1This is standards.info, produced by makeinfo version 4.8 from 2standards.texi. 3 4INFO-DIR-SECTION GNU organization 5START-INFO-DIR-ENTRY 6* Standards: (standards). GNU coding standards. 7END-INFO-DIR-ENTRY 8 9 The GNU coding standards, last updated November 15, 2006. 10 11 Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 122001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc. 13 14 Permission is granted to copy, distribute and/or modify this document 15under the terms of the GNU Free Documentation License, Version 1.2 or 16any later version published by the Free Software Foundation; with no 17Invariant Sections, with no Front-Cover Texts, and with no Back-Cover 18Texts. A copy of the license is included in the section entitled "GNU 19Free Documentation License". 20 21 22File: standards.info, Node: Top, Next: Preface, Prev: (dir), Up: (dir) 23 24Version 25******* 26 27The GNU coding standards, last updated November 15, 2006. 28 29 Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 302001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc. 31 32 Permission is granted to copy, distribute and/or modify this document 33under the terms of the GNU Free Documentation License, Version 1.2 or 34any later version published by the Free Software Foundation; with no 35Invariant Sections, with no Front-Cover Texts, and with no Back-Cover 36Texts. A copy of the license is included in the section entitled "GNU 37Free Documentation License". 38 39* Menu: 40 41* Preface:: About the GNU Coding Standards 42* Legal Issues:: Keeping Free Software Free 43* Design Advice:: General Program Design 44* Program Behavior:: Program Behavior for All Programs 45* Writing C:: Making The Best Use of C 46* Documentation:: Documenting Programs 47* Managing Releases:: The Release Process 48* References:: References to Non-Free Software or Documentation 49* Copying This Manual:: How to Make Copies of This Manual 50* Index:: 51 52 53File: standards.info, Node: Preface, Next: Legal Issues, Prev: Top, Up: Top 54 551 About the GNU Coding Standards 56******************************** 57 58The GNU Coding Standards were written by Richard Stallman and other GNU 59Project volunteers. Their purpose is to make the GNU system clean, 60consistent, and easy to install. This document can also be read as a 61guide to writing portable, robust and reliable programs. It focuses on 62programs written in C, but many of the rules and principles are useful 63even if you write in another programming language. The rules often 64state reasons for writing in a certain way. 65 66 This release of the GNU Coding Standards was last updated November 6715, 2006. 68 69 If you did not obtain this file directly from the GNU project and 70recently, please check for a newer version. You can get the GNU Coding 71Standards from the GNU web server in many different formats, including 72the Texinfo source, PDF, HTML, DVI, plain text, and more, at: 73`http://www.gnu.org/prep/standards/'. 74 75 Corrections or suggestions for this document should be sent to 76<bug-standards@gnu.org>. If you make a suggestion, please include a 77suggested new wording for it; our time is limited. We prefer a context 78diff to the `standards.texi' or `make-stds.texi' files, but if you 79don't have those files, please mail your suggestion anyway. 80 81 These standards cover the minimum of what is important when writing a 82GNU package. Likely, the needs for additional standards will come up. 83Sometimes, you might suggest that such standards be added to this 84document. If you think your standards would be generally useful, please 85do suggest them. 86 87 You should also set standards for your package on many questions not 88addressed or not firmly specified here. The most important point is to 89be self-consistent--try to stick to the conventions you pick, and try 90to document them as much as possible. That way, your program will be 91more maintainable by others. 92 93 The GNU Hello program serves as an example of how to follow the GNU 94coding standards for a trivial program. 95`http://www.gnu.org/software/hello/hello.html'. 96 97 98File: standards.info, Node: Legal Issues, Next: Design Advice, Prev: Preface, Up: Top 99 1002 Keeping Free Software Free 101**************************** 102 103This chapter discusses how you can make sure that GNU software avoids 104legal difficulties, and other related issues. 105 106* Menu: 107 108* Reading Non-Free Code:: Referring to Proprietary Programs 109* Contributions:: Accepting Contributions 110* Trademarks:: How We Deal with Trademark Issues 111 112 113File: standards.info, Node: Reading Non-Free Code, Next: Contributions, Up: Legal Issues 114 1152.1 Referring to Proprietary Programs 116===================================== 117 118Don't in any circumstances refer to Unix source code for or during your 119work on GNU! (Or to any other proprietary programs.) 120 121 If you have a vague recollection of the internals of a Unix program, 122this does not absolutely mean you can't write an imitation of it, but 123do try to organize the imitation internally along different lines, 124because this is likely to make the details of the Unix version 125irrelevant and dissimilar to your results. 126 127 For example, Unix utilities were generally optimized to minimize 128memory use; if you go for speed instead, your program will be very 129different. You could keep the entire input file in memory and scan it 130there instead of using stdio. Use a smarter algorithm discovered more 131recently than the Unix program. Eliminate use of temporary files. Do 132it in one pass instead of two (we did this in the assembler). 133 134 Or, on the contrary, emphasize simplicity instead of speed. For some 135applications, the speed of today's computers makes simpler algorithms 136adequate. 137 138 Or go for generality. For example, Unix programs often have static 139tables or fixed-size strings, which make for arbitrary limits; use 140dynamic allocation instead. Make sure your program handles NULs and 141other funny characters in the input files. Add a programming language 142for extensibility and write part of the program in that language. 143 144 Or turn some parts of the program into independently usable 145libraries. Or use a simple garbage collector instead of tracking 146precisely when to free memory, or use a new GNU facility such as 147obstacks. 148 149 150File: standards.info, Node: Contributions, Next: Trademarks, Prev: Reading Non-Free Code, Up: Legal Issues 151 1522.2 Accepting Contributions 153=========================== 154 155If the program you are working on is copyrighted by the Free Software 156Foundation, then when someone else sends you a piece of code to add to 157the program, we need legal papers to use it--just as we asked you to 158sign papers initially. _Each_ person who makes a nontrivial 159contribution to a program must sign some sort of legal papers in order 160for us to have clear title to the program; the main author alone is not 161enough. 162 163 So, before adding in any contributions from other people, please tell 164us, so we can arrange to get the papers. Then wait until we tell you 165that we have received the signed papers, before you actually use the 166contribution. 167 168 This applies both before you release the program and afterward. If 169you receive diffs to fix a bug, and they make significant changes, we 170need legal papers for that change. 171 172 This also applies to comments and documentation files. For copyright 173law, comments and code are just text. Copyright applies to all kinds of 174text, so we need legal papers for all kinds. 175 176 We know it is frustrating to ask for legal papers; it's frustrating 177for us as well. But if you don't wait, you are going out on a limb--for 178example, what if the contributor's employer won't sign a disclaimer? 179You might have to take that code out again! 180 181 You don't need papers for changes of a few lines here or there, since 182they are not significant for copyright purposes. Also, you don't need 183papers if all you get from the suggestion is some ideas, not actual code 184which you use. For example, if someone sent you one implementation, but 185you write a different implementation of the same idea, you don't need to 186get papers. 187 188 The very worst thing is if you forget to tell us about the other 189contributor. We could be very embarrassed in court some day as a 190result. 191 192 We have more detailed advice for maintainers of programs; if you have 193reached the stage of actually maintaining a program for GNU (whether 194released or not), please ask us for a copy. It is also available 195online for your perusal: `http://www.gnu.org/prep/maintain/'. 196 197 198File: standards.info, Node: Trademarks, Prev: Contributions, Up: Legal Issues 199 2002.3 Trademarks 201============== 202 203Please do not include any trademark acknowledgements in GNU software 204packages or documentation. 205 206 Trademark acknowledgements are the statements that such-and-such is a 207trademark of so-and-so. The GNU Project has no objection to the basic 208idea of trademarks, but these acknowledgements feel like kowtowing, and 209there is no legal requirement for them, so we don't use them. 210 211 What is legally required, as regards other people's trademarks, is to 212avoid using them in ways which a reader might reasonably understand as 213naming or labeling our own programs or activities. For example, since 214"Objective C" is (or at least was) a trademark, we made sure to say 215that we provide a "compiler for the Objective C language" rather than 216an "Objective C compiler". The latter would have been meant as a 217shorter way of saying the former, but it does not explicitly state the 218relationship, so it could be misinterpreted as using "Objective C" as a 219label for the compiler rather than for the language. 220 221 Please don't use "win" as an abbreviation for Microsoft Windows in 222GNU software or documentation. In hacker terminology, calling 223something a "win" is a form of praise. If you wish to praise Microsoft 224Windows when speaking on your own, by all means do so, but not in GNU 225software. Usually we write the name "Windows" in full, but when 226brevity is very important (as in file names and sometimes symbol 227names), we abbreviate it to "w". For instance, the files and functions 228in Emacs that deal with Windows start with `w32'. 229 230 231File: standards.info, Node: Design Advice, Next: Program Behavior, Prev: Legal Issues, Up: Top 232 2333 General Program Design 234************************ 235 236This chapter discusses some of the issues you should take into account 237when designing your program. 238 239* Menu: 240 241* Source Language:: Which languages to use. 242* Compatibility:: Compatibility with other implementations 243* Using Extensions:: Using non-standard features 244* Standard C:: Using Standard C features 245* Conditional Compilation:: Compiling Code Only If A Conditional is True 246 247 248File: standards.info, Node: Source Language, Next: Compatibility, Up: Design Advice 249 2503.1 Which Languages to Use 251========================== 252 253When you want to use a language that gets compiled and runs at high 254speed, the best language to use is C. Using another language is like 255using a non-standard feature: it will cause trouble for users. Even if 256GCC supports the other language, users may find it inconvenient to have 257to install the compiler for that other language in order to build your 258program. For example, if you write your program in C++, people will 259have to install the GNU C++ compiler in order to compile your program. 260 261 C has one other advantage over C++ and other compiled languages: more 262people know C, so more people will find it easy to read and modify the 263program if it is written in C. 264 265 So in general it is much better to use C, rather than the comparable 266alternatives. 267 268 But there are two exceptions to that conclusion: 269 270 * It is no problem to use another language to write a tool 271 specifically intended for use with that language. That is because 272 the only people who want to build the tool will be those who have 273 installed the other language anyway. 274 275 * If an application is of interest only to a narrow part of the 276 community, then the question of which language it is written in 277 has less effect on other people, so you may as well please 278 yourself. 279 280 Many programs are designed to be extensible: they include an 281interpreter for a language that is higher level than C. Often much of 282the program is written in that language, too. The Emacs editor 283pioneered this technique. 284 285 The standard extensibility interpreter for GNU software is GUILE 286(`http://www.gnu.org/software/guile/'), which implements the language 287Scheme (an especially clean and simple dialect of Lisp). We don't 288reject programs written in other "scripting languages" such as Perl and 289Python, but using GUILE is very important for the overall consistency 290of the GNU system. 291 292 293File: standards.info, Node: Compatibility, Next: Using Extensions, Prev: Source Language, Up: Design Advice 294 2953.2 Compatibility with Other Implementations 296============================================ 297 298With occasional exceptions, utility programs and libraries for GNU 299should be upward compatible with those in Berkeley Unix, and upward 300compatible with Standard C if Standard C specifies their behavior, and 301upward compatible with POSIX if POSIX specifies their behavior. 302 303 When these standards conflict, it is useful to offer compatibility 304modes for each of them. 305 306 Standard C and POSIX prohibit many kinds of extensions. Feel free 307to make the extensions anyway, and include a `--ansi', `--posix', or 308`--compatible' option to turn them off. However, if the extension has 309a significant chance of breaking any real programs or scripts, then it 310is not really upward compatible. So you should try to redesign its 311interface to make it upward compatible. 312 313 Many GNU programs suppress extensions that conflict with POSIX if the 314environment variable `POSIXLY_CORRECT' is defined (even if it is 315defined with a null value). Please make your program recognize this 316variable if appropriate. 317 318 When a feature is used only by users (not by programs or command 319files), and it is done poorly in Unix, feel free to replace it 320completely with something totally different and better. (For example, 321`vi' is replaced with Emacs.) But it is nice to offer a compatible 322feature as well. (There is a free `vi' clone, so we offer it.) 323 324 Additional useful features are welcome regardless of whether there 325is any precedent for them. 326 327 328File: standards.info, Node: Using Extensions, Next: Standard C, Prev: Compatibility, Up: Design Advice 329 3303.3 Using Non-standard Features 331=============================== 332 333Many GNU facilities that already exist support a number of convenient 334extensions over the comparable Unix facilities. Whether to use these 335extensions in implementing your program is a difficult question. 336 337 On the one hand, using the extensions can make a cleaner program. 338On the other hand, people will not be able to build the program unless 339the other GNU tools are available. This might cause the program to 340work on fewer kinds of machines. 341 342 With some extensions, it might be easy to provide both alternatives. 343For example, you can define functions with a "keyword" `INLINE' and 344define that as a macro to expand into either `inline' or nothing, 345depending on the compiler. 346 347 In general, perhaps it is best not to use the extensions if you can 348straightforwardly do without them, but to use the extensions if they 349are a big improvement. 350 351 An exception to this rule are the large, established programs (such 352as Emacs) which run on a great variety of systems. Using GNU 353extensions in such programs would make many users unhappy, so we don't 354do that. 355 356 Another exception is for programs that are used as part of 357compilation: anything that must be compiled with other compilers in 358order to bootstrap the GNU compilation facilities. If these require 359the GNU compiler, then no one can compile them without having them 360installed already. That would be extremely troublesome in certain 361cases. 362 363 364File: standards.info, Node: Standard C, Next: Conditional Compilation, Prev: Using Extensions, Up: Design Advice 365 3663.4 Standard C and Pre-Standard C 367================================= 368 3691989 Standard C is widespread enough now that it is ok to use its 370features in new programs. There is one exception: do not ever use the 371"trigraph" feature of Standard C. 372 373 1999 Standard C is not widespread yet, so please do not require its 374features in programs. It is ok to use its features if they are present. 375 376 However, it is easy to support pre-standard compilers in most 377programs, so if you know how to do that, feel free. If a program you 378are maintaining has such support, you should try to keep it working. 379 380 To support pre-standard C, instead of writing function definitions in 381standard prototype form, 382 383 int 384 foo (int x, int y) 385 ... 386 387write the definition in pre-standard style like this, 388 389 int 390 foo (x, y) 391 int x, y; 392 ... 393 394and use a separate declaration to specify the argument prototype: 395 396 int foo (int, int); 397 398 You need such a declaration anyway, in a header file, to get the 399benefit of prototypes in all the files where the function is called. 400And once you have the declaration, you normally lose nothing by writing 401the function definition in the pre-standard style. 402 403 This technique does not work for integer types narrower than `int'. 404If you think of an argument as being of a type narrower than `int', 405declare it as `int' instead. 406 407 There are a few special cases where this technique is hard to use. 408For example, if a function argument needs to hold the system type 409`dev_t', you run into trouble, because `dev_t' is shorter than `int' on 410some machines; but you cannot use `int' instead, because `dev_t' is 411wider than `int' on some machines. There is no type you can safely use 412on all machines in a non-standard definition. The only way to support 413non-standard C and pass such an argument is to check the width of 414`dev_t' using Autoconf and choose the argument type accordingly. This 415may not be worth the trouble. 416 417 In order to support pre-standard compilers that do not recognize 418prototypes, you may want to use a preprocessor macro like this: 419 420 /* Declare the prototype for a general external function. */ 421 #if defined (__STDC__) || defined (WINDOWSNT) 422 #define P_(proto) proto 423 #else 424 #define P_(proto) () 425 #endif 426 427 428File: standards.info, Node: Conditional Compilation, Prev: Standard C, Up: Design Advice 429 4303.5 Conditional Compilation 431=========================== 432 433When supporting configuration options already known when building your 434program we prefer using `if (... )' over conditional compilation, as in 435the former case the compiler is able to perform more extensive checking 436of all possible code paths. 437 438 For example, please write 439 440 if (HAS_FOO) 441 ... 442 else 443 ... 444 445instead of: 446 447 #ifdef HAS_FOO 448 ... 449 #else 450 ... 451 #endif 452 453 A modern compiler such as GCC will generate exactly the same code in 454both cases, and we have been using similar techniques with good success 455in several projects. Of course, the former method assumes that 456`HAS_FOO' is defined as either 0 or 1. 457 458 While this is not a silver bullet solving all portability problems, 459and is not always appropriate, following this policy would have saved 460GCC developers many hours, or even days, per year. 461 462 In the case of function-like macros like `REVERSIBLE_CC_MODE' in GCC 463which cannot be simply used in `if( ...)' statements, there is an easy 464workaround. Simply introduce another macro `HAS_REVERSIBLE_CC_MODE' as 465in the following example: 466 467 #ifdef REVERSIBLE_CC_MODE 468 #define HAS_REVERSIBLE_CC_MODE 1 469 #else 470 #define HAS_REVERSIBLE_CC_MODE 0 471 #endif 472 473 474File: standards.info, Node: Program Behavior, Next: Writing C, Prev: Design Advice, Up: Top 475 4764 Program Behavior for All Programs 477*********************************** 478 479This chapter describes conventions for writing robust software. It 480also describes general standards for error messages, the command line 481interface, and how libraries should behave. 482 483* Menu: 484 485* Non-GNU Standards:: We consider standards such as POSIX; 486 we don't "obey" them. 487* Semantics:: Writing robust programs 488* Libraries:: Library behavior 489* Errors:: Formatting error messages 490* User Interfaces:: Standards about interfaces generally 491* Graphical Interfaces:: Standards for graphical interfaces 492* Command-Line Interfaces:: Standards for command line interfaces 493* Option Table:: Table of long options 494* Memory Usage:: When and how to care about memory needs 495* File Usage:: Which files to use, and where 496 497 498File: standards.info, Node: Non-GNU Standards, Next: Semantics, Up: Program Behavior 499 5004.1 Non-GNU Standards 501===================== 502 503The GNU Project regards standards published by other organizations as 504suggestions, not orders. We consider those standards, but we do not 505"obey" them. In developing a GNU program, you should implement an 506outside standard's specifications when that makes the GNU system better 507overall in an objective sense. When it doesn't, you shouldn't. 508 509 In most cases, following published standards is convenient for 510users--it means that their programs or scripts will work more portably. 511For instance, GCC implements nearly all the features of Standard C as 512specified by that standard. C program developers would be unhappy if 513it did not. And GNU utilities mostly follow specifications of POSIX.2; 514shell script writers and users would be unhappy if our programs were 515incompatible. 516 517 But we do not follow either of these specifications rigidly, and 518there are specific points on which we decided not to follow them, so as 519to make the GNU system better for users. 520 521 For instance, Standard C says that nearly all extensions to C are 522prohibited. How silly! GCC implements many extensions, some of which 523were later adopted as part of the standard. If you want these 524constructs to give an error message as "required" by the standard, you 525must specify `--pedantic', which was implemented only so that we can 526say "GCC is a 100% implementation of the standard," not because there 527is any reason to actually use it. 528 529 POSIX.2 specifies that `df' and `du' must output sizes by default in 530units of 512 bytes. What users want is units of 1k, so that is what we 531do by default. If you want the ridiculous behavior "required" by 532POSIX, you must set the environment variable `POSIXLY_CORRECT' (which 533was originally going to be named `POSIX_ME_HARDER'). 534 535 GNU utilities also depart from the letter of the POSIX.2 536specification when they support long-named command-line options, and 537intermixing options with ordinary arguments. This minor 538incompatibility with POSIX is never a problem in practice, and it is 539very useful. 540 541 In particular, don't reject a new feature, or remove an old one, 542merely because a standard says it is "forbidden" or "deprecated." 543 544 545File: standards.info, Node: Semantics, Next: Libraries, Prev: Non-GNU Standards, Up: Program Behavior 546 5474.2 Writing Robust Programs 548=========================== 549 550Avoid arbitrary limits on the length or number of _any_ data structure, 551including file names, lines, files, and symbols, by allocating all data 552structures dynamically. In most Unix utilities, "long lines are 553silently truncated". This is not acceptable in a GNU utility. 554 555 Utilities reading files should not drop NUL characters, or any other 556nonprinting characters _including those with codes above 0177_. The 557only sensible exceptions would be utilities specifically intended for 558interface to certain types of terminals or printers that can't handle 559those characters. Whenever possible, try to make programs work 560properly with sequences of bytes that represent multibyte characters, 561using encodings such as UTF-8 and others. 562 563 Check every system call for an error return, unless you know you 564wish to ignore errors. Include the system error text (from `perror' or 565equivalent) in _every_ error message resulting from a failing system 566call, as well as the name of the file if any and the name of the 567utility. Just "cannot open foo.c" or "stat failed" is not sufficient. 568 569 Check every call to `malloc' or `realloc' to see if it returned 570zero. Check `realloc' even if you are making the block smaller; in a 571system that rounds block sizes to a power of 2, `realloc' may get a 572different block if you ask for less space. 573 574 In Unix, `realloc' can destroy the storage block if it returns zero. 575GNU `realloc' does not have this bug: if it fails, the original block 576is unchanged. Feel free to assume the bug is fixed. If you wish to 577run your program on Unix, and wish to avoid lossage in this case, you 578can use the GNU `malloc'. 579 580 You must expect `free' to alter the contents of the block that was 581freed. Anything you want to fetch from the block, you must fetch before 582calling `free'. 583 584 If `malloc' fails in a noninteractive program, make that a fatal 585error. In an interactive program (one that reads commands from the 586user), it is better to abort the command and return to the command 587reader loop. This allows the user to kill other processes to free up 588virtual memory, and then try the command again. 589 590 Use `getopt_long' to decode arguments, unless the argument syntax 591makes this unreasonable. 592 593 When static storage is to be written in during program execution, use 594explicit C code to initialize it. Reserve C initialized declarations 595for data that will not be changed. 596 597 Try to avoid low-level interfaces to obscure Unix data structures 598(such as file directories, utmp, or the layout of kernel memory), since 599these are less likely to work compatibly. If you need to find all the 600files in a directory, use `readdir' or some other high-level interface. 601These are supported compatibly by GNU. 602 603 The preferred signal handling facilities are the BSD variant of 604`signal', and the POSIX `sigaction' function; the alternative USG 605`signal' interface is an inferior design. 606 607 Nowadays, using the POSIX signal functions may be the easiest way to 608make a program portable. If you use `signal', then on GNU/Linux 609systems running GNU libc version 1, you should include `bsd/signal.h' 610instead of `signal.h', so as to get BSD behavior. It is up to you 611whether to support systems where `signal' has only the USG behavior, or 612give up on them. 613 614 In error checks that detect "impossible" conditions, just abort. 615There is usually no point in printing any message. These checks 616indicate the existence of bugs. Whoever wants to fix the bugs will have 617to read the source code and run a debugger. So explain the problem with 618comments in the source. The relevant data will be in variables, which 619are easy to examine with the debugger, so there is no point moving them 620elsewhere. 621 622 Do not use a count of errors as the exit status for a program. 623_That does not work_, because exit status values are limited to 8 bits 624(0 through 255). A single run of the program might have 256 errors; if 625you try to return 256 as the exit status, the parent process will see 0 626as the status, and it will appear that the program succeeded. 627 628 If you make temporary files, check the `TMPDIR' environment 629variable; if that variable is defined, use the specified directory 630instead of `/tmp'. 631 632 In addition, be aware that there is a possible security problem when 633creating temporary files in world-writable directories. In C, you can 634avoid this problem by creating temporary files in this manner: 635 636 fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0600); 637 638or by using the `mkstemps' function from libiberty. 639 640 In bash, use `set -C' to avoid this problem. 641 642 643File: standards.info, Node: Libraries, Next: Errors, Prev: Semantics, Up: Program Behavior 644 6454.3 Library Behavior 646==================== 647 648Try to make library functions reentrant. If they need to do dynamic 649storage allocation, at least try to avoid any nonreentrancy aside from 650that of `malloc' itself. 651 652 Here are certain name conventions for libraries, to avoid name 653conflicts. 654 655 Choose a name prefix for the library, more than two characters long. 656All external function and variable names should start with this prefix. 657In addition, there should only be one of these in any given library 658member. This usually means putting each one in a separate source file. 659 660 An exception can be made when two external symbols are always used 661together, so that no reasonable program could use one without the 662other; then they can both go in the same file. 663 664 External symbols that are not documented entry points for the user 665should have names beginning with `_'. The `_' should be followed by 666the chosen name prefix for the library, to prevent collisions with 667other libraries. These can go in the same files with user entry points 668if you like. 669 670 Static functions and variables can be used as you like and need not 671fit any naming convention. 672 673 674File: standards.info, Node: Errors, Next: User Interfaces, Prev: Libraries, Up: Program Behavior 675 6764.4 Formatting Error Messages 677============================= 678 679Error messages from compilers should look like this: 680 681 SOURCE-FILE-NAME:LINENO: MESSAGE 682 683If you want to mention the column number, use one of these formats: 684 685 SOURCE-FILE-NAME:LINENO:COLUMN: MESSAGE 686 SOURCE-FILE-NAME:LINENO.COLUMN: MESSAGE 687 688Line numbers should start from 1 at the beginning of the file, and 689column numbers should start from 1 at the beginning of the line. (Both 690of these conventions are chosen for compatibility.) Calculate column 691numbers assuming that space and all ASCII printing characters have 692equal width, and assuming tab stops every 8 columns. 693 694 The error message can also give both the starting and ending 695positions of the erroneous text. There are several formats so that you 696can avoid redundant information such as a duplicate line number. Here 697are the possible formats: 698 699 SOURCE-FILE-NAME:LINENO-1.COLUMN-1-LINENO-2.COLUMN-2: MESSAGE 700 SOURCE-FILE-NAME:LINENO-1.COLUMN-1-COLUMN-2: MESSAGE 701 SOURCE-FILE-NAME:LINENO-1-LINENO-2: MESSAGE 702 703When an error is spread over several files, you can use this format: 704 705 FILE-1:LINENO-1.COLUMN-1-FILE-2:LINENO-2.COLUMN-2: MESSAGE 706 707 Error messages from other noninteractive programs should look like 708this: 709 710 PROGRAM:SOURCE-FILE-NAME:LINENO: MESSAGE 711 712when there is an appropriate source file, or like this: 713 714 PROGRAM: MESSAGE 715 716when there is no relevant source file. 717 718 If you want to mention the column number, use this format: 719 720 PROGRAM:SOURCE-FILE-NAME:LINENO:COLUMN: MESSAGE 721 722 In an interactive program (one that is reading commands from a 723terminal), it is better not to include the program name in an error 724message. The place to indicate which program is running is in the 725prompt or with the screen layout. (When the same program runs with 726input from a source other than a terminal, it is not interactive and 727would do best to print error messages using the noninteractive style.) 728 729 The string MESSAGE should not begin with a capital letter when it 730follows a program name and/or file name, because that isn't the 731beginning of a sentence. (The sentence conceptually starts at the 732beginning of the line.) Also, it should not end with a period. 733 734 Error messages from interactive programs, and other messages such as 735usage messages, should start with a capital letter. But they should not 736end with a period. 737 738 739File: standards.info, Node: User Interfaces, Next: Graphical Interfaces, Prev: Errors, Up: Program Behavior 740 7414.5 Standards for Interfaces Generally 742====================================== 743 744Please don't make the behavior of a utility depend on the name used to 745invoke it. It is useful sometimes to make a link to a utility with a 746different name, and that should not change what it does. 747 748 Instead, use a run time option or a compilation switch or both to 749select among the alternate behaviors. 750 751 Likewise, please don't make the behavior of the program depend on the 752type of output device it is used with. Device independence is an 753important principle of the system's design; do not compromise it merely 754to save someone from typing an option now and then. (Variation in error 755message syntax when using a terminal is ok, because that is a side issue 756that people do not depend on.) 757 758 If you think one behavior is most useful when the output is to a 759terminal, and another is most useful when the output is a file or a 760pipe, then it is usually best to make the default behavior the one that 761is useful with output to a terminal, and have an option for the other 762behavior. 763 764 Compatibility requires certain programs to depend on the type of 765output device. It would be disastrous if `ls' or `sh' did not do so in 766the way all users expect. In some of these cases, we supplement the 767program with a preferred alternate version that does not depend on the 768output device type. For example, we provide a `dir' program much like 769`ls' except that its default output format is always multi-column 770format. 771 772 773File: standards.info, Node: Graphical Interfaces, Next: Command-Line Interfaces, Prev: User Interfaces, Up: Program Behavior 774 7754.6 Standards for Graphical Interfaces 776====================================== 777 778When you write a program that provides a graphical user interface, 779please make it work with X Windows and the GTK+ toolkit unless the 780functionality specifically requires some alternative (for example, 781"displaying jpeg images while in console mode"). 782 783 In addition, please provide a command-line interface to control the 784functionality. (In many cases, the graphical user interface can be a 785separate program which invokes the command-line program.) This is so 786that the same jobs can be done from scripts. 787 788 Please also consider providing a CORBA interface (for use from 789GNOME), a library interface (for use from C), and perhaps a 790keyboard-driven console interface (for use by users from console mode). 791Once you are doing the work to provide the functionality and the 792graphical interface, these won't be much extra work. 793 794 795File: standards.info, Node: Command-Line Interfaces, Next: Option Table, Prev: Graphical Interfaces, Up: Program Behavior 796 7974.7 Standards for Command Line Interfaces 798========================================= 799 800It is a good idea to follow the POSIX guidelines for the command-line 801options of a program. The easiest way to do this is to use `getopt' to 802parse them. Note that the GNU version of `getopt' will normally permit 803options anywhere among the arguments unless the special argument `--' 804is used. This is not what POSIX specifies; it is a GNU extension. 805 806 Please define long-named options that are equivalent to the 807single-letter Unix-style options. We hope to make GNU more user 808friendly this way. This is easy to do with the GNU function 809`getopt_long'. 810 811 One of the advantages of long-named options is that they can be 812consistent from program to program. For example, users should be able 813to expect the "verbose" option of any GNU program which has one, to be 814spelled precisely `--verbose'. To achieve this uniformity, look at the 815table of common long-option names when you choose the option names for 816your program (*note Option Table::). 817 818 It is usually a good idea for file names given as ordinary arguments 819to be input files only; any output files would be specified using 820options (preferably `-o' or `--output'). Even if you allow an output 821file name as an ordinary argument for compatibility, try to provide an 822option as another way to specify it. This will lead to more consistency 823among GNU utilities, and fewer idiosyncrasies for users to remember. 824 825 All programs should support two standard options: `--version' and 826`--help'. CGI programs should accept these as command-line options, 827and also if given as the `PATH_INFO'; for instance, visiting 828`http://example.org/p.cgi/--help' in a browser should output the same 829information as invoking `p.cgi --help' from the command line. 830 831`--version' 832 This option should direct the program to print information about 833 its name, version, origin and legal status, all on standard 834 output, and then exit successfully. Other options and arguments 835 should be ignored once this is seen, and the program should not 836 perform its normal function. 837 838 The first line is meant to be easy for a program to parse; the 839 version number proper starts after the last space. In addition, 840 it contains the canonical name for this program, in this format: 841 842 GNU Emacs 19.30 843 844 The program's name should be a constant string; _don't_ compute it 845 from `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 847 find out the precise file name where a command is found in `PATH'. 848 849 If the program is a subsidiary part of a larger package, mention 850 the package name in parentheses, like this: 851 852 emacsserver (GNU Emacs) 19.30 853 854 If the package has a version number which is different from this 855 program's version number, you can mention the package version 856 number just before the close-parenthesis. 857 858 If you *need* to mention the version numbers of libraries which 859 are distributed separately from the package which contains this 860 program, you can do so by printing an additional line of version 861 info for each library you want to mention. Use the same format 862 for these lines as for the first line. 863 864 Please do not mention all of the libraries that the program uses 865 "just for completeness"--that would produce a lot of unhelpful 866 clutter. Please mention library version numbers only if you find 867 in practice that they are very important to you in debugging. 868 869 The following line, after the version number line or lines, should 870 be a copyright notice. If more than one copyright notice is 871 called for, put each on a separate line. 872 873 Next should follow a brief statement that the program is free 874 software, and that users are free to copy and change it on certain 875 conditions. If the program is covered by the GNU GPL, say so 876 here. Also mention that there is no warranty, to the extent 877 permitted by law. 878 879 It is ok to finish the output with a list of the major authors of 880 the program, as a way of giving credit. 881 882 Here's an example of output that follows these rules: 883 884 GNU Emacs 19.34.5 885 Copyright (C) 1996 Free Software Foundation, Inc. 886 GNU Emacs comes with NO WARRANTY, 887 to the extent permitted by law. 888 You may redistribute copies of GNU Emacs 889 under the terms of the GNU General Public License. 890 For more information about these matters, 891 see the files named COPYING. 892 893 You should adapt this to your program, of course, filling in the 894 proper year, copyright holder, name of program, and the references 895 to distribution terms, and changing the rest of the wording as 896 necessary. 897 898 This copyright notice only needs to mention the most recent year in 899 which changes were made--there's no need to list the years for 900 previous versions' changes. You don't have to mention the name of 901 the program in these notices, if that is inconvenient, since it 902 appeared in the first line. (The rules are different for 903 copyright notices in source files; see *Note Copyright Notices: 904 (maintain)Copyright Notices.) 905 906 Translations of the above lines must preserve the validity of the 907 copyright notices (*note Internationalization::). If the 908 translation's character set supports it, the `(C)' should be 909 replaced with the copyright symbol, as follows: 910 911 (the official copyright symbol, which is the letter C in a circle); 912 913 Write the word "Copyright" exactly like that, in English. Do not 914 translate it into another language. International treaties 915 recognize the English word "Copyright"; translations into other 916 languages do not have legal significance. 917 918`--help' 919 This option should output brief documentation for how to invoke the 920 program, on standard output, then exit successfully. Other 921 options and arguments should be ignored once this is seen, and the 922 program should not perform its normal function. 923 924 Near the end of the `--help' option's output there should be a line 925 that says where to mail bug reports. It should have this format: 926 927 Report bugs to MAILING-ADDRESS. 928 929 930File: standards.info, Node: Option Table, Next: Memory Usage, Prev: Command-Line Interfaces, Up: Program Behavior 931 9324.8 Table of Long Options 933========================= 934 935Here is a table of long options used by GNU programs. It is surely 936incomplete, but we aim to list all the options that a new program might 937want to be compatible with. If you use names not already in the table, 938please send <bug-standards@gnu.org> a list of them, with their 939meanings, so we can update the table. 940 941`after-date' 942 `-N' in `tar'. 943 944`all' 945 `-a' in `du', `ls', `nm', `stty', `uname', and `unexpand'. 946 947`all-text' 948 `-a' in `diff'. 949 950`almost-all' 951 `-A' in `ls'. 952 953`append' 954 `-a' in `etags', `tee', `time'; `-r' in `tar'. 955 956`archive' 957 `-a' in `cp'. 958 959`archive-name' 960 `-n' in `shar'. 961 962`arglength' 963 `-l' in `m4'. 964 965`ascii' 966 `-a' in `diff'. 967 968`assign' 969 `-v' in `gawk'. 970 971`assume-new' 972 `-W' in Make. 973 974`assume-old' 975 `-o' in Make. 976 977`auto-check' 978 `-a' in `recode'. 979 980`auto-pager' 981 `-a' in `wdiff'. 982 983`auto-reference' 984 `-A' in `ptx'. 985 986`avoid-wraps' 987 `-n' in `wdiff'. 988 989`background' 990 For server programs, run in the background. 991 992`backward-search' 993 `-B' in `ctags'. 994 995`basename' 996 `-f' in `shar'. 997 998`batch' 999 Used in GDB. 1000 1001`baud' 1002 Used in GDB. 1003 1004`before' 1005 `-b' in `tac'. 1006 1007`binary' 1008 `-b' in `cpio' and `diff'. 1009 1010`bits-per-code' 1011 `-b' in `shar'. 1012 1013`block-size' 1014 Used in `cpio' and `tar'. 1015 1016`blocks' 1017 `-b' in `head' and `tail'. 1018 1019`break-file' 1020 `-b' in `ptx'. 1021 1022`brief' 1023 Used in various programs to make output shorter. 1024 1025`bytes' 1026 `-c' in `head', `split', and `tail'. 1027 1028`c++' 1029 `-C' in `etags'. 1030 1031`catenate' 1032 `-A' in `tar'. 1033 1034`cd' 1035 Used in various programs to specify the directory to use. 1036 1037`changes' 1038 `-c' in `chgrp' and `chown'. 1039 1040`classify' 1041 `-F' in `ls'. 1042 1043`colons' 1044 `-c' in `recode'. 1045 1046`command' 1047 `-c' in `su'; `-x' in GDB. 1048 1049`compare' 1050 `-d' in `tar'. 1051 1052`compat' 1053 Used in `gawk'. 1054 1055`compress' 1056 `-Z' in `tar' and `shar'. 1057 1058`concatenate' 1059 `-A' in `tar'. 1060 1061`confirmation' 1062 `-w' in `tar'. 1063 1064`context' 1065 Used in `diff'. 1066 1067`copyleft' 1068 `-W copyleft' in `gawk'. 1069 1070`copyright' 1071 `-C' in `ptx', `recode', and `wdiff'; `-W copyright' in `gawk'. 1072 1073`core' 1074 Used in GDB. 1075 1076`count' 1077 `-q' in `who'. 1078 1079`count-links' 1080 `-l' in `du'. 1081 1082`create' 1083 Used in `tar' and `cpio'. 1084 1085`cut-mark' 1086 `-c' in `shar'. 1087 1088`cxref' 1089 `-x' in `ctags'. 1090 1091`date' 1092 `-d' in `touch'. 1093 1094`debug' 1095 `-d' in Make and `m4'; `-t' in Bison. 1096 1097`define' 1098 `-D' in `m4'. 1099 1100`defines' 1101 `-d' in Bison and `ctags'. 1102 1103`delete' 1104 `-D' in `tar'. 1105 1106`dereference' 1107 `-L' in `chgrp', `chown', `cpio', `du', `ls', and `tar'. 1108 1109`dereference-args' 1110 `-D' in `du'. 1111 1112`device' 1113 Specify an I/O device (special file name). 1114 1115`diacritics' 1116 `-d' in `recode'. 1117 1118`dictionary-order' 1119 `-d' in `look'. 1120 1121`diff' 1122 `-d' in `tar'. 1123 1124`digits' 1125 `-n' in `csplit'. 1126 1127`directory' 1128 Specify the directory to use, in various programs. In `ls', it 1129 means to show directories themselves rather than their contents. 1130 In `rm' and `ln', it means to not treat links to directories 1131 specially. 1132 1133`discard-all' 1134 `-x' in `strip'. 1135 1136`discard-locals' 1137 `-X' in `strip'. 1138 1139`dry-run' 1140 `-n' in Make. 1141 1142`ed' 1143 `-e' in `diff'. 1144 1145`elide-empty-files' 1146 `-z' in `csplit'. 1147 1148`end-delete' 1149 `-x' in `wdiff'. 1150 1151`end-insert' 1152 `-z' in `wdiff'. 1153 1154`entire-new-file' 1155 `-N' in `diff'. 1156 1157`environment-overrides' 1158 `-e' in Make. 1159 1160`eof' 1161 `-e' in `xargs'. 1162 1163`epoch' 1164 Used in GDB. 1165 1166`error-limit' 1167 Used in `makeinfo'. 1168 1169`error-output' 1170 `-o' in `m4'. 1171 1172`escape' 1173 `-b' in `ls'. 1174 1175`exclude-from' 1176 `-X' in `tar'. 1177 1178`exec' 1179 Used in GDB. 1180 1181`exit' 1182 `-x' in `xargs'. 1183 1184`exit-0' 1185 `-e' in `unshar'. 1186 1187`expand-tabs' 1188 `-t' in `diff'. 1189 1190`expression' 1191 `-e' in `sed'. 1192 1193`extern-only' 1194 `-g' in `nm'. 1195 1196`extract' 1197 `-i' in `cpio'; `-x' in `tar'. 1198 1199`faces' 1200 `-f' in `finger'. 1201 1202`fast' 1203 `-f' in `su'. 1204 1205`fatal-warnings' 1206 `-E' in `m4'. 1207 1208`file' 1209 `-f' in `info', `gawk', Make, `mt', and `tar'; `-n' in `sed'; `-r' 1210 in `touch'. 1211 1212`field-separator' 1213 `-F' in `gawk'. 1214 1215`file-prefix' 1216 `-b' in Bison. 1217 1218`file-type' 1219 `-F' in `ls'. 1220 1221`files-from' 1222 `-T' in `tar'. 1223 1224`fill-column' 1225 Used in `makeinfo'. 1226 1227`flag-truncation' 1228 `-F' in `ptx'. 1229 1230`fixed-output-files' 1231 `-y' in Bison. 1232 1233`follow' 1234 `-f' in `tail'. 1235 1236`footnote-style' 1237 Used in `makeinfo'. 1238 1239`force' 1240 `-f' in `cp', `ln', `mv', and `rm'. 1241 1242`force-prefix' 1243 `-F' in `shar'. 1244 1245`foreground' 1246 For server programs, run in the foreground; in other words, don't 1247 do anything special to run the server in the background. 1248 1249`format' 1250 Used in `ls', `time', and `ptx'. 1251 1252`freeze-state' 1253 `-F' in `m4'. 1254 1255`fullname' 1256 Used in GDB. 1257 1258`gap-size' 1259 `-g' in `ptx'. 1260 1261`get' 1262 `-x' in `tar'. 1263 1264`graphic' 1265 `-i' in `ul'. 1266 1267`graphics' 1268 `-g' in `recode'. 1269 1270`group' 1271 `-g' in `install'. 1272 1273`gzip' 1274 `-z' in `tar' and `shar'. 1275 1276`hashsize' 1277 `-H' in `m4'. 1278 1279`header' 1280 `-h' in `objdump' and `recode' 1281 1282`heading' 1283 `-H' in `who'. 1284 1285`help' 1286 Used to ask for brief usage information. 1287 1288`here-delimiter' 1289 `-d' in `shar'. 1290 1291`hide-control-chars' 1292 `-q' in `ls'. 1293 1294`html' 1295 In `makeinfo', output HTML. 1296 1297`idle' 1298 `-u' in `who'. 1299 1300`ifdef' 1301 `-D' in `diff'. 1302 1303`ignore' 1304 `-I' in `ls'; `-x' in `recode'. 1305 1306`ignore-all-space' 1307 `-w' in `diff'. 1308 1309`ignore-backups' 1310 `-B' in `ls'. 1311 1312`ignore-blank-lines' 1313 `-B' in `diff'. 1314 1315`ignore-case' 1316 `-f' in `look' and `ptx'; `-i' in `diff' and `wdiff'. 1317 1318`ignore-errors' 1319 `-i' in Make. 1320 1321`ignore-file' 1322 `-i' in `ptx'. 1323 1324`ignore-indentation' 1325 `-I' in `etags'. 1326 1327`ignore-init-file' 1328 `-f' in Oleo. 1329 1330`ignore-interrupts' 1331 `-i' in `tee'. 1332 1333`ignore-matching-lines' 1334 `-I' in `diff'. 1335 1336`ignore-space-change' 1337 `-b' in `diff'. 1338 1339`ignore-zeros' 1340 `-i' in `tar'. 1341 1342`include' 1343 `-i' in `etags'; `-I' in `m4'. 1344 1345`include-dir' 1346 `-I' in Make. 1347 1348`incremental' 1349 `-G' in `tar'. 1350 1351`info' 1352 `-i', `-l', and `-m' in Finger. 1353 1354`init-file' 1355 In some programs, specify the name of the file to read as the 1356 user's init file. 1357 1358`initial' 1359 `-i' in `expand'. 1360 1361`initial-tab' 1362 `-T' in `diff'. 1363 1364`inode' 1365 `-i' in `ls'. 1366 1367`interactive' 1368 `-i' in `cp', `ln', `mv', `rm'; `-e' in `m4'; `-p' in `xargs'; 1369 `-w' in `tar'. 1370 1371`intermix-type' 1372 `-p' in `shar'. 1373 1374`iso-8601' 1375 Used in `date' 1376 1377`jobs' 1378 `-j' in Make. 1379 1380`just-print' 1381 `-n' in Make. 1382 1383`keep-going' 1384 `-k' in Make. 1385 1386`keep-files' 1387 `-k' in `csplit'. 1388 1389`kilobytes' 1390 `-k' in `du' and `ls'. 1391 1392`language' 1393 `-l' in `etags'. 1394 1395`less-mode' 1396 `-l' in `wdiff'. 1397 1398`level-for-gzip' 1399 `-g' in `shar'. 1400 1401`line-bytes' 1402 `-C' in `split'. 1403 1404`lines' 1405 Used in `split', `head', and `tail'. 1406 1407`link' 1408 `-l' in `cpio'. 1409 1410`lint' 1411`lint-old' 1412 Used in `gawk'. 1413 1414`list' 1415 `-t' in `cpio'; `-l' in `recode'. 1416 1417`list' 1418 `-t' in `tar'. 1419 1420`literal' 1421 `-N' in `ls'. 1422 1423`load-average' 1424 `-l' in Make. 1425 1426`login' 1427 Used in `su'. 1428 1429`machine' 1430 Used in `uname'. 1431 1432`macro-name' 1433 `-M' in `ptx'. 1434 1435`mail' 1436 `-m' in `hello' and `uname'. 1437 1438`make-directories' 1439 `-d' in `cpio'. 1440 1441`makefile' 1442 `-f' in Make. 1443 1444`mapped' 1445 Used in GDB. 1446 1447`max-args' 1448 `-n' in `xargs'. 1449 1450`max-chars' 1451 `-n' in `xargs'. 1452 1453`max-lines' 1454 `-l' in `xargs'. 1455 1456`max-load' 1457 `-l' in Make. 1458 1459`max-procs' 1460 `-P' in `xargs'. 1461 1462`mesg' 1463 `-T' in `who'. 1464 1465`message' 1466 `-T' in `who'. 1467 1468`minimal' 1469 `-d' in `diff'. 1470 1471`mixed-uuencode' 1472 `-M' in `shar'. 1473 1474`mode' 1475 `-m' in `install', `mkdir', and `mkfifo'. 1476 1477`modification-time' 1478 `-m' in `tar'. 1479 1480`multi-volume' 1481 `-M' in `tar'. 1482 1483`name-prefix' 1484 `-a' in Bison. 1485 1486`nesting-limit' 1487 `-L' in `m4'. 1488 1489`net-headers' 1490 `-a' in `shar'. 1491 1492`new-file' 1493 `-W' in Make. 1494 1495`no-builtin-rules' 1496 `-r' in Make. 1497 1498`no-character-count' 1499 `-w' in `shar'. 1500 1501`no-check-existing' 1502 `-x' in `shar'. 1503 1504`no-common' 1505 `-3' in `wdiff'. 1506 1507`no-create' 1508 `-c' in `touch'. 1509 1510`no-defines' 1511 `-D' in `etags'. 1512 1513`no-deleted' 1514 `-1' in `wdiff'. 1515 1516`no-dereference' 1517 `-d' in `cp'. 1518 1519`no-inserted' 1520 `-2' in `wdiff'. 1521 1522`no-keep-going' 1523 `-S' in Make. 1524 1525`no-lines' 1526 `-l' in Bison. 1527 1528`no-piping' 1529 `-P' in `shar'. 1530 1531`no-prof' 1532 `-e' in `gprof'. 1533 1534`no-regex' 1535 `-R' in `etags'. 1536 1537`no-sort' 1538 `-p' in `nm'. 1539 1540`no-splash' 1541 Don't print a startup splash screen. 1542 1543`no-split' 1544 Used in `makeinfo'. 1545 1546`no-static' 1547 `-a' in `gprof'. 1548 1549`no-time' 1550 `-E' in `gprof'. 1551 1552`no-timestamp' 1553 `-m' in `shar'. 1554 1555`no-validate' 1556 Used in `makeinfo'. 1557 1558`no-wait' 1559 Used in `emacsclient'. 1560 1561`no-warn' 1562 Used in various programs to inhibit warnings. 1563 1564`node' 1565 `-n' in `info'. 1566 1567`nodename' 1568 `-n' in `uname'. 1569 1570`nonmatching' 1571 `-f' in `cpio'. 1572 1573`nstuff' 1574 `-n' in `objdump'. 1575 1576`null' 1577 `-0' in `xargs'. 1578 1579`number' 1580 `-n' in `cat'. 1581 1582`number-nonblank' 1583 `-b' in `cat'. 1584 1585`numeric-sort' 1586 `-n' in `nm'. 1587 1588`numeric-uid-gid' 1589 `-n' in `cpio' and `ls'. 1590 1591`nx' 1592 Used in GDB. 1593 1594`old-archive' 1595 `-o' in `tar'. 1596 1597`old-file' 1598 `-o' in Make. 1599 1600`one-file-system' 1601 `-l' in `tar', `cp', and `du'. 1602 1603`only-file' 1604 `-o' in `ptx'. 1605 1606`only-prof' 1607 `-f' in `gprof'. 1608 1609`only-time' 1610 `-F' in `gprof'. 1611 1612`options' 1613 `-o' in `getopt', `fdlist', `fdmount', `fdmountd', and `fdumount'. 1614 1615`output' 1616 In various programs, specify the output file name. 1617 1618`output-prefix' 1619 `-o' in `shar'. 1620 1621`override' 1622 `-o' in `rm'. 1623 1624`overwrite' 1625 `-c' in `unshar'. 1626 1627`owner' 1628 `-o' in `install'. 1629 1630`paginate' 1631 `-l' in `diff'. 1632 1633`paragraph-indent' 1634 Used in `makeinfo'. 1635 1636`parents' 1637 `-p' in `mkdir' and `rmdir'. 1638 1639`pass-all' 1640 `-p' in `ul'. 1641 1642`pass-through' 1643 `-p' in `cpio'. 1644 1645`port' 1646 `-P' in `finger'. 1647 1648`portability' 1649 `-c' in `cpio' and `tar'. 1650 1651`posix' 1652 Used in `gawk'. 1653 1654`prefix-builtins' 1655 `-P' in `m4'. 1656 1657`prefix' 1658 `-f' in `csplit'. 1659 1660`preserve' 1661 Used in `tar' and `cp'. 1662 1663`preserve-environment' 1664 `-p' in `su'. 1665 1666`preserve-modification-time' 1667 `-m' in `cpio'. 1668 1669`preserve-order' 1670 `-s' in `tar'. 1671 1672`preserve-permissions' 1673 `-p' in `tar'. 1674 1675`print' 1676 `-l' in `diff'. 1677 1678`print-chars' 1679 `-L' in `cmp'. 1680 1681`print-data-base' 1682 `-p' in Make. 1683 1684`print-directory' 1685 `-w' in Make. 1686 1687`print-file-name' 1688 `-o' in `nm'. 1689 1690`print-symdefs' 1691 `-s' in `nm'. 1692 1693`printer' 1694 `-p' in `wdiff'. 1695 1696`prompt' 1697 `-p' in `ed'. 1698 1699`proxy' 1700 Specify an HTTP proxy. 1701 1702`query-user' 1703 `-X' in `shar'. 1704 1705`question' 1706 `-q' in Make. 1707 1708`quiet' 1709 Used in many programs to inhibit the usual output. Every program 1710 accepting `--quiet' should accept `--silent' as a synonym. 1711 1712`quiet-unshar' 1713 `-Q' in `shar' 1714 1715`quote-name' 1716 `-Q' in `ls'. 1717 1718`rcs' 1719 `-n' in `diff'. 1720 1721`re-interval' 1722 Used in `gawk'. 1723 1724`read-full-blocks' 1725 `-B' in `tar'. 1726 1727`readnow' 1728 Used in GDB. 1729 1730`recon' 1731 `-n' in Make. 1732 1733`record-number' 1734 `-R' in `tar'. 1735 1736`recursive' 1737 Used in `chgrp', `chown', `cp', `ls', `diff', and `rm'. 1738 1739`reference-limit' 1740 Used in `makeinfo'. 1741 1742`references' 1743 `-r' in `ptx'. 1744 1745`regex' 1746 `-r' in `tac' and `etags'. 1747 1748`release' 1749 `-r' in `uname'. 1750 1751`reload-state' 1752 `-R' in `m4'. 1753 1754`relocation' 1755 `-r' in `objdump'. 1756 1757`rename' 1758 `-r' in `cpio'. 1759 1760`replace' 1761 `-i' in `xargs'. 1762 1763`report-identical-files' 1764 `-s' in `diff'. 1765 1766`reset-access-time' 1767 `-a' in `cpio'. 1768 1769`reverse' 1770 `-r' in `ls' and `nm'. 1771 1772`reversed-ed' 1773 `-f' in `diff'. 1774 1775`right-side-defs' 1776 `-R' in `ptx'. 1777 1778`same-order' 1779 `-s' in `tar'. 1780 1781`same-permissions' 1782 `-p' in `tar'. 1783 1784`save' 1785 `-g' in `stty'. 1786 1787`se' 1788 Used in GDB. 1789 1790`sentence-regexp' 1791 `-S' in `ptx'. 1792 1793`separate-dirs' 1794 `-S' in `du'. 1795 1796`separator' 1797 `-s' in `tac'. 1798 1799`sequence' 1800 Used by `recode' to chose files or pipes for sequencing passes. 1801 1802`shell' 1803 `-s' in `su'. 1804 1805`show-all' 1806 `-A' in `cat'. 1807 1808`show-c-function' 1809 `-p' in `diff'. 1810 1811`show-ends' 1812 `-E' in `cat'. 1813 1814`show-function-line' 1815 `-F' in `diff'. 1816 1817`show-tabs' 1818 `-T' in `cat'. 1819 1820`silent' 1821 Used in many programs to inhibit the usual output. Every program 1822 accepting `--silent' should accept `--quiet' as a synonym. 1823 1824`size' 1825 `-s' in `ls'. 1826 1827`socket' 1828 Specify a file descriptor for a network server to use for its 1829 socket, instead of opening and binding a new socket. This 1830 provides a way to run, in a non-privileged process, a server that 1831 normally needs a reserved port number. 1832 1833`sort' 1834 Used in `ls'. 1835 1836`source' 1837 `-W source' in `gawk'. 1838 1839`sparse' 1840 `-S' in `tar'. 1841 1842`speed-large-files' 1843 `-H' in `diff'. 1844 1845`split-at' 1846 `-E' in `unshar'. 1847 1848`split-size-limit' 1849 `-L' in `shar'. 1850 1851`squeeze-blank' 1852 `-s' in `cat'. 1853 1854`start-delete' 1855 `-w' in `wdiff'. 1856 1857`start-insert' 1858 `-y' in `wdiff'. 1859 1860`starting-file' 1861 Used in `tar' and `diff' to specify which file within a directory 1862 to start processing with. 1863 1864`statistics' 1865 `-s' in `wdiff'. 1866 1867`stdin-file-list' 1868 `-S' in `shar'. 1869 1870`stop' 1871 `-S' in Make. 1872 1873`strict' 1874 `-s' in `recode'. 1875 1876`strip' 1877 `-s' in `install'. 1878 1879`strip-all' 1880 `-s' in `strip'. 1881 1882`strip-debug' 1883 `-S' in `strip'. 1884 1885`submitter' 1886 `-s' in `shar'. 1887 1888`suffix' 1889 `-S' in `cp', `ln', `mv'. 1890 1891`suffix-format' 1892 `-b' in `csplit'. 1893 1894`sum' 1895 `-s' in `gprof'. 1896 1897`summarize' 1898 `-s' in `du'. 1899 1900`symbolic' 1901 `-s' in `ln'. 1902 1903`symbols' 1904 Used in GDB and `objdump'. 1905 1906`synclines' 1907 `-s' in `m4'. 1908 1909`sysname' 1910 `-s' in `uname'. 1911 1912`tabs' 1913 `-t' in `expand' and `unexpand'. 1914 1915`tabsize' 1916 `-T' in `ls'. 1917 1918`terminal' 1919 `-T' in `tput' and `ul'. `-t' in `wdiff'. 1920 1921`text' 1922 `-a' in `diff'. 1923 1924`text-files' 1925 `-T' in `shar'. 1926 1927`time' 1928 Used in `ls' and `touch'. 1929 1930`timeout' 1931 Specify how long to wait before giving up on some operation. 1932 1933`to-stdout' 1934 `-O' in `tar'. 1935 1936`total' 1937 `-c' in `du'. 1938 1939`touch' 1940 `-t' in Make, `ranlib', and `recode'. 1941 1942`trace' 1943 `-t' in `m4'. 1944 1945`traditional' 1946 `-t' in `hello'; `-W traditional' in `gawk'; `-G' in `ed', `m4', 1947 and `ptx'. 1948 1949`tty' 1950 Used in GDB. 1951 1952`typedefs' 1953 `-t' in `ctags'. 1954 1955`typedefs-and-c++' 1956 `-T' in `ctags'. 1957 1958`typeset-mode' 1959 `-t' in `ptx'. 1960 1961`uncompress' 1962 `-z' in `tar'. 1963 1964`unconditional' 1965 `-u' in `cpio'. 1966 1967`undefine' 1968 `-U' in `m4'. 1969 1970`undefined-only' 1971 `-u' in `nm'. 1972 1973`update' 1974 `-u' in `cp', `ctags', `mv', `tar'. 1975 1976`usage' 1977 Used in `gawk'; same as `--help'. 1978 1979`uuencode' 1980 `-B' in `shar'. 1981 1982`vanilla-operation' 1983 `-V' in `shar'. 1984 1985`verbose' 1986 Print more information about progress. Many programs support this. 1987 1988`verify' 1989 `-W' in `tar'. 1990 1991`version' 1992 Print the version number. 1993 1994`version-control' 1995 `-V' in `cp', `ln', `mv'. 1996 1997`vgrind' 1998 `-v' in `ctags'. 1999 2000`volume' 2001 `-V' in `tar'. 2002 2003`what-if' 2004 `-W' in Make. 2005 2006`whole-size-limit' 2007 `-l' in `shar'. 2008 2009`width' 2010 `-w' in `ls' and `ptx'. 2011 2012`word-regexp' 2013 `-W' in `ptx'. 2014 2015`writable' 2016 `-T' in `who'. 2017 2018`zeros' 2019 `-z' in `gprof'. 2020 2021 2022File: standards.info, Node: Memory Usage, Next: File Usage, Prev: Option Table, Up: Program Behavior 2023 20244.9 Memory Usage 2025================ 2026 2027If a program typically uses just a few meg of memory, don't bother 2028making any effort to reduce memory usage. For example, if it is 2029impractical for other reasons to operate on files more than a few meg 2030long, it is reasonable to read entire input files into memory to 2031operate on them. 2032 2033 However, for programs such as `cat' or `tail', that can usefully 2034operate on very large files, it is important to avoid using a technique 2035that would artificially limit the size of files it can handle. If a 2036program works by lines and could be applied to arbitrary user-supplied 2037input files, it should keep only a line in memory, because this is not 2038very hard and users will want to be able to operate on input files that 2039are bigger than will fit in memory all at once. 2040 2041 If your program creates complicated data structures, just make them 2042in memory and give a fatal error if `malloc' returns zero. 2043 2044 2045File: standards.info, Node: File Usage, Prev: Memory Usage, Up: Program Behavior 2046 20474.10 File Usage 2048=============== 2049 2050Programs should be prepared to operate when `/usr' and `/etc' are 2051read-only file systems. Thus, if the program manages log files, lock 2052files, backup files, score files, or any other files which are modified 2053for internal purposes, these files should not be stored in `/usr' or 2054`/etc'. 2055 2056 There are two exceptions. `/etc' is used to store system 2057configuration information; it is reasonable for a program to modify 2058files in `/etc' when its job is to update the system configuration. 2059Also, if the user explicitly asks to modify one file in a directory, it 2060is reasonable for the program to store other files in the same 2061directory. 2062 2063 2064File: standards.info, Node: Writing C, Next: Documentation, Prev: Program Behavior, Up: Top 2065 20665 Making The Best Use of C 2067************************** 2068 2069This chapter provides advice on how best to use the C language when 2070writing GNU software. 2071 2072* Menu: 2073 2074* Formatting:: Formatting Your Source Code 2075* Comments:: Commenting Your Work 2076* Syntactic Conventions:: Clean Use of C Constructs 2077* Names:: Naming Variables, Functions, and Files 2078* System Portability:: Portability between different operating systems 2079* CPU Portability:: Supporting the range of CPU types 2080* System Functions:: Portability and ``standard'' library functions 2081* Internationalization:: Techniques for internationalization 2082* Character Set:: Use ASCII by default. 2083* Quote Characters:: Use `...' in the C locale. 2084* Mmap:: How you can safely use `mmap'. 2085 2086 2087File: standards.info, Node: Formatting, Next: Comments, Up: Writing C 2088 20895.1 Formatting Your Source Code 2090=============================== 2091 2092It is important to put the open-brace that starts the body of a C 2093function in column one, and avoid putting any other open-brace or 2094open-parenthesis or open-bracket in column one. Several tools look for 2095open-braces in column one to find the beginnings of C functions. These 2096tools will not work on code not formatted that way. 2097 2098 It is also important for function definitions to start the name of 2099the function in column one. This helps people to search for function 2100definitions, and may also help certain tools recognize them. Thus, 2101using Standard C syntax, the format is this: 2102 2103 static char * 2104 concat (char *s1, char *s2) 2105 { 2106 ... 2107 } 2108 2109or, if you want to use traditional C syntax, format the definition like 2110this: 2111 2112 static char * 2113 concat (s1, s2) /* Name starts in column one here */ 2114 char *s1, *s2; 2115 { /* Open brace in column one here */ 2116 ... 2117 } 2118 2119 In Standard C, if the arguments don't fit nicely on one line, split 2120it like this: 2121 2122 int 2123 lots_of_args (int an_integer, long a_long, short a_short, 2124 double a_double, float a_float) 2125 ... 2126 2127 The rest of this section gives our recommendations for other aspects 2128of C formatting style, which is also the default style of the `indent' 2129program in version 1.2 and newer. It corresponds to the options 2130 2131 -nbad -bap -nbc -bbo -bl -bli2 -bls -ncdb -nce -cp1 -cs -di2 2132 -ndj -nfc1 -nfca -hnl -i2 -ip5 -lp -pcs -psl -nsc -nsob 2133 2134 We don't think of these recommendations as requirements, because it 2135causes no problems for users if two different programs have different 2136formatting styles. 2137 2138 But whatever style you use, please use it consistently, since a 2139mixture of styles within one program tends to look ugly. If you are 2140contributing changes to an existing program, please follow the style of 2141that program. 2142 2143 For the body of the function, our recommended style looks like this: 2144 2145 if (x < foo (y, z)) 2146 haha = bar[4] + 5; 2147 else 2148 { 2149 while (z) 2150 { 2151 haha += foo (z, z); 2152 z--; 2153 } 2154 return ++x + bar (); 2155 } 2156 2157 We find it easier to read a program when it has spaces before the 2158open-parentheses and after the commas. Especially after the commas. 2159 2160 When you split an expression into multiple lines, split it before an 2161operator, not after one. Here is the right way: 2162 2163 if (foo_this_is_long && bar > win (x, y, z) 2164 && remaining_condition) 2165 2166 Try to avoid having two operators of different precedence at the same 2167level of indentation. For example, don't write this: 2168 2169 mode = (inmode[j] == VOIDmode 2170 || GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j]) 2171 ? outmode[j] : inmode[j]); 2172 2173 Instead, use extra parentheses so that the indentation shows the 2174nesting: 2175 2176 mode = ((inmode[j] == VOIDmode 2177 || (GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j]))) 2178 ? outmode[j] : inmode[j]); 2179 2180 Insert extra parentheses so that Emacs will indent the code properly. 2181For example, the following indentation looks nice if you do it by hand, 2182 2183 v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000 2184 + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000; 2185 2186but Emacs would alter it. Adding a set of parentheses produces 2187something that looks equally nice, and which Emacs will preserve: 2188 2189 v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000 2190 + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000); 2191 2192 Format do-while statements like this: 2193 2194 do 2195 { 2196 a = foo (a); 2197 } 2198 while (a > 0); 2199 2200 Please use formfeed characters (control-L) to divide the program into 2201pages at logical places (but not within a function). It does not matter 2202just how long the pages are, since they do not have to fit on a printed 2203page. The formfeeds should appear alone on lines by themselves. 2204 2205 2206File: standards.info, Node: Comments, Next: Syntactic Conventions, Prev: Formatting, Up: Writing C 2207 22085.2 Commenting Your Work 2209======================== 2210 2211Every program should start with a comment saying briefly what it is for. 2212Example: `fmt - filter for simple filling of text'. This comment 2213should be at the top of the source file containing the `main' function 2214of the program. 2215 2216 Also, please write a brief comment at the start of each source file, 2217with the file name and a line or two about the overall purpose of the 2218file. 2219 2220 Please write the comments in a GNU program in English, because 2221English is the one language that nearly all programmers in all 2222countries can read. If you do not write English well, please write 2223comments in English as well as you can, then ask other people to help 2224rewrite them. If you can't write comments in English, please find 2225someone to work with you and translate your comments into English. 2226 2227 Please put a comment on each function saying what the function does, 2228what sorts of arguments it gets, and what the possible values of 2229arguments mean and are used for. It is not necessary to duplicate in 2230words the meaning of the C argument declarations, if a C type is being 2231used in its customary fashion. If there is anything nonstandard about 2232its use (such as an argument of type `char *' which is really the 2233address of the second character of a string, not the first), or any 2234possible values that would not work the way one would expect (such as, 2235that strings containing newlines are not guaranteed to work), be sure 2236to say so. 2237 2238 Also explain the significance of the return value, if there is one. 2239 2240 Please put two spaces after the end of a sentence in your comments, 2241so that the Emacs sentence commands will work. Also, please write 2242complete sentences and capitalize the first word. If a lower-case 2243identifier comes at the beginning of a sentence, don't capitalize it! 2244Changing the spelling makes it a different identifier. If you don't 2245like starting a sentence with a lower case letter, write the sentence 2246differently (e.g., "The identifier lower-case is ..."). 2247 2248 The comment on a function is much clearer if you use the argument 2249names to speak about the argument values. The variable name itself 2250should be lower case, but write it in upper case when you are speaking 2251about the value rather than the variable itself. Thus, "the inode 2252number NODE_NUM" rather than "an inode". 2253 2254 There is usually no purpose in restating the name of the function in 2255the comment before it, because the reader can see that for himself. 2256There might be an exception when the comment is so long that the 2257function itself would be off the bottom of the screen. 2258 2259 There should be a comment on each static variable as well, like this: 2260 2261 /* Nonzero means truncate lines in the display; 2262 zero means continue them. */ 2263 int truncate_lines; 2264 2265 Every `#endif' should have a comment, except in the case of short 2266conditionals (just a few lines) that are not nested. The comment should 2267state the condition of the conditional that is ending, _including its 2268sense_. `#else' should have a comment describing the condition _and 2269sense_ of the code that follows. For example: 2270 2271 #ifdef foo 2272 ... 2273 #else /* not foo */ 2274 ... 2275 #endif /* not foo */ 2276 #ifdef foo 2277 ... 2278 #endif /* foo */ 2279 2280but, by contrast, write the comments this way for a `#ifndef': 2281 2282 #ifndef foo 2283 ... 2284 #else /* foo */ 2285 ... 2286 #endif /* foo */ 2287 #ifndef foo 2288 ... 2289 #endif /* not foo */ 2290 2291 2292File: standards.info, Node: Syntactic Conventions, Next: Names, Prev: Comments, Up: Writing C 2293 22945.3 Clean Use of C Constructs 2295============================= 2296 2297Please explicitly declare the types of all objects. For example, you 2298should explicitly declare all arguments to functions, and you should 2299declare functions to return `int' rather than omitting the `int'. 2300 2301 Some programmers like to use the GCC `-Wall' option, and change the 2302code whenever it issues a warning. If you want to do this, then do. 2303Other programmers prefer not to use `-Wall', because it gives warnings 2304for valid and legitimate code which they do not want to change. If you 2305want to do this, then do. The compiler should be your servant, not 2306your master. 2307 2308 Declarations of external functions and functions to appear later in 2309the source file should all go in one place near the beginning of the 2310file (somewhere before the first function definition in the file), or 2311else should go in a header file. Don't put `extern' declarations inside 2312functions. 2313 2314 It used to be common practice to use the same local variables (with 2315names like `tem') over and over for different values within one 2316function. Instead of doing this, it is better to declare a separate 2317local variable for each distinct purpose, and give it a name which is 2318meaningful. This not only makes programs easier to understand, it also 2319facilitates optimization by good compilers. You can also move the 2320declaration of each local variable into the smallest scope that includes 2321all its uses. This makes the program even cleaner. 2322 2323 Don't use local variables or parameters that shadow global 2324identifiers. 2325 2326 Don't declare multiple variables in one declaration that spans lines. 2327Start a new declaration on each line, instead. For example, instead of 2328this: 2329 2330 int foo, 2331 bar; 2332 2333write either this: 2334 2335 int foo, bar; 2336 2337or this: 2338 2339 int foo; 2340 int bar; 2341 2342(If they are global variables, each should have a comment preceding it 2343anyway.) 2344 2345 When you have an `if'-`else' statement nested in another `if' 2346statement, always put braces around the `if'-`else'. Thus, never write 2347like this: 2348 2349 if (foo) 2350 if (bar) 2351 win (); 2352 else 2353 lose (); 2354 2355always like this: 2356 2357 if (foo) 2358 { 2359 if (bar) 2360 win (); 2361 else 2362 lose (); 2363 } 2364 2365 If you have an `if' statement nested inside of an `else' statement, 2366either write `else if' on one line, like this, 2367 2368 if (foo) 2369 ... 2370 else if (bar) 2371 ... 2372 2373with its `then'-part indented like the preceding `then'-part, or write 2374the nested `if' within braces like this: 2375 2376 if (foo) 2377 ... 2378 else 2379 { 2380 if (bar) 2381 ... 2382 } 2383 2384 Don't declare both a structure tag and variables or typedefs in the 2385same declaration. Instead, declare the structure tag separately and 2386then use it to declare the variables or typedefs. 2387 2388 Try to avoid assignments inside `if'-conditions (assignments inside 2389`while'-conditions are ok). For example, don't write this: 2390 2391 if ((foo = (char *) malloc (sizeof *foo)) == 0) 2392 fatal ("virtual memory exhausted"); 2393 2394instead, write this: 2395 2396 foo = (char *) malloc (sizeof *foo); 2397 if (foo == 0) 2398 fatal ("virtual memory exhausted"); 2399 2400 Don't make the program ugly to placate `lint'. Please don't insert 2401any casts to `void'. Zero without a cast is perfectly fine as a null 2402pointer constant, except when calling a varargs function. 2403 2404 2405File: standards.info, Node: Names, Next: System Portability, Prev: Syntactic Conventions, Up: Writing C 2406 24075.4 Naming Variables, Functions, and Files 2408========================================== 2409 2410The names of global variables and functions in a program serve as 2411comments of a sort. So don't choose terse names--instead, look for 2412names that give useful information about the meaning of the variable or 2413function. In a GNU program, names should be English, like other 2414comments. 2415 2416 Local variable names can be shorter, because they are used only 2417within one context, where (presumably) comments explain their purpose. 2418 2419 Try to limit your use of abbreviations in symbol names. It is ok to 2420make a few abbreviations, explain what they mean, and then use them 2421frequently, but don't use lots of obscure abbreviations. 2422 2423 Please use underscores to separate words in a name, so that the Emacs 2424word commands can be useful within them. Stick to lower case; reserve 2425upper case for macros and `enum' constants, and for name-prefixes that 2426follow a uniform convention. 2427 2428 For example, you should use names like `ignore_space_change_flag'; 2429don't use names like `iCantReadThis'. 2430 2431 Variables that indicate whether command-line options have been 2432specified should be named after the meaning of the option, not after 2433the option-letter. A comment should state both the exact meaning of 2434the option and its letter. For example, 2435 2436 /* Ignore changes in horizontal whitespace (-b). */ 2437 int ignore_space_change_flag; 2438 2439 When you want to define names with constant integer values, use 2440`enum' rather than `#define'. GDB knows about enumeration constants. 2441 2442 You might want to make sure that none of the file names would 2443conflict if the files were loaded onto an MS-DOS file system which 2444shortens the names. You can use the program `doschk' to test for this. 2445 2446 Some GNU programs were designed to limit themselves to file names of 244714 characters or less, to avoid file name conflicts if they are read 2448into older System V systems. Please preserve this feature in the 2449existing GNU programs that have it, but there is no need to do this in 2450new GNU programs. `doschk' also reports file names longer than 14 2451characters. 2452 2453 2454File: standards.info, Node: System Portability, Next: CPU Portability, Prev: Names, Up: Writing C 2455 24565.5 Portability between System Types 2457==================================== 2458 2459In the Unix world, "portability" refers to porting to different Unix 2460versions. For a GNU program, this kind of portability is desirable, but 2461not paramount. 2462 2463 The primary purpose of GNU software is to run on top of the GNU 2464kernel, compiled with the GNU C compiler, on various types of CPU. So 2465the kinds of portability that are absolutely necessary are quite 2466limited. But it is important to support Linux-based GNU systems, since 2467they are the form of GNU that is popular. 2468 2469 Beyond that, it is good to support the other free operating systems 2470(*BSD), and it is nice to support other Unix-like systems if you want 2471to. Supporting a variety of Unix-like systems is desirable, although 2472not paramount. It is usually not too hard, so you may as well do it. 2473But you don't have to consider it an obligation, if it does turn out to 2474be hard. 2475 2476 The easiest way to achieve portability to most Unix-like systems is 2477to use Autoconf. It's unlikely that your program needs to know more 2478information about the host platform than Autoconf can provide, simply 2479because most of the programs that need such knowledge have already been 2480written. 2481 2482 Avoid using the format of semi-internal data bases (e.g., 2483directories) when there is a higher-level alternative (`readdir'). 2484 2485 As for systems that are not like Unix, such as MSDOS, Windows, VMS, 2486MVS, and older Macintosh systems, supporting them is often a lot of 2487work. When that is the case, it is better to spend your time adding 2488features that will be useful on GNU and GNU/Linux, rather than on 2489supporting other incompatible systems. 2490 2491 If you do support Windows, please do not abbreviate it as "win". In 2492hacker terminology, calling something a "win" is a form of praise. 2493You're free to praise Microsoft Windows on your own if you want, but 2494please don't do this in GNU packages. Instead of abbreviating 2495"Windows" to "un", you can write it in full or abbreviate it to "woe" 2496or "w". In GNU Emacs, for instance, we use `w32' in file names of 2497Windows-specific files, but the macro for Windows conditionals is 2498called `WINDOWSNT'. 2499 2500 It is a good idea to define the "feature test macro" `_GNU_SOURCE' 2501when compiling your C files. When you compile on GNU or GNU/Linux, 2502this will enable the declarations of GNU library extension functions, 2503and that will usually give you a compiler error message if you define 2504the same function names in some other way in your program. (You don't 2505have to actually _use_ these functions, if you prefer to make the 2506program more portable to other systems.) 2507 2508 But whether or not you use these GNU extensions, you should avoid 2509using their names for any other meanings. Doing so would make it hard 2510to move your code into other GNU programs. 2511 2512 2513File: standards.info, Node: CPU Portability, Next: System Functions, Prev: System Portability, Up: Writing C 2514 25155.6 Portability between CPUs 2516============================ 2517 2518Even GNU systems will differ because of differences among CPU 2519types--for example, difference in byte ordering and alignment 2520requirements. It is absolutely essential to handle these differences. 2521However, don't make any effort to cater to the possibility that an 2522`int' will be less than 32 bits. We don't support 16-bit machines in 2523GNU. 2524 2525 Similarly, don't make any effort to cater to the possibility that 2526`long' will be smaller than predefined types like `size_t'. For 2527example, the following code is ok: 2528 2529 printf ("size = %lu\n", (unsigned long) sizeof array); 2530 printf ("diff = %ld\n", (long) (pointer2 - pointer1)); 2531 2532 1989 Standard C requires this to work, and we know of only one 2533counterexample: 64-bit programs on Microsoft Windows. We will leave it 2534to those who want to port GNU programs to that environment to figure 2535out how to do it. 2536 2537 Predefined file-size types like `off_t' are an exception: they are 2538longer than `long' on many platforms, so code like the above won't work 2539with them. One way to print an `off_t' value portably is to print its 2540digits yourself, one by one. 2541 2542 Don't assume that the address of an `int' object is also the address 2543of its least-significant byte. This is false on big-endian machines. 2544Thus, don't make the following mistake: 2545 2546 int c; 2547 ... 2548 while ((c = getchar ()) != EOF) 2549 write (file_descriptor, &c, 1); 2550 2551Instead, use `unsigned char' as follows. (The `unsigned' is for 2552portability to unusual systems where `char' is signed and where there 2553is integer overflow checking.) 2554 2555 int c; 2556 while ((c = getchar ()) != EOF) 2557 { 2558 unsigned char u = c; 2559 write (file_descriptor, &u, 1); 2560 } 2561 2562 It used to be ok to not worry about the difference between pointers 2563and integers when passing arguments to functions. However, on most 2564modern 64-bit machines pointers are wider than `int'. Conversely, 2565integer types like `long long int' and `off_t' are wider than pointers 2566on most modern 32-bit machines. Hence it's often better nowadays to 2567use prototypes to define functions whose argument types are not trivial. 2568 2569 In particular, if functions accept varying argument counts or types 2570they should be declared using prototypes containing `...' and defined 2571using `stdarg.h'. For an example of this, please see the Gnulib 2572(http://www.gnu.org/software/gnulib/) error module, which declares and 2573defines the following function: 2574 2575 /* Print a message with `fprintf (stderr, FORMAT, ...)'; 2576 if ERRNUM is nonzero, follow it with ": " and strerror (ERRNUM). 2577 If STATUS is nonzero, terminate the program with `exit (STATUS)'. */ 2578 2579 void error (int status, int errnum, const char *format, ...); 2580 2581 A simple way to use the Gnulib error module is to obtain the two 2582source files `error.c' and `error.h' from the Gnulib library source 2583code repository at 2584`http://savannah.gnu.org/cgi-bin/viewcvs/gnulib/gnulib/lib/'. Here's a 2585sample use: 2586 2587 #include "error.h" 2588 #include <errno.h> 2589 #include <stdio.h> 2590 2591 char *program_name = "myprogram"; 2592 2593 FILE * 2594 xfopen (char const *name) 2595 { 2596 FILE *fp = fopen (name, "r"); 2597 if (! fp) 2598 error (1, errno, "cannot read %s", name); 2599 return fp; 2600 } 2601 2602 Avoid casting pointers to integers if you can. Such casts greatly 2603reduce portability, and in most programs they are easy to avoid. In the 2604cases where casting pointers to integers is essential--such as, a Lisp 2605interpreter which stores type information as well as an address in one 2606word--you'll have to make explicit provisions to handle different word 2607sizes. You will also need to make provision for systems in which the 2608normal range of addresses you can get from `malloc' starts far away 2609from zero. 2610 2611 2612File: standards.info, Node: System Functions, Next: Internationalization, Prev: CPU Portability, Up: Writing C 2613 26145.7 Calling System Functions 2615============================ 2616 2617C implementations differ substantially. Standard C reduces but does 2618not eliminate the incompatibilities; meanwhile, many GNU packages still 2619support pre-standard compilers because this is not hard to do. This 2620chapter gives recommendations for how to use the more-or-less standard C 2621library functions to avoid unnecessary loss of portability. 2622 2623 * Don't use the return value of `sprintf'. It returns the number of 2624 characters written on some systems, but not on all systems. 2625 2626 * Be aware that `vfprintf' is not always available. 2627 2628 * `main' should be declared to return type `int'. It should 2629 terminate either by calling `exit' or by returning the integer 2630 status code; make sure it cannot ever return an undefined value. 2631 2632 * Don't declare system functions explicitly. 2633 2634 Almost any declaration for a system function is wrong on some 2635 system. To minimize conflicts, leave it to the system header 2636 files to declare system functions. If the headers don't declare a 2637 function, let it remain undeclared. 2638 2639 While it may seem unclean to use a function without declaring it, 2640 in practice this works fine for most system library functions on 2641 the systems where this really happens; thus, the disadvantage is 2642 only theoretical. By contrast, actual declarations have 2643 frequently caused actual conflicts. 2644 2645 * If you must declare a system function, don't specify the argument 2646 types. Use an old-style declaration, not a Standard C prototype. 2647 The more you specify about the function, the more likely a 2648 conflict. 2649 2650 * In particular, don't unconditionally declare `malloc' or `realloc'. 2651 2652 Most GNU programs use those functions just once, in functions 2653 conventionally named `xmalloc' and `xrealloc'. These functions 2654 call `malloc' and `realloc', respectively, and check the results. 2655 2656 Because `xmalloc' and `xrealloc' are defined in your program, you 2657 can declare them in other files without any risk of type conflict. 2658 2659 On most systems, `int' is the same length as a pointer; thus, the 2660 calls to `malloc' and `realloc' work fine. For the few 2661 exceptional systems (mostly 64-bit machines), you can use 2662 *conditionalized* declarations of `malloc' and `realloc'--or put 2663 these declarations in configuration files specific to those 2664 systems. 2665 2666 * The string functions require special treatment. Some Unix systems 2667 have a header file `string.h'; others have `strings.h'. Neither 2668 file name is portable. There are two things you can do: use 2669 Autoconf to figure out which file to include, or don't include 2670 either file. 2671 2672 * If you don't include either strings file, you can't get 2673 declarations for the string functions from the header file in the 2674 usual way. 2675 2676 That causes less of a problem than you might think. The newer 2677 standard string functions should be avoided anyway because many 2678 systems still don't support them. The string functions you can 2679 use are these: 2680 2681 strcpy strncpy strcat strncat 2682 strlen strcmp strncmp 2683 strchr strrchr 2684 2685 The copy and concatenate functions work fine without a declaration 2686 as long as you don't use their values. Using their values without 2687 a declaration fails on systems where the width of a pointer 2688 differs from the width of `int', and perhaps in other cases. It 2689 is trivial to avoid using their values, so do that. 2690 2691 The compare functions and `strlen' work fine without a declaration 2692 on most systems, possibly all the ones that GNU software runs on. 2693 You may find it necessary to declare them *conditionally* on a few 2694 systems. 2695 2696 The search functions must be declared to return `char *'. Luckily, 2697 there is no variation in the data type they return. But there is 2698 variation in their names. Some systems give these functions the 2699 names `index' and `rindex'; other systems use the names `strchr' 2700 and `strrchr'. Some systems support both pairs of names, but 2701 neither pair works on all systems. 2702 2703 You should pick a single pair of names and use it throughout your 2704 program. (Nowadays, it is better to choose `strchr' and `strrchr' 2705 for new programs, since those are the standard names.) Declare 2706 both of those names as functions returning `char *'. On systems 2707 which don't support those names, define them as macros in terms of 2708 the other pair. For example, here is what to put at the beginning 2709 of your file (or in a header) if you want to use the names 2710 `strchr' and `strrchr' throughout: 2711 2712 #ifndef HAVE_STRCHR 2713 #define strchr index 2714 #endif 2715 #ifndef HAVE_STRRCHR 2716 #define strrchr rindex 2717 #endif 2718 2719 char *strchr (); 2720 char *strrchr (); 2721 2722 Here we assume that `HAVE_STRCHR' and `HAVE_STRRCHR' are macros 2723defined in systems where the corresponding functions exist. One way to 2724get them properly defined is to use Autoconf. 2725 2726 2727File: standards.info, Node: Internationalization, Next: Character Set, Prev: System Functions, Up: Writing C 2728 27295.8 Internationalization 2730======================== 2731 2732GNU has a library called GNU gettext that makes it easy to translate the 2733messages in a program into various languages. You should use this 2734library in every program. Use English for the messages as they appear 2735in the program, and let gettext provide the way to translate them into 2736other languages. 2737 2738 Using GNU gettext involves putting a call to the `gettext' macro 2739around each string that might need translation--like this: 2740 2741 printf (gettext ("Processing file `%s'...")); 2742 2743This permits GNU gettext to replace the string `"Processing file 2744`%s'..."' with a translated version. 2745 2746 Once a program uses gettext, please make a point of writing calls to 2747`gettext' when you add new strings that call for translation. 2748 2749 Using GNU gettext in a package involves specifying a "text domain 2750name" for the package. The text domain name is used to separate the 2751translations for this package from the translations for other packages. 2752Normally, the text domain name should be the same as the name of the 2753package--for example, `coreutils' for the GNU core utilities. 2754 2755 To enable gettext to work well, avoid writing code that makes 2756assumptions about the structure of words or sentences. When you want 2757the precise text of a sentence to vary depending on the data, use two or 2758more alternative string constants each containing a complete sentences, 2759rather than inserting conditionalized words or phrases into a single 2760sentence framework. 2761 2762 Here is an example of what not to do: 2763 2764 printf ("%s is full", capacity > 5000000 ? "disk" : "floppy disk"); 2765 2766 If you apply gettext to all strings, like this, 2767 2768 printf (gettext ("%s is full"), 2769 capacity > 5000000 ? gettext ("disk") : gettext ("floppy disk")); 2770 2771the translator will hardly know that "disk" and "floppy disk" are meant 2772to be substituted in the other string. Worse, in some languages (like 2773French) the construction will not work: the translation of the word 2774"full" depends on the gender of the first part of the sentence; it 2775happens to be not the same for "disk" as for "floppy disk". 2776 2777 Complete sentences can be translated without problems: 2778 2779 printf (capacity > 5000000 ? gettext ("disk is full") 2780 : gettext ("floppy disk is full")); 2781 2782 A similar problem appears at the level of sentence structure with 2783this code: 2784 2785 printf ("# Implicit rule search has%s been done.\n", 2786 f->tried_implicit ? "" : " not"); 2787 2788Adding `gettext' calls to this code cannot give correct results for all 2789languages, because negation in some languages requires adding words at 2790more than one place in the sentence. By contrast, adding `gettext' 2791calls does the job straightforwardly if the code starts out like this: 2792 2793 printf (f->tried_implicit 2794 ? "# Implicit rule search has been done.\n", 2795 : "# Implicit rule search has not been done.\n"); 2796 2797 Another example is this one: 2798 2799 printf ("%d file%s processed", nfiles, 2800 nfiles != 1 ? "s" : ""); 2801 2802The problem with this example is that it assumes that plurals are made 2803by adding `s'. If you apply gettext to the format string, like this, 2804 2805 printf (gettext ("%d file%s processed"), nfiles, 2806 nfiles != 1 ? "s" : ""); 2807 2808the message can use different words, but it will still be forced to use 2809`s' for the plural. Here is a better way, with gettext being applied to 2810the two strings independently: 2811 2812 printf ((nfiles != 1 ? gettext ("%d files processed") 2813 : gettext ("%d file processed")), 2814 nfiles); 2815 2816But this still doesn't work for languages like Polish, which has three 2817plural forms: one for nfiles == 1, one for nfiles == 2, 3, 4, 22, 23, 281824, ... and one for the rest. The GNU `ngettext' function solves this 2819problem: 2820 2821 printf (ngettext ("%d files processed", "%d file processed", nfiles), 2822 nfiles); 2823 2824 2825File: standards.info, Node: Character Set, Next: Quote Characters, Prev: Internationalization, Up: Writing C 2826 28275.9 Character Set 2828================= 2829 2830Sticking to the ASCII character set (plain text, 7-bit characters) is 2831preferred in GNU source code comments, text documents, and other 2832contexts, unless there is good reason to do something else because of 2833the application domain. For example, if source code deals with the 2834French Revolutionary calendar, it is OK if its literal strings contain 2835accented characters in month names like "Flore'al". Also, it is OK to 2836use non-ASCII characters to represent proper names of contributors in 2837change logs (*note Change Logs::). 2838 2839 If you need to use non-ASCII characters, you should normally stick 2840with one encoding, as one cannot in general mix encodings reliably. 2841 2842 2843File: standards.info, Node: Quote Characters, Next: Mmap, Prev: Character Set, Up: Writing C 2844 28455.10 Quote Characters 2846===================== 2847 2848In the C locale, GNU programs should stick to plain ASCII for quotation 2849characters in messages to users: preferably 0x60 (``') for left quotes 2850and 0x27 (`'') for right quotes. It is ok, but not required, to use 2851locale-specific quotes in other locales. 2852 2853 The Gnulib (http://www.gnu.org/software/gnulib/) `quote' and 2854`quotearg' modules provide a reasonably straightforward way to support 2855locale-specific quote characters, as well as taking care of other 2856issues, such as quoting a filename that itself contains a quote 2857character. See the Gnulib documentation for usage details. 2858 2859 In any case, the documentation for your program should clearly 2860specify how it does quoting, if different than the preferred method of 2861``' and `''. This is especially important if the output of your 2862program is ever likely to be parsed by another program. 2863 2864 Quotation characters are a difficult area in the computing world at 2865this time: there are no true left or right quote characters in Latin1; 2866the ``' character we use was standardized there as a grave accent. 2867Moreover, Latin1 is still not universally usable. 2868 2869 Unicode contains the unambiguous quote characters required, and its 2870common encoding UTF-8 is upward compatible with Latin1. However, 2871Unicode and UTF-8 are not universally well-supported, either. 2872 2873 This may change over the next few years, and then we will revisit 2874this. 2875 2876 2877File: standards.info, Node: Mmap, Prev: Quote Characters, Up: Writing C 2878 28795.11 Mmap 2880========= 2881 2882Don't assume that `mmap' either works on all files or fails for all 2883files. It may work on some files and fail on others. 2884 2885 The proper way to use `mmap' is to try it on the specific file for 2886which you want to use it--and if `mmap' doesn't work, fall back on 2887doing the job in another way using `read' and `write'. 2888 2889 The reason this precaution is needed is that the GNU kernel (the 2890HURD) provides a user-extensible file system, in which there can be many 2891different kinds of "ordinary files." Many of them support `mmap', but 2892some do not. It is important to make programs handle all these kinds 2893of files. 2894 2895 2896File: standards.info, Node: Documentation, Next: Managing Releases, Prev: Writing C, Up: Top 2897 28986 Documenting Programs 2899********************** 2900 2901A GNU program should ideally come with full free documentation, adequate 2902for both reference and tutorial purposes. If the package can be 2903programmed or extended, the documentation should cover programming or 2904extending it, as well as just using it. 2905 2906* Menu: 2907 2908* GNU Manuals:: Writing proper manuals. 2909* Doc Strings and Manuals:: Compiling doc strings doesn't make a manual. 2910* Manual Structure Details:: Specific structure conventions. 2911* License for Manuals:: Writing the distribution terms for a manual. 2912* Manual Credits:: Giving credit to documentation contributors. 2913* Printed Manuals:: Mentioning the printed manual. 2914* NEWS File:: NEWS files supplement manuals. 2915* Change Logs:: Recording Changes 2916* Man Pages:: Man pages are secondary. 2917* Reading other Manuals:: How far you can go in learning 2918 from other manuals. 2919 2920 2921File: standards.info, Node: GNU Manuals, Next: Doc Strings and Manuals, Up: Documentation 2922 29236.1 GNU Manuals 2924=============== 2925 2926The preferred document format for the GNU system is the Texinfo 2927formatting language. Every GNU package should (ideally) have 2928documentation in Texinfo both for reference and for learners. Texinfo 2929makes it possible to produce a good quality formatted book, using TeX, 2930and to generate an Info file. It is also possible to generate HTML 2931output from Texinfo source. See the Texinfo manual, either the 2932hardcopy, or the on-line version available through `info' or the Emacs 2933Info subsystem (`C-h i'). 2934 2935 Nowadays some other formats such as Docbook and Sgmltexi can be 2936converted automatically into Texinfo. It is ok to produce the Texinfo 2937documentation by conversion this way, as long as it gives good results. 2938 2939 Make sure your manual is clear to a reader who knows nothing about 2940the topic and reads it straight through. This means covering basic 2941topics at the beginning, and advanced topics only later. This also 2942means defining every specialized term when it is first used. 2943 2944 Programmers tend to carry over the structure of the program as the 2945structure for its documentation. But this structure is not necessarily 2946good for explaining how to use the program; it may be irrelevant and 2947confusing for a user. 2948 2949 Instead, the right way to structure documentation is according to the 2950concepts and questions that a user will have in mind when reading it. 2951This principle applies at every level, from the lowest (ordering 2952sentences in a paragraph) to the highest (ordering of chapter topics 2953within the manual). Sometimes this structure of ideas matches the 2954structure of the implementation of the software being documented--but 2955often they are different. An important part of learning to write good 2956documentation is to learn to notice when you have unthinkingly 2957structured the documentation like the implementation, stop yourself, 2958and look for better alternatives. 2959 2960 For example, each program in the GNU system probably ought to be 2961documented in one manual; but this does not mean each program should 2962have its own manual. That would be following the structure of the 2963implementation, rather than the structure that helps the user 2964understand. 2965 2966 Instead, each manual should cover a coherent _topic_. For example, 2967instead of a manual for `diff' and a manual for `diff3', we have one 2968manual for "comparison of files" which covers both of those programs, 2969as well as `cmp'. By documenting these programs together, we can make 2970the whole subject clearer. 2971 2972 The manual which discusses a program should certainly document all of 2973the program's command-line options and all of its commands. It should 2974give examples of their use. But don't organize the manual as a list of 2975features. Instead, organize it logically, by subtopics. Address the 2976questions that a user will ask when thinking about the job that the 2977program does. Don't just tell the reader what each feature can do--say 2978what jobs it is good for, and show how to use it for those jobs. 2979Explain what is recommended usage, and what kinds of usage users should 2980avoid. 2981 2982 In general, a GNU manual should serve both as tutorial and reference. 2983It should be set up for convenient access to each topic through Info, 2984and for reading straight through (appendixes aside). A GNU manual 2985should give a good introduction to a beginner reading through from the 2986start, and should also provide all the details that hackers want. The 2987Bison manual is a good example of this--please take a look at it to see 2988what we mean. 2989 2990 That is not as hard as it first sounds. Arrange each chapter as a 2991logical breakdown of its topic, but order the sections, and write their 2992text, so that reading the chapter straight through makes sense. Do 2993likewise when structuring the book into chapters, and when structuring a 2994section into paragraphs. The watchword is, _at each point, address the 2995most fundamental and important issue raised by the preceding text._ 2996 2997 If necessary, add extra chapters at the beginning of the manual which 2998are purely tutorial and cover the basics of the subject. These provide 2999the framework for a beginner to understand the rest of the manual. The 3000Bison manual provides a good example of how to do this. 3001 3002 To serve as a reference, a manual should have an Index that list all 3003the functions, variables, options, and important concepts that are part 3004of the program. One combined Index should do for a short manual, but 3005sometimes for a complex package it is better to use multiple indices. 3006The Texinfo manual includes advice on preparing good index entries, see 3007*Note Making Index Entries: (texinfo)Index Entries, and see *Note 3008Defining the Entries of an Index: (texinfo)Indexing Commands. 3009 3010 Don't use Unix man pages as a model for how to write GNU 3011documentation; most of them are terse, badly structured, and give 3012inadequate explanation of the underlying concepts. (There are, of 3013course, some exceptions.) Also, Unix man pages use a particular format 3014which is different from what we use in GNU manuals. 3015 3016 Please include an email address in the manual for where to report 3017bugs _in the text of the manual_. 3018 3019 Please do not use the term "pathname" that is used in Unix 3020documentation; use "file name" (two words) instead. We use the term 3021"path" only for search paths, which are lists of directory names. 3022 3023 Please do not use the term "illegal" to refer to erroneous input to 3024a computer program. Please use "invalid" for this, and reserve the 3025term "illegal" for activities prohibited by law. 3026 3027 Please do not write `()' after a function name just to indicate it 3028is a function. `foo ()' is not a function, it is a function call with 3029no arguments. 3030 3031 3032File: standards.info, Node: Doc Strings and Manuals, Next: Manual Structure Details, Prev: GNU Manuals, Up: Documentation 3033 30346.2 Doc Strings and Manuals 3035=========================== 3036 3037Some programming systems, such as Emacs, provide a documentation string 3038for each function, command or variable. You may be tempted to write a 3039reference manual by compiling the documentation strings and writing a 3040little additional text to go around them--but you must not do it. That 3041approach is a fundamental mistake. The text of well-written 3042documentation strings will be entirely wrong for a manual. 3043 3044 A documentation string needs to stand alone--when it appears on the 3045screen, there will be no other text to introduce or explain it. 3046Meanwhile, it can be rather informal in style. 3047 3048 The text describing a function or variable in a manual must not stand 3049alone; it appears in the context of a section or subsection. Other text 3050at the beginning of the section should explain some of the concepts, and 3051should often make some general points that apply to several functions or 3052variables. The previous descriptions of functions and variables in the 3053section will also have given information about the topic. A description 3054written to stand alone would repeat some of that information; this 3055redundancy looks bad. Meanwhile, the informality that is acceptable in 3056a documentation string is totally unacceptable in a manual. 3057 3058 The only good way to use documentation strings in writing a good 3059manual is to use them as a source of information for writing good text. 3060 3061 3062File: standards.info, Node: Manual Structure Details, Next: License for Manuals, Prev: Doc Strings and Manuals, Up: Documentation 3063 30646.3 Manual Structure Details 3065============================ 3066 3067The title page of the manual should state the version of the programs or 3068packages documented in the manual. The Top node of the manual should 3069also contain this information. If the manual is changing more 3070frequently than or independent of the program, also state a version 3071number for the manual in both of these places. 3072 3073 Each program documented in the manual should have a node named 3074`PROGRAM Invocation' or `Invoking PROGRAM'. This node (together with 3075its subnodes, if any) should describe the program's command line 3076arguments and how to run it (the sort of information people would look 3077for in a man page). Start with an `@example' containing a template for 3078all the options and arguments that the program uses. 3079 3080 Alternatively, put a menu item in some menu whose item name fits one 3081of the above patterns. This identifies the node which that item points 3082to as the node for this purpose, regardless of the node's actual name. 3083 3084 The `--usage' feature of the Info reader looks for such a node or 3085menu item in order to find the relevant text, so it is essential for 3086every Texinfo file to have one. 3087 3088 If one manual describes several programs, it should have such a node 3089for each program described in the manual. 3090 3091 3092File: standards.info, Node: License for Manuals, Next: Manual Credits, Prev: Manual Structure Details, Up: Documentation 3093 30946.4 License for Manuals 3095======================= 3096 3097Please use the GNU Free Documentation License for all GNU manuals that 3098are more than a few pages long. Likewise for a collection of short 3099documents--you only need one copy of the GNU FDL for the whole 3100collection. For a single short document, you can use a very permissive 3101non-copyleft license, to avoid taking up space with a long license. 3102 3103 See `http://www.gnu.org/copyleft/fdl-howto.html' for more explanation 3104of how to employ the GFDL. 3105 3106 Note that it is not obligatory to include a copy of the GNU GPL or 3107GNU LGPL in a manual whose license is neither the GPL nor the LGPL. It 3108can be a good idea to include the program's license in a large manual; 3109in a short manual, whose size would be increased considerably by 3110including the program's license, it is probably better not to include 3111it. 3112 3113 3114File: standards.info, Node: Manual Credits, Next: Printed Manuals, Prev: License for Manuals, Up: Documentation 3115 31166.5 Manual Credits 3117================== 3118 3119Please credit the principal human writers of the manual as the authors, 3120on the title page of the manual. If a company sponsored the work, thank 3121the company in a suitable place in the manual, but do not cite the 3122company as an author. 3123 3124 3125File: standards.info, Node: Printed Manuals, Next: NEWS File, Prev: Manual Credits, Up: Documentation 3126 31276.6 Printed Manuals 3128=================== 3129 3130The FSF publishes some GNU manuals in printed form. To encourage sales 3131of these manuals, the on-line versions of the manual should mention at 3132the very start that the printed manual is available and should point at 3133information for getting it--for instance, with a link to the page 3134`http://www.gnu.org/order/order.html'. This should not be included in 3135the printed manual, though, because there it is redundant. 3136 3137 It is also useful to explain in the on-line forms of the manual how 3138the user can print out the manual from the sources. 3139 3140 3141File: standards.info, Node: NEWS File, Next: Change Logs, Prev: Printed Manuals, Up: Documentation 3142 31436.7 The NEWS File 3144================= 3145 3146In addition to its manual, the package should have a file named `NEWS' 3147which contains a list of user-visible changes worth mentioning. In 3148each new release, add items to the front of the file and identify the 3149version they pertain to. Don't discard old items; leave them in the 3150file after the newer items. This way, a user upgrading from any 3151previous version can see what is new. 3152 3153 If the `NEWS' file gets very long, move some of the older items into 3154a file named `ONEWS' and put a note at the end referring the user to 3155that file. 3156 3157 3158File: standards.info, Node: Change Logs, Next: Man Pages, Prev: NEWS File, Up: Documentation 3159 31606.8 Change Logs 3161=============== 3162 3163Keep a change log to describe all the changes made to program source 3164files. The purpose of this is so that people investigating bugs in the 3165future will know about the changes that might have introduced the bug. 3166Often a new bug can be found by looking at what was recently changed. 3167More importantly, change logs can help you eliminate conceptual 3168inconsistencies between different parts of a program, by giving you a 3169history of how the conflicting concepts arose and who they came from. 3170 3171* Menu: 3172 3173* Change Log Concepts:: 3174* Style of Change Logs:: 3175* Simple Changes:: 3176* Conditional Changes:: 3177* Indicating the Part Changed:: 3178 3179 3180File: standards.info, Node: Change Log Concepts, Next: Style of Change Logs, Up: Change Logs 3181 31826.8.1 Change Log Concepts 3183------------------------- 3184 3185You can think of the change log as a conceptual "undo list" which 3186explains how earlier versions were different from the current version. 3187People can see the current version; they don't need the change log to 3188tell them what is in it. What they want from a change log is a clear 3189explanation of how the earlier version differed. 3190 3191 The change log file is normally called `ChangeLog' and covers an 3192entire directory. Each directory can have its own change log, or a 3193directory can use the change log of its parent directory-it's up to you. 3194 3195 Another alternative is to record change log information with a 3196version control system such as RCS or CVS. This can be converted 3197automatically to a `ChangeLog' file using `rcs2log'; in Emacs, the 3198command `C-x v a' (`vc-update-change-log') does the job. 3199 3200 There's no need to describe the full purpose of the changes or how 3201they work together. If you think that a change calls for explanation, 3202you're probably right. Please do explain it--but please put the 3203explanation in comments in the code, where people will see it whenever 3204they see the code. For example, "New function" is enough for the 3205change log when you add a function, because there should be a comment 3206before the function definition to explain what it does. 3207 3208 In the past, we recommended not mentioning changes in non-software 3209files (manuals, help files, etc.) in change logs. However, we've been 3210advised that it is a good idea to include them, for the sake of 3211copyright records. 3212 3213 However, sometimes it is useful to write one line to describe the 3214overall purpose of a batch of changes. 3215 3216 The easiest way to add an entry to `ChangeLog' is with the Emacs 3217command `M-x add-change-log-entry'. An entry should have an asterisk, 3218the name of the changed file, and then in parentheses the name of the 3219changed functions, variables or whatever, followed by a colon. Then 3220describe the changes you made to that function or variable. 3221 3222 3223File: standards.info, Node: Style of Change Logs, Next: Simple Changes, Prev: Change Log Concepts, Up: Change Logs 3224 32256.8.2 Style of Change Logs 3226-------------------------- 3227 3228Here are some simple examples of change log entries, starting with the 3229header line that says who made the change and when it was installed, 3230followed by descriptions of specific changes. (These examples are 3231drawn from Emacs and GCC.) 3232 3233 1998-08-17 Richard Stallman <rms@gnu.org> 3234 3235 * register.el (insert-register): Return nil. 3236 (jump-to-register): Likewise. 3237 3238 * sort.el (sort-subr): Return nil. 3239 3240 * tex-mode.el (tex-bibtex-file, tex-file, tex-region): 3241 Restart the tex shell if process is gone or stopped. 3242 (tex-shell-running): New function. 3243 3244 * expr.c (store_one_arg): Round size up for move_block_to_reg. 3245 (expand_call): Round up when emitting USE insns. 3246 * stmt.c (assign_parms): Round size up for move_block_from_reg. 3247 3248 It's important to name the changed function or variable in full. 3249Don't abbreviate function or variable names, and don't combine them. 3250Subsequent maintainers will often search for a function name to find all 3251the change log entries that pertain to it; if you abbreviate the name, 3252they won't find it when they search. 3253 3254 For example, some people are tempted to abbreviate groups of function 3255names by writing `* register.el ({insert,jump-to}-register)'; this is 3256not a good idea, since searching for `jump-to-register' or 3257`insert-register' would not find that entry. 3258 3259 Separate unrelated change log entries with blank lines. When two 3260entries represent parts of the same change, so that they work together, 3261then don't put blank lines between them. Then you can omit the file 3262name 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`)', rather than `,', and opening the continuation with `(' as in this 3266example: 3267 3268 * keyboard.c (menu_bar_items, tool_bar_items) 3269 (Fexecute_extended_command): Deal with `keymap' property. 3270 3271 When you install someone else's changes, put the contributor's name 3272in the change log entry rather than in the text of the entry. In other 3273words, write this: 3274 3275 2002-07-14 John Doe <jdoe@gnu.org> 3276 3277 * sewing.c: Make it sew. 3278 3279rather than this: 3280 3281 2002-07-14 Usual Maintainer <usual@gnu.org> 3282 3283 * sewing.c: Make it sew. Patch by jdoe@gnu.org. 3284 3285 As for the date, that should be the date you applied the change. 3286 3287 3288File: standards.info, Node: Simple Changes, Next: Conditional Changes, Prev: Style of Change Logs, Up: Change Logs 3289 32906.8.3 Simple Changes 3291-------------------- 3292 3293Certain simple kinds of changes don't need much detail in the change 3294log. 3295 3296 When you change the calling sequence of a function in a simple 3297fashion, and you change all the callers of the function to use the new 3298calling sequence, there is no need to make individual entries for all 3299the callers that you changed. Just write in the entry for the function 3300being called, "All callers changed"--like this: 3301 3302 * keyboard.c (Fcommand_execute): New arg SPECIAL. 3303 All callers changed. 3304 3305 When you change just comments or doc strings, it is enough to write 3306an entry for the file, without mentioning the functions. Just "Doc 3307fixes" is enough for the change log. 3308 3309 There's no technical need to make change log entries for 3310documentation files. This is because documentation is not susceptible 3311to bugs that are hard to fix. Documentation does not consist of parts 3312that must interact in a precisely engineered fashion. To correct an 3313error, you need not know the history of the erroneous passage; it is 3314enough to compare what the documentation says with the way the program 3315actually works. 3316 3317 However, you should keep change logs for documentation files when the 3318project gets copyright assignments from its contributors, so as to make 3319the records of authorship more accurate. 3320 3321 3322File: standards.info, Node: Conditional Changes, Next: Indicating the Part Changed, Prev: Simple Changes, Up: Change Logs 3323 33246.8.4 Conditional Changes 3325------------------------- 3326 3327C programs often contain compile-time `#if' conditionals. Many changes 3328are conditional; sometimes you add a new definition which is entirely 3329contained in a conditional. It is very useful to indicate in the 3330change log the conditions for which the change applies. 3331 3332 Our convention for indicating conditional changes is to use square 3333brackets around the name of the condition. 3334 3335 Here is a simple example, describing a change which is conditional 3336but does not have a function or entity name associated with it: 3337 3338 * xterm.c [SOLARIS2]: Include string.h. 3339 3340 Here is an entry describing a new definition which is entirely 3341conditional. This new definition for the macro `FRAME_WINDOW_P' is 3342used only when `HAVE_X_WINDOWS' is defined: 3343 3344 * frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined. 3345 3346 Here is an entry for a change within the function `init_display', 3347whose definition as a whole is unconditional, but the changes themselves 3348are contained in a `#ifdef HAVE_LIBNCURSES' conditional: 3349 3350 * dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent. 3351 3352 Here is an entry for a change that takes affect only when a certain 3353macro is _not_ defined: 3354 3355 (gethostname) [!HAVE_SOCKETS]: Replace with winsock version. 3356 3357 3358File: standards.info, Node: Indicating the Part Changed, Prev: Conditional Changes, Up: Change Logs 3359 33606.8.5 Indicating the Part Changed 3361--------------------------------- 3362 3363Indicate the part of a function which changed by using angle brackets 3364enclosing an indication of what the changed part does. Here is an entry 3365for a change in the part of the function `sh-while-getopts' that deals 3366with `sh' commands: 3367 3368 * progmodes/sh-script.el (sh-while-getopts) <sh>: Handle case that 3369 user-specified option string is empty. 3370 3371 3372File: standards.info, Node: Man Pages, Next: Reading other Manuals, Prev: Change Logs, Up: Documentation 3373 33746.9 Man Pages 3375============= 3376 3377In the GNU project, man pages are secondary. It is not necessary or 3378expected for every GNU program to have a man page, but some of them do. 3379It's your choice whether to include a man page in your program. 3380 3381 When you make this decision, consider that supporting a man page 3382requires continual effort each time the program is changed. The time 3383you spend on the man page is time taken away from more useful work. 3384 3385 For a simple program which changes little, updating the man page may 3386be a small job. Then there is little reason not to include a man page, 3387if you have one. 3388 3389 For a large program that changes a great deal, updating a man page 3390may be a substantial burden. If a user offers to donate a man page, 3391you may find this gift costly to accept. It may be better to refuse 3392the man page unless the same person agrees to take full responsibility 3393for maintaining it--so that you can wash your hands of it entirely. If 3394this volunteer later ceases to do the job, then don't feel obliged to 3395pick it up yourself; it may be better to withdraw the man page from the 3396distribution until someone else agrees to update it. 3397 3398 When a program changes only a little, you may feel that the 3399discrepancies are small enough that the man page remains useful without 3400updating. If so, put a prominent note near the beginning of the man 3401page explaining that you don't maintain it and that the Texinfo manual 3402is more authoritative. The note should say how to access the Texinfo 3403documentation. 3404 3405 Be sure that man pages include a copyright statement and free 3406license. The simple all-permissive license is appropriate for simple 3407man pages: 3408 3409 Copying and distribution of this file, with or without modification, 3410 are permitted in any medium without royalty provided the copyright 3411 notice and this notice are preserved. 3412 3413 For long man pages, with enough explanation and documentation that 3414they can be considered true manuals, use the GFDL (*note License for 3415Manuals::). 3416 3417 Finally, the GNU help2man program 3418(`http://www.gnu.org/software/help2man/') is one way to automate 3419generation of a man page, in this case from `--help' output. This is 3420sufficient in many cases. 3421 3422 3423File: standards.info, Node: Reading other Manuals, Prev: Man Pages, Up: Documentation 3424 34256.10 Reading other Manuals 3426========================== 3427 3428There may be non-free books or documentation files that describe the 3429program you are documenting. 3430 3431 It is ok to use these documents for reference, just as the author of 3432a new algebra textbook can read other books on algebra. A large portion 3433of any non-fiction book consists of facts, in this case facts about how 3434a certain program works, and these facts are necessarily the same for 3435everyone who writes about the subject. But be careful not to copy your 3436outline structure, wording, tables or examples from preexisting non-free 3437documentation. Copying from free documentation may be ok; please check 3438with the FSF about the individual case. 3439 3440 3441File: standards.info, Node: Managing Releases, Next: References, Prev: Documentation, Up: Top 3442 34437 The Release Process 3444********************* 3445 3446Making a release is more than just bundling up your source files in a 3447tar file and putting it up for FTP. You should set up your software so 3448that it can be configured to run on a variety of systems. Your Makefile 3449should conform to the GNU standards described below, and your directory 3450layout should also conform to the standards discussed below. Doing so 3451makes it easy to include your package into the larger framework of all 3452GNU software. 3453 3454* Menu: 3455 3456* Configuration:: How Configuration Should Work 3457* Makefile Conventions:: Makefile Conventions 3458* Releases:: Making Releases 3459 3460 3461File: standards.info, Node: Configuration, Next: Makefile Conventions, Up: Managing Releases 3462 34637.1 How Configuration Should Work 3464================================= 3465 3466Each GNU distribution should come with a shell script named 3467`configure'. This script is given arguments which describe the kind of 3468machine and system you want to compile the program for. 3469 3470 The `configure' script must record the configuration options so that 3471they affect compilation. 3472 3473 One way to do this is to make a link from a standard name such as 3474`config.h' to the proper configuration file for the chosen system. If 3475you use this technique, the distribution should _not_ contain a file 3476named `config.h'. This is so that people won't be able to build the 3477program without configuring it first. 3478 3479 Another thing that `configure' can do is to edit the Makefile. If 3480you do this, the distribution should _not_ contain a file named 3481`Makefile'. Instead, it should include a file `Makefile.in' which 3482contains the input used for editing. Once again, this is so that people 3483won't be able to build the program without configuring it first. 3484 3485 If `configure' does write the `Makefile', then `Makefile' should 3486have a target named `Makefile' which causes `configure' to be rerun, 3487setting up the same configuration that was set up last time. The files 3488that `configure' reads should be listed as dependencies of `Makefile'. 3489 3490 All the files which are output from the `configure' script should 3491have comments at the beginning explaining that they were generated 3492automatically using `configure'. This is so that users won't think of 3493trying to edit them by hand. 3494 3495 The `configure' script should write a file named `config.status' 3496which describes which configuration options were specified when the 3497program was last configured. This file should be a shell script which, 3498if run, will recreate the same configuration. 3499 3500 The `configure' script should accept an option of the form 3501`--srcdir=DIRNAME' to specify the directory where sources are found (if 3502it is not the current directory). This makes it possible to build the 3503program in a separate directory, so that the actual source directory is 3504not modified. 3505 3506 If the user does not specify `--srcdir', then `configure' should 3507check both `.' and `..' to see if it can find the sources. If it finds 3508the sources in one of these places, it should use them from there. 3509Otherwise, it should report that it cannot find the sources, and should 3510exit with nonzero status. 3511 3512 Usually the easy way to support `--srcdir' is by editing a 3513definition of `VPATH' into the Makefile. Some rules may need to refer 3514explicitly to the specified source directory. To make this possible, 3515`configure' can add to the Makefile a variable named `srcdir' whose 3516value is precisely the specified directory. 3517 3518 The `configure' script should also take an argument which specifies 3519the type of system to build the program for. This argument should look 3520like this: 3521 3522 CPU-COMPANY-SYSTEM 3523 3524 For example, an Athlon-based GNU/Linux system might be 3525`i686-pc-linux-gnu'. 3526 3527 The `configure' script needs to be able to decode all plausible 3528alternatives for how to describe a machine. Thus, 3529`athlon-pc-gnu/linux' would be a valid alias. There is a shell script 3530called `config.sub' 3531(http://savannah.gnu.org/cgi-bin/viewcvs/*checkout*/config/config/config.sub) 3532that you can use as a subroutine to validate system types and 3533canonicalize aliases. 3534 3535 The `configure' script should also take the option 3536`--build=BUILDTYPE', which should be equivalent to a plain BUILDTYPE 3537argument. For example, `configure --build=i686-pc-linux-gnu' is 3538equivalent to `configure i686-pc-linux-gnu'. When the build type is 3539not specified by an option or argument, the `configure' script should 3540normally guess it using the shell script `config.guess' 3541(http://savannah.gnu.org/cgi-bin/viewcvs/*checkout*/config/config/config.guess). 3542 3543 Other options are permitted to specify in more detail the software 3544or hardware present on the machine, to include or exclude optional parts 3545of the package, or to adjust the name of some tools or arguments to 3546them: 3547 3548`--enable-FEATURE[=PARAMETER]' 3549 Configure the package to build and install an optional user-level 3550 facility called FEATURE. This allows users to choose which 3551 optional features to include. Giving an optional PARAMETER of 3552 `no' should omit FEATURE, if it is built by default. 3553 3554 No `--enable' option should *ever* cause one feature to replace 3555 another. No `--enable' option should ever substitute one useful 3556 behavior for another useful behavior. The only proper use for 3557 `--enable' is for questions of whether to build part of the program 3558 or exclude it. 3559 3560`--with-PACKAGE' 3561 The package PACKAGE will be installed, so configure this package 3562 to work with PACKAGE. 3563 3564 Possible values of PACKAGE include `gnu-as' (or `gas'), `gnu-ld', 3565 `gnu-libc', `gdb', `x', and `x-toolkit'. 3566 3567 Do not use a `--with' option to specify the file name to use to 3568 find certain files. That is outside the scope of what `--with' 3569 options are for. 3570 3571`VARIABLE=VALUE' 3572 Set the value of the variable VARIABLE to VALUE. This is used to 3573 override the default values of commands or arguments in the build 3574 process. For example, the user could issue `configure CFLAGS=-g 3575 CXXFLAGS=-g' to build with debugging information and without the 3576 default optimization. 3577 3578 Specifying variables as arguments to `configure', like this: 3579 ./configure CC=gcc 3580 is preferable to setting them in environment variables: 3581 CC=gcc ./configure 3582 as it helps to recreate the same configuration later with 3583 `config.status'. 3584 3585 All `configure' scripts should accept all of the "detail" options 3586and the variable settings, whether or not they make any difference to 3587the particular package at hand. In particular, they should accept any 3588option that starts with `--with-' or `--enable-'. This is so users 3589will be able to configure an entire GNU source tree at once with a 3590single set of options. 3591 3592 You will note that the categories `--with-' and `--enable-' are 3593narrow: they *do not* provide a place for any sort of option you might 3594think of. That is deliberate. We want to limit the possible 3595configuration options in GNU software. We do not want GNU programs to 3596have idiosyncratic configuration options. 3597 3598 Packages that perform part of the compilation process may support 3599cross-compilation. In such a case, the host and target machines for the 3600program may be different. 3601 3602 The `configure' script should normally treat the specified type of 3603system as both the host and the target, thus producing a program which 3604works for the same type of machine that it runs on. 3605 3606 To compile a program to run on a host type that differs from the 3607build type, use the configure option `--host=HOSTTYPE', where HOSTTYPE 3608uses the same syntax as BUILDTYPE. The host type normally defaults to 3609the build type. 3610 3611 To configure a cross-compiler, cross-assembler, or what have you, you 3612should specify a target different from the host, using the configure 3613option `--target=TARGETTYPE'. The syntax for TARGETTYPE is the same as 3614for the host type. So the command would look like this: 3615 3616 ./configure --host=HOSTTYPE --target=TARGETTYPE 3617 3618 The target type normally defaults to the host type. Programs for 3619which cross-operation is not meaningful need not accept the `--target' 3620option, because configuring an entire operating system for 3621cross-operation is not a meaningful operation. 3622 3623 Some programs have ways of configuring themselves automatically. If 3624your program is set up to do this, your `configure' script can simply 3625ignore most of its arguments. 3626 3627 3628File: standards.info, Node: Makefile Conventions, Next: Releases, Prev: Configuration, Up: Managing Releases 3629 36307.2 Makefile Conventions 3631======================== 3632 3633This node describes conventions for writing the Makefiles for GNU 3634programs. Using Automake will help you write a Makefile that follows 3635these conventions. 3636 3637* Menu: 3638 3639* Makefile Basics:: General conventions for Makefiles. 3640* Utilities in Makefiles:: Utilities to be used in Makefiles. 3641* Command Variables:: Variables for specifying commands. 3642* DESTDIR:: Supporting staged installs. 3643* Directory Variables:: Variables for installation directories. 3644* Standard Targets:: Standard targets for users. 3645* Install Command Categories:: Three categories of commands in the `install' 3646 rule: normal, pre-install and post-install. 3647 3648 3649File: standards.info, Node: Makefile Basics, Next: Utilities in Makefiles, Up: Makefile Conventions 3650 36517.2.1 General Conventions for Makefiles 3652--------------------------------------- 3653 3654Every Makefile should contain this line: 3655 3656 SHELL = /bin/sh 3657 3658to avoid trouble on systems where the `SHELL' variable might be 3659inherited from the environment. (This is never a problem with GNU 3660`make'.) 3661 3662 Different `make' programs have incompatible suffix lists and 3663implicit rules, and this sometimes creates confusion or misbehavior. So 3664it is a good idea to set the suffix list explicitly using only the 3665suffixes you need in the particular Makefile, like this: 3666 3667 .SUFFIXES: 3668 .SUFFIXES: .c .o 3669 3670The first line clears out the suffix list, the second introduces all 3671suffixes which may be subject to implicit rules in this Makefile. 3672 3673 Don't assume that `.' is in the path for command execution. When 3674you need to run programs that are a part of your package during the 3675make, please make sure that it uses `./' if the program is built as 3676part of the make or `$(srcdir)/' if the file is an unchanging part of 3677the source code. Without one of these prefixes, the current search 3678path is used. 3679 3680 The distinction between `./' (the "build directory") and 3681`$(srcdir)/' (the "source directory") is important because users can 3682build in a separate directory using the `--srcdir' option to 3683`configure'. A rule of the form: 3684 3685 foo.1 : foo.man sedscript 3686 sed -e sedscript foo.man > foo.1 3687 3688will fail when the build directory is not the source directory, because 3689`foo.man' and `sedscript' are in the source directory. 3690 3691 When using GNU `make', relying on `VPATH' to find the source file 3692will work in the case where there is a single dependency file, since 3693the `make' automatic variable `$<' will represent the source file 3694wherever it is. (Many versions of `make' set `$<' only in implicit 3695rules.) A Makefile target like 3696 3697 foo.o : bar.c 3698 $(CC) -I. -I$(srcdir) $(CFLAGS) -c bar.c -o foo.o 3699 3700should instead be written as 3701 3702 foo.o : bar.c 3703 $(CC) -I. -I$(srcdir) $(CFLAGS) -c $< -o $@ 3704 3705in order to allow `VPATH' to work correctly. When the target has 3706multiple dependencies, using an explicit `$(srcdir)' is the easiest way 3707to make the rule work well. For example, the target above for `foo.1' 3708is best written as: 3709 3710 foo.1 : foo.man sedscript 3711 sed -e $(srcdir)/sedscript $(srcdir)/foo.man > $@ 3712 3713 GNU distributions usually contain some files which are not source 3714files--for example, Info files, and the output from Autoconf, Automake, 3715Bison or Flex. Since these files normally appear in the source 3716directory, they should always appear in the source directory, not in the 3717build directory. So Makefile rules to update them should put the 3718updated files in the source directory. 3719 3720 However, if a file does not appear in the distribution, then the 3721Makefile should not put it in the source directory, because building a 3722program in ordinary circumstances should not modify the source directory 3723in any way. 3724 3725 Try to make the build and installation targets, at least (and all 3726their subtargets) work correctly with a parallel `make'. 3727 3728 3729File: standards.info, Node: Utilities in Makefiles, Next: Command Variables, Prev: Makefile Basics, Up: Makefile Conventions 3730 37317.2.2 Utilities in Makefiles 3732---------------------------- 3733 3734Write the Makefile commands (and any shell scripts, such as 3735`configure') to run in `sh', not in `csh'. Don't use any special 3736features of `ksh' or `bash'. 3737 3738 The `configure' script and the Makefile rules for building and 3739installation should not use any utilities directly except these: 3740 3741 cat cmp cp diff echo egrep expr false grep install-info 3742 ln ls mkdir mv pwd rm rmdir sed sleep sort tar test touch true 3743 3744 The compression program `gzip' can be used in the `dist' rule. 3745 3746 Stick to the generally supported options for these programs. For 3747example, don't use `mkdir -p', convenient as it may be, because most 3748systems don't support it. 3749 3750 It is a good idea to avoid creating symbolic links in makefiles, 3751since a few systems don't support them. 3752 3753 The Makefile rules for building and installation can also use 3754compilers and related programs, but should do so via `make' variables 3755so that the user can substitute alternatives. Here are some of the 3756programs we mean: 3757 3758 ar bison cc flex install ld ldconfig lex 3759 make makeinfo ranlib texi2dvi yacc 3760 3761 Use the following `make' variables to run those programs: 3762 3763 $(AR) $(BISON) $(CC) $(FLEX) $(INSTALL) $(LD) $(LDCONFIG) $(LEX) 3764 $(MAKE) $(MAKEINFO) $(RANLIB) $(TEXI2DVI) $(YACC) 3765 3766 When you use `ranlib' or `ldconfig', you should make sure nothing 3767bad happens if the system does not have the program in question. 3768Arrange to ignore an error from that command, and print a message before 3769the command to tell the user that failure of this command does not mean 3770a problem. (The Autoconf `AC_PROG_RANLIB' macro can help with this.) 3771 3772 If you use symbolic links, you should implement a fallback for 3773systems that don't have symbolic links. 3774 3775 Additional utilities that can be used via Make variables are: 3776 3777 chgrp chmod chown mknod 3778 3779 It is ok to use other utilities in Makefile portions (or scripts) 3780intended only for particular systems where you know those utilities 3781exist. 3782 3783 3784File: standards.info, Node: Command Variables, Next: DESTDIR, Prev: Utilities in Makefiles, Up: Makefile Conventions 3785 37867.2.3 Variables for Specifying Commands 3787--------------------------------------- 3788 3789Makefiles should provide variables for overriding certain commands, 3790options, and so on. 3791 3792 In particular, you should run most utility programs via variables. 3793Thus, if you use Bison, have a variable named `BISON' whose default 3794value is set with `BISON = bison', and refer to it with `$(BISON)' 3795whenever you need to use Bison. 3796 3797 File management utilities such as `ln', `rm', `mv', and so on, need 3798not be referred to through variables in this way, since users don't 3799need to replace them with other programs. 3800 3801 Each program-name variable should come with an options variable that 3802is used to supply options to the program. Append `FLAGS' to the 3803program-name variable name to get the options variable name--for 3804example, `BISONFLAGS'. (The names `CFLAGS' for the C compiler, 3805`YFLAGS' for yacc, and `LFLAGS' for lex, are exceptions to this rule, 3806but we keep them because they are standard.) Use `CPPFLAGS' in any 3807compilation command that runs the preprocessor, and use `LDFLAGS' in 3808any compilation command that does linking as well as in any direct use 3809of `ld'. 3810 3811 If there are C compiler options that _must_ be used for proper 3812compilation of certain files, do not include them in `CFLAGS'. Users 3813expect to be able to specify `CFLAGS' freely themselves. Instead, 3814arrange to pass the necessary options to the C compiler independently 3815of `CFLAGS', by writing them explicitly in the compilation commands or 3816by defining an implicit rule, like this: 3817 3818 CFLAGS = -g 3819 ALL_CFLAGS = -I. $(CFLAGS) 3820 .c.o: 3821 $(CC) -c $(CPPFLAGS) $(ALL_CFLAGS) $< 3822 3823 Do include the `-g' option in `CFLAGS', because that is not 3824_required_ for proper compilation. You can consider it a default that 3825is only recommended. If the package is set up so that it is compiled 3826with GCC by default, then you might as well include `-O' in the default 3827value of `CFLAGS' as well. 3828 3829 Put `CFLAGS' last in the compilation command, after other variables 3830containing compiler options, so the user can use `CFLAGS' to override 3831the others. 3832 3833 `CFLAGS' should be used in every invocation of the C compiler, both 3834those which do compilation and those which do linking. 3835 3836 Every Makefile should define the variable `INSTALL', which is the 3837basic command for installing a file into the system. 3838 3839 Every Makefile should also define the variables `INSTALL_PROGRAM' 3840and `INSTALL_DATA'. (The default for `INSTALL_PROGRAM' should be 3841`$(INSTALL)'; the default for `INSTALL_DATA' should be `${INSTALL} -m 3842644'.) Then it should use those variables as the commands for actual 3843installation, for executables and non-executables respectively. 3844Minimal use of these variables is as follows: 3845 3846 $(INSTALL_PROGRAM) foo $(bindir)/foo 3847 $(INSTALL_DATA) libfoo.a $(libdir)/libfoo.a 3848 3849 However, it is preferable to support a `DESTDIR' prefix on the 3850target files, as explained in the next section. 3851 3852Always use a file name, not a directory name, as the second argument of 3853the installation commands. Use a separate command for each file to be 3854installed. 3855 3856 3857File: standards.info, Node: DESTDIR, Next: Directory Variables, Prev: Command Variables, Up: Makefile Conventions 3858 38597.2.4 `DESTDIR': support for staged installs 3860-------------------------------------------- 3861 3862`DESTDIR' is a variable prepended to each installed target file, like 3863this: 3864 3865 $(INSTALL_PROGRAM) foo $(DESTDIR)$(bindir)/foo 3866 $(INSTALL_DATA) libfoo.a $(DESTDIR)$(libdir)/libfoo.a 3867 3868 The `DESTDIR' variable is specified by the user on the `make' 3869command line. For example: 3870 3871 make DESTDIR=/tmp/stage install 3872 3873`DESTDIR' should be supported only in the `install*' and `uninstall*' 3874targets, as those are the only targets where it is useful. 3875 3876 If your installation step would normally install 3877`/usr/local/bin/foo' and `/usr/local/lib/libfoo.a', then an 3878installation invoked as in the example above would install 3879`/tmp/stage/usr/local/bin/foo' and `/tmp/stage/usr/local/lib/libfoo.a' 3880instead. 3881 3882 Prepending the variable `DESTDIR' to each target in this way 3883provides for "staged installs", where the installed files are not 3884placed directly into their expected location but are instead copied 3885into a temporary location (`DESTDIR'). However, installed files 3886maintain their relative directory structure and any embedded file names 3887will not be modified. 3888 3889 You should not set the value of `DESTDIR' in your `Makefile' at all; 3890then the files are installed into their expected locations by default. 3891Also, specifying `DESTDIR' should not change the operation of the 3892software in any way, so its value should not be included in any file 3893contents. 3894 3895 `DESTDIR' support is commonly used in package creation. It is also 3896helpful to users who want to understand what a given package will 3897install where, and to allow users who don't normally have permissions 3898to install into protected areas to build and install before gaining 3899those permissions. Finally, it can be useful with tools such as 3900`stow', where code is installed in one place but made to appear to be 3901installed somewhere else using symbolic links or special mount 3902operations. So, we strongly recommend GNU packages support `DESTDIR', 3903though it is not an absolute requirement. 3904 3905 3906File: standards.info, Node: Directory Variables, Next: Standard Targets, Prev: DESTDIR, Up: Makefile Conventions 3907 39087.2.5 Variables for Installation Directories 3909-------------------------------------------- 3910 3911Installation directories should always be named by variables, so it is 3912easy to install in a nonstandard place. The standard names for these 3913variables and the values they should have in GNU packages are described 3914below. They are based on a standard file system layout; variants of it 3915are used in GNU/Linux and other modern operating systems. 3916 3917 Installers are expected to override these values when calling `make' 3918(e.g., `make prefix=/usr install' or `configure' (e.g., `configure 3919--prefix=/usr'). GNU packages should not try to guess which value 3920should be appropriate for these variables on the system they are being 3921installed onto: use the default settings specified here so that all GNU 3922packages behave identically, allowing the installer to achieve any 3923desired layout. 3924 3925 These first two variables set the root for the installation. All the 3926other installation directories should be subdirectories of one of these 3927two, and nothing should be directly installed into these two 3928directories. 3929 3930`prefix' 3931 A prefix used in constructing the default values of the variables 3932 listed below. The default value of `prefix' should be 3933 `/usr/local'. When building the complete GNU system, the prefix 3934 will be empty and `/usr' will be a symbolic link to `/'. (If you 3935 are using Autoconf, write it as `@prefix@'.) 3936 3937 Running `make install' with a different value of `prefix' from the 3938 one used to build the program should _not_ recompile the program. 3939 3940`exec_prefix' 3941 A prefix used in constructing the default values of some of the 3942 variables listed below. The default value of `exec_prefix' should 3943 be `$(prefix)'. (If you are using Autoconf, write it as 3944 `@exec_prefix@'.) 3945 3946 Generally, `$(exec_prefix)' is used for directories that contain 3947 machine-specific files (such as executables and subroutine 3948 libraries), while `$(prefix)' is used directly for other 3949 directories. 3950 3951 Running `make install' with a different value of `exec_prefix' 3952 from the one used to build the program should _not_ recompile the 3953 program. 3954 3955 Executable programs are installed in one of the following 3956directories. 3957 3958`bindir' 3959 The directory for installing executable programs that users can 3960 run. This should normally be `/usr/local/bin', but write it as 3961 `$(exec_prefix)/bin'. (If you are using Autoconf, write it as 3962 `@bindir@'.) 3963 3964`sbindir' 3965 The directory for installing executable programs that can be run 3966 from the shell, but are only generally useful to system 3967 administrators. This should normally be `/usr/local/sbin', but 3968 write it as `$(exec_prefix)/sbin'. (If you are using Autoconf, 3969 write it as `@sbindir@'.) 3970 3971`libexecdir' 3972 The directory for installing executable programs to be run by other 3973 programs rather than by users. This directory should normally be 3974 `/usr/local/libexec', but write it as `$(exec_prefix)/libexec'. 3975 (If you are using Autoconf, write it as `@libexecdir@'.) 3976 3977 The definition of `libexecdir' is the same for all packages, so 3978 you should install your data in a subdirectory thereof. Most 3979 packages install their data under `$(libexecdir)/PACKAGE-NAME/', 3980 possibly within additional subdirectories thereof, such as 3981 `$(libexecdir)/PACKAGE-NAME/MACHINE/VERSION'. 3982 3983 Data files used by the program during its execution are divided into 3984categories in two ways. 3985 3986 * Some files are normally modified by programs; others are never 3987 normally modified (though users may edit some of these). 3988 3989 * Some files are architecture-independent and can be shared by all 3990 machines at a site; some are architecture-dependent and can be 3991 shared only by machines of the same kind and operating system; 3992 others may never be shared between two machines. 3993 3994 This makes for six different possibilities. However, we want to 3995discourage the use of architecture-dependent files, aside from object 3996files and libraries. It is much cleaner to make other data files 3997architecture-independent, and it is generally not hard. 3998 3999 Here are the variables Makefiles should use to specify directories 4000to put these various kinds of files in: 4001 4002`datarootdir' 4003 The root of the directory tree for read-only 4004 architecture-independent data files. This should normally be 4005 `/usr/local/share', but write it as `$(prefix)/share'. (If you 4006 are using Autoconf, write it as `@datarootdir@'.) `datadir''s 4007 default value is based on this variable; so are `infodir', 4008 `mandir', and others. 4009 4010`datadir' 4011 The directory for installing idiosyncratic read-only 4012 architecture-independent data files for this program. This is 4013 usually the same place as `datarootdir', but we use the two 4014 separate variables so that you can move these program-specific 4015 files without altering the location for Info files, man pages, etc. 4016 4017 This should normally be `/usr/local/share', but write it as 4018 `$(datarootdir)'. (If you are using Autoconf, write it as 4019 `@datadir@'.) 4020 4021 The definition of `datadir' is the same for all packages, so you 4022 should install your data in a subdirectory thereof. Most packages 4023 install their data under `$(datadir)/PACKAGE-NAME/'. 4024 4025`sysconfdir' 4026 The directory for installing read-only data files that pertain to a 4027 single machine-that is to say, files for configuring a host. 4028 Mailer and network configuration files, `/etc/passwd', and so 4029 forth belong here. All the files in this directory should be 4030 ordinary ASCII text files. This directory should normally be 4031 `/usr/local/etc', but write it as `$(prefix)/etc'. (If you are 4032 using Autoconf, write it as `@sysconfdir@'.) 4033 4034 Do not install executables here in this directory (they probably 4035 belong in `$(libexecdir)' or `$(sbindir)'). Also do not install 4036 files that are modified in the normal course of their use (programs 4037 whose purpose is to change the configuration of the system 4038 excluded). Those probably belong in `$(localstatedir)'. 4039 4040`sharedstatedir' 4041 The directory for installing architecture-independent data files 4042 which the programs modify while they run. This should normally be 4043 `/usr/local/com', but write it as `$(prefix)/com'. (If you are 4044 using Autoconf, write it as `@sharedstatedir@'.) 4045 4046`localstatedir' 4047 The directory for installing data files which the programs modify 4048 while they run, and that pertain to one specific machine. Users 4049 should never need to modify files in this directory to configure 4050 the package's operation; put such configuration information in 4051 separate files that go in `$(datadir)' or `$(sysconfdir)'. 4052 `$(localstatedir)' should normally be `/usr/local/var', but write 4053 it as `$(prefix)/var'. (If you are using Autoconf, write it as 4054 `@localstatedir@'.) 4055 4056 These variables specify the directory for installing certain specific 4057types of files, if your program has them. Every GNU package should 4058have Info files, so every program needs `infodir', but not all need 4059`libdir' or `lispdir'. 4060 4061`includedir' 4062 The directory for installing header files to be included by user 4063 programs with the C `#include' preprocessor directive. This 4064 should normally be `/usr/local/include', but write it as 4065 `$(prefix)/include'. (If you are using Autoconf, write it as 4066 `@includedir@'.) 4067 4068 Most compilers other than GCC do not look for header files in 4069 directory `/usr/local/include'. So installing the header files 4070 this way is only useful with GCC. Sometimes this is not a problem 4071 because some libraries are only really intended to work with GCC. 4072 But some libraries are intended to work with other compilers. 4073 They should install their header files in two places, one 4074 specified by `includedir' and one specified by `oldincludedir'. 4075 4076`oldincludedir' 4077 The directory for installing `#include' header files for use with 4078 compilers other than GCC. This should normally be `/usr/include'. 4079 (If you are using Autoconf, you can write it as `@oldincludedir@'.) 4080 4081 The Makefile commands should check whether the value of 4082 `oldincludedir' is empty. If it is, they should not try to use 4083 it; they should cancel the second installation of the header files. 4084 4085 A package should not replace an existing header in this directory 4086 unless the header came from the same package. Thus, if your Foo 4087 package provides a header file `foo.h', then it should install the 4088 header file in the `oldincludedir' directory if either (1) there 4089 is no `foo.h' there or (2) the `foo.h' that exists came from the 4090 Foo package. 4091 4092 To tell whether `foo.h' came from the Foo package, put a magic 4093 string in the file--part of a comment--and `grep' for that string. 4094 4095`docdir' 4096 The directory for installing documentation files (other than Info) 4097 for this package. By default, it should be 4098 `/usr/local/share/doc/YOURPKG', but it should be written as 4099 `$(datarootdir)/doc/YOURPKG'. (If you are using Autoconf, write 4100 it as `@docdir@'.) The YOURPKG subdirectory, which may include a 4101 version number, prevents collisions among files with common names, 4102 such as `README'. 4103 4104`infodir' 4105 The directory for installing the Info files for this package. By 4106 default, it should be `/usr/local/share/info', but it should be 4107 written as `$(datarootdir)/info'. (If you are using Autoconf, 4108 write it as `@infodir@'.) `infodir' is separate from `docdir' for 4109 compatibility with existing practice. 4110 4111`htmldir' 4112`dvidir' 4113`pdfdir' 4114`psdir' 4115 Directories for installing documentation files in the particular 4116 format. They should all be set to `$(docdir)' by default. (If 4117 you are using Autoconf, write them as `@htmldir@', `@dvidir@', 4118 etc.) Packages which supply several translations of their 4119 documentation should install them in `$(htmldir)/'LL, 4120 `$(pdfdir)/'LL, etc. where LL is a locale abbreviation such as 4121 `en' or `pt_BR'. 4122 4123`libdir' 4124 The directory for object files and libraries of object code. Do 4125 not install executables here, they probably ought to go in 4126 `$(libexecdir)' instead. The value of `libdir' should normally be 4127 `/usr/local/lib', but write it as `$(exec_prefix)/lib'. (If you 4128 are using Autoconf, write it as `@libdir@'.) 4129 4130`lispdir' 4131 The directory for installing any Emacs Lisp files in this package. 4132 By default, it should be `/usr/local/share/emacs/site-lisp', but 4133 it should be written as `$(datarootdir)/emacs/site-lisp'. 4134 4135 If you are using Autoconf, write the default as `@lispdir@'. In 4136 order to make `@lispdir@' work, you need the following lines in 4137 your `configure.in' file: 4138 4139 lispdir='${datarootdir}/emacs/site-lisp' 4140 AC_SUBST(lispdir) 4141 4142`localedir' 4143 The directory for installing locale-specific message catalogs for 4144 this package. By default, it should be `/usr/local/share/locale', 4145 but it should be written as `$(datarootdir)/locale'. (If you are 4146 using Autoconf, write it as `@localedir@'.) This directory 4147 usually has a subdirectory per locale. 4148 4149 Unix-style man pages are installed in one of the following: 4150 4151`mandir' 4152 The top-level directory for installing the man pages (if any) for 4153 this package. It will normally be `/usr/local/share/man', but you 4154 should write it as `$(datarootdir)/man'. (If you are using 4155 Autoconf, write it as `@mandir@'.) 4156 4157`man1dir' 4158 The directory for installing section 1 man pages. Write it as 4159 `$(mandir)/man1'. 4160 4161`man2dir' 4162 The directory for installing section 2 man pages. Write it as 4163 `$(mandir)/man2' 4164 4165`...' 4166 *Don't make the primary documentation for any GNU software be a 4167 man page. Write a manual in Texinfo instead. Man pages are just 4168 for the sake of people running GNU software on Unix, which is a 4169 secondary application only.* 4170 4171`manext' 4172 The file name extension for the installed man page. This should 4173 contain a period followed by the appropriate digit; it should 4174 normally be `.1'. 4175 4176`man1ext' 4177 The file name extension for installed section 1 man pages. 4178 4179`man2ext' 4180 The file name extension for installed section 2 man pages. 4181 4182`...' 4183 Use these names instead of `manext' if the package needs to 4184 install man pages in more than one section of the manual. 4185 4186 And finally, you should set the following variable: 4187 4188`srcdir' 4189 The directory for the sources being compiled. The value of this 4190 variable is normally inserted by the `configure' shell script. 4191 (If you are using Autoconf, use `srcdir = @srcdir@'.) 4192 4193 For example: 4194 4195 # Common prefix for installation directories. 4196 # NOTE: This directory must exist when you start the install. 4197 prefix = /usr/local 4198 datarootdir = $(prefix)/share 4199 datadir = $(datarootdir) 4200 exec_prefix = $(prefix) 4201 # Where to put the executable for the command `gcc'. 4202 bindir = $(exec_prefix)/bin 4203 # Where to put the directories used by the compiler. 4204 libexecdir = $(exec_prefix)/libexec 4205 # Where to put the Info files. 4206 infodir = $(datarootdir)/info 4207 4208 If your program installs a large number of files into one of the 4209standard user-specified directories, it might be useful to group them 4210into a subdirectory particular to that program. If you do this, you 4211should write the `install' rule to create these subdirectories. 4212 4213 Do not expect the user to include the subdirectory name in the value 4214of any of the variables listed above. The idea of having a uniform set 4215of variable names for installation directories is to enable the user to 4216specify the exact same values for several different GNU packages. In 4217order for this to be useful, all the packages must be designed so that 4218they will work sensibly when the user does so. 4219 4220 At times, not all of these variables may be implemented in the 4221current release of Autoconf and/or Automake; but as of Autoconf 2.60, we 4222believe all of them are. When any are missing, the descriptions here 4223serve as specifications for what Autoconf will implement. As a 4224programmer, you can either use a development version of Autoconf or 4225avoid using these variables until a stable release is made which 4226supports them. 4227 4228 4229File: standards.info, Node: Standard Targets, Next: Install Command Categories, Prev: Directory Variables, Up: Makefile Conventions 4230 42317.2.6 Standard Targets for Users 4232-------------------------------- 4233 4234All GNU programs should have the following targets in their Makefiles: 4235 4236`all' 4237 Compile the entire program. This should be the default target. 4238 This target need not rebuild any documentation files; Info files 4239 should normally be included in the distribution, and DVI (and other 4240 documentation format) files should be made only when explicitly 4241 asked for. 4242 4243 By default, the Make rules should compile and link with `-g', so 4244 that executable programs have debugging symbols. Users who don't 4245 mind being helpless can strip the executables later if they wish. 4246 4247`install' 4248 Compile the program and copy the executables, libraries, and so on 4249 to the file names where they should reside for actual use. If 4250 there is a simple test to verify that a program is properly 4251 installed, this target should run that test. 4252 4253 Do not strip executables when installing them. Devil-may-care 4254 users can use the `install-strip' target to do that. 4255 4256 If possible, write the `install' target rule so that it does not 4257 modify anything in the directory where the program was built, 4258 provided `make all' has just been done. This is convenient for 4259 building the program under one user name and installing it under 4260 another. 4261 4262 The commands should create all the directories in which files are 4263 to be installed, if they don't already exist. This includes the 4264 directories specified as the values of the variables `prefix' and 4265 `exec_prefix', as well as all subdirectories that are needed. One 4266 way to do this is by means of an `installdirs' target as described 4267 below. 4268 4269 Use `-' before any command for installing a man page, so that 4270 `make' will ignore any errors. This is in case there are systems 4271 that don't have the Unix man page documentation system installed. 4272 4273 The way to install Info files is to copy them into `$(infodir)' 4274 with `$(INSTALL_DATA)' (*note Command Variables::), and then run 4275 the `install-info' program if it is present. `install-info' is a 4276 program that edits the Info `dir' file to add or update the menu 4277 entry for the given Info file; it is part of the Texinfo package. 4278 Here is a sample rule to install an Info file: 4279 4280 $(DESTDIR)$(infodir)/foo.info: foo.info 4281 $(POST_INSTALL) 4282 # There may be a newer info file in . than in srcdir. 4283 -if test -f foo.info; then d=.; \ 4284 else d=$(srcdir); fi; \ 4285 $(INSTALL_DATA) $$d/foo.info $(DESTDIR)$@; \ 4286 # Run install-info only if it exists. 4287 # Use `if' instead of just prepending `-' to the 4288 # line so we notice real errors from install-info. 4289 # We use `$(SHELL) -c' because some shells do not 4290 # fail gracefully when there is an unknown command. 4291 if $(SHELL) -c 'install-info --version' \ 4292 >/dev/null 2>&1; then \ 4293 install-info --dir-file=$(DESTDIR)$(infodir)/dir \ 4294 $(DESTDIR)$(infodir)/foo.info; \ 4295 else true; fi 4296 4297 When writing the `install' target, you must classify all the 4298 commands into three categories: normal ones, "pre-installation" 4299 commands and "post-installation" commands. *Note Install Command 4300 Categories::. 4301 4302`install-html' 4303`install-dvi' 4304`install-pdf' 4305`install-ps' 4306 These targets install documentation in formats other than Info; 4307 they're intended to be called explicitly by the person installing 4308 the package, if that format is desired. GNU prefers Info files, 4309 so these must be installed by the `install' target. 4310 4311 When you have many documentation files to install, we recommend 4312 that you avoid collisions and clutter by arranging for these 4313 targets to install in subdirectories of the appropriate 4314 installation directory, such as `htmldir'. As one example, if 4315 your package has multiple manuals, and you wish to install HTML 4316 documentation with many files (such as the "split" mode output by 4317 `makeinfo --html'), you'll certainly want to use subdirectories, 4318 or two nodes with the same name in different manuals will 4319 overwrite each other. 4320 4321 Please make these `install-FORMAT' targets invoke the commands for 4322 the FORMAT target, for example, by making FORMAT a dependency. 4323 4324`uninstall' 4325 Delete all the installed files--the copies that the `install' and 4326 `install-*' targets create. 4327 4328 This rule should not modify the directories where compilation is 4329 done, only the directories where files are installed. 4330 4331 The uninstallation commands are divided into three categories, 4332 just like the installation commands. *Note Install Command 4333 Categories::. 4334 4335`install-strip' 4336 Like `install', but strip the executable files while installing 4337 them. In simple cases, this target can use the `install' target in 4338 a simple way: 4339 4340 install-strip: 4341 $(MAKE) INSTALL_PROGRAM='$(INSTALL_PROGRAM) -s' \ 4342 install 4343 4344 But if the package installs scripts as well as real executables, 4345 the `install-strip' target can't just refer to the `install' 4346 target; it has to strip the executables but not the scripts. 4347 4348 `install-strip' should not strip the executables in the build 4349 directory which are being copied for installation. It should only 4350 strip the copies that are installed. 4351 4352 Normally we do not recommend stripping an executable unless you 4353 are sure the program has no bugs. However, it can be reasonable 4354 to install a stripped executable for actual execution while saving 4355 the unstripped executable elsewhere in case there is a bug. 4356 4357`clean' 4358 Delete all files in the current directory that are normally 4359 created by building the program. Also delete files in other 4360 directories if they are created by this makefile. However, don't 4361 delete the files that record the configuration. Also preserve 4362 files that could be made by building, but normally aren't because 4363 the distribution comes with them. There is no need to delete 4364 parent directories that were created with `mkdir -p', since they 4365 could have existed anyway. 4366 4367 Delete `.dvi' files here if they are not part of the distribution. 4368 4369`distclean' 4370 Delete all files in the current directory (or created by this 4371 makefile) that are created by configuring or building the program. 4372 If you have unpacked the source and built the program without 4373 creating any other files, `make distclean' should leave only the 4374 files that were in the distribution. However, there is no need to 4375 delete parent directories that were created with `mkdir -p', since 4376 they could have existed anyway. 4377 4378`mostlyclean' 4379 Like `clean', but may refrain from deleting a few files that people 4380 normally don't want to recompile. For example, the `mostlyclean' 4381 target for GCC does not delete `libgcc.a', because recompiling it 4382 is rarely necessary and takes a lot of time. 4383 4384`maintainer-clean' 4385 Delete almost everything that can be reconstructed with this 4386 Makefile. This typically includes everything deleted by 4387 `distclean', plus more: C source files produced by Bison, tags 4388 tables, Info files, and so on. 4389 4390 The reason we say "almost everything" is that running the command 4391 `make maintainer-clean' should not delete `configure' even if 4392 `configure' can be remade using a rule in the Makefile. More 4393 generally, `make maintainer-clean' should not delete anything that 4394 needs to exist in order to run `configure' and then begin to build 4395 the program. Also, there is no need to delete parent directories 4396 that were created with `mkdir -p', since they could have existed 4397 anyway. These are the only exceptions; `maintainer-clean' should 4398 delete everything else that can be rebuilt. 4399 4400 The `maintainer-clean' target is intended to be used by a 4401 maintainer of the package, not by ordinary users. You may need 4402 special tools to reconstruct some of the files that `make 4403 maintainer-clean' deletes. Since these files are normally 4404 included in the distribution, we don't take care to make them easy 4405 to reconstruct. If you find you need to unpack the full 4406 distribution again, don't blame us. 4407 4408 To help make users aware of this, the commands for the special 4409 `maintainer-clean' target should start with these two: 4410 4411 @echo 'This command is intended for maintainers to use; it' 4412 @echo 'deletes files that may need special tools to rebuild.' 4413 4414`TAGS' 4415 Update a tags table for this program. 4416 4417`info' 4418 Generate any Info files needed. The best way to write the rules 4419 is as follows: 4420 4421 info: foo.info 4422 4423 foo.info: foo.texi chap1.texi chap2.texi 4424 $(MAKEINFO) $(srcdir)/foo.texi 4425 4426 You must define the variable `MAKEINFO' in the Makefile. It should 4427 run the `makeinfo' program, which is part of the Texinfo 4428 distribution. 4429 4430 Normally a GNU distribution comes with Info files, and that means 4431 the Info files are present in the source directory. Therefore, 4432 the Make rule for an info file should update it in the source 4433 directory. When users build the package, ordinarily Make will not 4434 update the Info files because they will already be up to date. 4435 4436`dvi' 4437`html' 4438`pdf' 4439`ps' 4440 Generate documentation files in the given format. These targets 4441 should always exist, but any or all can be a no-op if the given 4442 output format cannot be generated. These targets should not be 4443 dependencies of the `all' target; the user must manually invoke 4444 them. 4445 4446 Here's an example rule for generating DVI files from Texinfo: 4447 4448 dvi: foo.dvi 4449 4450 foo.dvi: foo.texi chap1.texi chap2.texi 4451 $(TEXI2DVI) $(srcdir)/foo.texi 4452 4453 You must define the variable `TEXI2DVI' in the Makefile. It should 4454 run the program `texi2dvi', which is part of the Texinfo 4455 distribution.(1) Alternatively, write just the dependencies, and 4456 allow GNU `make' to provide the command. 4457 4458 Here's another example, this one for generating HTML from Texinfo: 4459 4460 html: foo.html 4461 4462 foo.html: foo.texi chap1.texi chap2.texi 4463 $(TEXI2HTML) $(srcdir)/foo.texi 4464 4465 Again, you would define the variable `TEXI2HTML' in the Makefile; 4466 for example, it might run `makeinfo --no-split --html' (`makeinfo' 4467 is part of the Texinfo distribution). 4468 4469`dist' 4470 Create a distribution tar file for this program. The tar file 4471 should be set up so that the file names in the tar file start with 4472 a subdirectory name which is the name of the package it is a 4473 distribution for. This name can include the version number. 4474 4475 For example, the distribution tar file of GCC version 1.40 unpacks 4476 into a subdirectory named `gcc-1.40'. 4477 4478 The easiest way to do this is to create a subdirectory 4479 appropriately named, use `ln' or `cp' to install the proper files 4480 in it, and then `tar' that subdirectory. 4481 4482 Compress the tar file with `gzip'. For example, the actual 4483 distribution file for GCC version 1.40 is called `gcc-1.40.tar.gz'. 4484 4485 The `dist' target should explicitly depend on all non-source files 4486 that are in the distribution, to make sure they are up to date in 4487 the distribution. *Note Making Releases: Releases. 4488 4489`check' 4490 Perform self-tests (if any). The user must build the program 4491 before running the tests, but need not install the program; you 4492 should write the self-tests so that they work when the program is 4493 built but not installed. 4494 4495 The following targets are suggested as conventional names, for 4496programs in which they are useful. 4497 4498`installcheck' 4499 Perform installation tests (if any). The user must build and 4500 install the program before running the tests. You should not 4501 assume that `$(bindir)' is in the search path. 4502 4503`installdirs' 4504 It's useful to add a target named `installdirs' to create the 4505 directories where files are installed, and their parent 4506 directories. There is a script called `mkinstalldirs' which is 4507 convenient for this; you can find it in the Texinfo package. You 4508 can use a rule like this: 4509 4510 # Make sure all installation directories (e.g. $(bindir)) 4511 # actually exist by making them if necessary. 4512 installdirs: mkinstalldirs 4513 $(srcdir)/mkinstalldirs $(bindir) $(datadir) \ 4514 $(libdir) $(infodir) \ 4515 $(mandir) 4516 4517 or, if you wish to support `DESTDIR', 4518 4519 # Make sure all installation directories (e.g. $(bindir)) 4520 # actually exist by making them if necessary. 4521 installdirs: mkinstalldirs 4522 $(srcdir)/mkinstalldirs \ 4523 $(DESTDIR)$(bindir) $(DESTDIR)$(datadir) \ 4524 $(DESTDIR)$(libdir) $(DESTDIR)$(infodir) \ 4525 $(DESTDIR)$(mandir) 4526 4527 This rule should not modify the directories where compilation is 4528 done. It should do nothing but create installation directories. 4529 4530 ---------- Footnotes ---------- 4531 4532 (1) `texi2dvi' uses TeX to do the real work of formatting. TeX is 4533not distributed with Texinfo. 4534 4535 4536File: standards.info, Node: Install Command Categories, Prev: Standard Targets, Up: Makefile Conventions 4537 45387.2.7 Install Command Categories 4539-------------------------------- 4540 4541When writing the `install' target, you must classify all the commands 4542into three categories: normal ones, "pre-installation" commands and 4543"post-installation" commands. 4544 4545 Normal commands move files into their proper places, and set their 4546modes. They may not alter any files except the ones that come entirely 4547from the package they belong to. 4548 4549 Pre-installation and post-installation commands may alter other 4550files; in particular, they can edit global configuration files or data 4551bases. 4552 4553 Pre-installation commands are typically executed before the normal 4554commands, and post-installation commands are typically run after the 4555normal commands. 4556 4557 The most common use for a post-installation command is to run 4558`install-info'. This cannot be done with a normal command, since it 4559alters a file (the Info directory) which does not come entirely and 4560solely from the package being installed. It is a post-installation 4561command because it needs to be done after the normal command which 4562installs the package's Info files. 4563 4564 Most programs don't need any pre-installation commands, but we have 4565the feature just in case it is needed. 4566 4567 To classify the commands in the `install' rule into these three 4568categories, insert "category lines" among them. A category line 4569specifies the category for the commands that follow. 4570 4571 A category line consists of a tab and a reference to a special Make 4572variable, plus an optional comment at the end. There are three 4573variables you can use, one for each category; the variable name 4574specifies the category. Category lines are no-ops in ordinary execution 4575because these three Make variables are normally undefined (and you 4576_should not_ define them in the makefile). 4577 4578 Here are the three possible category lines, each with a comment that 4579explains what it means: 4580 4581 $(PRE_INSTALL) # Pre-install commands follow. 4582 $(POST_INSTALL) # Post-install commands follow. 4583 $(NORMAL_INSTALL) # Normal commands follow. 4584 4585 If you don't use a category line at the beginning of the `install' 4586rule, all the commands are classified as normal until the first category 4587line. If you don't use any category lines, all the commands are 4588classified as normal. 4589 4590 These are the category lines for `uninstall': 4591 4592 $(PRE_UNINSTALL) # Pre-uninstall commands follow. 4593 $(POST_UNINSTALL) # Post-uninstall commands follow. 4594 $(NORMAL_UNINSTALL) # Normal commands follow. 4595 4596 Typically, a pre-uninstall command would be used for deleting entries 4597from the Info directory. 4598 4599 If the `install' or `uninstall' target has any dependencies which 4600act as subroutines of installation, then you should start _each_ 4601dependency's commands with a category line, and start the main target's 4602commands with a category line also. This way, you can ensure that each 4603command is placed in the right category regardless of which of the 4604dependencies actually run. 4605 4606 Pre-installation and post-installation commands should not run any 4607programs except for these: 4608 4609 [ basename bash cat chgrp chmod chown cmp cp dd diff echo 4610 egrep expand expr false fgrep find getopt grep gunzip gzip 4611 hostname install install-info kill ldconfig ln ls md5sum 4612 mkdir mkfifo mknod mv printenv pwd rm rmdir sed sort tee 4613 test touch true uname xargs yes 4614 4615 The reason for distinguishing the commands in this way is for the 4616sake of making binary packages. Typically a binary package contains 4617all the executables and other files that need to be installed, and has 4618its own method of installing them--so it does not need to run the normal 4619installation commands. But installing the binary package does need to 4620execute the pre-installation and post-installation commands. 4621 4622 Programs to build binary packages work by extracting the 4623pre-installation and post-installation commands. Here is one way of 4624extracting the pre-installation commands (the `-s' option to `make' is 4625needed to silence messages about entering subdirectories): 4626 4627 make -s -n install -o all \ 4628 PRE_INSTALL=pre-install \ 4629 POST_INSTALL=post-install \ 4630 NORMAL_INSTALL=normal-install \ 4631 | gawk -f pre-install.awk 4632 4633where the file `pre-install.awk' could contain this: 4634 4635 $0 ~ /^(normal-install|post-install)[ \t]*$/ {on = 0} 4636 on {print $0} 4637 $0 ~ /^pre-install[ \t]*$/ {on = 1} 4638 4639 4640File: standards.info, Node: Releases, Prev: Makefile Conventions, Up: Managing Releases 4641 46427.3 Making Releases 4643=================== 4644 4645You should identify each release with a pair of version numbers, a 4646major version and a minor. We have no objection to using more than two 4647numbers, but it is very unlikely that you really need them. 4648 4649 Package the distribution of `Foo version 69.96' up in a gzipped tar 4650file with the name `foo-69.96.tar.gz'. It should unpack into a 4651subdirectory named `foo-69.96'. 4652 4653 Building and installing the program should never modify any of the 4654files contained in the distribution. This means that all the files 4655that form part of the program in any way must be classified into "source 4656files" and "non-source files". Source files are written by humans and 4657never changed automatically; non-source files are produced from source 4658files by programs under the control of the Makefile. 4659 4660 The distribution should contain a file named `README' which gives 4661the name of the package, and a general description of what it does. It 4662is also good to explain the purpose of each of the first-level 4663subdirectories in the package, if there are any. The `README' file 4664should either state the version number of the package, or refer to where 4665in the package it can be found. 4666 4667 The `README' file should refer to the file `INSTALL', which should 4668contain an explanation of the installation procedure. 4669 4670 The `README' file should also refer to the file which contains the 4671copying conditions. The GNU GPL, if used, should be in a file called 4672`COPYING'. If the GNU LGPL is used, it should be in a file called 4673`COPYING.LIB'. 4674 4675 Naturally, all the source files must be in the distribution. It is 4676okay to include non-source files in the distribution, provided they are 4677up-to-date and machine-independent, so that building the distribution 4678normally will never modify them. We commonly include non-source files 4679produced by Bison, `lex', TeX, and `makeinfo'; this helps avoid 4680unnecessary dependencies between our distributions, so that users can 4681install whichever packages they want to install. 4682 4683 Non-source files that might actually be modified by building and 4684installing the program should *never* be included in the distribution. 4685So if you do distribute non-source files, always make sure they are up 4686to date when you make a new distribution. 4687 4688 Make sure that the directory into which the distribution unpacks (as 4689well as any subdirectories) are all world-writable (octal mode 777). 4690This is so that old versions of `tar' which preserve the ownership and 4691permissions of the files from the tar archive will be able to extract 4692all the files even if the user is unprivileged. 4693 4694 Make sure that all the files in the distribution are world-readable. 4695 4696 Don't include any symbolic links in the distribution itself. If the 4697tar file contains symbolic links, then people cannot even unpack it on 4698systems that don't support symbolic links. Also, don't use multiple 4699names for one file in different directories, because certain file 4700systems cannot handle this and that prevents unpacking the distribution. 4701 4702 Try to make sure that all the file names will be unique on MS-DOS. A 4703name on MS-DOS consists of up to 8 characters, optionally followed by a 4704period and up to three characters. MS-DOS will truncate extra 4705characters both before and after the period. Thus, `foobarhacker.c' 4706and `foobarhacker.o' are not ambiguous; they are truncated to 4707`foobarha.c' and `foobarha.o', which are distinct. 4708 4709 Include in your distribution a copy of the `texinfo.tex' you used to 4710test print any `*.texinfo' or `*.texi' files. 4711 4712 Likewise, if your program uses small GNU software packages like 4713regex, getopt, obstack, or termcap, include them in the distribution 4714file. Leaving them out would make the distribution file a little 4715smaller at the expense of possible inconvenience to a user who doesn't 4716know what other files to get. 4717 4718 4719File: standards.info, Node: References, Next: Copying This Manual, Prev: Managing Releases, Up: Top 4720 47218 References to Non-Free Software and Documentation 4722*************************************************** 4723 4724A GNU program should not recommend use of any non-free program. We 4725can't stop some people from writing proprietary programs, or stop other 4726people from using them, but we can and should refuse to advertise them 4727to new potential customers. Proprietary software is a social and 4728ethical problem, and the point of GNU is to solve that problem. 4729 4730 The GNU definition of free software is found on the GNU web site at 4731`http://www.gnu.org/philosophy/free-sw.html', and the definition of 4732free documentation is found at 4733`http://www.gnu.org/philosophy/free-doc.html'. A list of important 4734licenses and whether they qualify as free is in 4735`http://www.gnu.org/licenses/license-list.html'. The terms "free" and 4736"non-free", used in this document, refer to that definition. If it is 4737not clear whether a license qualifies as free under this definition, 4738please ask the GNU Project by writing to <licensing@gnu.org>. We will 4739answer, and if the license is an important one, we will add it to the 4740list. 4741 4742 When a non-free program or system is well known, you can mention it 4743in passing--that is harmless, since users who might want to use it 4744probably already know about it. For instance, it is fine to explain 4745how to build your package on top of some widely used non-free operating 4746system, or how to use it together with some widely used non-free 4747program. 4748 4749 However, you should give only the necessary information to help those 4750who already use the non-free program to use your program with it--don't 4751give, or refer to, any further information about the proprietary 4752program, and don't imply that the proprietary program enhances your 4753program, or that its existence is in any way a good thing. The goal 4754should be that people already using the proprietary program will get 4755the advice they need about how to use your free program with it, while 4756people who don't already use the proprietary program will not see 4757anything to lead them to take an interest in it. 4758 4759 If a non-free program or system is obscure in your program's domain, 4760your program should not mention or support it at all, since doing so 4761would tend to popularize the non-free program more than it popularizes 4762your program. (You cannot hope to find many additional users among the 4763users of Foobar if the users of Foobar are few.) 4764 4765 Sometimes a program is free software in itself but depends on a 4766non-free platform in order to run. For instance, many Java programs 4767depend on Sun's Java implementation, and won't run on the GNU Java 4768Compiler (which does not yet have all the features) or won't run with 4769the GNU Java libraries. To recommend that program is inherently to 4770recommend the non-free platform as well; if you should not do the 4771latter, then don't do the former. 4772 4773 A GNU package should not refer the user to any non-free documentation 4774for free software. Free documentation that can be included in free 4775operating systems is essential for completing the GNU system, or any 4776free operating system, so it is a major focus of the GNU Project; to 4777recommend use of documentation that we are not allowed to use in GNU 4778would weaken the impetus for the community to produce documentation 4779that we can include. So GNU packages should never recommend non-free 4780documentation. 4781 4782 By contrast, it is ok to refer to journal articles and textbooks in 4783the comments of a program for explanation of how it functions, even 4784though they be non-free. This is because we don't include such things 4785in the GNU system even if we are allowed to-they are outside the scope 4786of an operating system project. 4787 4788 Referring to a web site that describes or recommends a non-free 4789program is in effect promoting that software, so please do not make 4790links (or mention by name) web sites that contain such material. This 4791policy is relevant particularly for the web pages for a GNU package. 4792 4793 Following links from nearly any web site can lead to non-free 4794software; this is an inescapable aspect of the nature of the web, and 4795in itself is no objection to linking to a site. As long as the site 4796does not itself recommend a non-free program, there is no need be 4797concerned about the sites it links to for other reasons. 4798 4799 Thus, for example, you should not make a link to AT&T's web site, 4800because that recommends AT&T's non-free software packages; you should 4801not make a link to a site that links to AT&T's site saying it is a 4802place to get a non-free program; but if a site you want to link to 4803refers to AT&T's web site in some other context (such as long-distance 4804telephone service), that is not a problem. 4805 4806 4807File: standards.info, Node: Copying This Manual, Next: Index, Prev: References, Up: Top 4808 4809Appendix A Copying This Manual 4810****************************** 4811 4812* Menu: 4813 4814* GNU Free Documentation License:: License for copying this manual 4815 4816 4817File: standards.info, Node: GNU Free Documentation License, Up: Copying This Manual 4818 4819A.1 GNU Free Documentation License 4820================================== 4821 4822 Version 1.2, November 2002 4823 4824 Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 4825 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA 4826 4827 Everyone is permitted to copy and distribute verbatim copies 4828 of this license document, but changing it is not allowed. 4829 4830 0. PREAMBLE 4831 4832 The purpose of this License is to make a manual, textbook, or other 4833 functional and useful document "free" in the sense of freedom: to 4834 assure everyone the effective freedom to copy and redistribute it, 4835 with or without modifying it, either commercially or 4836 noncommercially. Secondarily, this License preserves for the 4837 author and publisher a way to get credit for their work, while not 4838 being considered responsible for modifications made by others. 4839 4840 This License is a kind of "copyleft", which means that derivative 4841 works of the document must themselves be free in the same sense. 4842 It complements the GNU General Public License, which is a copyleft 4843 license designed for free software. 4844 4845 We have designed this License in order to use it for manuals for 4846 free software, because free software needs free documentation: a 4847 free program should come with manuals providing the same freedoms 4848 that the software does. But this License is not limited to 4849 software manuals; it can be used for any textual work, regardless 4850 of subject matter or whether it is published as a printed book. 4851 We recommend this License principally for works whose purpose is 4852 instruction or reference. 4853 4854 1. APPLICABILITY AND DEFINITIONS 4855 4856 This License applies to any manual or other work, in any medium, 4857 that contains a notice placed by the copyright holder saying it 4858 can be distributed under the terms of this License. Such a notice 4859 grants a world-wide, royalty-free license, unlimited in duration, 4860 to use that work under the conditions stated herein. The 4861 "Document", below, refers to any such manual or work. Any member 4862 of the public is a licensee, and is addressed as "you". You 4863 accept the license if you copy, modify or distribute the work in a 4864 way requiring permission under copyright law. 4865 4866 A "Modified Version" of the Document means any work containing the 4867 Document or a portion of it, either copied verbatim, or with 4868 modifications and/or translated into another language. 4869 4870 A "Secondary Section" is a named appendix or a front-matter section 4871 of the Document that deals exclusively with the relationship of the 4872 publishers or authors of the Document to the Document's overall 4873 subject (or to related matters) and contains nothing that could 4874 fall directly within that overall subject. (Thus, if the Document 4875 is in part a textbook of mathematics, a Secondary Section may not 4876 explain any mathematics.) The relationship could be a matter of 4877 historical connection with the subject or with related matters, or 4878 of legal, commercial, philosophical, ethical or political position 4879 regarding them. 4880 4881 The "Invariant Sections" are certain Secondary Sections whose 4882 titles are designated, as being those of Invariant Sections, in 4883 the notice that says that the Document is released under this 4884 License. If a section does not fit the above definition of 4885 Secondary then it is not allowed to be designated as Invariant. 4886 The Document may contain zero Invariant Sections. If the Document 4887 does not identify any Invariant Sections then there are none. 4888 4889 The "Cover Texts" are certain short passages of text that are 4890 listed, as Front-Cover Texts or Back-Cover Texts, in the notice 4891 that says that the Document is released under this License. A 4892 Front-Cover Text may be at most 5 words, and a Back-Cover Text may 4893 be at most 25 words. 4894 4895 A "Transparent" copy of the Document means a machine-readable copy, 4896 represented in a format whose specification is available to the 4897 general public, that is suitable for revising the document 4898 straightforwardly with generic text editors or (for images 4899 composed of pixels) generic paint programs or (for drawings) some 4900 widely available drawing editor, and that is suitable for input to 4901 text formatters or for automatic translation to a variety of 4902 formats suitable for input to text formatters. A copy made in an 4903 otherwise Transparent file format whose markup, or absence of 4904 markup, has been arranged to thwart or discourage subsequent 4905 modification by readers is not Transparent. An image format is 4906 not Transparent if used for any substantial amount of text. A 4907 copy that is not "Transparent" is called "Opaque". 4908 4909 Examples of suitable formats for Transparent copies include plain 4910 ASCII without markup, Texinfo input format, LaTeX input format, 4911 SGML or XML using a publicly available DTD, and 4912 standard-conforming simple HTML, PostScript or PDF designed for 4913 human modification. Examples of transparent image formats include 4914 PNG, XCF and JPG. Opaque formats include proprietary formats that 4915 can be read and edited only by proprietary word processors, SGML or 4916 XML for which the DTD and/or processing tools are not generally 4917 available, and the machine-generated HTML, PostScript or PDF 4918 produced by some word processors for output purposes only. 4919 4920 The "Title Page" means, for a printed book, the title page itself, 4921 plus such following pages as are needed to hold, legibly, the 4922 material this License requires to appear in the title page. For 4923 works in formats which do not have any title page as such, "Title 4924 Page" means the text near the most prominent appearance of the 4925 work's title, preceding the beginning of the body of the text. 4926 4927 A section "Entitled XYZ" means a named subunit of the Document 4928 whose title either is precisely XYZ or contains XYZ in parentheses 4929 following text that translates XYZ in another language. (Here XYZ 4930 stands for a specific section name mentioned below, such as 4931 "Acknowledgements", "Dedications", "Endorsements", or "History".) 4932 To "Preserve the Title" of such a section when you modify the 4933 Document means that it remains a section "Entitled XYZ" according 4934 to this definition. 4935 4936 The Document may include Warranty Disclaimers next to the notice 4937 which states that this License applies to the Document. These 4938 Warranty Disclaimers are considered to be included by reference in 4939 this License, but only as regards disclaiming warranties: any other 4940 implication that these Warranty Disclaimers may have is void and 4941 has no effect on the meaning of this License. 4942 4943 2. VERBATIM COPYING 4944 4945 You may copy and distribute the Document in any medium, either 4946 commercially or noncommercially, provided that this License, the 4947 copyright notices, and the license notice saying this License 4948 applies to the Document are reproduced in all copies, and that you 4949 add no other conditions whatsoever to those of this License. You 4950 may not use technical measures to obstruct or control the reading 4951 or further copying of the copies you make or distribute. However, 4952 you may accept compensation in exchange for copies. If you 4953 distribute a large enough number of copies you must also follow 4954 the conditions in section 3. 4955 4956 You may also lend copies, under the same conditions stated above, 4957 and you may publicly display copies. 4958 4959 3. COPYING IN QUANTITY 4960 4961 If you publish printed copies (or copies in media that commonly 4962 have printed covers) of the Document, numbering more than 100, and 4963 the Document's license notice requires Cover Texts, you must 4964 enclose the copies in covers that carry, clearly and legibly, all 4965 these Cover Texts: Front-Cover Texts on the front cover, and 4966 Back-Cover Texts on the back cover. Both covers must also clearly 4967 and legibly identify you as the publisher of these copies. The 4968 front cover must present the full title with all words of the 4969 title equally prominent and visible. You may add other material 4970 on the covers in addition. Copying with changes limited to the 4971 covers, as long as they preserve the title of the Document and 4972 satisfy these conditions, can be treated as verbatim copying in 4973 other respects. 4974 4975 If the required texts for either cover are too voluminous to fit 4976 legibly, you should put the first ones listed (as many as fit 4977 reasonably) on the actual cover, and continue the rest onto 4978 adjacent pages. 4979 4980 If you publish or distribute Opaque copies of the Document 4981 numbering more than 100, you must either include a 4982 machine-readable Transparent copy along with each Opaque copy, or 4983 state in or with each Opaque copy a computer-network location from 4984 which the general network-using public has access to download 4985 using public-standard network protocols a complete Transparent 4986 copy of the Document, free of added material. If you use the 4987 latter option, you must take reasonably prudent steps, when you 4988 begin distribution of Opaque copies in quantity, to ensure that 4989 this Transparent copy will remain thus accessible at the stated 4990 location until at least one year after the last time you 4991 distribute an Opaque copy (directly or through your agents or 4992 retailers) of that edition to the public. 4993 4994 It is requested, but not required, that you contact the authors of 4995 the Document well before redistributing any large number of 4996 copies, to give them a chance to provide you with an updated 4997 version of the Document. 4998 4999 4. MODIFICATIONS 5000 5001 You may copy and distribute a Modified Version of the Document 5002 under the conditions of sections 2 and 3 above, provided that you 5003 release the Modified Version under precisely this License, with 5004 the Modified Version filling the role of the Document, thus 5005 licensing distribution and modification of the Modified Version to 5006 whoever possesses a copy of it. In addition, you must do these 5007 things in the Modified Version: 5008 5009 A. Use in the Title Page (and on the covers, if any) a title 5010 distinct from that of the Document, and from those of 5011 previous versions (which should, if there were any, be listed 5012 in the History section of the Document). You may use the 5013 same title as a previous version if the original publisher of 5014 that version gives permission. 5015 5016 B. List on the Title Page, as authors, one or more persons or 5017 entities responsible for authorship of the modifications in 5018 the Modified Version, together with at least five of the 5019 principal authors of the Document (all of its principal 5020 authors, if it has fewer than five), unless they release you 5021 from this requirement. 5022 5023 C. State on the Title page the name of the publisher of the 5024 Modified Version, as the publisher. 5025 5026 D. Preserve all the copyright notices of the Document. 5027 5028 E. Add an appropriate copyright notice for your modifications 5029 adjacent to the other copyright notices. 5030 5031 F. Include, immediately after the copyright notices, a license 5032 notice giving the public permission to use the Modified 5033 Version under the terms of this License, in the form shown in 5034 the Addendum below. 5035 5036 G. Preserve in that license notice the full lists of Invariant 5037 Sections and required Cover Texts given in the Document's 5038 license notice. 5039 5040 H. Include an unaltered copy of this License. 5041 5042 I. Preserve the section Entitled "History", Preserve its Title, 5043 and add to it an item stating at least the title, year, new 5044 authors, and publisher of the Modified Version as given on 5045 the Title Page. If there is no section Entitled "History" in 5046 the Document, create one stating the title, year, authors, 5047 and publisher of the Document as given on its Title Page, 5048 then add an item describing the Modified Version as stated in 5049 the previous sentence. 5050 5051 J. Preserve the network location, if any, given in the Document 5052 for public access to a Transparent copy of the Document, and 5053 likewise the network locations given in the Document for 5054 previous versions it was based on. These may be placed in 5055 the "History" section. You may omit a network location for a 5056 work that was published at least four years before the 5057 Document itself, or if the original publisher of the version 5058 it refers to gives permission. 5059 5060 K. For any section Entitled "Acknowledgements" or "Dedications", 5061 Preserve the Title of the section, and preserve in the 5062 section all the substance and tone of each of the contributor 5063 acknowledgements and/or dedications given therein. 5064 5065 L. Preserve all the Invariant Sections of the Document, 5066 unaltered in their text and in their titles. Section numbers 5067 or the equivalent are not considered part of the section 5068 titles. 5069 5070 M. Delete any section Entitled "Endorsements". Such a section 5071 may not be included in the Modified Version. 5072 5073 N. Do not retitle any existing section to be Entitled 5074 "Endorsements" or to conflict in title with any Invariant 5075 Section. 5076 5077 O. Preserve any Warranty Disclaimers. 5078 5079 If the Modified Version includes new front-matter sections or 5080 appendices that qualify as Secondary Sections and contain no 5081 material copied from the Document, you may at your option 5082 designate some or all of these sections as invariant. To do this, 5083 add their titles to the list of Invariant Sections in the Modified 5084 Version's license notice. These titles must be distinct from any 5085 other section titles. 5086 5087 You may add a section Entitled "Endorsements", provided it contains 5088 nothing but endorsements of your Modified Version by various 5089 parties--for example, statements of peer review or that the text 5090 has been approved by an organization as the authoritative 5091 definition of a standard. 5092 5093 You may add a passage of up to five words as a Front-Cover Text, 5094 and a passage of up to 25 words as a Back-Cover Text, to the end 5095 of the list of Cover Texts in the Modified Version. Only one 5096 passage of Front-Cover Text and one of Back-Cover Text may be 5097 added by (or through arrangements made by) any one entity. If the 5098 Document already includes a cover text for the same cover, 5099 previously added by you or by arrangement made by the same entity 5100 you are acting on behalf of, you may not add another; but you may 5101 replace the old one, on explicit permission from the previous 5102 publisher that added the old one. 5103 5104 The author(s) and publisher(s) of the Document do not by this 5105 License give permission to use their names for publicity for or to 5106 assert or imply endorsement of any Modified Version. 5107 5108 5. COMBINING DOCUMENTS 5109 5110 You may combine the Document with other documents released under 5111 this License, under the terms defined in section 4 above for 5112 modified versions, provided that you include in the combination 5113 all of the Invariant Sections of all of the original documents, 5114 unmodified, and list them all as Invariant Sections of your 5115 combined work in its license notice, and that you preserve all 5116 their Warranty Disclaimers. 5117 5118 The combined work need only contain one copy of this License, and 5119 multiple identical Invariant Sections may be replaced with a single 5120 copy. If there are multiple Invariant Sections with the same name 5121 but different contents, make the title of each such section unique 5122 by adding at the end of it, in parentheses, the name of the 5123 original author or publisher of that section if known, or else a 5124 unique number. Make the same adjustment to the section titles in 5125 the list of Invariant Sections in the license notice of the 5126 combined work. 5127 5128 In the combination, you must combine any sections Entitled 5129 "History" in the various original documents, forming one section 5130 Entitled "History"; likewise combine any sections Entitled 5131 "Acknowledgements", and any sections Entitled "Dedications". You 5132 must delete all sections Entitled "Endorsements." 5133 5134 6. COLLECTIONS OF DOCUMENTS 5135 5136 You may make a collection consisting of the Document and other 5137 documents released under this License, and replace the individual 5138 copies of this License in the various documents with a single copy 5139 that is included in the collection, provided that you follow the 5140 rules of this License for verbatim copying of each of the 5141 documents in all other respects. 5142 5143 You may extract a single document from such a collection, and 5144 distribute it individually under this License, provided you insert 5145 a copy of this License into the extracted document, and follow 5146 this License in all other respects regarding verbatim copying of 5147 that document. 5148 5149 7. AGGREGATION WITH INDEPENDENT WORKS 5150 5151 A compilation of the Document or its derivatives with other 5152 separate and independent documents or works, in or on a volume of 5153 a storage or distribution medium, is called an "aggregate" if the 5154 copyright resulting from the compilation is not used to limit the 5155 legal rights of the compilation's users beyond what the individual 5156 works permit. When the Document is included in an aggregate, this 5157 License does not apply to the other works in the aggregate which 5158 are not themselves derivative works of the Document. 5159 5160 If the Cover Text requirement of section 3 is applicable to these 5161 copies of the Document, then if the Document is less than one half 5162 of the entire aggregate, the Document's Cover Texts may be placed 5163 on covers that bracket the Document within the aggregate, or the 5164 electronic equivalent of covers if the Document is in electronic 5165 form. Otherwise they must appear on printed covers that bracket 5166 the whole aggregate. 5167 5168 8. TRANSLATION 5169 5170 Translation is considered a kind of modification, so you may 5171 distribute translations of the Document under the terms of section 5172 4. Replacing Invariant Sections with translations requires special 5173 permission from their copyright holders, but you may include 5174 translations of some or all Invariant Sections in addition to the 5175 original versions of these Invariant Sections. You may include a 5176 translation of this License, and all the license notices in the 5177 Document, and any Warranty Disclaimers, provided that you also 5178 include the original English version of this License and the 5179 original versions of those notices and disclaimers. In case of a 5180 disagreement between the translation and the original version of 5181 this License or a notice or disclaimer, the original version will 5182 prevail. 5183 5184 If a section in the Document is Entitled "Acknowledgements", 5185 "Dedications", or "History", the requirement (section 4) to 5186 Preserve its Title (section 1) will typically require changing the 5187 actual title. 5188 5189 9. TERMINATION 5190 5191 You may not copy, modify, sublicense, or distribute the Document 5192 except as expressly provided for under this License. Any other 5193 attempt to copy, modify, sublicense or distribute the Document is 5194 void, and will automatically terminate your rights under this 5195 License. However, parties who have received copies, or rights, 5196 from you under this License will not have their licenses 5197 terminated so long as such parties remain in full compliance. 5198 5199 10. FUTURE REVISIONS OF THIS LICENSE 5200 5201 The Free Software Foundation may publish new, revised versions of 5202 the GNU Free Documentation License from time to time. Such new 5203 versions will be similar in spirit to the present version, but may 5204 differ in detail to address new problems or concerns. See 5205 `http://www.gnu.org/copyleft/'. 5206 5207 Each version of the License is given a distinguishing version 5208 number. If the Document specifies that a particular numbered 5209 version of this License "or any later version" applies to it, you 5210 have the option of following the terms and conditions either of 5211 that specified version or of any later version that has been 5212 published (not as a draft) by the Free Software Foundation. If 5213 the Document does not specify a version number of this License, 5214 you may choose any version ever published (not as a draft) by the 5215 Free Software Foundation. 5216 5217ADDENDUM: How to use this License for your documents 5218==================================================== 5219 5220To use this License in a document you have written, include a copy of 5221the License in the document and put the following copyright and license 5222notices just after the title page: 5223 5224 Copyright (C) YEAR YOUR NAME. 5225 Permission is granted to copy, distribute and/or modify this document 5226 under the terms of the GNU Free Documentation License, Version 1.2 5227 or any later version published by the Free Software Foundation; 5228 with no Invariant Sections, no Front-Cover Texts, and no Back-Cover 5229 Texts. A copy of the license is included in the section entitled ``GNU 5230 Free Documentation License''. 5231 5232 If you have Invariant Sections, Front-Cover Texts and Back-Cover 5233Texts, replace the "with...Texts." line with this: 5234 5235 with the Invariant Sections being LIST THEIR TITLES, with 5236 the Front-Cover Texts being LIST, and with the Back-Cover Texts 5237 being LIST. 5238 5239 If you have Invariant Sections without Cover Texts, or some other 5240combination of the three, merge those two alternatives to suit the 5241situation. 5242 5243 If your document contains nontrivial examples of program code, we 5244recommend releasing these examples in parallel under your choice of 5245free software license, such as the GNU General Public License, to 5246permit their use in free software. 5247 5248 5249File: standards.info, Node: Index, Prev: Copying This Manual, Up: Top 5250 5251Index 5252***** 5253 5254[index] 5255* Menu: 5256 5257* #endif, commenting: Comments. (line 60) 5258* --help option: Command-Line Interfaces. 5259 (line 124) 5260* --version option: Command-Line Interfaces. 5261 (line 37) 5262* -Wall compiler option: Syntactic Conventions. 5263 (line 10) 5264* accepting contributions: Contributions. (line 6) 5265* address for bug reports: Command-Line Interfaces. 5266 (line 130) 5267* ANSI C standard: Standard C. (line 6) 5268* arbitrary limits on data: Semantics. (line 6) 5269* ASCII characters: Character Set. (line 6) 5270* autoconf: System Portability. (line 23) 5271* avoiding proprietary code: Reading Non-Free Code. 5272 (line 6) 5273* behavior, dependent on program's name: User Interfaces. (line 6) 5274* binary packages: Install Command Categories. 5275 (line 80) 5276* bindir: Directory Variables. (line 54) 5277* braces, in C source: Formatting. (line 6) 5278* bug reports: Command-Line Interfaces. 5279 (line 130) 5280* canonical name of a program: Command-Line Interfaces. 5281 (line 44) 5282* casting pointers to integers: CPU Portability. (line 90) 5283* CGI programs, standard options for: Command-Line Interfaces. 5284 (line 31) 5285* change logs: Change Logs. (line 6) 5286* change logs, conditional changes: Conditional Changes. (line 6) 5287* change logs, style: Style of Change Logs. 5288 (line 6) 5289* character set: Character Set. (line 6) 5290* command-line arguments, decoding: Semantics. (line 46) 5291* command-line interface: Command-Line Interfaces. 5292 (line 6) 5293* commenting: Comments. (line 6) 5294* compatibility with C and POSIX standards: Compatibility. (line 6) 5295* compiler warnings: Syntactic Conventions. 5296 (line 10) 5297* conditional changes, and change logs: Conditional Changes. (line 6) 5298* conditionals, comments for: Comments. (line 60) 5299* configure: Configuration. (line 6) 5300* control-L: Formatting. (line 114) 5301* conventions for makefiles: Makefile Conventions. 5302 (line 6) 5303* corba: Graphical Interfaces. 5304 (line 16) 5305* credits for manuals: Manual Credits. (line 6) 5306* data types, and portability: CPU Portability. (line 6) 5307* declaration for system functions: System Functions. (line 21) 5308* DESTDIR: DESTDIR. (line 6) 5309* documentation: Documentation. (line 6) 5310* doschk: Names. (line 38) 5311* downloading this manual: Preface. (line 17) 5312* encodings: Character Set. (line 6) 5313* error messages: Semantics. (line 19) 5314* error messages, formatting: Errors. (line 6) 5315* exec_prefix: Directory Variables. (line 36) 5316* expressions, splitting: Formatting. (line 77) 5317* FDL, GNU Free Documentation License: GNU Free Documentation License. 5318 (line 6) 5319* file usage: File Usage. (line 6) 5320* file-name limitations: Names. (line 38) 5321* formatting error messages: Errors. (line 6) 5322* formatting source code: Formatting. (line 6) 5323* formfeed: Formatting. (line 114) 5324* function argument, declaring: Syntactic Conventions. 5325 (line 6) 5326* function prototypes: Standard C. (line 17) 5327* getopt: Command-Line Interfaces. 5328 (line 6) 5329* gettext: Internationalization. 5330 (line 6) 5331* gnome: Graphical Interfaces. 5332 (line 16) 5333* graphical user interface: Graphical Interfaces. 5334 (line 6) 5335* grave accent: Quote Characters. (line 6) 5336* gtk+: Graphical Interfaces. 5337 (line 6) 5338* GUILE: Source Language. (line 38) 5339* implicit int: Syntactic Conventions. 5340 (line 6) 5341* impossible conditions: Semantics. (line 70) 5342* installations, staged: DESTDIR. (line 6) 5343* internationalization: Internationalization. 5344 (line 6) 5345* left quote: Quote Characters. (line 6) 5346* legal aspects: Legal Issues. (line 6) 5347* legal papers: Contributions. (line 6) 5348* libexecdir: Directory Variables. (line 67) 5349* libraries: Libraries. (line 6) 5350* library functions, and portability: System Functions. (line 6) 5351* license for manuals: License for Manuals. (line 6) 5352* lint: Syntactic Conventions. 5353 (line 109) 5354* locale-specific quote characters: Quote Characters. (line 6) 5355* long option names: Option Table. (line 6) 5356* long-named options: Command-Line Interfaces. 5357 (line 12) 5358* makefile, conventions for: Makefile Conventions. 5359 (line 6) 5360* malloc return value: Semantics. (line 25) 5361* man pages: Man Pages. (line 6) 5362* manual structure: Manual Structure Details. 5363 (line 6) 5364* memory allocation failure: Semantics. (line 25) 5365* memory usage: Memory Usage. (line 6) 5366* message text, and internationalization: Internationalization. 5367 (line 29) 5368* mmap: Mmap. (line 6) 5369* multiple variables in a line: Syntactic Conventions. 5370 (line 35) 5371* names of variables, functions, and files: Names. (line 6) 5372* NEWS file: NEWS File. (line 6) 5373* non-ASCII characters: Character Set. (line 6) 5374* non-POSIX systems, and portability: System Portability. (line 32) 5375* non-standard extensions: Using Extensions. (line 6) 5376* NUL characters: Semantics. (line 11) 5377* open brace: Formatting. (line 6) 5378* optional features, configure-time: Configuration. (line 83) 5379* options for compatibility: Compatibility. (line 14) 5380* options, standard command-line: Command-Line Interfaces. 5381 (line 31) 5382* output device and program's behavior: User Interfaces. (line 13) 5383* packaging: Releases. (line 6) 5384* PATH_INFO, specifying standard options as: Command-Line Interfaces. 5385 (line 31) 5386* portability, and data types: CPU Portability. (line 6) 5387* portability, and library functions: System Functions. (line 6) 5388* portability, between system types: System Portability. (line 6) 5389* POSIX compatibility: Compatibility. (line 6) 5390* POSIXLY_CORRECT, environment variable: Compatibility. (line 21) 5391* post-installation commands: Install Command Categories. 5392 (line 6) 5393* pre-installation commands: Install Command Categories. 5394 (line 6) 5395* prefix: Directory Variables. (line 26) 5396* program configuration: Configuration. (line 6) 5397* program design: Design Advice. (line 6) 5398* program name and its behavior: User Interfaces. (line 6) 5399* program's canonical name: Command-Line Interfaces. 5400 (line 44) 5401* programming languages: Source Language. (line 6) 5402* proprietary programs: Reading Non-Free Code. 5403 (line 6) 5404* quote characters: Quote Characters. (line 6) 5405* README file: Releases. (line 21) 5406* references to non-free material: References. (line 6) 5407* releasing: Managing Releases. (line 6) 5408* sbindir: Directory Variables. (line 60) 5409* signal handling: Semantics. (line 59) 5410* spaces before open-paren: Formatting. (line 71) 5411* staged installs: DESTDIR. (line 6) 5412* standard command-line options: Command-Line Interfaces. 5413 (line 31) 5414* standards for makefiles: Makefile Conventions. 5415 (line 6) 5416* string library functions: System Functions. (line 55) 5417* syntactic conventions: Syntactic Conventions. 5418 (line 6) 5419* table of long options: Option Table. (line 6) 5420* temporary files: Semantics. (line 84) 5421* temporary variables: Syntactic Conventions. 5422 (line 23) 5423* texinfo.tex, in a distribution: Releases. (line 70) 5424* TMPDIR environment variable: Semantics. (line 84) 5425* trademarks: Trademarks. (line 6) 5426* where to obtain standards.texi: Preface. (line 17) 5427 5428 5429 5430Tag Table: 5431Node: Top792 5432Node: Preface2039 5433Node: Legal Issues4159 5434Node: Reading Non-Free Code4626 5435Node: Contributions6356 5436Node: Trademarks8594 5437Node: Design Advice10229 5438Node: Source Language10817 5439Node: Compatibility12829 5440Node: Using Extensions14457 5441Node: Standard C16033 5442Node: Conditional Compilation18436 5443Node: Program Behavior19834 5444Node: Non-GNU Standards20881 5445Node: Semantics23162 5446Node: Libraries27881 5447Node: Errors29126 5448Node: User Interfaces31619 5449Node: Graphical Interfaces33224 5450Node: Command-Line Interfaces34260 5451Node: Option Table40717 5452Node: Memory Usage55658 5453Node: File Usage56689 5454Node: Writing C57439 5455Node: Formatting58405 5456Node: Comments62484 5457Node: Syntactic Conventions66036 5458Node: Names69498 5459Node: System Portability71710 5460Node: CPU Portability74600 5461Node: System Functions78512 5462Node: Internationalization83709 5463Node: Character Set87703 5464Node: Quote Characters88516 5465Node: Mmap90036 5466Node: Documentation90744 5467Node: GNU Manuals91849 5468Node: Doc Strings and Manuals97587 5469Node: Manual Structure Details99140 5470Node: License for Manuals100558 5471Node: Manual Credits101532 5472Node: Printed Manuals101925 5473Node: NEWS File102611 5474Node: Change Logs103289 5475Node: Change Log Concepts104043 5476Node: Style of Change Logs106132 5477Node: Simple Changes108632 5478Node: Conditional Changes110074 5479Node: Indicating the Part Changed111496 5480Node: Man Pages112023 5481Node: Reading other Manuals114335 5482Node: Managing Releases115126 5483Node: Configuration115889 5484Node: Makefile Conventions123609 5485Node: Makefile Basics124491 5486Node: Utilities in Makefiles127665 5487Node: Command Variables129810 5488Node: DESTDIR133032 5489Node: Directory Variables135181 5490Node: Standard Targets149674 5491Ref: Standard Targets-Footnote-1163189 5492Node: Install Command Categories163289 5493Node: Releases167822 5494Node: References171749 5495Node: Copying This Manual176489 5496Node: GNU Free Documentation License176725 5497Node: Index199126 5498 5499End Tag Table 5500