r{[}=@var{parameter}@r{]} |
| 3926 | Configure the package to build and install an optional user-level |
| 3927 | facility called @var{feature}. This allows users to choose which |
| 3928 | optional features to include. Giving an optional @var{parameter} of |
| 3929 | @samp{no} should omit @var{feature}, if it is built by default. |
| 3930 | |
| 3931 | No @samp{--enable} option should @strong{ever} cause one feature to |
| 3932 | replace another. No @samp{--enable} option should ever substitute one |
| 3933 | useful behavior for another useful behavior. The only proper use for |
| 3934 | @samp{--enable} is for questions of whether to build part of the program |
| 3935 | or exclude it. |
| 3936 | |
| 3937 | @item --with-@var{package} |
| 3938 | @c @r{[}=@var{parameter}@r{]} |
| 3939 | The package @var{package} will be installed, so configure this package |
| 3940 | to work with @var{package}. |
| 3941 | |
| 3942 | @c Giving an optional @var{parameter} of |
| 3943 | @c @samp{no} should omit @var{package}, if it is used by default. |
| 3944 | |
| 3945 | Possible values of @var{package} include |
| 3946 | @samp{gnu-as} (or @samp{gas}), @samp{gnu-ld}, @samp{gnu-libc}, |
| 3947 | @samp{gdb}, |
| 3948 | @samp{x}, |
| 3949 | and |
| 3950 | @samp{x-toolkit}. |
| 3951 | |
| 3952 | Do not use a @samp{--with} option to specify the file name to use to |
| 3953 | find certain files. That is outside the scope of what @samp{--with} |
| 3954 | options are for. |
| 3955 | |
| 3956 | @item @var{variable}=@var{value} |
| 3957 | Set the value of the variable @var{variable} to @var{value}. This is |
| 3958 | used to override the default values of commands or arguments in the |
| 3959 | build process. For example, the user could issue @samp{configure |
| 3960 | CFLAGS=-g CXXFLAGS=-g} to build with debugging information and without |
| 3961 | the default optimization. |
| 3962 | |
| 3963 | Specifying variables as arguments to @code{configure}, like this: |
| 3964 | @example |
| 3965 | ./configure CC=gcc |
| 3966 | @end example |
| 3967 | is preferable to setting them in environment variables: |
| 3968 | @example |
| 3969 | CC=gcc ./configure |
| 3970 | @end example |
| 3971 | as it helps to recreate the same configuration later with |
| 3972 | @file{config.status}. However, both methods should be supported. |
| 3973 | @end table |
| 3974 | |
| 3975 | All @code{configure} scripts should accept all of the ``detail'' |
| 3976 | options and the variable settings, whether or not they make any |
| 3977 | difference to the particular package at hand. In particular, they |
| 3978 | should accept any option that starts with @samp{--with-} or |
| 3979 | @samp{--enable-}. This is so users will be able to configure an |
| 3980 | entire GNU source tree at once with a single set of options. |
| 3981 | |
| 3982 | You will note that the categories @samp{--with-} and @samp{--enable-} |
| 3983 | are narrow: they @strong{do not} provide a place for any sort of option |
| 3984 | you might think of. That is deliberate. We want to limit the possible |
| 3985 | configuration options in GNU software. We do not want GNU programs to |
| 3986 | have idiosyncratic configuration options. |
| 3987 | |
| 3988 | Packages that perform part of the compilation process may support |
| 3989 | cross-compilation. In such a case, the host and target machines for the |
| 3990 | program may be different. |
| 3991 | |
| 3992 | The @code{configure} script should normally treat the specified type of |
| 3993 | system as both the host and the target, thus producing a program which |
| 3994 | works for the same type of machine that it runs on. |
| 3995 | |
| 3996 | To compile a program to run on a host type that differs from the build |
| 3997 | type, use the configure option @option{--host=@var{hosttype}}, where |
| 3998 | @var{hosttype} uses the same syntax as @var{buildtype}. The host type |
| 3999 | normally defaults to the build type. |
| 4000 | |
| 4001 | To configure a cross-compiler, cross-assembler, or what have you, you |
| 4002 | should specify a target different from the host, using the configure |
| 4003 | option @samp{--target=@var{targettype}}. The syntax for |
| 4004 | @var{targettype} is the same as for the host type. So the command would |
| 4005 | look like this: |
| 4006 | |
| 4007 | @example |
| 4008 | ./configure --host=@var{hosttype} --target=@var{targettype} |
| 4009 | @end example |
| 4010 | |
| 4011 | The target type normally defaults to the host type. |
| 4012 | Programs for which cross-operation is not meaningful need not accept the |
| 4013 | @samp{--target} option, because configuring an entire operating system for |
| 4014 | cross-operation is not a meaningful operation. |
| 4015 | |
| 4016 | Some programs have ways of configuring themselves automatically. If |
| 4017 | your program is set up to do this, your @code{configure} script can simply |
| 4018 | ignore most of its arguments. |
| 4019 | |
| 4020 | @comment The makefile standards are in a separate file that is also |
| 4021 | @comment included by make.texinfo. Done by roland@gnu.ai.mit.edu on 1/6/93. |
| 4022 | @comment For this document, turn chapters into sections, etc. |
| 4023 | @lowersections |
| 4024 | @include make-stds.texi |
| 4025 | @raisesections |
| 4026 | |
| 4027 | @node Releases |
| 4028 | @section Making Releases |
| 4029 | @cindex packaging |
| 4030 | |
| 4031 | You should identify each release with a pair of version numbers, a |
| 4032 | major version and a minor. We have no objection to using more than |
| 4033 | two numbers, but it is very unlikely that you really need them. |
| 4034 | |
| 4035 | Package the distribution of @code{Foo version 69.96} up in a gzipped tar |
| 4036 | file with the name @file{foo-69.96.tar.gz}. It should unpack into a |
| 4037 | subdirectory named @file{foo-69.96}. |
| 4038 | |
| 4039 | Building and installing the program should never modify any of the files |
| 4040 | contained in the distribution. This means that all the files that form |
| 4041 | part of the program in any way must be classified into @dfn{source |
| 4042 | files} and @dfn{non-source files}. Source files are written by humans |
| 4043 | and never changed automatically; non-source files are produced from |
| 4044 | source files by programs under the control of the Makefile. |
| 4045 | |
| 4046 | @cindex @file{README} file |
| 4047 | The distribution should contain a file named @file{README} which gives |
| 4048 | the name of the package, and a general description of what it does. It |
| 4049 | is also good to explain the purpose of each of the first-level |
| 4050 | subdirectories in the package, if there are any. The @file{README} file |
| 4051 | should either state the version number of the package, or refer to where |
| 4052 | in the package it can be found. |
| 4053 | |
| 4054 | The @file{README} file should refer to the file @file{INSTALL}, which |
| 4055 | should contain an explanation of the installation procedure. |
| 4056 | |
| 4057 | The @file{README} file should also refer to the file which contains the |
| 4058 | copying conditions. The GNU GPL, if used, should be in a file called |
| 4059 | @file{COPYING}. If the GNU LGPL is used, it should be in a file called |
| 4060 | @file{COPYING.LESSER}. |
| 4061 | |
| 4062 | Naturally, all the source files must be in the distribution. It is okay |
| 4063 | to include non-source files in the distribution, provided they are |
| 4064 | up-to-date and machine-independent, so that building the distribution |
| 4065 | normally will never modify them. We commonly include non-source files |
| 4066 | produced by Bison, @code{lex}, @TeX{}, and @code{makeinfo}; this helps avoid |
| 4067 | unnecessary dependencies between our distributions, so that users can |
| 4068 | install whichever packages they want to install. |
| 4069 | |
| 4070 | Non-source files that might actually be modified by building and |
| 4071 | installing the program should @strong{never} be included in the |
| 4072 | distribution. So if you do distribute non-source files, always make |
| 4073 | sure they are up to date when you make a new distribution. |
| 4074 | |
| 4075 | Make sure that all the files in the distribution are world-readable, and |
| 4076 | that directories are world-readable and world-searchable (octal mode 755). |
| 4077 | We used to recommend that all directories in the distribution also be |
| 4078 | world-writable (octal mode 777), because ancient versions of @code{tar} |
| 4079 | would otherwise not cope when extracting the archive as an unprivileged |
| 4080 | user. That can easily lead to security issues when creating the archive, |
| 4081 | however, so now we recommend against that. |
| 4082 | |
| 4083 | Don't include any symbolic links in the distribution itself. If the tar |
| 4084 | file contains symbolic links, then people cannot even unpack it on |
| 4085 | systems that don't support symbolic links. Also, don't use multiple |
| 4086 | names for one file in different directories, because certain file |
| 4087 | systems cannot handle this and that prevents unpacking the |
| 4088 | distribution. |
| 4089 | |
| 4090 | Try to make sure that all the file names will be unique on MS-DOS. A |
| 4091 | name on MS-DOS consists of up to 8 characters, optionally followed by a |
| 4092 | period and up to three characters. MS-DOS will truncate extra |
| 4093 | characters both before and after the period. Thus, |
| 4094 | @file{foobarhacker.c} and @file{foobarhacker.o} are not ambiguous; they |
| 4095 | are truncated to @file{foobarha.c} and @file{foobarha.o}, which are |
| 4096 | distinct. |
| 4097 | |
| 4098 | @cindex @file{texinfo.tex}, in a distribution |
| 4099 | Include in your distribution a copy of the @file{texinfo.tex} you used |
| 4100 | to test print any @file{*.texinfo} or @file{*.texi} files. |
| 4101 | |
| 4102 | Likewise, if your program uses small GNU software packages like regex, |
| 4103 | getopt, obstack, or termcap, include them in the distribution file. |
| 4104 | Leaving them out would make the distribution file a little smaller at |
| 4105 | the expense of possible inconvenience to a user who doesn't know what |
| 4106 | other files to get. |
| 4107 | |
| 4108 | @node References |
| 4109 | @chapter References to Non-Free Software and Documentation |
| 4110 | @cindex references to non-free material |
| 4111 | |
| 4112 | A GNU program should not recommend, promote, or grant legitimacy to |
| 4113 | the use of any non-free program. Proprietary software is a social and |
| 4114 | ethical problem, and our aim is to put an end to that problem. We |
| 4115 | can't stop some people from writing proprietary programs, or stop |
| 4116 | other people from using them, but we can and should refuse to |
| 4117 | advertise them to new potential customers, or to give the public the |
| 4118 | idea that their existence is ethical. |
| 4119 | |
| 4120 | The GNU definition of free software is found on the GNU web site at |
| 4121 | @url{http://www.gnu.org/@/philosophy/@/free-sw.html}, and the definition |
| 4122 | of free documentation is found at |
| 4123 | @url{http://www.gnu.org/@/philosophy/@/free-doc.html}. The terms ``free'' |
| 4124 | and ``non-free'', used in this document, refer to those definitions. |
| 4125 | |
| 4126 | A list of important licenses and whether they qualify as free is in |
| 4127 | @url{http://www.gnu.org/@/licenses/@/license-list.html}. If it is not |
| 4128 | clear whether a license qualifies as free, please ask the GNU Project |
| 4129 | by writing to @email{licensing@@gnu.org}. We will answer, and if the |
| 4130 | license is an important one, we will add it to the list. |
| 4131 | |
| 4132 | When a non-free program or system is well known, you can mention it in |
| 4133 | passing---that is harmless, since users who might want to use it |
| 4134 | probably already know about it. For instance, it is fine to explain |
| 4135 | how to build your package on top of some widely used non-free |
| 4136 | operating system, or how to use it together with some widely used |
| 4137 | non-free program. |
| 4138 | |
| 4139 | However, you should give only the necessary information to help those |
| 4140 | who already use the non-free program to use your program with |
| 4141 | it---don't give, or refer to, any further information about the |
| 4142 | proprietary program, and don't imply that the proprietary program |
| 4143 | enhances your program, or that its existence is in any way a good |
| 4144 | thing. The goal should be that people already using the proprietary |
| 4145 | program will get the advice they need about how to use your free |
| 4146 | program with it, while people who don't already use the proprietary |
| 4147 | program will not see anything likely to lead them to take an interest |
| 4148 | in it. |
| 4149 | |
| 4150 | If a non-free program or system is obscure in your program's domain, |
| 4151 | your program should not mention or support it at all, since doing so |
| 4152 | would tend to popularize the non-free program more than it popularizes |
| 4153 | your program. (You cannot hope to find many additional users for your |
| 4154 | program among the users of Foobar, if the existence of Foobar is not |
| 4155 | generally known among people who might want to use your program.) |
| 4156 | |
| 4157 | Sometimes a program is free software in itself but depends on a |
| 4158 | non-free platform in order to run. For instance, many Java programs |
| 4159 | depend on some non-free Java libraries. To recommend or promote such |
| 4160 | a program is to promote the other programs it needs. This is why we |
| 4161 | are careful about listing Java programs in the Free Software |
| 4162 | Directory: we don't want to promote the non-free Java libraries. |
| 4163 | |
| 4164 | We hope this particular problem with Java will be gone by and by, as |
| 4165 | we replace the remaining non-free standard Java libraries with free |
| 4166 | software, but the general principle will remain the same: don't |
| 4167 | recommend, promote or legitimize programs that depend on non-free |
| 4168 | software to run. |
| 4169 | |
| 4170 | Some free programs strongly encourage the use of non-free software. A |
| 4171 | typical example is @command{mplayer}. It is free software in itself, |
| 4172 | and the free code can handle some kinds of files. However, |
| 4173 | @command{mplayer} recommends use of non-free codecs for other kinds of |
| 4174 | files, and users that install @command{mplayer} are very likely to |
| 4175 | install those codecs along with it. To recommend @command{mplayer} |
| 4176 | is, in effect, to promote use of the non-free codecs. |
| 4177 | |
| 4178 | Thus, you should not recommend programs that strongly encourage the |
| 4179 | use of non-free software. This is why we do not list |
| 4180 | @command{mplayer} in the Free Software Directory. |
| 4181 | |
| 4182 | A GNU package should not refer the user to any non-free documentation |
| 4183 | for free software. Free documentation that can be included in free |
| 4184 | operating systems is essential for completing the GNU system, or any |
| 4185 | free operating system, so encouraging it is a priority; to recommend |
| 4186 | use of documentation that we are not allowed to include undermines the |
| 4187 | impetus for the community to produce documentation that we can |
| 4188 | include. So GNU packages should never recommend non-free |
| 4189 | documentation. |
| 4190 | |
| 4191 | By contrast, it is ok to refer to journal articles and textbooks in |
| 4192 | the comments of a program for explanation of how it functions, even |
| 4193 | though they are non-free. This is because we don't include such |
| 4194 | things in the GNU system even they are free---they are outside the |
| 4195 | scope of what a software distribution needs to include. |
| 4196 | |
| 4197 | Referring to a web site that describes or recommends a non-free |
| 4198 | program is promoting that program, so please do not make links (or |
| 4199 | mention by name) web sites that contain such material. This policy is |
| 4200 | relevant particularly for the web pages for a GNU package. |
| 4201 | |
| 4202 | Following links from nearly any web site can lead eventually to |
| 4203 | non-free software; this is inherent in the nature of the web. So it |
| 4204 | makes no sense to criticize a site for having such links. As long as |
| 4205 | the site does not itself recommend a non-free program, there is no |
| 4206 | need to consider the question of the sites that it links to for other |
| 4207 | reasons. |
| 4208 | |
| 4209 | Thus, for example, you should not refer to AT&T's web site if that |
| 4210 | recommends AT&T's non-free software packages; you should not refer to |
| 4211 | a site that links to AT&T's site presenting it as a place to get some |
| 4212 | non-free program, because that link recommends and legitimizes the |
| 4213 | non-free program. However, that a site contains a link to AT&T's web |
| 4214 | site for some other purpose (such as long-distance telephone service) |
| 4215 | is not an objection against it. |
| 4216 | |
| 4217 | @node GNU Free Documentation License |
| 4218 | @appendix GNU Free Documentation License |
| 4219 | |
| 4220 | @cindex FDL, GNU Free Documentation License |
| 4221 | @include fdl.texi |
| 4222 | |
| 4223 | @node Index |
| 4224 | @unnumbered Index |
| 4225 | @printindex cp |
| 4226 | |
| 4227 | @bye |
| 4228 | |
| 4229 | Local variables: |
| 4230 | eval: (add-hook 'write-file-hooks 'time-stamp) |
| 4231 | time-stamp-start: "@set lastupdate " |
| 4232 | time-stamp-end: "$" |
| 4233 | time-stamp-format: "%:b %:d, %:y" |
| 4234 | compile-command: "cd work.s && make" |
| 4235 | End: |