| 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 February 14, 2002 |
| 7 | @c %**end of header |
| 8 | |
| 9 | @ifinfo |
| 10 | @format |
| 11 | START-INFO-DIR-ENTRY |
| 12 | * Standards: (standards). GNU coding standards. |
| 13 | END-INFO-DIR-ENTRY |
| 14 | @end format |
| 15 | @end ifinfo |
| 16 | |
| 17 | @c @setchapternewpage odd |
| 18 | @setchapternewpage off |
| 19 | |
| 20 | @c Put everything in one index (arbitrarily chosen to be the concept index). |
| 21 | @syncodeindex fn cp |
| 22 | @syncodeindex ky cp |
| 23 | @syncodeindex pg cp |
| 24 | @syncodeindex vr cp |
| 25 | |
| 26 | @c This is used by a cross ref in make-stds.texi |
| 27 | @set CODESTD 1 |
| 28 | @iftex |
| 29 | @set CHAPTER chapter |
| 30 | @end iftex |
| 31 | @ifinfo |
| 32 | @set CHAPTER node |
| 33 | @end ifinfo |
| 34 | |
| 35 | @ifinfo |
| 36 | GNU Coding Standards |
| 37 | Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc. |
| 38 | |
| 39 | Permission is granted to copy, distribute and/or modify this document |
| 40 | under the terms of the GNU Free Documentation License, Version 1.1 |
| 41 | or any later version published by the Free Software Foundation; |
| 42 | with no Invariant Sections, with no |
| 43 | Front-Cover Texts, and with no Back-Cover Texts. |
| 44 | A copy of the license is included in the section entitled ``GNU |
| 45 | Free Documentation License''. |
| 46 | @end ifinfo |
| 47 | |
| 48 | @titlepage |
| 49 | @title GNU Coding Standards |
| 50 | @author Richard Stallman, et al. |
| 51 | @author last updated @value{lastupdate} |
| 52 | @page |
| 53 | |
| 54 | @vskip 0pt plus 1filll |
| 55 | Copyright @copyright{} 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc. |
| 56 | |
| 57 | Permission is granted to copy, distribute and/or modify this document |
| 58 | under the terms of the GNU Free Documentation License, Version 1.1 |
| 59 | or any later version published by the Free Software Foundation; |
| 60 | with no Invariant Sections, with no |
| 61 | Front-Cover Texts, and with no Back-Cover Texts. |
| 62 | A copy of the license is included in the section entitled ``GNU |
| 63 | Free Documentation License''. |
| 64 | @end titlepage |
| 65 | |
| 66 | @ifinfo |
| 67 | @node Top, Preface, (dir), (dir) |
| 68 | @top Version |
| 69 | |
| 70 | Last updated @value{lastupdate}. |
| 71 | @end ifinfo |
| 72 | |
| 73 | @menu |
| 74 | * Preface:: About the GNU Coding Standards |
| 75 | * Legal Issues:: Keeping Free Software Free |
| 76 | * Design Advice:: General Program Design |
| 77 | * Program Behavior:: Program Behavior for All Programs |
| 78 | * Writing C:: Making The Best Use of C |
| 79 | * Documentation:: Documenting Programs |
| 80 | * Managing Releases:: The Release Process |
| 81 | * References:: References to Non-Free Software or Documentation |
| 82 | * Copying This Manual:: How to Make Copies of This Manual |
| 83 | * Index:: |
| 84 | |
| 85 | @end menu |
| 86 | |
| 87 | @node Preface |
| 88 | @chapter About the GNU Coding Standards |
| 89 | |
| 90 | The GNU Coding Standards were written by Richard Stallman and other GNU |
| 91 | Project volunteers. Their purpose is to make the GNU system clean, |
| 92 | consistent, and easy to install. This document can also be read as a |
| 93 | guide to writing portable, robust and reliable programs. It focuses on |
| 94 | programs written in C, but many of the rules and principles are useful |
| 95 | even if you write in another programming language. The rules often |
| 96 | state reasons for writing in a certain way. |
| 97 | |
| 98 | This release of the GNU Coding Standards was last updated |
| 99 | @value{lastupdate}. |
| 100 | |
| 101 | @cindex where to obtain @code{standards.texi} |
| 102 | @cindex downloading this manual |
| 103 | If you did not obtain this file directly from the GNU project and |
| 104 | recently, please check for a newer version. You can ftp the GNU |
| 105 | Coding Standards from any GNU FTP host in the directory |
| 106 | @file{/pub/gnu/standards/}. The GNU Coding Standards are available |
| 107 | there in several different formats: @file{standards.text}, |
| 108 | @file{standards.info}, and @file{standards.dvi}, as well as the |
| 109 | Texinfo ``source'' which is divided in two files: |
| 110 | @file{standards.texi} and @file{make-stds.texi}. The GNU Coding |
| 111 | Standards are also available on the GNU World Wide Web server: |
| 112 | @uref{http://www.gnu.org/prep/standards_toc.html}. |
| 113 | |
| 114 | Corrections or suggestions for this document should be sent to |
| 115 | @email{bug-standards@@gnu.org}. If you make a suggestion, please include a |
| 116 | suggested new wording for it; our time is limited. We prefer a context |
| 117 | diff to the @file{standards.texi} or @file{make-stds.texi} files, but if |
| 118 | you don't have those files, please mail your suggestion anyway. |
| 119 | |
| 120 | These standards cover the minimum of what is important when writing a |
| 121 | GNU package. Likely, the needs for additional standards will come up. |
| 122 | Sometimes, you might suggest that such standards be added to this |
| 123 | document. If you think your standards would be generally useful, please |
| 124 | do suggest them. |
| 125 | |
| 126 | You should also set standards for your package on many questions not |
| 127 | addressed or not firmly specified here. The most important point is to |
| 128 | be self-consistent---try to stick to the conventions you pick, and try |
| 129 | to document them as much as possible. That way, your program will be |
| 130 | more maintainable by others. |
| 131 | |
| 132 | @node Legal Issues |
| 133 | @chapter Keeping Free Software Free |
| 134 | @cindex legal aspects |
| 135 | |
| 136 | This @value{CHAPTER} discusses how you can make sure that GNU software |
| 137 | avoids legal difficulties, and other related issues. |
| 138 | |
| 139 | @menu |
| 140 | * Reading Non-Free Code:: Referring to Proprietary Programs |
| 141 | * Contributions:: Accepting Contributions |
| 142 | * Trademarks:: How We Deal with Trademark Issues |
| 143 | @end menu |
| 144 | |
| 145 | @node Reading Non-Free Code |
| 146 | @section Referring to Proprietary Programs |
| 147 | @cindex proprietary programs |
| 148 | @cindex avoiding proprietary code |
| 149 | |
| 150 | Don't in any circumstances refer to Unix source code for or during |
| 151 | your work on GNU! (Or to any other proprietary programs.) |
| 152 | |
| 153 | If you have a vague recollection of the internals of a Unix program, |
| 154 | this does not absolutely mean you can't write an imitation of it, but |
| 155 | do try to organize the imitation internally along different lines, |
| 156 | because this is likely to make the details of the Unix version |
| 157 | irrelevant and dissimilar to your results. |
| 158 | |
| 159 | For example, Unix utilities were generally optimized to minimize |
| 160 | memory use; if you go for speed instead, your program will be very |
| 161 | different. You could keep the entire input file in core and scan it |
| 162 | there instead of using stdio. Use a smarter algorithm discovered more |
| 163 | recently than the Unix program. Eliminate use of temporary files. Do |
| 164 | it in one pass instead of two (we did this in the assembler). |
| 165 | |
| 166 | Or, on the contrary, emphasize simplicity instead of speed. For some |
| 167 | applications, the speed of today's computers makes simpler algorithms |
| 168 | adequate. |
| 169 | |
| 170 | Or go for generality. For example, Unix programs often have static |
| 171 | tables or fixed-size strings, which make for arbitrary limits; use |
| 172 | dynamic allocation instead. Make sure your program handles NULs and |
| 173 | other funny characters in the input files. Add a programming language |
| 174 | for extensibility and write part of the program in that language. |
| 175 | |
| 176 | Or turn some parts of the program into independently usable libraries. |
| 177 | Or use a simple garbage collector instead of tracking precisely when |
| 178 | to free memory, or use a new GNU facility such as obstacks. |
| 179 | |
| 180 | @node Contributions |
| 181 | @section Accepting Contributions |
| 182 | @cindex legal papers |
| 183 | @cindex accepting contributions |
| 184 | |
| 185 | If the program you are working on is copyrighted by the Free Software |
| 186 | Foundation, then when someone else sends you a piece of code to add to |
| 187 | the program, we need legal papers to use it---just as we asked you to |
| 188 | sign papers initially. @emph{Each} person who makes a nontrivial |
| 189 | contribution to a program must sign some sort of legal papers in order |
| 190 | for us to have clear title to the program; the main author alone is not |
| 191 | enough. |
| 192 | |
| 193 | So, before adding in any contributions from other people, please tell |
| 194 | us, so we can arrange to get the papers. Then wait until we tell you |
| 195 | that we have received the signed papers, before you actually use the |
| 196 | contribution. |
| 197 | |
| 198 | This applies both before you release the program and afterward. If |
| 199 | you receive diffs to fix a bug, and they make significant changes, we |
| 200 | need legal papers for that change. |
| 201 | |
| 202 | This also applies to comments and documentation files. For copyright |
| 203 | law, comments and code are just text. Copyright applies to all kinds of |
| 204 | text, so we need legal papers for all kinds. |
| 205 | |
| 206 | We know it is frustrating to ask for legal papers; it's frustrating for |
| 207 | us as well. But if you don't wait, you are going out on a limb---for |
| 208 | example, what if the contributor's employer won't sign a disclaimer? |
| 209 | You might have to take that code out again! |
| 210 | |
| 211 | You don't need papers for changes of a few lines here or there, since |
| 212 | they are not significant for copyright purposes. Also, you don't need |
| 213 | papers if all you get from the suggestion is some ideas, not actual code |
| 214 | which you use. For example, if someone send you one implementation, but |
| 215 | you write a different implementation of the same idea, you don't need to |
| 216 | get papers. |
| 217 | |
| 218 | The very worst thing is if you forget to tell us about the other |
| 219 | contributor. We could be very embarrassed in court some day as a |
| 220 | result. |
| 221 | |
| 222 | We have more detailed advice for maintainers of programs; if you have |
| 223 | reached the stage of actually maintaining a program for GNU (whether |
| 224 | released or not), please ask us for a copy. |
| 225 | |
| 226 | @node Trademarks |
| 227 | @section Trademarks |
| 228 | @cindex trademarks |
| 229 | |
| 230 | Please do not include any trademark acknowledgements in GNU software |
| 231 | packages or documentation. |
| 232 | |
| 233 | Trademark acknowledgements are the statements that such-and-such is a |
| 234 | trademark of so-and-so. The GNU Project has no objection to the basic |
| 235 | idea of trademarks, but these acknowledgements feel like kowtowing, so |
| 236 | we don't use them. There is no legal requirement for them. |
| 237 | |
| 238 | What is legally required, as regards other people's trademarks, is to |
| 239 | avoid using them in ways which a reader might read as naming or labeling |
| 240 | our own programs or activities. For example, since ``Objective C'' is |
| 241 | (or at least was) a trademark, we made sure to say that we provide a |
| 242 | ``compiler for the Objective C language'' rather than an ``Objective C |
| 243 | compiler''. The latter is meant to be short for the former, but it does |
| 244 | not explicitly state the relationship, so it could be misinterpreted as |
| 245 | using ``Objective C'' as a label for the compiler rather than for the |
| 246 | language. |
| 247 | |
| 248 | @node Design Advice |
| 249 | @chapter General Program Design |
| 250 | @cindex program design |
| 251 | |
| 252 | This @value{CHAPTER} discusses some of the issues you should take into |
| 253 | account when designing your program. |
| 254 | |
| 255 | @c Standard or ANSI C |
| 256 | @c |
| 257 | @c In 1989 the American National Standards Institute (ANSI) standardized |
| 258 | @c C as standard X3.159-1989. In December of that year the |
| 259 | @c International Standards Organization ISO adopted the ANSI C standard |
| 260 | @c making minor changes. In 1990 ANSI then re-adopted ISO standard |
| 261 | @c C. This version of C is known as either ANSI C or Standard C. |
| 262 | |
| 263 | @c A major revision of the C Standard appeared in 1999. |
| 264 | |
| 265 | @menu |
| 266 | * Source Language:: Which languges to use. |
| 267 | * Compatibility:: Compatibility with other implementations |
| 268 | * Using Extensions:: Using non-standard features |
| 269 | * Standard C:: Using Standard C features |
| 270 | * Conditional Compilation:: Compiling Code Only If A Conditional is True |
| 271 | @end menu |
| 272 | |
| 273 | @node Source Language |
| 274 | @section Which Languages to Use |
| 275 | @cindex programming languges |
| 276 | |
| 277 | When you want to use a language that gets compiled and runs at high |
| 278 | speed, the best language to use is C. Using another language is like |
| 279 | using a non-standard feature: it will cause trouble for users. Even if |
| 280 | GCC supports the other language, users may find it inconvenient to have |
| 281 | to install the compiler for that other language in order to build your |
| 282 | program. For example, if you write your program in C++, people will |
| 283 | have to install the GNU C++ compiler in order to compile your program. |
| 284 | |
| 285 | C has one other advantage over C++ and other compiled languages: more |
| 286 | people know C, so more people will find it easy to read and modify the |
| 287 | program if it is written in C. |
| 288 | |
| 289 | So in general it is much better to use C, rather than the |
| 290 | comparable alternatives. |
| 291 | |
| 292 | But there are two exceptions to that conclusion: |
| 293 | |
| 294 | @itemize @bullet |
| 295 | @item |
| 296 | It is no problem to use another language to write a tool specifically |
| 297 | intended for use with that language. That is because the only people |
| 298 | who want to build the tool will be those who have installed the other |
| 299 | language anyway. |
| 300 | |
| 301 | @item |
| 302 | If an application is of interest only to a narrow part of the community, |
| 303 | then the question of which language it is written in has less effect on |
| 304 | other people, so you may as well please yourself. |
| 305 | @end itemize |
| 306 | |
| 307 | Many programs are designed to be extensible: they include an interpreter |
| 308 | for a language that is higher level than C. Often much of the program |
| 309 | is written in that language, too. The Emacs editor pioneered this |
| 310 | technique. |
| 311 | |
| 312 | @cindex GUILE |
| 313 | The standard extensibility interpreter for GNU software is GUILE, which |
| 314 | implements the language Scheme (an especially clean and simple dialect |
| 315 | of Lisp). @uref{http://www.gnu.org/software/guile/}. We don't reject |
| 316 | programs written in other ``scripting languages'' such as Perl and |
| 317 | Python, but using GUILE is very important for the overall consistency of |
| 318 | the GNU system. |
| 319 | |
| 320 | @node Compatibility |
| 321 | @section Compatibility with Other Implementations |
| 322 | @cindex compatibility with C and @sc{posix} standards |
| 323 | @cindex @sc{posix} compatibility |
| 324 | |
| 325 | With occasional exceptions, utility programs and libraries for GNU |
| 326 | should be upward compatible with those in Berkeley Unix, and upward |
| 327 | compatible with Standard C if Standard C specifies their |
| 328 | behavior, and upward compatible with @sc{posix} if @sc{posix} specifies |
| 329 | their behavior. |
| 330 | |
| 331 | When these standards conflict, it is useful to offer compatibility |
| 332 | modes for each of them. |
| 333 | |
| 334 | @cindex options for compatibility |
| 335 | Standard C and @sc{posix} prohibit many kinds of extensions. Feel |
| 336 | free to make the extensions anyway, and include a @samp{--ansi}, |
| 337 | @samp{--posix}, or @samp{--compatible} option to turn them off. |
| 338 | However, if the extension has a significant chance of breaking any real |
| 339 | programs or scripts, then it is not really upward compatible. So you |
| 340 | should try to redesign its interface to make it upward compatible. |
| 341 | |
| 342 | @cindex @code{POSIXLY_CORRECT}, environment variable |
| 343 | Many GNU programs suppress extensions that conflict with @sc{posix} if the |
| 344 | environment variable @code{POSIXLY_CORRECT} is defined (even if it is |
| 345 | defined with a null value). Please make your program recognize this |
| 346 | variable if appropriate. |
| 347 | |
| 348 | When a feature is used only by users (not by programs or command |
| 349 | files), and it is done poorly in Unix, feel free to replace it |
| 350 | completely with something totally different and better. (For example, |
| 351 | @code{vi} is replaced with Emacs.) But it is nice to offer a compatible |
| 352 | feature as well. (There is a free @code{vi} clone, so we offer it.) |
| 353 | |
| 354 | Additional useful features are welcome regardless of whether |
| 355 | there is any precedent for them. |
| 356 | |
| 357 | @node Using Extensions |
| 358 | @section Using Non-standard Features |
| 359 | @cindex non-standard extensions |
| 360 | |
| 361 | Many GNU facilities that already exist support a number of convenient |
| 362 | extensions over the comparable Unix facilities. Whether to use these |
| 363 | extensions in implementing your program is a difficult question. |
| 364 | |
| 365 | On the one hand, using the extensions can make a cleaner program. |
| 366 | On the other hand, people will not be able to build the program |
| 367 | unless the other GNU tools are available. This might cause the |
| 368 | program to work on fewer kinds of machines. |
| 369 | |
| 370 | With some extensions, it might be easy to provide both alternatives. |
| 371 | For example, you can define functions with a ``keyword'' @code{INLINE} |
| 372 | and define that as a macro to expand into either @code{inline} or |
| 373 | nothing, depending on the compiler. |
| 374 | |
| 375 | In general, perhaps it is best not to use the extensions if you can |
| 376 | straightforwardly do without them, but to use the extensions if they |
| 377 | are a big improvement. |
| 378 | |
| 379 | An exception to this rule are the large, established programs (such as |
| 380 | Emacs) which run on a great variety of systems. Using GNU extensions in |
| 381 | such programs would make many users unhappy, so we don't do that. |
| 382 | |
| 383 | Another exception is for programs that are used as part of compilation: |
| 384 | anything that must be compiled with other compilers in order to |
| 385 | bootstrap the GNU compilation facilities. If these require the GNU |
| 386 | compiler, then no one can compile them without having them installed |
| 387 | already. That would be extremely troublesome in certain cases. |
| 388 | |
| 389 | @node Standard C |
| 390 | @section Standard C and Pre-Standard C |
| 391 | @cindex @sc{ansi} C standard |
| 392 | |
| 393 | 1989 Standard C is widespread enough now that it is ok to use its |
| 394 | features in new programs. There is one exception: do not ever use the |
| 395 | ``trigraph'' feature of Standard C. |
| 396 | |
| 397 | 1999 Standard C is not widespread yet, so please do not require its |
| 398 | features in programs. It is ok to use its features if they are present. |
| 399 | |
| 400 | However, it is easy to support pre-standard compilers in most programs, |
| 401 | so if you know how to do that, feel free. If a program you are |
| 402 | maintaining has such support, you should try to keep it working. |
| 403 | |
| 404 | @cindex function prototypes |
| 405 | To support pre-standard C, instead of writing function definitions in |
| 406 | standard prototype form, |
| 407 | |
| 408 | @example |
| 409 | int |
| 410 | foo (int x, int y) |
| 411 | @dots{} |
| 412 | @end example |
| 413 | |
| 414 | @noindent |
| 415 | write the definition in pre-standard style like this, |
| 416 | |
| 417 | @example |
| 418 | int |
| 419 | foo (x, y) |
| 420 | int x, y; |
| 421 | @dots{} |
| 422 | @end example |
| 423 | |
| 424 | @noindent |
| 425 | and use a separate declaration to specify the argument prototype: |
| 426 | |
| 427 | @example |
| 428 | int foo (int, int); |
| 429 | @end example |
| 430 | |
| 431 | You need such a declaration anyway, in a header file, to get the benefit |
| 432 | of prototypes in all the files where the function is called. And once |
| 433 | you have the declaration, you normally lose nothing by writing the |
| 434 | function definition in the pre-standard style. |
| 435 | |
| 436 | This technique does not work for integer types narrower than @code{int}. |
| 437 | If you think of an argument as being of a type narrower than @code{int}, |
| 438 | declare it as @code{int} instead. |
| 439 | |
| 440 | There are a few special cases where this technique is hard to use. For |
| 441 | example, if a function argument needs to hold the system type |
| 442 | @code{dev_t}, you run into trouble, because @code{dev_t} is shorter than |
| 443 | @code{int} on some machines; but you cannot use @code{int} instead, |
| 444 | because @code{dev_t} is wider than @code{int} on some machines. There |
| 445 | is no type you can safely use on all machines in a non-standard |
| 446 | definition. The only way to support non-standard C and pass such an |
| 447 | argument is to check the width of @code{dev_t} using Autoconf and choose |
| 448 | the argument type accordingly. This may not be worth the trouble. |
| 449 | |
| 450 | In order to support pre-standard compilers that do not recognize |
| 451 | prototypes, you may want to use a preprocessor macro like this: |
| 452 | |
| 453 | @example |
| 454 | /* Declare the prototype for a general external function. */ |
| 455 | #if defined (__STDC__) || defined (WINDOWSNT) |
| 456 | #define P_(proto) proto |
| 457 | #else |
| 458 | #define P_(proto) () |
| 459 | #endif |
| 460 | @end example |
| 461 | |
| 462 | @node Conditional Compilation |
| 463 | @section Conditional Compilation |
| 464 | |
| 465 | When supporting configuration options already known when building your |
| 466 | program we prefer using @code{if (... )} over conditional compilation, |
| 467 | as in the former case the compiler is able to perform more extensive |
| 468 | checking of all possible code paths. |
| 469 | |
| 470 | For example, please write |
| 471 | |
| 472 | @smallexample |
| 473 | if (HAS_FOO) |
| 474 | ... |
| 475 | else |
| 476 | ... |
| 477 | @end smallexample |
| 478 | |
| 479 | instead of: |
| 480 | |
| 481 | @smallexample |
| 482 | #ifdef HAS_FOO |
| 483 | ... |
| 484 | #else |
| 485 | ... |
| 486 | #endif |
| 487 | @end smallexample |
| 488 | |
| 489 | A modern compiler such as GCC will generate exactly the same code in |
| 490 | both cases, and we have been using similar techniques with good success |
| 491 | in several projects. |
| 492 | |
| 493 | While this is not a silver bullet solving all portability problems, |
| 494 | following this policy would have saved the GCC project alone many person |
| 495 | hours if not days per year. |
| 496 | |
| 497 | In the case of function-like macros like @code{REVERSIBLE_CC_MODE} in |
| 498 | GCC which cannot be simply used in @code{if( ...)} statements, there is |
| 499 | an easy workaround. Simply introduce another macro |
| 500 | @code{HAS_REVERSIBLE_CC_MODE} as in the following example: |
| 501 | |
| 502 | @smallexample |
| 503 | #ifdef REVERSIBLE_CC_MODE |
| 504 | #define HAS_REVERSIBLE_CC_MODE 1 |
| 505 | #else |
| 506 | #define HAS_REVERSIBLE_CC_MODE 0 |
| 507 | #endif |
| 508 | @end smallexample |
| 509 | |
| 510 | @node Program Behavior |
| 511 | @chapter Program Behavior for All Programs |
| 512 | |
| 513 | This @value{CHAPTER} describes conventions for writing robust |
| 514 | software. It also describes general standards for error messages, the |
| 515 | command line interface, and how libraries should behave. |
| 516 | |
| 517 | @menu |
| 518 | * Semantics:: Writing robust programs |
| 519 | * Libraries:: Library behavior |
| 520 | * Errors:: Formatting error messages |
| 521 | * User Interfaces:: Standards about interfaces generally |
| 522 | * Graphical Interfaces:: Standards for graphical interfaces |
| 523 | * Command-Line Interfaces:: Standards for command line interfaces |
| 524 | * Option Table:: Table of long options |
| 525 | * Memory Usage:: When and how to care about memory needs |
| 526 | * File Usage:: Which files to use, and where |
| 527 | @end menu |
| 528 | |
| 529 | @node Semantics |
| 530 | @section Writing Robust Programs |
| 531 | |
| 532 | @cindex arbitrary limits on data |
| 533 | Avoid arbitrary limits on the length or number of @emph{any} data |
| 534 | structure, including file names, lines, files, and symbols, by allocating |
| 535 | all data structures dynamically. In most Unix utilities, ``long lines |
| 536 | are silently truncated''. This is not acceptable in a GNU utility. |
| 537 | |
| 538 | @cindex @code{NUL} characters |
| 539 | Utilities reading files should not drop NUL characters, or any other |
| 540 | nonprinting characters @emph{including those with codes above 0177}. |
| 541 | The only sensible exceptions would be utilities specifically intended |
| 542 | for interface to certain types of terminals or printers |
| 543 | that can't handle those characters. |
| 544 | Whenever possible, try to make programs work properly with |
| 545 | sequences of bytes that represent multibyte characters, using encodings |
| 546 | such as UTF-8 and others. |
| 547 | |
| 548 | @cindex error messages |
| 549 | Check every system call for an error return, unless you know you wish to |
| 550 | ignore errors. Include the system error text (from @code{perror} or |
| 551 | equivalent) in @emph{every} error message resulting from a failing |
| 552 | system call, as well as the name of the file if any and the name of the |
| 553 | utility. Just ``cannot open foo.c'' or ``stat failed'' is not |
| 554 | sufficient. |
| 555 | |
| 556 | @cindex @code{malloc} return value |
| 557 | @cindex memory allocation failure |
| 558 | Check every call to @code{malloc} or @code{realloc} to see if it |
| 559 | returned zero. Check @code{realloc} even if you are making the block |
| 560 | smaller; in a system that rounds block sizes to a power of 2, |
| 561 | @code{realloc} may get a different block if you ask for less space. |
| 562 | |
| 563 | In Unix, @code{realloc} can destroy the storage block if it returns |
| 564 | zero. GNU @code{realloc} does not have this bug: if it fails, the |
| 565 | original block is unchanged. Feel free to assume the bug is fixed. If |
| 566 | you wish to run your program on Unix, and wish to avoid lossage in this |
| 567 | case, you can use the GNU @code{malloc}. |
| 568 | |
| 569 | You must expect @code{free} to alter the contents of the block that was |
| 570 | freed. Anything you want to fetch from the block, you must fetch before |
| 571 | calling @code{free}. |
| 572 | |
| 573 | If @code{malloc} fails in a noninteractive program, make that a fatal |
| 574 | error. In an interactive program (one that reads commands from the |
| 575 | user), it is better to abort the command and return to the command |
| 576 | reader loop. This allows the user to kill other processes to free up |
| 577 | virtual memory, and then try the command again. |
| 578 | |
| 579 | @cindex command-line arguments, decoding |
| 580 | Use @code{getopt_long} to decode arguments, unless the argument syntax |
| 581 | makes this unreasonable. |
| 582 | |
| 583 | When static storage is to be written in during program execution, use |
| 584 | explicit C code to initialize it. Reserve C initialized declarations |
| 585 | for data that will not be changed. |
| 586 | @c ADR: why? |
| 587 | |
| 588 | Try to avoid low-level interfaces to obscure Unix data structures (such |
| 589 | as file directories, utmp, or the layout of kernel memory), since these |
| 590 | are less likely to work compatibly. If you need to find all the files |
| 591 | in a directory, use @code{readdir} or some other high-level interface. |
| 592 | These are supported compatibly by GNU. |
| 593 | |
| 594 | @cindex signal handling |
| 595 | The preferred signal handling facilities are the BSD variant of |
| 596 | @code{signal}, and the @sc{posix} @code{sigaction} function; the |
| 597 | alternative USG @code{signal} interface is an inferior design. |
| 598 | |
| 599 | Nowadays, using the @sc{posix} signal functions may be the easiest way |
| 600 | to make a program portable. If you use @code{signal}, then on GNU/Linux |
| 601 | systems running GNU libc version 1, you should include |
| 602 | @file{bsd/signal.h} instead of @file{signal.h}, so as to get BSD |
| 603 | behavior. It is up to you whether to support systems where |
| 604 | @code{signal} has only the USG behavior, or give up on them. |
| 605 | |
| 606 | @cindex impossible conditions |
| 607 | In error checks that detect ``impossible'' conditions, just abort. |
| 608 | There is usually no point in printing any message. These checks |
| 609 | indicate the existence of bugs. Whoever wants to fix the bugs will have |
| 610 | to read the source code and run a debugger. So explain the problem with |
| 611 | comments in the source. The relevant data will be in variables, which |
| 612 | are easy to examine with the debugger, so there is no point moving them |
| 613 | elsewhere. |
| 614 | |
| 615 | Do not use a count of errors as the exit status for a program. |
| 616 | @emph{That does not work}, because exit status values are limited to 8 |
| 617 | bits (0 through 255). A single run of the program might have 256 |
| 618 | errors; if you try to return 256 as the exit status, the parent process |
| 619 | will see 0 as the status, and it will appear that the program succeeded. |
| 620 | |
| 621 | @cindex temporary files |
| 622 | @cindex @code{TMPDIR} environment variable |
| 623 | If you make temporary files, check the @code{TMPDIR} environment |
| 624 | variable; if that variable is defined, use the specified directory |
| 625 | instead of @file{/tmp}. |
| 626 | |
| 627 | In addition, be aware that there is a possible security problem when |
| 628 | creating temporary files in world-writable directories. In C, you can |
| 629 | avoid this problem by creating temporary files in this manner: |
| 630 | |
| 631 | @example |
| 632 | fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0600); |
| 633 | @end example |
| 634 | |
| 635 | @noindent |
| 636 | or by using the @code{mkstemps} function from libiberty. |
| 637 | |
| 638 | In bash, use @code{set -C} to avoid this problem. |
| 639 | |
| 640 | @node Libraries |
| 641 | @section Library Behavior |
| 642 | @cindex libraries |
| 643 | |
| 644 | Try to make library functions reentrant. If they need to do dynamic |
| 645 | storage allocation, at least try to avoid any nonreentrancy aside from |
| 646 | that of @code{malloc} itself. |
| 647 | |
| 648 | Here are certain name conventions for libraries, to avoid name |
| 649 | conflicts. |
| 650 | |
| 651 | Choose a name prefix for the library, more than two characters long. |
| 652 | All external function and variable names should start with this |
| 653 | prefix. In addition, there should only be one of these in any given |
| 654 | library member. This usually means putting each one in a separate |
| 655 | source file. |
| 656 | |
| 657 | An exception can be made when two external symbols are always used |
| 658 | together, so that no reasonable program could use one without the |
| 659 | other; then they can both go in the same file. |
| 660 | |
| 661 | External symbols that are not documented entry points for the user |
| 662 | should have names beginning with @samp{_}. The @samp{_} should be |
| 663 | followed by the chosen name prefix for the library, to prevent |
| 664 | collisions with other libraries. These can go in the same files with |
| 665 | user entry points if you like. |
| 666 | |
| 667 | Static functions and variables can be used as you like and need not |
| 668 | fit any naming convention. |
| 669 | |
| 670 | @node Errors |
| 671 | @section Formatting Error Messages |
| 672 | @cindex formatting error messages |
| 673 | @cindex error messages, formatting |
| 674 | |
| 675 | Error messages from compilers should look like this: |
| 676 | |
| 677 | @example |
| 678 | @var{source-file-name}:@var{lineno}: @var{message} |
| 679 | @end example |
| 680 | |
| 681 | @noindent |
| 682 | If you want to mention the column number, use this format: |
| 683 | |
| 684 | @example |
| 685 | @var{source-file-name}:@var{lineno}:@var{column}: @var{message} |
| 686 | @end example |
| 687 | |
| 688 | @noindent |
| 689 | Line numbers should start from 1 at the beginning of the file, and |
| 690 | column numbers should start from 1 at the beginning of the line. (Both |
| 691 | of these conventions are chosen for compatibility.) Calculate column |
| 692 | numbers assuming that space and all ASCII printing characters have |
| 693 | equal width, and assuming tab stops every 8 columns. |
| 694 | |
| 695 | Error messages from other noninteractive programs should look like this: |
| 696 | |
| 697 | @example |
| 698 | @var{program}:@var{source-file-name}:@var{lineno}: @var{message} |
| 699 | @end example |
| 700 | |
| 701 | @noindent |
| 702 | when there is an appropriate source file, or like this: |
| 703 | |
| 704 | @example |
| 705 | @var{program}: @var{message} |
| 706 | @end example |
| 707 | |
| 708 | @noindent |
| 709 | when there is no relevant source file. |
| 710 | |
| 711 | If you want to mention the column number, use this format: |
| 712 | |
| 713 | @example |
| 714 | @var{program}:@var{source-file-name}:@var{lineno}:@var{column}: @var{message} |
| 715 | @end example |
| 716 | |
| 717 | In an interactive program (one that is reading commands from a |
| 718 | terminal), it is better not to include the program name in an error |
| 719 | message. The place to indicate which program is running is in the |
| 720 | prompt or with the screen layout. (When the same program runs with |
| 721 | input from a source other than a terminal, it is not interactive and |
| 722 | would do best to print error messages using the noninteractive style.) |
| 723 | |
| 724 | The string @var{message} should not begin with a capital letter when |
| 725 | it follows a program name and/or file name. Also, it should not end |
| 726 | with a period. |
| 727 | |
| 728 | Error messages from interactive programs, and other messages such as |
| 729 | usage messages, should start with a capital letter. But they should not |
| 730 | end with a period. |
| 731 | |
| 732 | @node User Interfaces |
| 733 | @section Standards for Interfaces Generally |
| 734 | |
| 735 | @cindex program name and its behavior |
| 736 | @cindex behavior, dependent on program's name |
| 737 | Please don't make the behavior of a utility depend on the name used |
| 738 | to invoke it. It is useful sometimes to make a link to a utility |
| 739 | with a different name, and that should not change what it does. |
| 740 | |
| 741 | Instead, use a run time option or a compilation switch or both |
| 742 | to select among the alternate behaviors. |
| 743 | |
| 744 | @cindex output device and program's behavior |
| 745 | Likewise, please don't make the behavior of the program depend on the |
| 746 | type of output device it is used with. Device independence is an |
| 747 | important principle of the system's design; do not compromise it merely |
| 748 | to save someone from typing an option now and then. (Variation in error |
| 749 | message syntax when using a terminal is ok, because that is a side issue |
| 750 | that people do not depend on.) |
| 751 | |
| 752 | If you think one behavior is most useful when the output is to a |
| 753 | terminal, and another is most useful when the output is a file or a |
| 754 | pipe, then it is usually best to make the default behavior the one that |
| 755 | is useful with output to a terminal, and have an option for the other |
| 756 | behavior. |
| 757 | |
| 758 | Compatibility requires certain programs to depend on the type of output |
| 759 | device. It would be disastrous if @code{ls} or @code{sh} did not do so |
| 760 | in the way all users expect. In some of these cases, we supplement the |
| 761 | program with a preferred alternate version that does not depend on the |
| 762 | output device type. For example, we provide a @code{dir} program much |
| 763 | like @code{ls} except that its default output format is always |
| 764 | multi-column format. |
| 765 | |
| 766 | @node Graphical Interfaces |
| 767 | @section Standards for Graphical Interfaces |
| 768 | @cindex graphical user interface |
| 769 | |
| 770 | @cindex gtk |
| 771 | When you write a program that provides a graphical user interface, |
| 772 | please make it work with X Windows and the GTK toolkit unless the |
| 773 | functionality specifically requires some alternative (for example, |
| 774 | ``displaying jpeg images while in console mode''). |
| 775 | |
| 776 | In addition, please provide a command-line interface to control the |
| 777 | functionality. (In many cases, the graphical user interface can be a |
| 778 | separate program which invokes the command-line program.) This is |
| 779 | so that the same jobs can be done from scripts. |
| 780 | |
| 781 | @cindex corba |
| 782 | @cindex gnome |
| 783 | Please also consider providing a CORBA interface (for use from GNOME), a |
| 784 | library interface (for use from C), and perhaps a keyboard-driven |
| 785 | console interface (for use by users from console mode). Once you are |
| 786 | doing the work to provide the functionality and the graphical interface, |
| 787 | these won't be much extra work. |
| 788 | |
| 789 | @node Command-Line Interfaces |
| 790 | @section Standards for Command Line Interfaces |
| 791 | @cindex command-line interface |
| 792 | |
| 793 | @findex getopt |
| 794 | It is a good idea to follow the @sc{posix} guidelines for the |
| 795 | command-line options of a program. The easiest way to do this is to use |
| 796 | @code{getopt} to parse them. Note that the GNU version of @code{getopt} |
| 797 | will normally permit options anywhere among the arguments unless the |
| 798 | special argument @samp{--} is used. This is not what @sc{posix} |
| 799 | specifies; it is a GNU extension. |
| 800 | |
| 801 | @cindex long-named options |
| 802 | Please define long-named options that are equivalent to the |
| 803 | single-letter Unix-style options. We hope to make GNU more user |
| 804 | friendly this way. This is easy to do with the GNU function |
| 805 | @code{getopt_long}. |
| 806 | |
| 807 | One of the advantages of long-named options is that they can be |
| 808 | consistent from program to program. For example, users should be able |
| 809 | to expect the ``verbose'' option of any GNU program which has one, to be |
| 810 | spelled precisely @samp{--verbose}. To achieve this uniformity, look at |
| 811 | the table of common long-option names when you choose the option names |
| 812 | for your program (@pxref{Option Table}). |
| 813 | |
| 814 | It is usually a good idea for file names given as ordinary arguments to |
| 815 | be input files only; any output files would be specified using options |
| 816 | (preferably @samp{-o} or @samp{--output}). Even if you allow an output |
| 817 | file name as an ordinary argument for compatibility, try to provide an |
| 818 | option as another way to specify it. This will lead to more consistency |
| 819 | among GNU utilities, and fewer idiosyncracies for users to remember. |
| 820 | |
| 821 | @cindex standard command-line options |
| 822 | All programs should support two standard options: @samp{--version} |
| 823 | and @samp{--help}. |
| 824 | |
| 825 | @table @code |
| 826 | @cindex @samp{--version} option |
| 827 | @item --version |
| 828 | This option should direct the program to print information about its name, |
| 829 | version, origin and legal status, all on standard output, and then exit |
| 830 | successfully. Other options and arguments should be ignored once this |
| 831 | is seen, and the program should not perform its normal function. |
| 832 | |
| 833 | @cindex canonical name of a program |
| 834 | @cindex program's canonical name |
| 835 | The first line is meant to be easy for a program to parse; the version |
| 836 | number proper starts after the last space. In addition, it contains |
| 837 | the canonical name for this program, in this format: |
| 838 | |
| 839 | @example |
| 840 | GNU Emacs 19.30 |
| 841 | @end example |
| 842 | |
| 843 | @noindent |
| 844 | The program's name should be a constant string; @emph{don't} compute it |
| 845 | from @code{argv[0]}. The idea is to state the standard or canonical |
| 846 | name for the program, not its file name. There are other ways to find |
| 847 | out the precise file name where a command is found in @code{PATH}. |
| 848 | |
| 849 | If the program is a subsidiary part of a larger package, mention the |
| 850 | package name in parentheses, like this: |
| 851 | |
| 852 | @example |
| 853 | emacsserver (GNU Emacs) 19.30 |
| 854 | @end example |
| 855 | |
| 856 | @noindent |
| 857 | If the package has a version number which is different from this |
| 858 | program's version number, you can mention the package version number |
| 859 | just before the close-parenthesis. |
| 860 | |
| 861 | If you @strong{need} to mention the version numbers of libraries which |
| 862 | are distributed separately from the package which contains this program, |
| 863 | you can do so by printing an additional line of version info for each |
| 864 | library you want to mention. Use the same format for these lines as for |
| 865 | the first line. |
| 866 | |
| 867 | Please do not mention all of the libraries that the program uses ``just |
| 868 | for completeness''---that would produce a lot of unhelpful clutter. |
| 869 | Please mention library version numbers only if you find in practice that |
| 870 | they are very important to you in debugging. |
| 871 | |
| 872 | The following line, after the version number line or lines, should be a |
| 873 | copyright notice. If more than one copyright notice is called for, put |
| 874 | each on a separate line. |
| 875 | |
| 876 | Next should follow a brief statement that the program is free software, |
| 877 | and that users are free to copy and change it on certain conditions. If |
| 878 | the program is covered by the GNU GPL, say so here. Also mention that |
| 879 | there is no warranty, to the extent permitted by law. |
| 880 | |
| 881 | It is ok to finish the output with a list of the major authors of the |
| 882 | program, as a way of giving credit. |
| 883 | |
| 884 | Here's an example of output that follows these rules: |
| 885 | |
| 886 | @smallexample |
| 887 | GNU Emacs 19.34.5 |
| 888 | Copyright (C) 1996 Free Software Foundation, Inc. |
| 889 | GNU Emacs comes with NO WARRANTY, |
| 890 | to the extent permitted by law. |
| 891 | You may redistribute copies of GNU Emacs |
| 892 | under the terms of the GNU General Public License. |
| 893 | For more information about these matters, |
| 894 | see the files named COPYING. |
| 895 | @end smallexample |
| 896 | |
| 897 | You should adapt this to your program, of course, filling in the proper |
| 898 | year, copyright holder, name of program, and the references to |
| 899 | distribution terms, and changing the rest of the wording as necessary. |
| 900 | |
| 901 | This copyright notice only needs to mention the most recent year in |
| 902 | which changes were made---there's no need to list the years for previous |
| 903 | versions' changes. You don't have to mention the name of the program in |
| 904 | these notices, if that is inconvenient, since it appeared in the first |
| 905 | line. |
| 906 | |
| 907 | Translations of the above lines must preserve the validity of the |
| 908 | copyright notices (@pxref{Internationalization}). If the translation's |
| 909 | character set supports it, the @samp{(C)} should be replaced with the |
| 910 | copyright symbol, as follows: |
| 911 | |
| 912 | @ifinfo |
| 913 | (the official copyright symbol, which is the letter C in a circle); |
| 914 | @end ifinfo |
| 915 | @ifnotinfo |
| 916 | @copyright{} |
| 917 | @end ifnotinfo |
| 918 | |
| 919 | Write the word ``Copyright'' exactly like that, in English. Do not |
| 920 | translate it into another language. International treaties recognize |
| 921 | the English word ``Copyright''; translations into other languages do not |
| 922 | have legal significance. |
| 923 | |
| 924 | |
| 925 | @cindex @samp{--help} option |
| 926 | @item --help |
| 927 | This option should output brief documentation for how to invoke the |
| 928 | program, on standard output, then exit successfully. Other options and |
| 929 | arguments should be ignored once this is seen, and the program should |
| 930 | not perform its normal function. |
| 931 | |
| 932 | @cindex address for bug reports |
| 933 | @cindex bug reports |
| 934 | Near the end of the @samp{--help} option's output there should be a line |
| 935 | that says where to mail bug reports. It should have this format: |
| 936 | |
| 937 | @example |
| 938 | Report bugs to @var{mailing-address}. |
| 939 | @end example |
| 940 | @end table |
| 941 | |
| 942 | @node Option Table |
| 943 | @section Table of Long Options |
| 944 | @cindex long option names |
| 945 | @cindex table of long options |
| 946 | |
| 947 | Here is a table of long options used by GNU programs. It is surely |
| 948 | incomplete, but we aim to list all the options that a new program might |
| 949 | want to be compatible with. If you use names not already in the table, |
| 950 | please send @email{bug-standards@@gnu.org} a list of them, with their |
| 951 | meanings, so we can update the table. |
| 952 | |
| 953 | @c Please leave newlines between items in this table; it's much easier |
| 954 | @c to update when it isn't completely squashed together and unreadable. |
| 955 | @c When there is more than one short option for a long option name, put |
| 956 | @c a semicolon between the lists of the programs that use them, not a |
| 957 | @c period. --friedman |
| 958 | |
| 959 | @table @samp |
| 960 | @item after-date |
| 961 | @samp{-N} in @code{tar}. |
| 962 | |
| 963 | @item all |
| 964 | @samp{-a} in @code{du}, @code{ls}, @code{nm}, @code{stty}, @code{uname}, |
| 965 | and @code{unexpand}. |
| 966 | |
| 967 | @item all-text |
| 968 | @samp{-a} in @code{diff}. |
| 969 | |
| 970 | @item almost-all |
| 971 | @samp{-A} in @code{ls}. |
| 972 | |
| 973 | @item append |
| 974 | @samp{-a} in @code{etags}, @code{tee}, @code{time}; |
| 975 | @samp{-r} in @code{tar}. |
| 976 | |
| 977 | @item archive |
| 978 | @samp{-a} in @code{cp}. |
| 979 | |
| 980 | @item archive-name |
| 981 | @samp{-n} in @code{shar}. |
| 982 | |
| 983 | @item arglength |
| 984 | @samp{-l} in @code{m4}. |
| 985 | |
| 986 | @item ascii |
| 987 | @samp{-a} in @code{diff}. |
| 988 | |
| 989 | @item assign |
| 990 | @samp{-v} in @code{gawk}. |
| 991 | |
| 992 | @item assume-new |
| 993 | @samp{-W} in Make. |
| 994 | |
| 995 | @item assume-old |
| 996 | @samp{-o} in Make. |
| 997 | |
| 998 | @item auto-check |
| 999 | @samp{-a} in @code{recode}. |
| 1000 | |
| 1001 | @item auto-pager |
| 1002 | @samp{-a} in @code{wdiff}. |
| 1003 | |
| 1004 | @item auto-reference |
| 1005 | @samp{-A} in @code{ptx}. |
| 1006 | |
| 1007 | @item avoid-wraps |
| 1008 | @samp{-n} in @code{wdiff}. |
| 1009 | |
| 1010 | @item background |
| 1011 | For server programs, run in the background. |
| 1012 | |
| 1013 | @item backward-search |
| 1014 | @samp{-B} in @code{ctags}. |
| 1015 | |
| 1016 | @item basename |
| 1017 | @samp{-f} in @code{shar}. |
| 1018 | |
| 1019 | @item batch |
| 1020 | Used in GDB. |
| 1021 | |
| 1022 | @item baud |
| 1023 | Used in GDB. |
| 1024 | |
| 1025 | @item before |
| 1026 | @samp{-b} in @code{tac}. |
| 1027 | |
| 1028 | @item binary |
| 1029 | @samp{-b} in @code{cpio} and @code{diff}. |
| 1030 | |
| 1031 | @item bits-per-code |
| 1032 | @samp{-b} in @code{shar}. |
| 1033 | |
| 1034 | @item block-size |
| 1035 | Used in @code{cpio} and @code{tar}. |
| 1036 | |
| 1037 | @item blocks |
| 1038 | @samp{-b} in @code{head} and @code{tail}. |
| 1039 | |
| 1040 | @item break-file |
| 1041 | @samp{-b} in @code{ptx}. |
| 1042 | |
| 1043 | @item brief |
| 1044 | Used in various programs to make output shorter. |
| 1045 | |
| 1046 | @item bytes |
| 1047 | @samp{-c} in @code{head}, @code{split}, and @code{tail}. |
| 1048 | |
| 1049 | @item c@t{++} |
| 1050 | @samp{-C} in @code{etags}. |
| 1051 | |
| 1052 | @item catenate |
| 1053 | @samp{-A} in @code{tar}. |
| 1054 | |
| 1055 | @item cd |
| 1056 | Used in various programs to specify the directory to use. |
| 1057 | |
| 1058 | @item changes |
| 1059 | @samp{-c} in @code{chgrp} and @code{chown}. |
| 1060 | |
| 1061 | @item classify |
| 1062 | @samp{-F} in @code{ls}. |
| 1063 | |
| 1064 | @item colons |
| 1065 | @samp{-c} in @code{recode}. |
| 1066 | |
| 1067 | @item command |
| 1068 | @samp{-c} in @code{su}; |
| 1069 | @samp{-x} in GDB. |
| 1070 | |
| 1071 | @item compare |
| 1072 | @samp{-d} in @code{tar}. |
| 1073 | |
| 1074 | @item compat |
| 1075 | Used in @code{gawk}. |
| 1076 | |
| 1077 | @item compress |
| 1078 | @samp{-Z} in @code{tar} and @code{shar}. |
| 1079 | |
| 1080 | @item concatenate |
| 1081 | @samp{-A} in @code{tar}. |
| 1082 | |
| 1083 | @item confirmation |
| 1084 | @samp{-w} in @code{tar}. |
| 1085 | |
| 1086 | @item context |
| 1087 | Used in @code{diff}. |
| 1088 | |
| 1089 | @item copyleft |
| 1090 | @samp{-W copyleft} in @code{gawk}. |
| 1091 | |
| 1092 | @item copyright |
| 1093 | @samp{-C} in @code{ptx}, @code{recode}, and @code{wdiff}; |
| 1094 | @samp{-W copyright} in @code{gawk}. |
| 1095 | |
| 1096 | @item core |
| 1097 | Used in GDB. |
| 1098 | |
| 1099 | @item count |
| 1100 | @samp{-q} in @code{who}. |
| 1101 | |
| 1102 | @item count-links |
| 1103 | @samp{-l} in @code{du}. |
| 1104 | |
| 1105 | @item create |
| 1106 | Used in @code{tar} and @code{cpio}. |
| 1107 | |
| 1108 | @item cut-mark |
| 1109 | @samp{-c} in @code{shar}. |
| 1110 | |
| 1111 | @item cxref |
| 1112 | @samp{-x} in @code{ctags}. |
| 1113 | |
| 1114 | @item date |
| 1115 | @samp{-d} in @code{touch}. |
| 1116 | |
| 1117 | @item debug |
| 1118 | @samp{-d} in Make and @code{m4}; |
| 1119 | @samp{-t} in Bison. |
| 1120 | |
| 1121 | @item define |
| 1122 | @samp{-D} in @code{m4}. |
| 1123 | |
| 1124 | @item defines |
| 1125 | @samp{-d} in Bison and @code{ctags}. |
| 1126 | |
| 1127 | @item delete |
| 1128 | @samp{-D} in @code{tar}. |
| 1129 | |
| 1130 | @item dereference |
| 1131 | @samp{-L} in @code{chgrp}, @code{chown}, @code{cpio}, @code{du}, |
| 1132 | @code{ls}, and @code{tar}. |
| 1133 | |
| 1134 | @item dereference-args |
| 1135 | @samp{-D} in @code{du}. |
| 1136 | |
| 1137 | @item device |
| 1138 | Specify an I/O device (special file name). |
| 1139 | |
| 1140 | @item diacritics |
| 1141 | @samp{-d} in @code{recode}. |
| 1142 | |
| 1143 | @item dictionary-order |
| 1144 | @samp{-d} in @code{look}. |
| 1145 | |
| 1146 | @item diff |
| 1147 | @samp{-d} in @code{tar}. |
| 1148 | |
| 1149 | @item digits |
| 1150 | @samp{-n} in @code{csplit}. |
| 1151 | |
| 1152 | @item directory |
| 1153 | Specify the directory to use, in various programs. In @code{ls}, it |
| 1154 | means to show directories themselves rather than their contents. In |
| 1155 | @code{rm} and @code{ln}, it means to not treat links to directories |
| 1156 | specially. |
| 1157 | |
| 1158 | @item discard-all |
| 1159 | @samp{-x} in @code{strip}. |
| 1160 | |
| 1161 | @item discard-locals |
| 1162 | @samp{-X} in @code{strip}. |
| 1163 | |
| 1164 | @item dry-run |
| 1165 | @samp{-n} in Make. |
| 1166 | |
| 1167 | @item ed |
| 1168 | @samp{-e} in @code{diff}. |
| 1169 | |
| 1170 | @item elide-empty-files |
| 1171 | @samp{-z} in @code{csplit}. |
| 1172 | |
| 1173 | @item end-delete |
| 1174 | @samp{-x} in @code{wdiff}. |
| 1175 | |
| 1176 | @item end-insert |
| 1177 | @samp{-z} in @code{wdiff}. |
| 1178 | |
| 1179 | @item entire-new-file |
| 1180 | @samp{-N} in @code{diff}. |
| 1181 | |
| 1182 | @item environment-overrides |
| 1183 | @samp{-e} in Make. |
| 1184 | |
| 1185 | @item eof |
| 1186 | @samp{-e} in @code{xargs}. |
| 1187 | |
| 1188 | @item epoch |
| 1189 | Used in GDB. |
| 1190 | |
| 1191 | @item error-limit |
| 1192 | Used in @code{makeinfo}. |
| 1193 | |
| 1194 | @item error-output |
| 1195 | @samp{-o} in @code{m4}. |
| 1196 | |
| 1197 | @item escape |
| 1198 | @samp{-b} in @code{ls}. |
| 1199 | |
| 1200 | @item exclude-from |
| 1201 | @samp{-X} in @code{tar}. |
| 1202 | |
| 1203 | @item exec |
| 1204 | Used in GDB. |
| 1205 | |
| 1206 | @item exit |
| 1207 | @samp{-x} in @code{xargs}. |
| 1208 | |
| 1209 | @item exit-0 |
| 1210 | @samp{-e} in @code{unshar}. |
| 1211 | |
| 1212 | @item expand-tabs |
| 1213 | @samp{-t} in @code{diff}. |
| 1214 | |
| 1215 | @item expression |
| 1216 | @samp{-e} in @code{sed}. |
| 1217 | |
| 1218 | @item extern-only |
| 1219 | @samp{-g} in @code{nm}. |
| 1220 | |
| 1221 | @item extract |
| 1222 | @samp{-i} in @code{cpio}; |
| 1223 | @samp{-x} in @code{tar}. |
| 1224 | |
| 1225 | @item faces |
| 1226 | @samp{-f} in @code{finger}. |
| 1227 | |
| 1228 | @item fast |
| 1229 | @samp{-f} in @code{su}. |
| 1230 | |
| 1231 | @item fatal-warnings |
| 1232 | @samp{-E} in @code{m4}. |
| 1233 | |
| 1234 | @item file |
| 1235 | @samp{-f} in @code{info}, @code{gawk}, Make, @code{mt}, and @code{tar}; |
| 1236 | @samp{-n} in @code{sed}; |
| 1237 | @samp{-r} in @code{touch}. |
| 1238 | |
| 1239 | @item field-separator |
| 1240 | @samp{-F} in @code{gawk}. |
| 1241 | |
| 1242 | @item file-prefix |
| 1243 | @samp{-b} in Bison. |
| 1244 | |
| 1245 | @item file-type |
| 1246 | @samp{-F} in @code{ls}. |
| 1247 | |
| 1248 | @item files-from |
| 1249 | @samp{-T} in @code{tar}. |
| 1250 | |
| 1251 | @item fill-column |
| 1252 | Used in @code{makeinfo}. |
| 1253 | |
| 1254 | @item flag-truncation |
| 1255 | @samp{-F} in @code{ptx}. |
| 1256 | |
| 1257 | @item fixed-output-files |
| 1258 | @samp{-y} in Bison. |
| 1259 | |
| 1260 | @item follow |
| 1261 | @samp{-f} in @code{tail}. |
| 1262 | |
| 1263 | @item footnote-style |
| 1264 | Used in @code{makeinfo}. |
| 1265 | |
| 1266 | @item force |
| 1267 | @samp{-f} in @code{cp}, @code{ln}, @code{mv}, and @code{rm}. |
| 1268 | |
| 1269 | @item force-prefix |
| 1270 | @samp{-F} in @code{shar}. |
| 1271 | |
| 1272 | @item foreground |
| 1273 | For server programs, run in the foreground; |
| 1274 | in other words, don't do anything special to run the server |
| 1275 | in the background. |
| 1276 | |
| 1277 | @item format |
| 1278 | Used in @code{ls}, @code{time}, and @code{ptx}. |
| 1279 | |
| 1280 | @item freeze-state |
| 1281 | @samp{-F} in @code{m4}. |
| 1282 | |
| 1283 | @item fullname |
| 1284 | Used in GDB. |
| 1285 | |
| 1286 | @item gap-size |
| 1287 | @samp{-g} in @code{ptx}. |
| 1288 | |
| 1289 | @item get |
| 1290 | @samp{-x} in @code{tar}. |
| 1291 | |
| 1292 | @item graphic |
| 1293 | @samp{-i} in @code{ul}. |
| 1294 | |
| 1295 | @item graphics |
| 1296 | @samp{-g} in @code{recode}. |
| 1297 | |
| 1298 | @item group |
| 1299 | @samp{-g} in @code{install}. |
| 1300 | |
| 1301 | @item gzip |
| 1302 | @samp{-z} in @code{tar} and @code{shar}. |
| 1303 | |
| 1304 | @item hashsize |
| 1305 | @samp{-H} in @code{m4}. |
| 1306 | |
| 1307 | @item header |
| 1308 | @samp{-h} in @code{objdump} and @code{recode} |
| 1309 | |
| 1310 | @item heading |
| 1311 | @samp{-H} in @code{who}. |
| 1312 | |
| 1313 | @item help |
| 1314 | Used to ask for brief usage information. |
| 1315 | |
| 1316 | @item here-delimiter |
| 1317 | @samp{-d} in @code{shar}. |
| 1318 | |
| 1319 | @item hide-control-chars |
| 1320 | @samp{-q} in @code{ls}. |
| 1321 | |
| 1322 | @item html |
| 1323 | In @code{makeinfo}, output HTML. |
| 1324 | |
| 1325 | @item idle |
| 1326 | @samp{-u} in @code{who}. |
| 1327 | |
| 1328 | @item ifdef |
| 1329 | @samp{-D} in @code{diff}. |
| 1330 | |
| 1331 | @item ignore |
| 1332 | @samp{-I} in @code{ls}; |
| 1333 | @samp{-x} in @code{recode}. |
| 1334 | |
| 1335 | @item ignore-all-space |
| 1336 | @samp{-w} in @code{diff}. |
| 1337 | |
| 1338 | @item ignore-backups |
| 1339 | @samp{-B} in @code{ls}. |
| 1340 | |
| 1341 | @item ignore-blank-lines |
| 1342 | @samp{-B} in @code{diff}. |
| 1343 | |
| 1344 | @item ignore-case |
| 1345 | @samp{-f} in @code{look} and @code{ptx}; |
| 1346 | @samp{-i} in @code{diff} and @code{wdiff}. |
| 1347 | |
| 1348 | @item ignore-errors |
| 1349 | @samp{-i} in Make. |
| 1350 | |
| 1351 | @item ignore-file |
| 1352 | @samp{-i} in @code{ptx}. |
| 1353 | |
| 1354 | @item ignore-indentation |
| 1355 | @samp{-I} in @code{etags}. |
| 1356 | |
| 1357 | @item ignore-init-file |
| 1358 | @samp{-f} in Oleo. |
| 1359 | |
| 1360 | @item ignore-interrupts |
| 1361 | @samp{-i} in @code{tee}. |
| 1362 | |
| 1363 | @item ignore-matching-lines |
| 1364 | @samp{-I} in @code{diff}. |
| 1365 | |
| 1366 | @item ignore-space-change |
| 1367 | @samp{-b} in @code{diff}. |
| 1368 | |
| 1369 | @item ignore-zeros |
| 1370 | @samp{-i} in @code{tar}. |
| 1371 | |
| 1372 | @item include |
| 1373 | @samp{-i} in @code{etags}; |
| 1374 | @samp{-I} in @code{m4}. |
| 1375 | |
| 1376 | @item include-dir |
| 1377 | @samp{-I} in Make. |
| 1378 | |
| 1379 | @item incremental |
| 1380 | @samp{-G} in @code{tar}. |
| 1381 | |
| 1382 | @item info |
| 1383 | @samp{-i}, @samp{-l}, and @samp{-m} in Finger. |
| 1384 | |
| 1385 | @item init-file |
| 1386 | In some programs, specify the name of the file to read as the user's |
| 1387 | init file. |
| 1388 | |
| 1389 | @item initial |
| 1390 | @samp{-i} in @code{expand}. |
| 1391 | |
| 1392 | @item initial-tab |
| 1393 | @samp{-T} in @code{diff}. |
| 1394 | |
| 1395 | @item inode |
| 1396 | @samp{-i} in @code{ls}. |
| 1397 | |
| 1398 | @item interactive |
| 1399 | @samp{-i} in @code{cp}, @code{ln}, @code{mv}, @code{rm}; |
| 1400 | @samp{-e} in @code{m4}; |
| 1401 | @samp{-p} in @code{xargs}; |
| 1402 | @samp{-w} in @code{tar}. |
| 1403 | |
| 1404 | @item intermix-type |
| 1405 | @samp{-p} in @code{shar}. |
| 1406 | |
| 1407 | @item iso-8601 |
| 1408 | Used in @code{date} |
| 1409 | |
| 1410 | @item jobs |
| 1411 | @samp{-j} in Make. |
| 1412 | |
| 1413 | @item just-print |
| 1414 | @samp{-n} in Make. |
| 1415 | |
| 1416 | @item keep-going |
| 1417 | @samp{-k} in Make. |
| 1418 | |
| 1419 | @item keep-files |
| 1420 | @samp{-k} in @code{csplit}. |
| 1421 | |
| 1422 | @item kilobytes |
| 1423 | @samp{-k} in @code{du} and @code{ls}. |
| 1424 | |
| 1425 | @item language |
| 1426 | @samp{-l} in @code{etags}. |
| 1427 | |
| 1428 | @item less-mode |
| 1429 | @samp{-l} in @code{wdiff}. |
| 1430 | |
| 1431 | @item level-for-gzip |
| 1432 | @samp{-g} in @code{shar}. |
| 1433 | |
| 1434 | @item line-bytes |
| 1435 | @samp{-C} in @code{split}. |
| 1436 | |
| 1437 | @item lines |
| 1438 | Used in @code{split}, @code{head}, and @code{tail}. |
| 1439 | |
| 1440 | @item link |
| 1441 | @samp{-l} in @code{cpio}. |
| 1442 | |
| 1443 | @item lint |
| 1444 | @itemx lint-old |
| 1445 | Used in @code{gawk}. |
| 1446 | |
| 1447 | @item list |
| 1448 | @samp{-t} in @code{cpio}; |
| 1449 | @samp{-l} in @code{recode}. |
| 1450 | |
| 1451 | @item list |
| 1452 | @samp{-t} in @code{tar}. |
| 1453 | |
| 1454 | @item literal |
| 1455 | @samp{-N} in @code{ls}. |
| 1456 | |
| 1457 | @item load-average |
| 1458 | @samp{-l} in Make. |
| 1459 | |
| 1460 | @item login |
| 1461 | Used in @code{su}. |
| 1462 | |
| 1463 | @item machine |
| 1464 | No listing of which programs already use this; |
| 1465 | someone should check to |
| 1466 | see if any actually do, and tell @email{gnu@@gnu.org}. |
| 1467 | |
| 1468 | @item macro-name |
| 1469 | @samp{-M} in @code{ptx}. |
| 1470 | |
| 1471 | @item mail |
| 1472 | @samp{-m} in @code{hello} and @code{uname}. |
| 1473 | |
| 1474 | @item make-directories |
| 1475 | @samp{-d} in @code{cpio}. |
| 1476 | |
| 1477 | @item makefile |
| 1478 | @samp{-f} in Make. |
| 1479 | |
| 1480 | @item mapped |
| 1481 | Used in GDB. |
| 1482 | |
| 1483 | @item max-args |
| 1484 | @samp{-n} in @code{xargs}. |
| 1485 | |
| 1486 | @item max-chars |
| 1487 | @samp{-n} in @code{xargs}. |
| 1488 | |
| 1489 | @item max-lines |
| 1490 | @samp{-l} in @code{xargs}. |
| 1491 | |
| 1492 | @item max-load |
| 1493 | @samp{-l} in Make. |
| 1494 | |
| 1495 | @item max-procs |
| 1496 | @samp{-P} in @code{xargs}. |
| 1497 | |
| 1498 | @item mesg |
| 1499 | @samp{-T} in @code{who}. |
| 1500 | |
| 1501 | @item message |
| 1502 | @samp{-T} in @code{who}. |
| 1503 | |
| 1504 | @item minimal |
| 1505 | @samp{-d} in @code{diff}. |
| 1506 | |
| 1507 | @item mixed-uuencode |
| 1508 | @samp{-M} in @code{shar}. |
| 1509 | |
| 1510 | @item mode |
| 1511 | @samp{-m} in @code{install}, @code{mkdir}, and @code{mkfifo}. |
| 1512 | |
| 1513 | @item modification-time |
| 1514 | @samp{-m} in @code{tar}. |
| 1515 | |
| 1516 | @item multi-volume |
| 1517 | @samp{-M} in @code{tar}. |
| 1518 | |
| 1519 | @item name-prefix |
| 1520 | @samp{-a} in Bison. |
| 1521 | |
| 1522 | @item nesting-limit |
| 1523 | @samp{-L} in @code{m4}. |
| 1524 | |
| 1525 | @item net-headers |
| 1526 | @samp{-a} in @code{shar}. |
| 1527 | |
| 1528 | @item new-file |
| 1529 | @samp{-W} in Make. |
| 1530 | |
| 1531 | @item no-builtin-rules |
| 1532 | @samp{-r} in Make. |
| 1533 | |
| 1534 | @item no-character-count |
| 1535 | @samp{-w} in @code{shar}. |
| 1536 | |
| 1537 | @item no-check-existing |
| 1538 | @samp{-x} in @code{shar}. |
| 1539 | |
| 1540 | @item no-common |
| 1541 | @samp{-3} in @code{wdiff}. |
| 1542 | |
| 1543 | @item no-create |
| 1544 | @samp{-c} in @code{touch}. |
| 1545 | |
| 1546 | @item no-defines |
| 1547 | @samp{-D} in @code{etags}. |
| 1548 | |
| 1549 | @item no-deleted |
| 1550 | @samp{-1} in @code{wdiff}. |
| 1551 | |
| 1552 | @item no-dereference |
| 1553 | @samp{-d} in @code{cp}. |
| 1554 | |
| 1555 | @item no-inserted |
| 1556 | @samp{-2} in @code{wdiff}. |
| 1557 | |
| 1558 | @item no-keep-going |
| 1559 | @samp{-S} in Make. |
| 1560 | |
| 1561 | @item no-lines |
| 1562 | @samp{-l} in Bison. |
| 1563 | |
| 1564 | @item no-piping |
| 1565 | @samp{-P} in @code{shar}. |
| 1566 | |
| 1567 | @item no-prof |
| 1568 | @samp{-e} in @code{gprof}. |
| 1569 | |
| 1570 | @item no-regex |
| 1571 | @samp{-R} in @code{etags}. |
| 1572 | |
| 1573 | @item no-sort |
| 1574 | @samp{-p} in @code{nm}. |
| 1575 | |
| 1576 | @item no-split |
| 1577 | Used in @code{makeinfo}. |
| 1578 | |
| 1579 | @item no-static |
| 1580 | @samp{-a} in @code{gprof}. |
| 1581 | |
| 1582 | @item no-time |
| 1583 | @samp{-E} in @code{gprof}. |
| 1584 | |
| 1585 | @item no-timestamp |
| 1586 | @samp{-m} in @code{shar}. |
| 1587 | |
| 1588 | @item no-validate |
| 1589 | Used in @code{makeinfo}. |
| 1590 | |
| 1591 | @item no-wait |
| 1592 | Used in @code{emacsclient}. |
| 1593 | |
| 1594 | @item no-warn |
| 1595 | Used in various programs to inhibit warnings. |
| 1596 | |
| 1597 | @item node |
| 1598 | @samp{-n} in @code{info}. |
| 1599 | |
| 1600 | @item nodename |
| 1601 | @samp{-n} in @code{uname}. |
| 1602 | |
| 1603 | @item nonmatching |
| 1604 | @samp{-f} in @code{cpio}. |
| 1605 | |
| 1606 | @item nstuff |
| 1607 | @samp{-n} in @code{objdump}. |
| 1608 | |
| 1609 | @item null |
| 1610 | @samp{-0} in @code{xargs}. |
| 1611 | |
| 1612 | @item number |
| 1613 | @samp{-n} in @code{cat}. |
| 1614 | |
| 1615 | @item number-nonblank |
| 1616 | @samp{-b} in @code{cat}. |
| 1617 | |
| 1618 | @item numeric-sort |
| 1619 | @samp{-n} in @code{nm}. |
| 1620 | |
| 1621 | @item numeric-uid-gid |
| 1622 | @samp{-n} in @code{cpio} and @code{ls}. |
| 1623 | |
| 1624 | @item nx |
| 1625 | Used in GDB. |
| 1626 | |
| 1627 | @item old-archive |
| 1628 | @samp{-o} in @code{tar}. |
| 1629 | |
| 1630 | @item old-file |
| 1631 | @samp{-o} in Make. |
| 1632 | |
| 1633 | @item one-file-system |
| 1634 | @samp{-l} in @code{tar}, @code{cp}, and @code{du}. |
| 1635 | |
| 1636 | @item only-file |
| 1637 | @samp{-o} in @code{ptx}. |
| 1638 | |
| 1639 | @item only-prof |
| 1640 | @samp{-f} in @code{gprof}. |
| 1641 | |
| 1642 | @item only-time |
| 1643 | @samp{-F} in @code{gprof}. |
| 1644 | |
| 1645 | @item options |
| 1646 | @samp{-o} in @code{getopt}, @code{fdlist}, @code{fdmount}, |
| 1647 | @code{fdmountd}, and @code{fdumount}. |
| 1648 | |
| 1649 | @item output |
| 1650 | In various programs, specify the output file name. |
| 1651 | |
| 1652 | @item output-prefix |
| 1653 | @samp{-o} in @code{shar}. |
| 1654 | |
| 1655 | @item override |
| 1656 | @samp{-o} in @code{rm}. |
| 1657 | |
| 1658 | @item overwrite |
| 1659 | @samp{-c} in @code{unshar}. |
| 1660 | |
| 1661 | @item owner |
| 1662 | @samp{-o} in @code{install}. |
| 1663 | |
| 1664 | @item paginate |
| 1665 | @samp{-l} in @code{diff}. |
| 1666 | |
| 1667 | @item paragraph-indent |
| 1668 | Used in @code{makeinfo}. |
| 1669 | |
| 1670 | @item parents |
| 1671 | @samp{-p} in @code{mkdir} and @code{rmdir}. |
| 1672 | |
| 1673 | @item pass-all |
| 1674 | @samp{-p} in @code{ul}. |
| 1675 | |
| 1676 | @item pass-through |
| 1677 | @samp{-p} in @code{cpio}. |
| 1678 | |
| 1679 | @item port |
| 1680 | @samp{-P} in @code{finger}. |
| 1681 | |
| 1682 | @item portability |
| 1683 | @samp{-c} in @code{cpio} and @code{tar}. |
| 1684 | |
| 1685 | @item posix |
| 1686 | Used in @code{gawk}. |
| 1687 | |
| 1688 | @item prefix-builtins |
| 1689 | @samp{-P} in @code{m4}. |
| 1690 | |
| 1691 | @item prefix |
| 1692 | @samp{-f} in @code{csplit}. |
| 1693 | |
| 1694 | @item preserve |
| 1695 | Used in @code{tar} and @code{cp}. |
| 1696 | |
| 1697 | @item preserve-environment |
| 1698 | @samp{-p} in @code{su}. |
| 1699 | |
| 1700 | @item preserve-modification-time |
| 1701 | @samp{-m} in @code{cpio}. |
| 1702 | |
| 1703 | @item preserve-order |
| 1704 | @samp{-s} in @code{tar}. |
| 1705 | |
| 1706 | @item preserve-permissions |
| 1707 | @samp{-p} in @code{tar}. |
| 1708 | |
| 1709 | @item print |
| 1710 | @samp{-l} in @code{diff}. |
| 1711 | |
| 1712 | @item print-chars |
| 1713 | @samp{-L} in @code{cmp}. |
| 1714 | |
| 1715 | @item print-data-base |
| 1716 | @samp{-p} in Make. |
| 1717 | |
| 1718 | @item print-directory |
| 1719 | @samp{-w} in Make. |
| 1720 | |
| 1721 | @item print-file-name |
| 1722 | @samp{-o} in @code{nm}. |
| 1723 | |
| 1724 | @item print-symdefs |
| 1725 | @samp{-s} in @code{nm}. |
| 1726 | |
| 1727 | @item printer |
| 1728 | @samp{-p} in @code{wdiff}. |
| 1729 | |
| 1730 | @item prompt |
| 1731 | @samp{-p} in @code{ed}. |
| 1732 | |
| 1733 | @item proxy |
| 1734 | Specify an HTTP proxy. |
| 1735 | |
| 1736 | @item query-user |
| 1737 | @samp{-X} in @code{shar}. |
| 1738 | |
| 1739 | @item question |
| 1740 | @samp{-q} in Make. |
| 1741 | |
| 1742 | @item quiet |
| 1743 | Used in many programs to inhibit the usual output. @strong{Note:} every |
| 1744 | program accepting @samp{--quiet} should accept @samp{--silent} as a |
| 1745 | synonym. |
| 1746 | |
| 1747 | @item quiet-unshar |
| 1748 | @samp{-Q} in @code{shar} |
| 1749 | |
| 1750 | @item quote-name |
| 1751 | @samp{-Q} in @code{ls}. |
| 1752 | |
| 1753 | @item rcs |
| 1754 | @samp{-n} in @code{diff}. |
| 1755 | |
| 1756 | @item re-interval |
| 1757 | Used in @code{gawk}. |
| 1758 | |
| 1759 | @item read-full-blocks |
| 1760 | @samp{-B} in @code{tar}. |
| 1761 | |
| 1762 | @item readnow |
| 1763 | Used in GDB. |
| 1764 | |
| 1765 | @item recon |
| 1766 | @samp{-n} in Make. |
| 1767 | |
| 1768 | @item record-number |
| 1769 | @samp{-R} in @code{tar}. |
| 1770 | |
| 1771 | @item recursive |
| 1772 | Used in @code{chgrp}, @code{chown}, @code{cp}, @code{ls}, @code{diff}, |
| 1773 | and @code{rm}. |
| 1774 | |
| 1775 | @item reference-limit |
| 1776 | Used in @code{makeinfo}. |
| 1777 | |
| 1778 | @item references |
| 1779 | @samp{-r} in @code{ptx}. |
| 1780 | |
| 1781 | @item regex |
| 1782 | @samp{-r} in @code{tac} and @code{etags}. |
| 1783 | |
| 1784 | @item release |
| 1785 | @samp{-r} in @code{uname}. |
| 1786 | |
| 1787 | @item reload-state |
| 1788 | @samp{-R} in @code{m4}. |
| 1789 | |
| 1790 | @item relocation |
| 1791 | @samp{-r} in @code{objdump}. |
| 1792 | |
| 1793 | @item rename |
| 1794 | @samp{-r} in @code{cpio}. |
| 1795 | |
| 1796 | @item replace |
| 1797 | @samp{-i} in @code{xargs}. |
| 1798 | |
| 1799 | @item report-identical-files |
| 1800 | @samp{-s} in @code{diff}. |
| 1801 | |
| 1802 | @item reset-access-time |
| 1803 | @samp{-a} in @code{cpio}. |
| 1804 | |
| 1805 | @item reverse |
| 1806 | @samp{-r} in @code{ls} and @code{nm}. |
| 1807 | |
| 1808 | @item reversed-ed |
| 1809 | @samp{-f} in @code{diff}. |
| 1810 | |
| 1811 | @item right-side-defs |
| 1812 | @samp{-R} in @code{ptx}. |
| 1813 | |
| 1814 | @item same-order |
| 1815 | @samp{-s} in @code{tar}. |
| 1816 | |
| 1817 | @item same-permissions |
| 1818 | @samp{-p} in @code{tar}. |
| 1819 | |
| 1820 | @item save |
| 1821 | @samp{-g} in @code{stty}. |
| 1822 | |
| 1823 | @item se |
| 1824 | Used in GDB. |
| 1825 | |
| 1826 | @item sentence-regexp |
| 1827 | @samp{-S} in @code{ptx}. |
| 1828 | |
| 1829 | @item separate-dirs |
| 1830 | @samp{-S} in @code{du}. |
| 1831 | |
| 1832 | @item separator |
| 1833 | @samp{-s} in @code{tac}. |
| 1834 | |
| 1835 | @item sequence |
| 1836 | Used by @code{recode} to chose files or pipes for sequencing passes. |
| 1837 | |
| 1838 | @item shell |
| 1839 | @samp{-s} in @code{su}. |
| 1840 | |
| 1841 | @item show-all |
| 1842 | @samp{-A} in @code{cat}. |
| 1843 | |
| 1844 | @item show-c-function |
| 1845 | @samp{-p} in @code{diff}. |
| 1846 | |
| 1847 | @item show-ends |
| 1848 | @samp{-E} in @code{cat}. |
| 1849 | |
| 1850 | @item show-function-line |
| 1851 | @samp{-F} in @code{diff}. |
| 1852 | |
| 1853 | @item show-tabs |
| 1854 | @samp{-T} in @code{cat}. |
| 1855 | |
| 1856 | @item silent |
| 1857 | Used in many programs to inhibit the usual output. |
| 1858 | @strong{Note:} every program accepting |
| 1859 | @samp{--silent} should accept @samp{--quiet} as a synonym. |
| 1860 | |
| 1861 | @item size |
| 1862 | @samp{-s} in @code{ls}. |
| 1863 | |
| 1864 | @item socket |
| 1865 | Specify a file descriptor for a network server to use for its socket, |
| 1866 | instead of opening and binding a new socket. This provides a way to |
| 1867 | run, in a nonpriveledged process, a server that normally needs a |
| 1868 | reserved port number. |
| 1869 | |
| 1870 | @item sort |
| 1871 | Used in @code{ls}. |
| 1872 | |
| 1873 | @item source |
| 1874 | @samp{-W source} in @code{gawk}. |
| 1875 | |
| 1876 | @item sparse |
| 1877 | @samp{-S} in @code{tar}. |
| 1878 | |
| 1879 | @item speed-large-files |
| 1880 | @samp{-H} in @code{diff}. |
| 1881 | |
| 1882 | @item split-at |
| 1883 | @samp{-E} in @code{unshar}. |
| 1884 | |
| 1885 | @item split-size-limit |
| 1886 | @samp{-L} in @code{shar}. |
| 1887 | |
| 1888 | @item squeeze-blank |
| 1889 | @samp{-s} in @code{cat}. |
| 1890 | |
| 1891 | @item start-delete |
| 1892 | @samp{-w} in @code{wdiff}. |
| 1893 | |
| 1894 | @item start-insert |
| 1895 | @samp{-y} in @code{wdiff}. |
| 1896 | |
| 1897 | @item starting-file |
| 1898 | Used in @code{tar} and @code{diff} to specify which file within |
| 1899 | a directory to start processing with. |
| 1900 | |
| 1901 | @item statistics |
| 1902 | @samp{-s} in @code{wdiff}. |
| 1903 | |
| 1904 | @item stdin-file-list |
| 1905 | @samp{-S} in @code{shar}. |
| 1906 | |
| 1907 | @item stop |
| 1908 | @samp{-S} in Make. |
| 1909 | |
| 1910 | @item strict |
| 1911 | @samp{-s} in @code{recode}. |
| 1912 | |
| 1913 | @item strip |
| 1914 | @samp{-s} in @code{install}. |
| 1915 | |
| 1916 | @item strip-all |
| 1917 | @samp{-s} in @code{strip}. |
| 1918 | |
| 1919 | @item strip-debug |
| 1920 | @samp{-S} in @code{strip}. |
| 1921 | |
| 1922 | @item submitter |
| 1923 | @samp{-s} in @code{shar}. |
| 1924 | |
| 1925 | @item suffix |
| 1926 | @samp{-S} in @code{cp}, @code{ln}, @code{mv}. |
| 1927 | |
| 1928 | @item suffix-format |
| 1929 | @samp{-b} in @code{csplit}. |
| 1930 | |
| 1931 | @item sum |
| 1932 | @samp{-s} in @code{gprof}. |
| 1933 | |
| 1934 | @item summarize |
| 1935 | @samp{-s} in @code{du}. |
| 1936 | |
| 1937 | @item symbolic |
| 1938 | @samp{-s} in @code{ln}. |
| 1939 | |
| 1940 | @item symbols |
| 1941 | Used in GDB and @code{objdump}. |
| 1942 | |
| 1943 | @item synclines |
| 1944 | @samp{-s} in @code{m4}. |
| 1945 | |
| 1946 | @item sysname |
| 1947 | @samp{-s} in @code{uname}. |
| 1948 | |
| 1949 | @item tabs |
| 1950 | @samp{-t} in @code{expand} and @code{unexpand}. |
| 1951 | |
| 1952 | @item tabsize |
| 1953 | @samp{-T} in @code{ls}. |
| 1954 | |
| 1955 | @item terminal |
| 1956 | @samp{-T} in @code{tput} and @code{ul}. |
| 1957 | @samp{-t} in @code{wdiff}. |
| 1958 | |
| 1959 | @item text |
| 1960 | @samp{-a} in @code{diff}. |
| 1961 | |
| 1962 | @item text-files |
| 1963 | @samp{-T} in @code{shar}. |
| 1964 | |
| 1965 | @item time |
| 1966 | Used in @code{ls} and @code{touch}. |
| 1967 | |
| 1968 | @item timeout |
| 1969 | Specify how long to wait before giving up on some operation. |
| 1970 | |
| 1971 | @item to-stdout |
| 1972 | @samp{-O} in @code{tar}. |
| 1973 | |
| 1974 | @item total |
| 1975 | @samp{-c} in @code{du}. |
| 1976 | |
| 1977 | @item touch |
| 1978 | @samp{-t} in Make, @code{ranlib}, and @code{recode}. |
| 1979 | |
| 1980 | @item trace |
| 1981 | @samp{-t} in @code{m4}. |
| 1982 | |
| 1983 | @item traditional |
| 1984 | @samp{-t} in @code{hello}; |
| 1985 | @samp{-W traditional} in @code{gawk}; |
| 1986 | @samp{-G} in @code{ed}, @code{m4}, and @code{ptx}. |
| 1987 | |
| 1988 | @item tty |
| 1989 | Used in GDB. |
| 1990 | |
| 1991 | @item typedefs |
| 1992 | @samp{-t} in @code{ctags}. |
| 1993 | |
| 1994 | @item typedefs-and-c++ |
| 1995 | @samp{-T} in @code{ctags}. |
| 1996 | |
| 1997 | @item typeset-mode |
| 1998 | @samp{-t} in @code{ptx}. |
| 1999 | |
| 2000 | @item uncompress |
| 2001 | @samp{-z} in @code{tar}. |
| 2002 | |
| 2003 | @item unconditional |
| 2004 | @samp{-u} in @code{cpio}. |
| 2005 | |
| 2006 | @item undefine |
| 2007 | @samp{-U} in @code{m4}. |
| 2008 | |
| 2009 | @item undefined-only |
| 2010 | @samp{-u} in @code{nm}. |
| 2011 | |
| 2012 | @item update |
| 2013 | @samp{-u} in @code{cp}, @code{ctags}, @code{mv}, @code{tar}. |
| 2014 | |
| 2015 | @item usage |
| 2016 | Used in @code{gawk}; same as @samp{--help}. |
| 2017 | |
| 2018 | @item uuencode |
| 2019 | @samp{-B} in @code{shar}. |
| 2020 | |
| 2021 | @item vanilla-operation |
| 2022 | @samp{-V} in @code{shar}. |
| 2023 | |
| 2024 | @item verbose |
| 2025 | Print more information about progress. Many programs support this. |
| 2026 | |
| 2027 | @item verify |
| 2028 | @samp{-W} in @code{tar}. |
| 2029 | |
| 2030 | @item version |
| 2031 | Print the version number. |
| 2032 | |
| 2033 | @item version-control |
| 2034 | @samp{-V} in @code{cp}, @code{ln}, @code{mv}. |
| 2035 | |
| 2036 | @item vgrind |
| 2037 | @samp{-v} in @code{ctags}. |
| 2038 | |
| 2039 | @item volume |
| 2040 | @samp{-V} in @code{tar}. |
| 2041 | |
| 2042 | @item what-if |
| 2043 | @samp{-W} in Make. |
| 2044 | |
| 2045 | @item whole-size-limit |
| 2046 | @samp{-l} in @code{shar}. |
| 2047 | |
| 2048 | @item width |
| 2049 | @samp{-w} in @code{ls} and @code{ptx}. |
| 2050 | |
| 2051 | @item word-regexp |
| 2052 | @samp{-W} in @code{ptx}. |
| 2053 | |
| 2054 | @item writable |
| 2055 | @samp{-T} in @code{who}. |
| 2056 | |
| 2057 | @item zeros |
| 2058 | @samp{-z} in @code{gprof}. |
| 2059 | @end table |
| 2060 | |
| 2061 | @node Memory Usage |
| 2062 | @section Memory Usage |
| 2063 | @cindex memory usage |
| 2064 | |
| 2065 | If a program typically uses just a few meg of memory, don't bother making any |
| 2066 | effort to reduce memory usage. For example, if it is impractical for |
| 2067 | other reasons to operate on files more than a few meg long, it is |
| 2068 | reasonable to read entire input files into core to operate on them. |
| 2069 | |
| 2070 | However, for programs such as @code{cat} or @code{tail}, that can |
| 2071 | usefully operate on very large files, it is important to avoid using a |
| 2072 | technique that would artificially limit the size of files it can handle. |
| 2073 | If a program works by lines and could be applied to arbitrary |
| 2074 | user-supplied input files, it should keep only a line in memory, because |
| 2075 | this is not very hard and users will want to be able to operate on input |
| 2076 | files that are bigger than will fit in core all at once. |
| 2077 | |
| 2078 | If your program creates complicated data structures, just make them in |
| 2079 | core and give a fatal error if @code{malloc} returns zero. |
| 2080 | |
| 2081 | @node File Usage |
| 2082 | @section File Usage |
| 2083 | @cindex file usage |
| 2084 | |
| 2085 | Programs should be prepared to operate when @file{/usr} and @file{/etc} |
| 2086 | are read-only file systems. Thus, if the program manages log files, |
| 2087 | lock files, backup files, score files, or any other files which are |
| 2088 | modified for internal purposes, these files should not be stored in |
| 2089 | @file{/usr} or @file{/etc}. |
| 2090 | |
| 2091 | There are two exceptions. @file{/etc} is used to store system |
| 2092 | configuration information; it is reasonable for a program to modify |
| 2093 | files in @file{/etc} when its job is to update the system configuration. |
| 2094 | Also, if the user explicitly asks to modify one file in a directory, it |
| 2095 | is reasonable for the program to store other files in the same |
| 2096 | directory. |
| 2097 | |
| 2098 | @node Writing C |
| 2099 | @chapter Making The Best Use of C |
| 2100 | |
| 2101 | This @value{CHAPTER} provides advice on how best to use the C language |
| 2102 | when writing GNU software. |
| 2103 | |
| 2104 | @menu |
| 2105 | * Formatting:: Formatting Your Source Code |
| 2106 | * Comments:: Commenting Your Work |
| 2107 | * Syntactic Conventions:: Clean Use of C Constructs |
| 2108 | * Names:: Naming Variables, Functions, and Files |
| 2109 | * System Portability:: Portability between different operating systems |
| 2110 | * CPU Portability:: Supporting the range of CPU types |
| 2111 | * System Functions:: Portability and ``standard'' library functions |
| 2112 | * Internationalization:: Techniques for internationalization |
| 2113 | * Mmap:: How you can safely use @code{mmap}. |
| 2114 | @end menu |
| 2115 | |
| 2116 | @node Formatting |
| 2117 | @section Formatting Your Source Code |
| 2118 | @cindex formatting source code |
| 2119 | |
| 2120 | @cindex open brace |
| 2121 | @cindex braces, in C source |
| 2122 | It is important to put the open-brace that starts the body of a C |
| 2123 | function in column zero, and avoid putting any other open-brace or |
| 2124 | open-parenthesis or open-bracket in column zero. Several tools look |
| 2125 | for open-braces in column zero to find the beginnings of C functions. |
| 2126 | These tools will not work on code not formatted that way. |
| 2127 | |
| 2128 | It is also important for function definitions to start the name of the |
| 2129 | function in column zero. This helps people to search for function |
| 2130 | definitions, and may also help certain tools recognize them. Thus, |
| 2131 | the proper format is this: |
| 2132 | |
| 2133 | @example |
| 2134 | static char * |
| 2135 | concat (s1, s2) /* Name starts in column zero here */ |
| 2136 | char *s1, *s2; |
| 2137 | @{ /* Open brace in column zero here */ |
| 2138 | @dots{} |
| 2139 | @} |
| 2140 | @end example |
| 2141 | |
| 2142 | @noindent |
| 2143 | or, if you want to use Standard C syntax, format the definition like |
| 2144 | this: |
| 2145 | |
| 2146 | @example |
| 2147 | static char * |
| 2148 | concat (char *s1, char *s2) |
| 2149 | @{ |
| 2150 | @dots{} |
| 2151 | @} |
| 2152 | @end example |
| 2153 | |
| 2154 | In Standard C, if the arguments don't fit nicely on one line, |
| 2155 | split it like this: |
| 2156 | |
| 2157 | @example |
| 2158 | int |
| 2159 | lots_of_args (int an_integer, long a_long, short a_short, |
| 2160 | double a_double, float a_float) |
| 2161 | @dots{} |
| 2162 | @end example |
| 2163 | |
| 2164 | The rest of this section gives our recommendations for other aspects of |
| 2165 | C formatting style, which is also the default style of the @code{indent} |
| 2166 | program in version 1.2 and newer. It corresponds to the options |
| 2167 | |
| 2168 | @smallexample |
| 2169 | -nbad -bap -nbc -bbo -bl -bli2 -bls -ncdb -nce -cp1 -cs -di2 |
| 2170 | -ndj -nfc1 -nfca -hnl -i2 -ip5 -lp -pcs -psl -nsc -nsob |
| 2171 | @end smallexample |
| 2172 | |
| 2173 | We don't think of these recommendations as requirements, because it |
| 2174 | causes no problems for users if two different programs have different |
| 2175 | formatting styles. |
| 2176 | |
| 2177 | But whatever style you use, please use it consistently, since a mixture |
| 2178 | of styles within one program tends to look ugly. If you are |
| 2179 | contributing changes to an existing program, please follow the style of |
| 2180 | that program. |
| 2181 | |
| 2182 | For the body of the function, our recommended style looks like this: |
| 2183 | |
| 2184 | @example |
| 2185 | if (x < foo (y, z)) |
| 2186 | haha = bar[4] + 5; |
| 2187 | else |
| 2188 | @{ |
| 2189 | while (z) |
| 2190 | @{ |
| 2191 | haha += foo (z, z); |
| 2192 | z--; |
| 2193 | @} |
| 2194 | return ++x + bar (); |
| 2195 | @} |
| 2196 | @end example |
| 2197 | |
| 2198 | @cindex spaces before open-paren |
| 2199 | We find it easier to read a program when it has spaces before the |
| 2200 | open-parentheses and after the commas. Especially after the commas. |
| 2201 | |
| 2202 | When you split an expression into multiple lines, split it |
| 2203 | before an operator, not after one. Here is the right way: |
| 2204 | |
| 2205 | @cindex expressions, splitting |
| 2206 | @example |
| 2207 | if (foo_this_is_long && bar > win (x, y, z) |
| 2208 | && remaining_condition) |
| 2209 | @end example |
| 2210 | |
| 2211 | Try to avoid having two operators of different precedence at the same |
| 2212 | level of indentation. For example, don't write this: |
| 2213 | |
| 2214 | @example |
| 2215 | mode = (inmode[j] == VOIDmode |
| 2216 | || GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j]) |
| 2217 | ? outmode[j] : inmode[j]); |
| 2218 | @end example |
| 2219 | |
| 2220 | Instead, use extra parentheses so that the indentation shows the nesting: |
| 2221 | |
| 2222 | @example |
| 2223 | mode = ((inmode[j] == VOIDmode |
| 2224 | || (GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j]))) |
| 2225 | ? outmode[j] : inmode[j]); |
| 2226 | @end example |
| 2227 | |
| 2228 | Insert extra parentheses so that Emacs will indent the code properly. |
| 2229 | For example, the following indentation looks nice if you do it by hand, |
| 2230 | |
| 2231 | @example |
| 2232 | v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000 |
| 2233 | + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000; |
| 2234 | @end example |
| 2235 | |
| 2236 | @noindent |
| 2237 | but Emacs would alter it. Adding a set of parentheses produces |
| 2238 | something that looks equally nice, and which Emacs will preserve: |
| 2239 | |
| 2240 | @example |
| 2241 | v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000 |
| 2242 | + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000); |
| 2243 | @end example |
| 2244 | |
| 2245 | Format do-while statements like this: |
| 2246 | |
| 2247 | @example |
| 2248 | do |
| 2249 | @{ |
| 2250 | a = foo (a); |
| 2251 | @} |
| 2252 | while (a > 0); |
| 2253 | @end example |
| 2254 | |
| 2255 | @cindex formfeed |
| 2256 | @cindex control-L |
| 2257 | Please use formfeed characters (control-L) to divide the program into |
| 2258 | pages at logical places (but not within a function). It does not matter |
| 2259 | just how long the pages are, since they do not have to fit on a printed |
| 2260 | page. The formfeeds should appear alone on lines by themselves. |
| 2261 | |
| 2262 | @node Comments |
| 2263 | @section Commenting Your Work |
| 2264 | @cindex commenting |
| 2265 | |
| 2266 | Every program should start with a comment saying briefly what it is for. |
| 2267 | Example: @samp{fmt - filter for simple filling of text}. |
| 2268 | |
| 2269 | Please write the comments in a GNU program in English, because English |
| 2270 | is the one language that nearly all programmers in all countries can |
| 2271 | read. If you do not write English well, please write comments in |
| 2272 | English as well as you can, then ask other people to help rewrite them. |
| 2273 | If you can't write comments in English, please find someone to work with |
| 2274 | you and translate your comments into English. |
| 2275 | |
| 2276 | Please put a comment on each function saying what the function does, |
| 2277 | what sorts of arguments it gets, and what the possible values of |
| 2278 | arguments mean and are used for. It is not necessary to duplicate in |
| 2279 | words the meaning of the C argument declarations, if a C type is being |
| 2280 | used in its customary fashion. If there is anything nonstandard about |
| 2281 | its use (such as an argument of type @code{char *} which is really the |
| 2282 | address of the second character of a string, not the first), or any |
| 2283 | possible values that would not work the way one would expect (such as, |
| 2284 | that strings containing newlines are not guaranteed to work), be sure |
| 2285 | to say so. |
| 2286 | |
| 2287 | Also explain the significance of the return value, if there is one. |
| 2288 | |
| 2289 | Please put two spaces after the end of a sentence in your comments, so |
| 2290 | that the Emacs sentence commands will work. Also, please write |
| 2291 | complete sentences and capitalize the first word. If a lower-case |
| 2292 | identifier comes at the beginning of a sentence, don't capitalize it! |
| 2293 | Changing the spelling makes it a different identifier. If you don't |
| 2294 | like starting a sentence with a lower case letter, write the sentence |
| 2295 | differently (e.g., ``The identifier lower-case is @dots{}''). |
| 2296 | |
| 2297 | The comment on a function is much clearer if you use the argument |
| 2298 | names to speak about the argument values. The variable name itself |
| 2299 | should be lower case, but write it in upper case when you are speaking |
| 2300 | about the value rather than the variable itself. Thus, ``the inode |
| 2301 | number NODE_NUM'' rather than ``an inode''. |
| 2302 | |
| 2303 | There is usually no purpose in restating the name of the function in |
| 2304 | the comment before it, because the reader can see that for himself. |
| 2305 | There might be an exception when the comment is so long that the function |
| 2306 | itself would be off the bottom of the screen. |
| 2307 | |
| 2308 | There should be a comment on each static variable as well, like this: |
| 2309 | |
| 2310 | @example |
| 2311 | /* Nonzero means truncate lines in the display; |
| 2312 | zero means continue them. */ |
| 2313 | int truncate_lines; |
| 2314 | @end example |
| 2315 | |
| 2316 | @cindex conditionals, comments for |
| 2317 | @cindex @code{#endif}, commenting |
| 2318 | Every @samp{#endif} should have a comment, except in the case of short |
| 2319 | conditionals (just a few lines) that are not nested. The comment should |
| 2320 | state the condition of the conditional that is ending, @emph{including |
| 2321 | its sense}. @samp{#else} should have a comment describing the condition |
| 2322 | @emph{and sense} of the code that follows. For example: |
| 2323 | |
| 2324 | @example |
| 2325 | @group |
| 2326 | #ifdef foo |
| 2327 | @dots{} |
| 2328 | #else /* not foo */ |
| 2329 | @dots{} |
| 2330 | #endif /* not foo */ |
| 2331 | @end group |
| 2332 | @group |
| 2333 | #ifdef foo |
| 2334 | @dots{} |
| 2335 | #endif /* foo */ |
| 2336 | @end group |
| 2337 | @end example |
| 2338 | |
| 2339 | @noindent |
| 2340 | but, by contrast, write the comments this way for a @samp{#ifndef}: |
| 2341 | |
| 2342 | @example |
| 2343 | @group |
| 2344 | #ifndef foo |
| 2345 | @dots{} |
| 2346 | #else /* foo */ |
| 2347 | @dots{} |
| 2348 | #endif /* foo */ |
| 2349 | @end group |
| 2350 | @group |
| 2351 | #ifndef foo |
| 2352 | @dots{} |
| 2353 | #endif /* not foo */ |
| 2354 | @end group |
| 2355 | @end example |
| 2356 | |
| 2357 | @node Syntactic Conventions |
| 2358 | @section Clean Use of C Constructs |
| 2359 | @cindex syntactic conventions |
| 2360 | |
| 2361 | @cindex implicit @code{int} |
| 2362 | @cindex function argument, declaring |
| 2363 | Please explicitly declare the types of all objects. For example, you |
| 2364 | should explicitly declare all arguments to functions, and you should |
| 2365 | declare functions to return @code{int} rather than omitting the |
| 2366 | @code{int}. |
| 2367 | |
| 2368 | @cindex compiler warnings |
| 2369 | @cindex @samp{-Wall} compiler option |
| 2370 | Some programmers like to use the GCC @samp{-Wall} option, and change the |
| 2371 | code whenever it issues a warning. If you want to do this, then do. |
| 2372 | Other programmers prefer not to use @samp{-Wall}, because it gives |
| 2373 | warnings for valid and legitimate code which they do not want to change. |
| 2374 | If you want to do this, then do. The compiler should be your servant, |
| 2375 | not your master. |
| 2376 | |
| 2377 | Declarations of external functions and functions to appear later in the |
| 2378 | source file should all go in one place near the beginning of the file |
| 2379 | (somewhere before the first function definition in the file), or else |
| 2380 | should go in a header file. Don't put @code{extern} declarations inside |
| 2381 | functions. |
| 2382 | |
| 2383 | @cindex temporary variables |
| 2384 | It used to be common practice to use the same local variables (with |
| 2385 | names like @code{tem}) over and over for different values within one |
| 2386 | function. Instead of doing this, it is better declare a separate local |
| 2387 | variable for each distinct purpose, and give it a name which is |
| 2388 | meaningful. This not only makes programs easier to understand, it also |
| 2389 | facilitates optimization by good compilers. You can also move the |
| 2390 | declaration of each local variable into the smallest scope that includes |
| 2391 | all its uses. This makes the program even cleaner. |
| 2392 | |
| 2393 | Don't use local variables or parameters that shadow global identifiers. |
| 2394 | |
| 2395 | @cindex multiple variables in a line |
| 2396 | Don't declare multiple variables in one declaration that spans lines. |
| 2397 | Start a new declaration on each line, instead. For example, instead |
| 2398 | of this: |
| 2399 | |
| 2400 | @example |
| 2401 | @group |
| 2402 | int foo, |
| 2403 | bar; |
| 2404 | @end group |
| 2405 | @end example |
| 2406 | |
| 2407 | @noindent |
| 2408 | write either this: |
| 2409 | |
| 2410 | @example |
| 2411 | int foo, bar; |
| 2412 | @end example |
| 2413 | |
| 2414 | @noindent |
| 2415 | or this: |
| 2416 | |
| 2417 | @example |
| 2418 | int foo; |
| 2419 | int bar; |
| 2420 | @end example |
| 2421 | |
| 2422 | @noindent |
| 2423 | (If they are global variables, each should have a comment preceding it |
| 2424 | anyway.) |
| 2425 | |
| 2426 | When you have an @code{if}-@code{else} statement nested in another |
| 2427 | @code{if} statement, always put braces around the @code{if}-@code{else}. |
| 2428 | Thus, never write like this: |
| 2429 | |
| 2430 | @example |
| 2431 | if (foo) |
| 2432 | if (bar) |
| 2433 | win (); |
| 2434 | else |
| 2435 | lose (); |
| 2436 | @end example |
| 2437 | |
| 2438 | @noindent |
| 2439 | always like this: |
| 2440 | |
| 2441 | @example |
| 2442 | if (foo) |
| 2443 | @{ |
| 2444 | if (bar) |
| 2445 | win (); |
| 2446 | else |
| 2447 | lose (); |
| 2448 | @} |
| 2449 | @end example |
| 2450 | |
| 2451 | If you have an @code{if} statement nested inside of an @code{else} |
| 2452 | statement, either write @code{else if} on one line, like this, |
| 2453 | |
| 2454 | @example |
| 2455 | if (foo) |
| 2456 | @dots{} |
| 2457 | else if (bar) |
| 2458 | @dots{} |
| 2459 | @end example |
| 2460 | |
| 2461 | @noindent |
| 2462 | with its @code{then}-part indented like the preceding @code{then}-part, |
| 2463 | or write the nested @code{if} within braces like this: |
| 2464 | |
| 2465 | @example |
| 2466 | if (foo) |
| 2467 | @dots{} |
| 2468 | else |
| 2469 | @{ |
| 2470 | if (bar) |
| 2471 | @dots{} |
| 2472 | @} |
| 2473 | @end example |
| 2474 | |
| 2475 | Don't declare both a structure tag and variables or typedefs in the |
| 2476 | same declaration. Instead, declare the structure tag separately |
| 2477 | and then use it to declare the variables or typedefs. |
| 2478 | |
| 2479 | Try to avoid assignments inside @code{if}-conditions. For example, |
| 2480 | don't write this: |
| 2481 | |
| 2482 | @example |
| 2483 | if ((foo = (char *) malloc (sizeof *foo)) == 0) |
| 2484 | fatal ("virtual memory exhausted"); |
| 2485 | @end example |
| 2486 | |
| 2487 | @noindent |
| 2488 | instead, write this: |
| 2489 | |
| 2490 | @example |
| 2491 | foo = (char *) malloc (sizeof *foo); |
| 2492 | if (foo == 0) |
| 2493 | fatal ("virtual memory exhausted"); |
| 2494 | @end example |
| 2495 | |
| 2496 | @pindex lint |
| 2497 | Don't make the program ugly to placate @code{lint}. Please don't insert any |
| 2498 | casts to @code{void}. Zero without a cast is perfectly fine as a null |
| 2499 | pointer constant, except when calling a varargs function. |
| 2500 | |
| 2501 | @node Names |
| 2502 | @section Naming Variables, Functions, and Files |
| 2503 | |
| 2504 | @cindex names of variables, functions, and files |
| 2505 | The names of global variables and functions in a program serve as |
| 2506 | comments of a sort. So don't choose terse names---instead, look for |
| 2507 | names that give useful information about the meaning of the variable or |
| 2508 | function. In a GNU program, names should be English, like other |
| 2509 | comments. |
| 2510 | |
| 2511 | Local variable names can be shorter, because they are used only within |
| 2512 | one context, where (presumably) comments explain their purpose. |
| 2513 | |
| 2514 | Try to limit your use of abbreviations in symbol names. It is ok to |
| 2515 | make a few abbreviations, explain what they mean, and then use them |
| 2516 | frequently, but don't use lots of obscure abbreviations. |
| 2517 | |
| 2518 | Please use underscores to separate words in a name, so that the Emacs |
| 2519 | word commands can be useful within them. Stick to lower case; reserve |
| 2520 | upper case for macros and @code{enum} constants, and for name-prefixes |
| 2521 | that follow a uniform convention. |
| 2522 | |
| 2523 | For example, you should use names like @code{ignore_space_change_flag}; |
| 2524 | don't use names like @code{iCantReadThis}. |
| 2525 | |
| 2526 | Variables that indicate whether command-line options have been |
| 2527 | specified should be named after the meaning of the option, not after |
| 2528 | the option-letter. A comment should state both the exact meaning of |
| 2529 | the option and its letter. For example, |
| 2530 | |
| 2531 | @example |
| 2532 | @group |
| 2533 | /* Ignore changes in horizontal whitespace (-b). */ |
| 2534 | int ignore_space_change_flag; |
| 2535 | @end group |
| 2536 | @end example |
| 2537 | |
| 2538 | When you want to define names with constant integer values, use |
| 2539 | @code{enum} rather than @samp{#define}. GDB knows about enumeration |
| 2540 | constants. |
| 2541 | |
| 2542 | @cindex file-name limitations |
| 2543 | @pindex doschk |
| 2544 | You might want to make sure that none of the file names would conflict |
| 2545 | the files were loaded onto an MS-DOS file system which shortens the |
| 2546 | names. You can use the program @code{doschk} to test for this. |
| 2547 | |
| 2548 | Some GNU programs were designed to limit themselves to file names of 14 |
| 2549 | characters or less, to avoid file name conflicts if they are read into |
| 2550 | older System V systems. Please preserve this feature in the existing |
| 2551 | GNU programs that have it, but there is no need to do this in new GNU |
| 2552 | programs. @code{doschk} also reports file names longer than 14 |
| 2553 | characters. |
| 2554 | |
| 2555 | @node System Portability |
| 2556 | @section Portability between System Types |
| 2557 | @cindex portability, between system types |
| 2558 | |
| 2559 | In the Unix world, ``portability'' refers to porting to different Unix |
| 2560 | versions. For a GNU program, this kind of portability is desirable, but |
| 2561 | not paramount. |
| 2562 | |
| 2563 | The primary purpose of GNU software is to run on top of the GNU kernel, |
| 2564 | compiled with the GNU C compiler, on various types of @sc{cpu}. So the |
| 2565 | kinds of portability that are absolutely necessary are quite limited. |
| 2566 | But it is important to support Linux-based GNU systems, since they |
| 2567 | are the form of GNU that is popular. |
| 2568 | |
| 2569 | Beyond that, it is good to support the other free operating systems |
| 2570 | (*BSD), and it is nice to support other Unix-like systems if you want |
| 2571 | to. Supporting a variety of Unix-like systems is desirable, although |
| 2572 | not paramount. It is usually not too hard, so you may as well do it. |
| 2573 | But you don't have to consider it an obligation, if it does turn out to |
| 2574 | be hard. |
| 2575 | |
| 2576 | @pindex autoconf |
| 2577 | The easiest way to achieve portability to most Unix-like systems is to |
| 2578 | use Autoconf. It's unlikely that your program needs to know more |
| 2579 | information about the host platform than Autoconf can provide, simply |
| 2580 | because most of the programs that need such knowledge have already been |
| 2581 | written. |
| 2582 | |
| 2583 | Avoid using the format of semi-internal data bases (e.g., directories) |
| 2584 | when there is a higher-level alternative (@code{readdir}). |
| 2585 | |
| 2586 | @cindex non-@sc{posix} systems, and portability |
| 2587 | As for systems that are not like Unix, such as MSDOS, Windows, the |
| 2588 | Macintosh, VMS, and MVS, supporting them is often a lot of work. When |
| 2589 | that is the case, it is better to spend your time adding features that |
| 2590 | will be useful on GNU and GNU/Linux, rather than on supporting other |
| 2591 | incompatible systems. |
| 2592 | |
| 2593 | It is a good idea to define the ``feature test macro'' |
| 2594 | @code{_GNU_SOURCE} when compiling your C files. When you compile on GNU |
| 2595 | or GNU/Linux, this will enable the declarations of GNU library extension |
| 2596 | functions, and that will usually give you a compiler error message if |
| 2597 | you define the same function names in some other way in your program. |
| 2598 | (You don't have to actually @emph{use} these functions, if you prefer |
| 2599 | to make the program more portable to other systems.) |
| 2600 | |
| 2601 | But whether or not you use these GNU extensions, you should avoid |
| 2602 | using their names for any other meanings. Doing so would make it hard |
| 2603 | to move your code into other GNU programs. |
| 2604 | |
| 2605 | @node CPU Portability |
| 2606 | @section Portability between @sc{cpu}s |
| 2607 | |
| 2608 | @cindex data types, and portability |
| 2609 | @cindex portability, and data types |
| 2610 | Even GNU systems will differ because of differences among @sc{cpu} |
| 2611 | types---for example, difference in byte ordering and alignment |
| 2612 | requirements. It is absolutely essential to handle these differences. |
| 2613 | However, don't make any effort to cater to the possibility that an |
| 2614 | @code{int} will be less than 32 bits. We don't support 16-bit machines |
| 2615 | in GNU. |
| 2616 | |
| 2617 | Similarly, don't make any effort to cater to the possibility that |
| 2618 | @code{long} will be smaller than predefined types like @code{size_t}. |
| 2619 | For example, the following code is ok: |
| 2620 | |
| 2621 | @example |
| 2622 | printf ("size = %lu\n", (unsigned long) sizeof array); |
| 2623 | printf ("diff = %ld\n", (long) (pointer2 - pointer1)); |
| 2624 | @end example |
| 2625 | |
| 2626 | 1989 Standard C requires this to work, and we know of only one |
| 2627 | counterexample: 64-bit programs on Microsoft Windows IA-64. We will |
| 2628 | leave it to those who want to port GNU programs to that environment |
| 2629 | to figure out how to do it. |
| 2630 | |
| 2631 | Predefined file-size types like @code{off_t} are an exception: they are |
| 2632 | longer than @code{long} on many platforms, so code like the above won't |
| 2633 | work with them. One way to print an @code{off_t} value portably is to |
| 2634 | print its digits yourself, one by one. |
| 2635 | |
| 2636 | Don't assume that the address of an @code{int} object is also the |
| 2637 | address of its least-significant byte. This is false on big-endian |
| 2638 | machines. Thus, don't make the following mistake: |
| 2639 | |
| 2640 | @example |
| 2641 | int c; |
| 2642 | @dots{} |
| 2643 | while ((c = getchar()) != EOF) |
| 2644 | write(file_descriptor, &c, 1); |
| 2645 | @end example |
| 2646 | |
| 2647 | When calling functions, you need not worry about the difference between |
| 2648 | pointers of various types, or between pointers and integers. On most |
| 2649 | machines, there's no difference anyway. As for the few machines where |
| 2650 | there is a difference, all of them support Standard C prototypes, so you can |
| 2651 | use prototypes (perhaps conditionalized to be active only in Standard C) |
| 2652 | to make the code work on those systems. |
| 2653 | |
| 2654 | In certain cases, it is ok to pass integer and pointer arguments |
| 2655 | indiscriminately to the same function, and use no prototype on any |
| 2656 | system. For example, many GNU programs have error-reporting functions |
| 2657 | that pass their arguments along to @code{printf} and friends: |
| 2658 | |
| 2659 | @example |
| 2660 | error (s, a1, a2, a3) |
| 2661 | char *s; |
| 2662 | char *a1, *a2, *a3; |
| 2663 | @{ |
| 2664 | fprintf (stderr, "error: "); |
| 2665 | fprintf (stderr, s, a1, a2, a3); |
| 2666 | @} |
| 2667 | @end example |
| 2668 | |
| 2669 | @noindent |
| 2670 | In practice, this works on all machines, since a pointer is generally |
| 2671 | the widest possible kind of argument; it is much simpler than any |
| 2672 | ``correct'' alternative. Be sure @emph{not} to use a prototype for such |
| 2673 | functions. |
| 2674 | |
| 2675 | If you have decided to use Standard C, then you can instead define |
| 2676 | @code{error} using @file{stdarg.h}, and pass the arguments along to |
| 2677 | @code{vfprintf}. |
| 2678 | |
| 2679 | @cindex casting pointers to integers |
| 2680 | Avoid casting pointers to integers if you can. Such casts greatly |
| 2681 | reduce portability, and in most programs they are easy to avoid. In the |
| 2682 | cases where casting pointers to integers is essential---such as, a Lisp |
| 2683 | interpreter which stores type information as well as an address in one |
| 2684 | word---you'll have to make explicit provisions to handle different word |
| 2685 | sizes. You will also need to make provision for systems in which the |
| 2686 | normal range of addresses you can get from @code{malloc} starts far away |
| 2687 | from zero. |
| 2688 | |
| 2689 | @node System Functions |
| 2690 | @section Calling System Functions |
| 2691 | @cindex library functions, and portability |
| 2692 | @cindex portability, and library functions |
| 2693 | |
| 2694 | C implementations differ substantially. Standard C reduces but does |
| 2695 | not eliminate the incompatibilities; meanwhile, many GNU packages still |
| 2696 | support pre-standard compilers because this is not hard to do. This |
| 2697 | chapter gives recommendations for how to use the more-or-less standard C |
| 2698 | library functions to avoid unnecessary loss of portability. |
| 2699 | |
| 2700 | @itemize @bullet |
| 2701 | @item |
| 2702 | Don't use the return value of @code{sprintf}. It returns the number of |
| 2703 | characters written on some systems, but not on all systems. |
| 2704 | |
| 2705 | @item |
| 2706 | Be aware that @code{vfprintf} is not always available. |
| 2707 | |
| 2708 | @item |
| 2709 | @code{main} should be declared to return type @code{int}. It should |
| 2710 | terminate either by calling @code{exit} or by returning the integer |
| 2711 | status code; make sure it cannot ever return an undefined value. |
| 2712 | |
| 2713 | @cindex declaration for system functions |
| 2714 | @item |
| 2715 | Don't declare system functions explicitly. |
| 2716 | |
| 2717 | Almost any declaration for a system function is wrong on some system. |
| 2718 | To minimize conflicts, leave it to the system header files to declare |
| 2719 | system functions. If the headers don't declare a function, let it |
| 2720 | remain undeclared. |
| 2721 | |
| 2722 | While it may seem unclean to use a function without declaring it, in |
| 2723 | practice this works fine for most system library functions on the |
| 2724 | systems where this really happens; thus, the disadvantage is only |
| 2725 | theoretical. By contrast, actual declarations have frequently caused |
| 2726 | actual conflicts. |
| 2727 | |
| 2728 | @item |
| 2729 | If you must declare a system function, don't specify the argument types. |
| 2730 | Use an old-style declaration, not a Standard C prototype. The more you |
| 2731 | specify about the function, the more likely a conflict. |
| 2732 | |
| 2733 | @item |
| 2734 | In particular, don't unconditionally declare @code{malloc} or |
| 2735 | @code{realloc}. |
| 2736 | |
| 2737 | Most GNU programs use those functions just once, in functions |
| 2738 | conventionally named @code{xmalloc} and @code{xrealloc}. These |
| 2739 | functions call @code{malloc} and @code{realloc}, respectively, and |
| 2740 | check the results. |
| 2741 | |
| 2742 | Because @code{xmalloc} and @code{xrealloc} are defined in your program, |
| 2743 | you can declare them in other files without any risk of type conflict. |
| 2744 | |
| 2745 | On most systems, @code{int} is the same length as a pointer; thus, the |
| 2746 | calls to @code{malloc} and @code{realloc} work fine. For the few |
| 2747 | exceptional systems (mostly 64-bit machines), you can use |
| 2748 | @strong{conditionalized} declarations of @code{malloc} and |
| 2749 | @code{realloc}---or put these declarations in configuration files |
| 2750 | specific to those systems. |
| 2751 | |
| 2752 | @cindex string library functions |
| 2753 | @item |
| 2754 | The string functions require special treatment. Some Unix systems have |
| 2755 | a header file @file{string.h}; others have @file{strings.h}. Neither |
| 2756 | file name is portable. There are two things you can do: use Autoconf to |
| 2757 | figure out which file to include, or don't include either file. |
| 2758 | |
| 2759 | @item |
| 2760 | If you don't include either strings file, you can't get declarations for |
| 2761 | the string functions from the header file in the usual way. |
| 2762 | |
| 2763 | That causes less of a problem than you might think. The newer standard |
| 2764 | string functions should be avoided anyway because many systems still |
| 2765 | don't support them. The string functions you can use are these: |
| 2766 | |
| 2767 | @example |
| 2768 | strcpy strncpy strcat strncat |
| 2769 | strlen strcmp strncmp |
| 2770 | strchr strrchr |
| 2771 | @end example |
| 2772 | |
| 2773 | The copy and concatenate functions work fine without a declaration as |
| 2774 | long as you don't use their values. Using their values without a |
| 2775 | declaration fails on systems where the width of a pointer differs from |
| 2776 | the width of @code{int}, and perhaps in other cases. It is trivial to |
| 2777 | avoid using their values, so do that. |
| 2778 | |
| 2779 | The compare functions and @code{strlen} work fine without a declaration |
| 2780 | on most systems, possibly all the ones that GNU software runs on. |
| 2781 | You may find it necessary to declare them @strong{conditionally} on a |
| 2782 | few systems. |
| 2783 | |
| 2784 | The search functions must be declared to return @code{char *}. Luckily, |
| 2785 | there is no variation in the data type they return. But there is |
| 2786 | variation in their names. Some systems give these functions the names |
| 2787 | @code{index} and @code{rindex}; other systems use the names |
| 2788 | @code{strchr} and @code{strrchr}. Some systems support both pairs of |
| 2789 | names, but neither pair works on all systems. |
| 2790 | |
| 2791 | You should pick a single pair of names and use it throughout your |
| 2792 | program. (Nowadays, it is better to choose @code{strchr} and |
| 2793 | @code{strrchr} for new programs, since those are the standard |
| 2794 | names.) Declare both of those names as functions returning @code{char |
| 2795 | *}. On systems which don't support those names, define them as macros |
| 2796 | in terms of the other pair. For example, here is what to put at the |
| 2797 | beginning of your file (or in a header) if you want to use the names |
| 2798 | @code{strchr} and @code{strrchr} throughout: |
| 2799 | |
| 2800 | @example |
| 2801 | #ifndef HAVE_STRCHR |
| 2802 | #define strchr index |
| 2803 | #endif |
| 2804 | #ifndef HAVE_STRRCHR |
| 2805 | #define strrchr rindex |
| 2806 | #endif |
| 2807 | |
| 2808 | char *strchr (); |
| 2809 | char *strrchr (); |
| 2810 | @end example |
| 2811 | @end itemize |
| 2812 | |
| 2813 | Here we assume that @code{HAVE_STRCHR} and @code{HAVE_STRRCHR} are |
| 2814 | macros defined in systems where the corresponding functions exist. |
| 2815 | One way to get them properly defined is to use Autoconf. |
| 2816 | |
| 2817 | @node Internationalization |
| 2818 | @section Internationalization |
| 2819 | @cindex internationalization |
| 2820 | |
| 2821 | @pindex gettext |
| 2822 | GNU has a library called GNU gettext that makes it easy to translate the |
| 2823 | messages in a program into various languages. You should use this |
| 2824 | library in every program. Use English for the messages as they appear |
| 2825 | in the program, and let gettext provide the way to translate them into |
| 2826 | other languages. |
| 2827 | |
| 2828 | Using GNU gettext involves putting a call to the @code{gettext} macro |
| 2829 | around each string that might need translation---like this: |
| 2830 | |
| 2831 | @example |
| 2832 | printf (gettext ("Processing file `%s'...")); |
| 2833 | @end example |
| 2834 | |
| 2835 | @noindent |
| 2836 | This permits GNU gettext to replace the string @code{"Processing file |
| 2837 | `%s'..."} with a translated version. |
| 2838 | |
| 2839 | Once a program uses gettext, please make a point of writing calls to |
| 2840 | @code{gettext} when you add new strings that call for translation. |
| 2841 | |
| 2842 | Using GNU gettext in a package involves specifying a @dfn{text domain |
| 2843 | name} for the package. The text domain name is used to separate the |
| 2844 | translations for this package from the translations for other packages. |
| 2845 | Normally, the text domain name should be the same as the name of the |
| 2846 | package---for example, @samp{fileutils} for the GNU file utilities. |
| 2847 | |
| 2848 | @cindex message text, and internationalization |
| 2849 | To enable gettext to work well, avoid writing code that makes |
| 2850 | assumptions about the structure of words or sentences. When you want |
| 2851 | the precise text of a sentence to vary depending on the data, use two or |
| 2852 | more alternative string constants each containing a complete sentences, |
| 2853 | rather than inserting conditionalized words or phrases into a single |
| 2854 | sentence framework. |
| 2855 | |
| 2856 | Here is an example of what not to do: |
| 2857 | |
| 2858 | @example |
| 2859 | printf ("%d file%s processed", nfiles, |
| 2860 | nfiles != 1 ? "s" : ""); |
| 2861 | @end example |
| 2862 | |
| 2863 | @noindent |
| 2864 | The problem with that example is that it assumes that plurals are made |
| 2865 | by adding `s'. If you apply gettext to the format string, like this, |
| 2866 | |
| 2867 | @example |
| 2868 | printf (gettext ("%d file%s processed"), nfiles, |
| 2869 | nfiles != 1 ? "s" : ""); |
| 2870 | @end example |
| 2871 | |
| 2872 | @noindent |
| 2873 | the message can use different words, but it will still be forced to use |
| 2874 | `s' for the plural. Here is a better way: |
| 2875 | |
| 2876 | @example |
| 2877 | printf ((nfiles != 1 ? "%d files processed" |
| 2878 | : "%d file processed"), |
| 2879 | nfiles); |
| 2880 | @end example |
| 2881 | |
| 2882 | @noindent |
| 2883 | This way, you can apply gettext to each of the two strings |
| 2884 | independently: |
| 2885 | |
| 2886 | @example |
| 2887 | printf ((nfiles != 1 ? gettext ("%d files processed") |
| 2888 | : gettext ("%d file processed")), |
| 2889 | nfiles); |
| 2890 | @end example |
| 2891 | |
| 2892 | @noindent |
| 2893 | This can be any method of forming the plural of the word for ``file'', and |
| 2894 | also handles languages that require agreement in the word for |
| 2895 | ``processed''. |
| 2896 | |
| 2897 | A similar problem appears at the level of sentence structure with this |
| 2898 | code: |
| 2899 | |
| 2900 | @example |
| 2901 | printf ("# Implicit rule search has%s been done.\n", |
| 2902 | f->tried_implicit ? "" : " not"); |
| 2903 | @end example |
| 2904 | |
| 2905 | @noindent |
| 2906 | Adding @code{gettext} calls to this code cannot give correct results for |
| 2907 | all languages, because negation in some languages requires adding words |
| 2908 | at more than one place in the sentence. By contrast, adding |
| 2909 | @code{gettext} calls does the job straightfowardly if the code starts |
| 2910 | out like this: |
| 2911 | |
| 2912 | @example |
| 2913 | printf (f->tried_implicit |
| 2914 | ? "# Implicit rule search has been done.\n", |
| 2915 | : "# Implicit rule search has not been done.\n"); |
| 2916 | @end example |
| 2917 | |
| 2918 | @node Mmap |
| 2919 | @section Mmap |
| 2920 | @findex mmap |
| 2921 | |
| 2922 | Don't assume that @code{mmap} either works on all files or fails |
| 2923 | for all files. It may work on some files and fail on others. |
| 2924 | |
| 2925 | The proper way to use @code{mmap} is to try it on the specific file for |
| 2926 | which you want to use it---and if @code{mmap} doesn't work, fall back on |
| 2927 | doing the job in another way using @code{read} and @code{write}. |
| 2928 | |
| 2929 | The reason this precaution is needed is that the GNU kernel (the HURD) |
| 2930 | provides a user-extensible file system, in which there can be many |
| 2931 | different kinds of ``ordinary files.'' Many of them support |
| 2932 | @code{mmap}, but some do not. It is important to make programs handle |
| 2933 | all these kinds of files. |
| 2934 | |
| 2935 | @node Documentation |
| 2936 | @chapter Documenting Programs |
| 2937 | @cindex documentation |
| 2938 | |
| 2939 | A GNU program should ideally come with full free documentation, adequate |
| 2940 | for both reference and tutorial purposes. If the package can be |
| 2941 | programmed or extended, the documentation should cover programming or |
| 2942 | extending it, as well as just using it. |
| 2943 | |
| 2944 | @menu |
| 2945 | * GNU Manuals:: Writing proper manuals. |
| 2946 | * Doc Strings and Manuals:: Compiling doc strings doesn't make a manual. |
| 2947 | * Manual Structure Details:: Specific structure conventions. |
| 2948 | * License for Manuals:: Writing the distribution terms for a manual. |
| 2949 | * Manual Credits:: Giving credit to documentation contributors. |
| 2950 | * Printed Manuals:: Mentioning the printed manual. |
| 2951 | * NEWS File:: NEWS files supplement manuals. |
| 2952 | * Change Logs:: Recording Changes |
| 2953 | * Man Pages:: Man pages are secondary. |
| 2954 | * Reading other Manuals:: How far you can go in learning |
| 2955 | from other manuals. |
| 2956 | @end menu |
| 2957 | |
| 2958 | @node GNU Manuals |
| 2959 | @section GNU Manuals |
| 2960 | |
| 2961 | The preferred document format for the GNU system is the Texinfo |
| 2962 | formatting language. Every GNU package should (ideally) have |
| 2963 | documentation in Texinfo both for reference and for learners. Texinfo |
| 2964 | makes it possible to produce a good quality formatted book, using |
| 2965 | @TeX{}, and to generate an Info file. It is also possible to generate |
| 2966 | HTML output from Texinfo source. See the Texinfo manual, either the |
| 2967 | hardcopy, or the on-line version available through @code{info} or the |
| 2968 | Emacs Info subsystem (@kbd{C-h i}). |
| 2969 | |
| 2970 | Nowadays some other formats such as Docbook and Sgmltexi can be |
| 2971 | converted automatically into Texinfo. It is ok to produce the Texinfo |
| 2972 | documentation by conversion this way, as long as it gives good results. |
| 2973 | |
| 2974 | Programmers often find it most natural to structure the documentation |
| 2975 | following the structure of the implementation, which they know. But |
| 2976 | this structure is not necessarily good for explaining how to use the |
| 2977 | program; it may be irrelevant and confusing for a user. |
| 2978 | |
| 2979 | At every level, from the sentences in a paragraph to the grouping of |
| 2980 | topics into separate manuals, the right way to structure documentation |
| 2981 | is according to the concepts and questions that a user will have in mind |
| 2982 | when reading it. Sometimes this structure of ideas matches the |
| 2983 | structure of the implementation of the software being documented---but |
| 2984 | often they are different. Often the most important part of learning to |
| 2985 | write good documentation is learning to notice when you are structuring |
| 2986 | the documentation like the implementation, and think about better |
| 2987 | alternatives. |
| 2988 | |
| 2989 | For example, each program in the GNU system probably ought to be |
| 2990 | documented in one manual; but this does not mean each program should |
| 2991 | have its own manual. That would be following the structure of the |
| 2992 | implementation, rather than the structure that helps the user |
| 2993 | understand. |
| 2994 | |
| 2995 | Instead, each manual should cover a coherent @emph{topic}. For example, |
| 2996 | instead of a manual for @code{diff} and a manual for @code{diff3}, we |
| 2997 | have one manual for ``comparison of files'' which covers both of those |
| 2998 | programs, as well as @code{cmp}. By documenting these programs |
| 2999 | together, we can make the whole subject clearer. |
| 3000 | |
| 3001 | The manual which discusses a program should certainly document all of |
| 3002 | the program's command-line options and all of its commands. It should |
| 3003 | give examples of their use. But don't organize the manual as a list of |
| 3004 | features. Instead, organize it logically, by subtopics. Address the |
| 3005 | questions that a user will ask when thinking about the job that the |
| 3006 | program does. |
| 3007 | |
| 3008 | In general, a GNU manual should serve both as tutorial and reference. |
| 3009 | It should be set up for convenient access to each topic through Info, |
| 3010 | and for reading straight through (appendixes aside). A GNU manual |
| 3011 | should give a good introduction to a beginner reading through from the |
| 3012 | start, and should also provide all the details that hackers want. |
| 3013 | The Bison manual is a good example of this---please take a look at it |
| 3014 | to see what we mean. |
| 3015 | |
| 3016 | That is not as hard as it first sounds. Arrange each chapter as a |
| 3017 | logical breakdown of its topic, but order the sections, and write their |
| 3018 | text, so that reading the chapter straight through makes sense. Do |
| 3019 | likewise when structuring the book into chapters, and when structuring a |
| 3020 | section into paragraphs. The watchword is, @emph{at each point, address |
| 3021 | the most fundamental and important issue raised by the preceding text.} |
| 3022 | |
| 3023 | If necessary, add extra chapters at the beginning of the manual which |
| 3024 | are purely tutorial and cover the basics of the subject. These provide |
| 3025 | the framework for a beginner to understand the rest of the manual. The |
| 3026 | Bison manual provides a good example of how to do this. |
| 3027 | |
| 3028 | To serve as a reference, a manual should have an Index that list all the |
| 3029 | functions, variables, options, and important concepts that are part of |
| 3030 | the program. One combined Index should do for a short manual, but |
| 3031 | sometimes for a complex package it is better to use multiple indices. |
| 3032 | The Texinfo manual includes advice on preparing good index entries, see |
| 3033 | @ref{Index Entries, , Making Index Entries, texinfo, The GNU Texinfo |
| 3034 | Manual}, and see @ref{Indexing Commands, , Defining the Entries of an |
| 3035 | Index, texinfo, The GNU Texinfo manual}. |
| 3036 | |
| 3037 | Don't use Unix man pages as a model for how to write GNU documentation; |
| 3038 | most of them are terse, badly structured, and give inadequate |
| 3039 | explanation of the underlying concepts. (There are, of course, some |
| 3040 | exceptions.) Also, Unix man pages use a particular format which is |
| 3041 | different from what we use in GNU manuals. |
| 3042 | |
| 3043 | Please include an email address in the manual for where to report |
| 3044 | bugs @emph{in the manual}. |
| 3045 | |
| 3046 | Please do not use the term ``pathname'' that is used in Unix |
| 3047 | documentation; use ``file name'' (two words) instead. We use the term |
| 3048 | ``path'' only for search paths, which are lists of directory names. |
| 3049 | |
| 3050 | Please do not use the term ``illegal'' to refer to erroneous input to a |
| 3051 | computer program. Please use ``invalid'' for this, and reserve the term |
| 3052 | ``illegal'' for activities punishable by law. |
| 3053 | |
| 3054 | @node Doc Strings and Manuals |
| 3055 | @section Doc Strings and Manuals |
| 3056 | |
| 3057 | Some programming systems, such as Emacs, provide a documentation string |
| 3058 | for each function, command or variable. You may be tempted to write a |
| 3059 | reference manual by compiling the documentation strings and writing a |
| 3060 | little additional text to go around them---but you must not do it. That |
| 3061 | approach is a fundamental mistake. The text of well-written |
| 3062 | documentation strings will be entirely wrong for a manual. |
| 3063 | |
| 3064 | A documentation string needs to stand alone---when it appears on the |
| 3065 | screen, there will be no other text to introduce or explain it. |
| 3066 | Meanwhile, it can be rather informal in style. |
| 3067 | |
| 3068 | The text describing a function or variable in a manual must not stand |
| 3069 | alone; it appears in the context of a section or subsection. Other text |
| 3070 | at the beginning of the section should explain some of the concepts, and |
| 3071 | should often make some general points that apply to several functions or |
| 3072 | variables. The previous descriptions of functions and variables in the |
| 3073 | section will also have given information about the topic. A description |
| 3074 | written to stand alone would repeat some of that information; this |
| 3075 | redundance looks bad. Meanwhile, the informality that is acceptable in |
| 3076 | a documentation string is totally unacceptable in a manual. |
| 3077 | |
| 3078 | The only good way to use documentation strings in writing a good manual |
| 3079 | is to use them as a source of information for writing good text. |
| 3080 | |
| 3081 | @node Manual Structure Details |
| 3082 | @section Manual Structure Details |
| 3083 | @cindex manual structure |
| 3084 | |
| 3085 | The title page of the manual should state the version of the programs or |
| 3086 | packages documented in the manual. The Top node of the manual should |
| 3087 | also contain this information. If the manual is changing more |
| 3088 | frequently than or independent of the program, also state a version |
| 3089 | number for the manual in both of these places. |
| 3090 | |
| 3091 | Each program documented in the manual should have a node named |
| 3092 | @samp{@var{program} Invocation} or @samp{Invoking @var{program}}. This |
| 3093 | node (together with its subnodes, if any) should describe the program's |
| 3094 | command line arguments and how to run it (the sort of information people |
| 3095 | would look in a man page for). Start with an @samp{@@example} |
| 3096 | containing a template for all the options and arguments that the program |
| 3097 | uses. |
| 3098 | |
| 3099 | Alternatively, put a menu item in some menu whose item name fits one of |
| 3100 | the above patterns. This identifies the node which that item points to |
| 3101 | as the node for this purpose, regardless of the node's actual name. |
| 3102 | |
| 3103 | The @samp{--usage} feature of the Info reader looks for such a node |
| 3104 | or menu item in order to find the relevant text, so it is essential |
| 3105 | for every Texinfo file to have one. |
| 3106 | |
| 3107 | If one manual describes several programs, it should have such a node for |
| 3108 | each program described in the manual. |
| 3109 | |
| 3110 | @node License for Manuals |
| 3111 | @section License for Manuals |
| 3112 | @cindex license for manuals |
| 3113 | |
| 3114 | Please use the GNU Free Documentation License for all GNU manuals that |
| 3115 | are more than a few pages long. Likewise for a collection of short |
| 3116 | documents---you only need one copy of the GNU FDL for the whole |
| 3117 | collection. For a single short document, you can use a very permissive |
| 3118 | non-copyleft license, to avoid taking up space with a long license. |
| 3119 | |
| 3120 | See @uref{http://www.gnu.org/copyleft/fdl-howto.html} for more explanation |
| 3121 | of how to employ the GFDL. |
| 3122 | |
| 3123 | Note that it is not obligatory to include a copy of the GNU GPL or GNU |
| 3124 | LGPL in a manual whose license is neither the GPL nor the LGPL. It can |
| 3125 | be a good idea to include the program's license in a large manual; in a |
| 3126 | short manual, whose size would be increased considerably by including |
| 3127 | the program's license, it is probably better not to include it. |
| 3128 | |
| 3129 | @node Manual Credits |
| 3130 | @section Manual Credits |
| 3131 | @cindex credits for manuals |
| 3132 | |
| 3133 | Please credit the principal human writers of the manual as the authors, |
| 3134 | on the title page of the manual. If a company sponsored the work, thank |
| 3135 | the company in a suitable place in the manual, but do not cite the |
| 3136 | company as an author. |
| 3137 | |
| 3138 | @node Printed Manuals |
| 3139 | @section Printed Manuals |
| 3140 | |
| 3141 | The FSF publishes some GNU manuals in printed form. To encourage sales |
| 3142 | of these manuals, the on-line versions of the manual should mention at |
| 3143 | the very start that the printed manual is available and should point at |
| 3144 | information for getting it---for instance, with a link to the page |
| 3145 | @url{http://www.gnu.org/order/order.html}. This should not be included |
| 3146 | in the printed manual, though, because there it is redundant. |
| 3147 | |
| 3148 | It is also useful to explain in the on-line forms of the manual how the |
| 3149 | user can print out the manual from the sources. |
| 3150 | |
| 3151 | @node NEWS File |
| 3152 | @section The NEWS File |
| 3153 | @cindex @file{NEWS} file |
| 3154 | |
| 3155 | In addition to its manual, the package should have a file named |
| 3156 | @file{NEWS} which contains a list of user-visible changes worth |
| 3157 | mentioning. In each new release, add items to the front of the file and |
| 3158 | identify the version they pertain to. Don't discard old items; leave |
| 3159 | them in the file after the newer items. This way, a user upgrading from |
| 3160 | any previous version can see what is new. |
| 3161 | |
| 3162 | If the @file{NEWS} file gets very long, move some of the older items |
| 3163 | into a file named @file{ONEWS} and put a note at the end referring the |
| 3164 | user to that file. |
| 3165 | |
| 3166 | @node Change Logs |
| 3167 | @section Change Logs |
| 3168 | @cindex change logs |
| 3169 | |
| 3170 | Keep a change log to describe all the changes made to program source |
| 3171 | files. The purpose of this is so that people investigating bugs in the |
| 3172 | future will know about the changes that might have introduced the bug. |
| 3173 | Often a new bug can be found by looking at what was recently changed. |
| 3174 | More importantly, change logs can help you eliminate conceptual |
| 3175 | inconsistencies between different parts of a program, by giving you a |
| 3176 | history of how the conflicting concepts arose and who they came from. |
| 3177 | |
| 3178 | @menu |
| 3179 | * Change Log Concepts:: |
| 3180 | * Style of Change Logs:: |
| 3181 | * Simple Changes:: |
| 3182 | * Conditional Changes:: |
| 3183 | * Indicating the Part Changed:: |
| 3184 | @end menu |
| 3185 | |
| 3186 | @node Change Log Concepts |
| 3187 | @subsection Change Log Concepts |
| 3188 | |
| 3189 | You can think of the change log as a conceptual ``undo list'' which |
| 3190 | explains how earlier versions were different from the current version. |
| 3191 | People can see the current version; they don't need the change log |
| 3192 | to tell them what is in it. What they want from a change log is a |
| 3193 | clear explanation of how the earlier version differed. |
| 3194 | |
| 3195 | The change log file is normally called @file{ChangeLog} and covers an |
| 3196 | entire directory. Each directory can have its own change log, or a |
| 3197 | directory can use the change log of its parent directory--it's up to |
| 3198 | you. |
| 3199 | |
| 3200 | Another alternative is to record change log information with a version |
| 3201 | control system such as RCS or CVS. This can be converted automatically |
| 3202 | to a @file{ChangeLog} file using @code{rcs2log}; in Emacs, the command |
| 3203 | @kbd{C-x v a} (@code{vc-update-change-log}) does the job. |
| 3204 | |
| 3205 | There's no need to describe the full purpose of the changes or how they |
| 3206 | work together. If you think that a change calls for explanation, you're |
| 3207 | probably right. Please do explain it---but please put the explanation |
| 3208 | in comments in the code, where people will see it whenever they see the |
| 3209 | code. For example, ``New function'' is enough for the change log when |
| 3210 | you add a function, because there should be a comment before the |
| 3211 | function definition to explain what it does. |
| 3212 | |
| 3213 | However, sometimes it is useful to write one line to describe the |
| 3214 | overall purpose of a batch of changes. |
| 3215 | |
| 3216 | The easiest way to add an entry to @file{ChangeLog} is with the Emacs |
| 3217 | command @kbd{M-x add-change-log-entry}. An entry should have an |
| 3218 | asterisk, the name of the changed file, and then in parentheses the name |
| 3219 | of the changed functions, variables or whatever, followed by a colon. |
| 3220 | Then describe the changes you made to that function or variable. |
| 3221 | |
| 3222 | @node Style of Change Logs |
| 3223 | @subsection Style of Change Logs |
| 3224 | @cindex change logs, style |
| 3225 | |
| 3226 | Here are some simple examples of change log entries, starting with the |
| 3227 | header line that says who made the change and when, followed by |
| 3228 | descriptions of specific changes. (These examples are drawn from Emacs |
| 3229 | and GCC.) |
| 3230 | |
| 3231 | @example |
| 3232 | 1998-08-17 Richard Stallman <rms@@gnu.org> |
| 3233 | |
| 3234 | * register.el (insert-register): Return nil. |
| 3235 | (jump-to-register): Likewise. |
| 3236 | |
| 3237 | * sort.el (sort-subr): Return nil. |
| 3238 | |
| 3239 | * tex-mode.el (tex-bibtex-file, tex-file, tex-region): |
| 3240 | Restart the tex shell if process is gone or stopped. |
| 3241 | (tex-shell-running): New function. |
| 3242 | |
| 3243 | * expr.c (store_one_arg): Round size up for move_block_to_reg. |
| 3244 | (expand_call): Round up when emitting USE insns. |
| 3245 | * stmt.c (assign_parms): Round size up for move_block_from_reg. |
| 3246 | @end example |
| 3247 | |
| 3248 | It's important to name the changed function or variable in full. Don't |
| 3249 | abbreviate function or variable names, and don't combine them. |
| 3250 | Subsequent maintainers will often search for a function name to find all |
| 3251 | the change log entries that pertain to it; if you abbreviate the name, |
| 3252 | they won't find it when they search. |
| 3253 | |
| 3254 | For example, some people are tempted to abbreviate groups of function |
| 3255 | names by writing @samp{* register.el (@{insert,jump-to@}-register)}; |
| 3256 | this is not a good idea, since searching for @code{jump-to-register} or |
| 3257 | @code{insert-register} would not find that entry. |
| 3258 | |
| 3259 | Separate unrelated change log entries with blank lines. When two |
| 3260 | entries represent parts of the same change, so that they work together, |
| 3261 | then don't put blank lines between them. Then you can omit the file |
| 3262 | name and the asterisk when successive entries are in the same file. |
| 3263 | |
| 3264 | Break long lists of function names by closing continued lines with |
| 3265 | @samp{)}, rather than @samp{,}, and opening the continuation with |
| 3266 | @samp{(} as in this example: |
| 3267 | |
| 3268 | @example |
| 3269 | * keyboard.c (menu_bar_items, tool_bar_items) |
| 3270 | (Fexecute_extended_command): Deal with `keymap' property. |
| 3271 | @end example |
| 3272 | |
| 3273 | @node Simple Changes |
| 3274 | @subsection Simple Changes |
| 3275 | |
| 3276 | Certain simple kinds of changes don't need much detail in the change |
| 3277 | log. |
| 3278 | |
| 3279 | When you change the calling sequence of a function in a simple fashion, |
| 3280 | and you change all the callers of the function to use the new calling |
| 3281 | sequence, there is no need to make individual entries for all the |
| 3282 | callers that you changed. Just write in the entry for the function |
| 3283 | being called, ``All callers changed''---like this: |
| 3284 | |
| 3285 | @example |
| 3286 | * keyboard.c (Fcommand_execute): New arg SPECIAL. |
| 3287 | All callers changed. |
| 3288 | @end example |
| 3289 | |
| 3290 | When you change just comments or doc strings, it is enough to write an |
| 3291 | entry for the file, without mentioning the functions. Just ``Doc |
| 3292 | fixes'' is enough for the change log. |
| 3293 | |
| 3294 | There's no need to make change log entries for documentation files. |
| 3295 | This is because documentation is not susceptible to bugs that are hard |
| 3296 | to fix. Documentation does not consist of parts that must interact in a |
| 3297 | precisely engineered fashion. To correct an error, you need not know |
| 3298 | the history of the erroneous passage; it is enough to compare what the |
| 3299 | documentation says with the way the program actually works. |
| 3300 | |
| 3301 | @node Conditional Changes |
| 3302 | @subsection Conditional Changes |
| 3303 | @cindex conditional changes, and change logs |
| 3304 | @cindex change logs, conditional changes |
| 3305 | |
| 3306 | C programs often contain compile-time @code{#if} conditionals. Many |
| 3307 | changes are conditional; sometimes you add a new definition which is |
| 3308 | entirely contained in a conditional. It is very useful to indicate in |
| 3309 | the change log the conditions for which the change applies. |
| 3310 | |
| 3311 | Our convention for indicating conditional changes is to use square |
| 3312 | brackets around the name of the condition. |
| 3313 | |
| 3314 | Here is a simple example, describing a change which is conditional but |
| 3315 | does not have a function or entity name associated with it: |
| 3316 | |
| 3317 | @example |
| 3318 | * xterm.c [SOLARIS2]: Include string.h. |
| 3319 | @end example |
| 3320 | |
| 3321 | Here is an entry describing a new definition which is entirely |
| 3322 | conditional. This new definition for the macro @code{FRAME_WINDOW_P} is |
| 3323 | used only when @code{HAVE_X_WINDOWS} is defined: |
| 3324 | |
| 3325 | @example |
| 3326 | * frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined. |
| 3327 | @end example |
| 3328 | |
| 3329 | Here is an entry for a change within the function @code{init_display}, |
| 3330 | whose definition as a whole is unconditional, but the changes themselves |
| 3331 | are contained in a @samp{#ifdef HAVE_LIBNCURSES} conditional: |
| 3332 | |
| 3333 | @example |
| 3334 | * dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent. |
| 3335 | @end example |
| 3336 | |
| 3337 | Here is an entry for a change that takes affect only when |
| 3338 | a certain macro is @emph{not} defined: |
| 3339 | |
| 3340 | @example |
| 3341 | (gethostname) [!HAVE_SOCKETS]: Replace with winsock version. |
| 3342 | @end example |
| 3343 | |
| 3344 | @node Indicating the Part Changed |
| 3345 | @subsection Indicating the Part Changed |
| 3346 | |
| 3347 | Indicate the part of a function which changed by using angle brackets |
| 3348 | enclosing an indication of what the changed part does. Here is an entry |
| 3349 | for a change in the part of the function @code{sh-while-getopts} that |
| 3350 | deals with @code{sh} commands: |
| 3351 | |
| 3352 | @example |
| 3353 | * progmodes/sh-script.el (sh-while-getopts) <sh>: Handle case that |
| 3354 | user-specified option string is empty. |
| 3355 | @end example |
| 3356 | |
| 3357 | |
| 3358 | @node Man Pages |
| 3359 | @section Man Pages |
| 3360 | @cindex man pages |
| 3361 | |
| 3362 | In the GNU project, man pages are secondary. It is not necessary or |
| 3363 | expected for every GNU program to have a man page, but some of them do. |
| 3364 | It's your choice whether to include a man page in your program. |
| 3365 | |
| 3366 | When you make this decision, consider that supporting a man page |
| 3367 | requires continual effort each time the program is changed. The time |
| 3368 | you spend on the man page is time taken away from more useful work. |
| 3369 | |
| 3370 | For a simple program which changes little, updating the man page may be |
| 3371 | a small job. Then there is little reason not to include a man page, if |
| 3372 | you have one. |
| 3373 | |
| 3374 | For a large program that changes a great deal, updating a man page may |
| 3375 | be a substantial burden. If a user offers to donate a man page, you may |
| 3376 | find this gift costly to accept. It may be better to refuse the man |
| 3377 | page unless the same person agrees to take full responsibility for |
| 3378 | maintaining it---so that you can wash your hands of it entirely. If |
| 3379 | this volunteer later ceases to do the job, then don't feel obliged to |
| 3380 | pick it up yourself; it may be better to withdraw the man page from the |
| 3381 | distribution until someone else agrees to update it. |
| 3382 | |
| 3383 | When a program changes only a little, you may feel that the |
| 3384 | discrepancies are small enough that the man page remains useful without |
| 3385 | updating. If so, put a prominent note near the beginning of the man |
| 3386 | page explaining that you don't maintain it and that the Texinfo manual |
| 3387 | is more authoritative. The note should say how to access the Texinfo |
| 3388 | documentation. |
| 3389 | |
| 3390 | @node Reading other Manuals |
| 3391 | @section Reading other Manuals |
| 3392 | |
| 3393 | There may be non-free books or documentation files that describe the |
| 3394 | program you are documenting. |
| 3395 | |
| 3396 | It is ok to use these documents for reference, just as the author of a |
| 3397 | new algebra textbook can read other books on algebra. A large portion |
| 3398 | of any non-fiction book consists of facts, in this case facts about how |
| 3399 | a certain program works, and these facts are necessarily the same for |
| 3400 | everyone who writes about the subject. But be careful not to copy your |
| 3401 | outline structure, wording, tables or examples from preexisting non-free |
| 3402 | documentation. Copying from free documentation may be ok; please check |
| 3403 | with the FSF about the individual case. |
| 3404 | |
| 3405 | @node Managing Releases |
| 3406 | @chapter The Release Process |
| 3407 | @cindex releasing |
| 3408 | |
| 3409 | Making a release is more than just bundling up your source files in a |
| 3410 | tar file and putting it up for FTP. You should set up your software so |
| 3411 | that it can be configured to run on a variety of systems. Your Makefile |
| 3412 | should conform to the GNU standards described below, and your directory |
| 3413 | layout should also conform to the standards discussed below. Doing so |
| 3414 | makes it easy to include your package into the larger framework of |
| 3415 | all GNU software. |
| 3416 | |
| 3417 | @menu |
| 3418 | * Configuration:: How Configuration Should Work |
| 3419 | * Makefile Conventions:: Makefile Conventions |
| 3420 | * Releases:: Making Releases |
| 3421 | @end menu |
| 3422 | |
| 3423 | @node Configuration |
| 3424 | @section How Configuration Should Work |
| 3425 | @cindex program configuration |
| 3426 | |
| 3427 | @pindex configure |
| 3428 | Each GNU distribution should come with a shell script named |
| 3429 | @code{configure}. This script is given arguments which describe the |
| 3430 | kind of machine and system you want to compile the program for. |
| 3431 | |
| 3432 | The @code{configure} script must record the configuration options so |
| 3433 | that they affect compilation. |
| 3434 | |
| 3435 | One way to do this is to make a link from a standard name such as |
| 3436 | @file{config.h} to the proper configuration file for the chosen system. |
| 3437 | If you use this technique, the distribution should @emph{not} contain a |
| 3438 | file named @file{config.h}. This is so that people won't be able to |
| 3439 | build the program without configuring it first. |
| 3440 | |
| 3441 | Another thing that @code{configure} can do is to edit the Makefile. If |
| 3442 | you do this, the distribution should @emph{not} contain a file named |
| 3443 | @file{Makefile}. Instead, it should include a file @file{Makefile.in} which |
| 3444 | contains the input used for editing. Once again, this is so that people |
| 3445 | won't be able to build the program without configuring it first. |
| 3446 | |
| 3447 | If @code{configure} does write the @file{Makefile}, then @file{Makefile} |
| 3448 | should have a target named @file{Makefile} which causes @code{configure} |
| 3449 | to be rerun, setting up the same configuration that was set up last |
| 3450 | time. The files that @code{configure} reads should be listed as |
| 3451 | dependencies of @file{Makefile}. |
| 3452 | |
| 3453 | All the files which are output from the @code{configure} script should |
| 3454 | have comments at the beginning explaining that they were generated |
| 3455 | automatically using @code{configure}. This is so that users won't think |
| 3456 | of trying to edit them by hand. |
| 3457 | |
| 3458 | The @code{configure} script should write a file named @file{config.status} |
| 3459 | which describes which configuration options were specified when the |
| 3460 | program was last configured. This file should be a shell script which, |
| 3461 | if run, will recreate the same configuration. |
| 3462 | |
| 3463 | The @code{configure} script should accept an option of the form |
| 3464 | @samp{--srcdir=@var{dirname}} to specify the directory where sources are found |
| 3465 | (if it is not the current directory). This makes it possible to build |
| 3466 | the program in a separate directory, so that the actual source directory |
| 3467 | is not modified. |
| 3468 | |
| 3469 | If the user does not specify @samp{--srcdir}, then @code{configure} should |
| 3470 | check both @file{.} and @file{..} to see if it can find the sources. If |
| 3471 | it finds the sources in one of these places, it should use them from |
| 3472 | there. Otherwise, it should report that it cannot find the sources, and |
| 3473 | should exit with nonzero status. |
| 3474 | |
| 3475 | Usually the easy way to support @samp{--srcdir} is by editing a |
| 3476 | definition of @code{VPATH} into the Makefile. Some rules may need to |
| 3477 | refer explicitly to the specified source directory. To make this |
| 3478 | possible, @code{configure} can add to the Makefile a variable named |
| 3479 | @code{srcdir} whose value is precisely the specified directory. |
| 3480 | |
| 3481 | The @code{configure} script should also take an argument which specifies the |
| 3482 | type of system to build the program for. This argument should look like |
| 3483 | this: |
| 3484 | |
| 3485 | @example |
| 3486 | @var{cpu}-@var{company}-@var{system} |
| 3487 | @end example |
| 3488 | |
| 3489 | For example, a Sun 3 might be @samp{m68k-sun-sunos4.1}. |
| 3490 | |
| 3491 | The @code{configure} script needs to be able to decode all plausible |
| 3492 | alternatives for how to describe a machine. Thus, @samp{sun3-sunos4.1} |
| 3493 | would be a valid alias. For many programs, @samp{vax-dec-ultrix} would |
| 3494 | be an alias for @samp{vax-dec-bsd}, simply because the differences |
| 3495 | between Ultrix and @sc{bsd} are rarely noticeable, but a few programs |
| 3496 | might need to distinguish them. |
| 3497 | @c Real 4.4BSD now runs on some Suns. |
| 3498 | |
| 3499 | There is a shell script called @file{config.sub} that you can use |
| 3500 | as a subroutine to validate system types and canonicalize aliases. |
| 3501 | |
| 3502 | @cindex optional features, configure-time |
| 3503 | Other options are permitted to specify in more detail the software |
| 3504 | or hardware present on the machine, and include or exclude optional |
| 3505 | parts of the package: |
| 3506 | |
| 3507 | @table @samp |
| 3508 | @item --enable-@var{feature}@r{[}=@var{parameter}@r{]} |
| 3509 | Configure the package to build and install an optional user-level |
| 3510 | facility called @var{feature}. This allows users to choose which |
| 3511 | optional features to include. Giving an optional @var{parameter} of |
| 3512 | @samp{no} should omit @var{feature}, if it is built by default. |
| 3513 | |
| 3514 | No @samp{--enable} option should @strong{ever} cause one feature to |
| 3515 | replace another. No @samp{--enable} option should ever substitute one |
| 3516 | useful behavior for another useful behavior. The only proper use for |
| 3517 | @samp{--enable} is for questions of whether to build part of the program |
| 3518 | or exclude it. |
| 3519 | |
| 3520 | @item --with-@var{package} |
| 3521 | @c @r{[}=@var{parameter}@r{]} |
| 3522 | The package @var{package} will be installed, so configure this package |
| 3523 | to work with @var{package}. |
| 3524 | |
| 3525 | @c Giving an optional @var{parameter} of |
| 3526 | @c @samp{no} should omit @var{package}, if it is used by default. |
| 3527 | |
| 3528 | Possible values of @var{package} include |
| 3529 | @samp{gnu-as} (or @samp{gas}), @samp{gnu-ld}, @samp{gnu-libc}, |
| 3530 | @samp{gdb}, |
| 3531 | @samp{x}, |
| 3532 | and |
| 3533 | @samp{x-toolkit}. |
| 3534 | |
| 3535 | Do not use a @samp{--with} option to specify the file name to use to |
| 3536 | find certain files. That is outside the scope of what @samp{--with} |
| 3537 | options are for. |
| 3538 | @end table |
| 3539 | |
| 3540 | All @code{configure} scripts should accept all of these ``detail'' |
| 3541 | options, whether or not they make any difference to the particular |
| 3542 | package at hand. In particular, they should accept any option that |
| 3543 | starts with @samp{--with-} or @samp{--enable-}. This is so users will |
| 3544 | be able to configure an entire GNU source tree at once with a single set |
| 3545 | of options. |
| 3546 | |
| 3547 | You will note that the categories @samp{--with-} and @samp{--enable-} |
| 3548 | are narrow: they @strong{do not} provide a place for any sort of option |
| 3549 | you might think of. That is deliberate. We want to limit the possible |
| 3550 | configuration options in GNU software. We do not want GNU programs to |
| 3551 | have idiosyncratic configuration options. |
| 3552 | |
| 3553 | Packages that perform part of the compilation process may support |
| 3554 | cross-compilation. In such a case, the host and target machines for the |
| 3555 | program may be different. |
| 3556 | |
| 3557 | The @code{configure} script should normally treat the specified type of |
| 3558 | system as both the host and the target, thus producing a program which |
| 3559 | works for the same type of machine that it runs on. |
| 3560 | |
| 3561 | To configure a cross-compiler, cross-assembler, or what have you, you |
| 3562 | should specify a target different from the host, using the configure |
| 3563 | option @samp{--target=@var{targettype}}. The syntax for |
| 3564 | @var{targettype} is the same as for the host type. So the command would |
| 3565 | look like this: |
| 3566 | |
| 3567 | @example |
| 3568 | ./configure @var{hosttype} --target=@var{targettype} |
| 3569 | @end example |
| 3570 | |
| 3571 | Programs for which cross-operation is not meaningful need not accept the |
| 3572 | @samp{--target} option, because configuring an entire operating system for |
| 3573 | cross-operation is not a meaningful operation. |
| 3574 | |
| 3575 | Bootstrapping a cross-compiler requires compiling it on a machine other |
| 3576 | than the host it will run on. Compilation packages accept a |
| 3577 | configuration option @samp{--build=@var{buildtype}} for specifying the |
| 3578 | configuration on which you will compile them, but the configure script |
| 3579 | should normally guess the build machine type (using |
| 3580 | @file{config.guess}), so this option is probably not necessary. The |
| 3581 | host and target types normally default from the build type, so in |
| 3582 | bootstrapping a cross-compiler you must specify them both explicitly. |
| 3583 | |
| 3584 | Some programs have ways of configuring themselves automatically. If |
| 3585 | your program is set up to do this, your @code{configure} script can simply |
| 3586 | ignore most of its arguments. |
| 3587 | |
| 3588 | @comment The makefile standards are in a separate file that is also |
| 3589 | @comment included by make.texinfo. Done by roland@gnu.ai.mit.edu on 1/6/93. |
| 3590 | @comment For this document, turn chapters into sections, etc. |
| 3591 | @lowersections |
| 3592 | @include make-stds.texi |
| 3593 | @raisesections |
| 3594 | |
| 3595 | @node Releases |
| 3596 | @section Making Releases |
| 3597 | @cindex packaging |
| 3598 | |
| 3599 | Package the distribution of @code{Foo version 69.96} up in a gzipped tar |
| 3600 | file with the name @file{foo-69.96.tar.gz}. It should unpack into a |
| 3601 | subdirectory named @file{foo-69.96}. |
| 3602 | |
| 3603 | Building and installing the program should never modify any of the files |
| 3604 | contained in the distribution. This means that all the files that form |
| 3605 | part of the program in any way must be classified into @dfn{source |
| 3606 | files} and @dfn{non-source files}. Source files are written by humans |
| 3607 | and never changed automatically; non-source files are produced from |
| 3608 | source files by programs under the control of the Makefile. |
| 3609 | |
| 3610 | @cindex @file{README} file |
| 3611 | The distribution should contain a file named @file{README} which gives |
| 3612 | the name of the package, and a general description of what it does. It |
| 3613 | is also good to explain the purpose of each of the first-level |
| 3614 | subdirectories in the package, if there are any. The @file{README} file |
| 3615 | should either state the version number of the package, or refer to where |
| 3616 | in the package it can be found. |
| 3617 | |
| 3618 | The @file{README} file should refer to the file @file{INSTALL}, which |
| 3619 | should contain an explanation of the installation procedure. |
| 3620 | |
| 3621 | The @file{README} file should also refer to the file which contains the |
| 3622 | copying conditions. The GNU GPL, if used, should be in a file called |
| 3623 | @file{COPYING}. If the GNU LGPL is used, it should be in a file called |
| 3624 | @file{COPYING.LIB}. |
| 3625 | |
| 3626 | Naturally, all the source files must be in the distribution. It is okay |
| 3627 | to include non-source files in the distribution, provided they are |
| 3628 | up-to-date and machine-independent, so that building the distribution |
| 3629 | normally will never modify them. We commonly include non-source files |
| 3630 | produced by Bison, @code{lex}, @TeX{}, and @code{makeinfo}; this helps avoid |
| 3631 | unnecessary dependencies between our distributions, so that users can |
| 3632 | install whichever packages they want to install. |
| 3633 | |
| 3634 | Non-source files that might actually be modified by building and |
| 3635 | installing the program should @strong{never} be included in the |
| 3636 | distribution. So if you do distribute non-source files, always make |
| 3637 | sure they are up to date when you make a new distribution. |
| 3638 | |
| 3639 | Make sure that the directory into which the distribution unpacks (as |
| 3640 | well as any subdirectories) are all world-writable (octal mode 777). |
| 3641 | This is so that old versions of @code{tar} which preserve the |
| 3642 | ownership and permissions of the files from the tar archive will be |
| 3643 | able to extract all the files even if the user is unprivileged. |
| 3644 | |
| 3645 | Make sure that all the files in the distribution are world-readable. |
| 3646 | |
| 3647 | Make sure that no file name in the distribution is more than 14 |
| 3648 | characters long. Likewise, no file created by building the program |
| 3649 | should have a name longer than 14 characters. The reason for this is |
| 3650 | that some systems adhere to a foolish interpretation of the @sc{posix} |
| 3651 | standard, and refuse to open a longer name, rather than truncating as |
| 3652 | they did in the past. |
| 3653 | |
| 3654 | Don't include any symbolic links in the distribution itself. If the tar |
| 3655 | file contains symbolic links, then people cannot even unpack it on |
| 3656 | systems that don't support symbolic links. Also, don't use multiple |
| 3657 | names for one file in different directories, because certain file |
| 3658 | systems cannot handle this and that prevents unpacking the |
| 3659 | distribution. |
| 3660 | |
| 3661 | Try to make sure that all the file names will be unique on MS-DOS. A |
| 3662 | name on MS-DOS consists of up to 8 characters, optionally followed by a |
| 3663 | period and up to three characters. MS-DOS will truncate extra |
| 3664 | characters both before and after the period. Thus, |
| 3665 | @file{foobarhacker.c} and @file{foobarhacker.o} are not ambiguous; they |
| 3666 | are truncated to @file{foobarha.c} and @file{foobarha.o}, which are |
| 3667 | distinct. |
| 3668 | |
| 3669 | @cindex @file{texinfo.tex}, in a distribution |
| 3670 | Include in your distribution a copy of the @file{texinfo.tex} you used |
| 3671 | to test print any @file{*.texinfo} or @file{*.texi} files. |
| 3672 | |
| 3673 | Likewise, if your program uses small GNU software packages like regex, |
| 3674 | getopt, obstack, or termcap, include them in the distribution file. |
| 3675 | Leaving them out would make the distribution file a little smaller at |
| 3676 | the expense of possible inconvenience to a user who doesn't know what |
| 3677 | other files to get. |
| 3678 | |
| 3679 | @node References |
| 3680 | @chapter References to Non-Free Software and Documentation |
| 3681 | @cindex references to non-free material |
| 3682 | |
| 3683 | A GNU program should not recommend use of any non-free program. We |
| 3684 | can't stop some people from writing proprietary programs, or stop |
| 3685 | other people from using them, but we can and should avoid helping to |
| 3686 | advertise them to new potential customers. Proprietary software is a |
| 3687 | social and ethical problem, and the point of GNU is to solve that |
| 3688 | problem. |
| 3689 | |
| 3690 | When a non-free program or system is well known, you can mention it in |
| 3691 | passing---that is harmless, since users who might want to use it |
| 3692 | probably already know about it. For instance, it is fine to explain |
| 3693 | how to build your package on top of some non-free operating system, or |
| 3694 | how to use it together with some widely used non-free program. |
| 3695 | |
| 3696 | However, you should give only the necessary information to help those |
| 3697 | who already use the non-free program to use your program with |
| 3698 | it---don't give, or refer to, any further information about the |
| 3699 | proprietary program, and don't imply that the proprietary program |
| 3700 | enhances your program, or that its existence is in any way a good |
| 3701 | thing. The goal should be that people already using the proprietary |
| 3702 | program will get the advice they need about how to use your free |
| 3703 | program, while people who don't already use the proprietary program |
| 3704 | will not see anything to lead them to take an interest in it. |
| 3705 | |
| 3706 | If a non-free program or system is obscure in your program's domain, |
| 3707 | your program should not mention or support it at all, since doing so |
| 3708 | would tend to popularize the non-free program more than it popularizes |
| 3709 | your program. (You cannot hope to find many additional users among |
| 3710 | the users of Foobar if the users of Foobar are few.) |
| 3711 | |
| 3712 | A GNU package should not refer the user to any non-free documentation |
| 3713 | for free software. Free documentation that can be included in free |
| 3714 | operating systems is essential for completing the GNU system, so it is |
| 3715 | a major focus of the GNU Project; to recommend use of documentation |
| 3716 | that we are not allowed to use in GNU would undermine the efforts to |
| 3717 | get documentation that we can include. So GNU packages should never |
| 3718 | recommend non-free documentation. |
| 3719 | |
| 3720 | @node Copying This Manual |
| 3721 | @appendix Copying This Manual |
| 3722 | |
| 3723 | @menu |
| 3724 | * GNU Free Documentation License:: License for copying this manual |
| 3725 | @end menu |
| 3726 | |
| 3727 | @include fdl.texi |
| 3728 | |
| 3729 | @node Index |
| 3730 | @unnumbered Index |
| 3731 | @printindex cp |
| 3732 | |
| 3733 | @contents |
| 3734 | |
| 3735 | @bye |
| 3736 | @c Local variables: |
| 3737 | @c eval: (add-hook 'write-file-hooks 'time-stamp) |
| 3738 | @c time-stamp-start: "@set lastupdate " |
| 3739 | @c time-stamp-end: "$" |
| 3740 | @c time-stamp-format: "%:b %:d, %:y" |
| 3741 | @c compile-command: "make just-standards" |
| 3742 | @c End: |