-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathstandards.info
5727 lines (4410 loc) · 218 KB
/
standards.info
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
This is standards.info, produced by makeinfo version 4.13 from
standards.texi.
INFO-DIR-SECTION GNU organization
START-INFO-DIR-ENTRY
* Standards: (standards). GNU coding standards.
END-INFO-DIR-ENTRY
The GNU coding standards, last updated September 14, 2009.
Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software
Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled "GNU
Free Documentation License".
File: standards.info, Node: Top, Next: Preface, Prev: (dir), Up: (dir)
Version
*******
The GNU coding standards, last updated September 14, 2009.
Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software
Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled "GNU
Free Documentation License".
* Menu:
* Preface:: About the GNU Coding Standards.
* Legal Issues:: Keeping free software free.
* Design Advice:: General program design.
* Program Behavior:: Program behavior for all programs
* Writing C:: Making the best use of C.
* Documentation:: Documenting programs.
* Managing Releases:: The release process.
* References:: Mentioning non-free software or documentation.
* GNU Free Documentation License:: Copying and sharing this manual.
* Index::
File: standards.info, Node: Preface, Next: Legal Issues, Prev: Top, Up: Top
1 About the GNU Coding Standards
********************************
The GNU Coding Standards were written by Richard Stallman and other GNU
Project volunteers. Their purpose is to make the GNU system clean,
consistent, and easy to install. This document can also be read as a
guide to writing portable, robust and reliable programs. It focuses on
programs written in C, but many of the rules and principles are useful
even if you write in another programming language. The rules often
state reasons for writing in a certain way.
This release of the GNU Coding Standards was last updated September
14, 2009.
If you did not obtain this file directly from the GNU project and
recently, please check for a newer version. You can get the GNU Coding
Standards from the GNU web server in many different formats, including
the Texinfo source, PDF, HTML, DVI, plain text, and more, at:
`http://www.gnu.org/prep/standards/'.
Corrections or suggestions for this document should be sent to
<[email protected]>. If you make a suggestion, please include a
suggested new wording for it; our time is limited. We prefer a context
diff to the `standards.texi' or `make-stds.texi' files, but if you
don't have those files, please mail your suggestion anyway.
These standards cover the minimum of what is important when writing a
GNU package. Likely, the need for additional standards will come up.
Sometimes, you might suggest that such standards be added to this
document. If you think your standards would be generally useful, please
do suggest them.
You should also set standards for your package on many questions not
addressed or not firmly specified here. The most important point is to
be self-consistent--try to stick to the conventions you pick, and try
to document them as much as possible. That way, your program will be
more maintainable by others.
The GNU Hello program serves as an example of how to follow the GNU
coding standards for a trivial program.
`http://www.gnu.org/software/hello/hello.html'.
File: standards.info, Node: Legal Issues, Next: Design Advice, Prev: Preface, Up: Top
2 Keeping Free Software Free
****************************
This chapter discusses how you can make sure that GNU software avoids
legal difficulties, and other related issues.
* Menu:
* Reading Non-Free Code:: Referring to proprietary programs.
* Contributions:: Accepting contributions.
* Trademarks:: How we deal with trademark issues.
File: standards.info, Node: Reading Non-Free Code, Next: Contributions, Up: Legal Issues
2.1 Referring to Proprietary Programs
=====================================
Don't in any circumstances refer to Unix source code for or during your
work on GNU! (Or to any other proprietary programs.)
If you have a vague recollection of the internals of a Unix program,
this does not absolutely mean you can't write an imitation of it, but
do try to organize the imitation internally along different lines,
because this is likely to make the details of the Unix version
irrelevant and dissimilar to your results.
For example, Unix utilities were generally optimized to minimize
memory use; if you go for speed instead, your program will be very
different. You could keep the entire input file in memory and scan it
there instead of using stdio. Use a smarter algorithm discovered more
recently than the Unix program. Eliminate use of temporary files. Do
it in one pass instead of two (we did this in the assembler).
Or, on the contrary, emphasize simplicity instead of speed. For some
applications, the speed of today's computers makes simpler algorithms
adequate.
Or go for generality. For example, Unix programs often have static
tables or fixed-size strings, which make for arbitrary limits; use
dynamic allocation instead. Make sure your program handles NULs and
other funny characters in the input files. Add a programming language
for extensibility and write part of the program in that language.
Or turn some parts of the program into independently usable
libraries. Or use a simple garbage collector instead of tracking
precisely when to free memory, or use a new GNU facility such as
obstacks.
File: standards.info, Node: Contributions, Next: Trademarks, Prev: Reading Non-Free Code, Up: Legal Issues
2.2 Accepting Contributions
===========================
If the program you are working on is copyrighted by the Free Software
Foundation, then when someone else sends you a piece of code to add to
the program, we need legal papers to use it--just as we asked you to
sign papers initially. _Each_ person who makes a nontrivial
contribution to a program must sign some sort of legal papers in order
for us to have clear title to the program; the main author alone is not
enough.
So, before adding in any contributions from other people, please tell
us, so we can arrange to get the papers. Then wait until we tell you
that we have received the signed papers, before you actually use the
contribution.
This applies both before you release the program and afterward. If
you receive diffs to fix a bug, and they make significant changes, we
need legal papers for that change.
This also applies to comments and documentation files. For copyright
law, comments and code are just text. Copyright applies to all kinds of
text, so we need legal papers for all kinds.
We know it is frustrating to ask for legal papers; it's frustrating
for us as well. But if you don't wait, you are going out on a limb--for
example, what if the contributor's employer won't sign a disclaimer?
You might have to take that code out again!
You don't need papers for changes of a few lines here or there, since
they are not significant for copyright purposes. Also, you don't need
papers if all you get from the suggestion is some ideas, not actual code
which you use. For example, if someone sent you one implementation, but
you write a different implementation of the same idea, you don't need to
get papers.
The very worst thing is if you forget to tell us about the other
contributor. We could be very embarrassed in court some day as a
result.
We have more detailed advice for maintainers of programs; if you have
reached the stage of actually maintaining a program for GNU (whether
released or not), please ask us for a copy. It is also available
online for your perusal: `http://www.gnu.org/prep/maintain/'.
File: standards.info, Node: Trademarks, Prev: Contributions, Up: Legal Issues
2.3 Trademarks
==============
Please do not include any trademark acknowledgements in GNU software
packages or documentation.
Trademark acknowledgements are the statements that such-and-such is a
trademark of so-and-so. The GNU Project has no objection to the basic
idea of trademarks, but these acknowledgements feel like kowtowing, and
there is no legal requirement for them, so we don't use them.
What is legally required, as regards other people's trademarks, is to
avoid using them in ways which a reader might reasonably understand as
naming or labeling our own programs or activities. For example, since
"Objective C" is (or at least was) a trademark, we made sure to say
that we provide a "compiler for the Objective C language" rather than
an "Objective C compiler". The latter would have been meant as a
shorter way of saying the former, but it does not explicitly state the
relationship, so it could be misinterpreted as using "Objective C" as a
label for the compiler rather than for the language.
Please don't use "win" as an abbreviation for Microsoft Windows in
GNU software or documentation. In hacker terminology, calling
something a "win" is a form of praise. If you wish to praise Microsoft
Windows when speaking on your own, by all means do so, but not in GNU
software. Usually we write the name "Windows" in full, but when
brevity is very important (as in file names and sometimes symbol
names), we abbreviate it to "w". For instance, the files and functions
in Emacs that deal with Windows start with `w32'.
File: standards.info, Node: Design Advice, Next: Program Behavior, Prev: Legal Issues, Up: Top
3 General Program Design
************************
This chapter discusses some of the issues you should take into account
when designing your program.
* Menu:
* Source Language:: Which languages to use.
* Compatibility:: Compatibility with other implementations.
* Using Extensions:: Using non-standard features.
* Standard C:: Using standard C features.
* Conditional Compilation:: Compiling code only if a conditional is true.
File: standards.info, Node: Source Language, Next: Compatibility, Up: Design Advice
3.1 Which Languages to Use
==========================
When you want to use a language that gets compiled and runs at high
speed, the best language to use is C. Using another language is like
using a non-standard feature: it will cause trouble for users. Even if
GCC supports the other language, users may find it inconvenient to have
to install the compiler for that other language in order to build your
program. For example, if you write your program in C++, people will
have to install the GNU C++ compiler in order to compile your program.
C has one other advantage over C++ and other compiled languages: more
people know C, so more people will find it easy to read and modify the
program if it is written in C.
So in general it is much better to use C, rather than the comparable
alternatives.
But there are two exceptions to that conclusion:
* It is no problem to use another language to write a tool
specifically intended for use with that language. That is because
the only people who want to build the tool will be those who have
installed the other language anyway.
* If an application is of interest only to a narrow part of the
community, then the question of which language it is written in
has less effect on other people, so you may as well please
yourself.
Many programs are designed to be extensible: they include an
interpreter for a language that is higher level than C. Often much of
the program is written in that language, too. The Emacs editor
pioneered this technique.
The standard extensibility interpreter for GNU software is Guile
(`http://www.gnu.org/software/guile/'), which implements the language
Scheme (an especially clean and simple dialect of Lisp). Guile also
includes bindings for GTK+/GNOME, making it practical to write modern
GUI functionality within Guile. We don't reject programs written in
other "scripting languages" such as Perl and Python, but using Guile is
very important for the overall consistency of the GNU system.
File: standards.info, Node: Compatibility, Next: Using Extensions, Prev: Source Language, Up: Design Advice
3.2 Compatibility with Other Implementations
============================================
With occasional exceptions, utility programs and libraries for GNU
should be upward compatible with those in Berkeley Unix, and upward
compatible with Standard C if Standard C specifies their behavior, and
upward compatible with POSIX if POSIX specifies their behavior.
When these standards conflict, it is useful to offer compatibility
modes for each of them.
Standard C and POSIX prohibit many kinds of extensions. Feel free
to make the extensions anyway, and include a `--ansi', `--posix', or
`--compatible' option to turn them off. However, if the extension has
a significant chance of breaking any real programs or scripts, then it
is not really upward compatible. So you should try to redesign its
interface to make it upward compatible.
Many GNU programs suppress extensions that conflict with POSIX if the
environment variable `POSIXLY_CORRECT' is defined (even if it is
defined with a null value). Please make your program recognize this
variable if appropriate.
When a feature is used only by users (not by programs or command
files), and it is done poorly in Unix, feel free to replace it
completely with something totally different and better. (For example,
`vi' is replaced with Emacs.) But it is nice to offer a compatible
feature as well. (There is a free `vi' clone, so we offer it.)
Additional useful features are welcome regardless of whether there
is any precedent for them.
File: standards.info, Node: Using Extensions, Next: Standard C, Prev: Compatibility, Up: Design Advice
3.3 Using Non-standard Features
===============================
Many GNU facilities that already exist support a number of convenient
extensions over the comparable Unix facilities. Whether to use these
extensions in implementing your program is a difficult question.
On the one hand, using the extensions can make a cleaner program.
On the other hand, people will not be able to build the program unless
the other GNU tools are available. This might cause the program to
work on fewer kinds of machines.
With some extensions, it might be easy to provide both alternatives.
For example, you can define functions with a "keyword" `INLINE' and
define that as a macro to expand into either `inline' or nothing,
depending on the compiler.
In general, perhaps it is best not to use the extensions if you can
straightforwardly do without them, but to use the extensions if they
are a big improvement.
An exception to this rule are the large, established programs (such
as Emacs) which run on a great variety of systems. Using GNU
extensions in such programs would make many users unhappy, so we don't
do that.
Another exception is for programs that are used as part of
compilation: anything that must be compiled with other compilers in
order to bootstrap the GNU compilation facilities. If these require
the GNU compiler, then no one can compile them without having them
installed already. That would be extremely troublesome in certain
cases.
File: standards.info, Node: Standard C, Next: Conditional Compilation, Prev: Using Extensions, Up: Design Advice
3.4 Standard C and Pre-Standard C
=================================
1989 Standard C is widespread enough now that it is ok to use its
features in new programs. There is one exception: do not ever use the
"trigraph" feature of Standard C.
1999 Standard C is not widespread yet, so please do not require its
features in programs. It is ok to use its features if they are present.
However, it is easy to support pre-standard compilers in most
programs, so if you know how to do that, feel free. If a program you
are maintaining has such support, you should try to keep it working.
To support pre-standard C, instead of writing function definitions in
standard prototype form,
int
foo (int x, int y)
...
write the definition in pre-standard style like this,
int
foo (x, y)
int x, y;
...
and use a separate declaration to specify the argument prototype:
int foo (int, int);
You need such a declaration anyway, in a header file, to get the
benefit of prototypes in all the files where the function is called.
And once you have the declaration, you normally lose nothing by writing
the function definition in the pre-standard style.
This technique does not work for integer types narrower than `int'.
If you think of an argument as being of a type narrower than `int',
declare it as `int' instead.
There are a few special cases where this technique is hard to use.
For example, if a function argument needs to hold the system type
`dev_t', you run into trouble, because `dev_t' is shorter than `int' on
some machines; but you cannot use `int' instead, because `dev_t' is
wider than `int' on some machines. There is no type you can safely use
on all machines in a non-standard definition. The only way to support
non-standard C and pass such an argument is to check the width of
`dev_t' using Autoconf and choose the argument type accordingly. This
may not be worth the trouble.
In order to support pre-standard compilers that do not recognize
prototypes, you may want to use a preprocessor macro like this:
/* Declare the prototype for a general external function. */
#if defined (__STDC__) || defined (WINDOWSNT)
#define P_(proto) proto
#else
#define P_(proto) ()
#endif
File: standards.info, Node: Conditional Compilation, Prev: Standard C, Up: Design Advice
3.5 Conditional Compilation
===========================
When supporting configuration options already known when building your
program we prefer using `if (... )' over conditional compilation, as in
the former case the compiler is able to perform more extensive checking
of all possible code paths.
For example, please write
if (HAS_FOO)
...
else
...
instead of:
#ifdef HAS_FOO
...
#else
...
#endif
A modern compiler such as GCC will generate exactly the same code in
both cases, and we have been using similar techniques with good success
in several projects. Of course, the former method assumes that
`HAS_FOO' is defined as either 0 or 1.
While this is not a silver bullet solving all portability problems,
and is not always appropriate, following this policy would have saved
GCC developers many hours, or even days, per year.
In the case of function-like macros like `REVERSIBLE_CC_MODE' in GCC
which cannot be simply used in `if( ...)' statements, there is an easy
workaround. Simply introduce another macro `HAS_REVERSIBLE_CC_MODE' as
in the following example:
#ifdef REVERSIBLE_CC_MODE
#define HAS_REVERSIBLE_CC_MODE 1
#else
#define HAS_REVERSIBLE_CC_MODE 0
#endif
File: standards.info, Node: Program Behavior, Next: Writing C, Prev: Design Advice, Up: Top
4 Program Behavior for All Programs
***********************************
This chapter describes conventions for writing robust software. It
also describes general standards for error messages, the command line
interface, and how libraries should behave.
* Menu:
* Non-GNU Standards:: We consider standards such as POSIX;
we don't "obey" them.
* Semantics:: Writing robust programs.
* Libraries:: Library behavior.
* Errors:: Formatting error messages.
* User Interfaces:: Standards about interfaces generally.
* Graphical Interfaces:: Standards for graphical interfaces.
* Command-Line Interfaces:: Standards for command line interfaces.
* Option Table:: Table of long options.
* OID Allocations:: Table of OID slots for GNU.
* Memory Usage:: When and how to care about memory needs.
* File Usage:: Which files to use, and where.
File: standards.info, Node: Non-GNU Standards, Next: Semantics, Up: Program Behavior
4.1 Non-GNU Standards
=====================
The GNU Project regards standards published by other organizations as
suggestions, not orders. We consider those standards, but we do not
"obey" them. In developing a GNU program, you should implement an
outside standard's specifications when that makes the GNU system better
overall in an objective sense. When it doesn't, you shouldn't.
In most cases, following published standards is convenient for
users--it means that their programs or scripts will work more portably.
For instance, GCC implements nearly all the features of Standard C as
specified by that standard. C program developers would be unhappy if
it did not. And GNU utilities mostly follow specifications of POSIX.2;
shell script writers and users would be unhappy if our programs were
incompatible.
But we do not follow either of these specifications rigidly, and
there are specific points on which we decided not to follow them, so as
to make the GNU system better for users.
For instance, Standard C says that nearly all extensions to C are
prohibited. How silly! GCC implements many extensions, some of which
were later adopted as part of the standard. If you want these
constructs to give an error message as "required" by the standard, you
must specify `--pedantic', which was implemented only so that we can
say "GCC is a 100% implementation of the standard," not because there
is any reason to actually use it.
POSIX.2 specifies that `df' and `du' must output sizes by default in
units of 512 bytes. What users want is units of 1k, so that is what we
do by default. If you want the ridiculous behavior "required" by
POSIX, you must set the environment variable `POSIXLY_CORRECT' (which
was originally going to be named `POSIX_ME_HARDER').
GNU utilities also depart from the letter of the POSIX.2
specification when they support long-named command-line options, and
intermixing options with ordinary arguments. This minor
incompatibility with POSIX is never a problem in practice, and it is
very useful.
In particular, don't reject a new feature, or remove an old one,
merely because a standard says it is "forbidden" or "deprecated."
File: standards.info, Node: Semantics, Next: Libraries, Prev: Non-GNU Standards, Up: Program Behavior
4.2 Writing Robust Programs
===========================
Avoid arbitrary limits on the length or number of _any_ data structure,
including file names, lines, files, and symbols, by allocating all data
structures dynamically. In most Unix utilities, "long lines are
silently truncated". This is not acceptable in a GNU utility.
Utilities reading files should not drop NUL characters, or any other
nonprinting characters _including those with codes above 0177_. The
only sensible exceptions would be utilities specifically intended for
interface to certain types of terminals or printers that can't handle
those characters. Whenever possible, try to make programs work
properly with sequences of bytes that represent multibyte characters,
using encodings such as UTF-8 and others.
Check every system call for an error return, unless you know you
wish to ignore errors. Include the system error text (from `perror' or
equivalent) in _every_ error message resulting from a failing system
call, as well as the name of the file if any and the name of the
utility. Just "cannot open foo.c" or "stat failed" is not sufficient.
Check every call to `malloc' or `realloc' to see if it returned
zero. Check `realloc' even if you are making the block smaller; in a
system that rounds block sizes to a power of 2, `realloc' may get a
different block if you ask for less space.
In Unix, `realloc' can destroy the storage block if it returns zero.
GNU `realloc' does not have this bug: if it fails, the original block
is unchanged. Feel free to assume the bug is fixed. If you wish to
run your program on Unix, and wish to avoid lossage in this case, you
can use the GNU `malloc'.
You must expect `free' to alter the contents of the block that was
freed. Anything you want to fetch from the block, you must fetch before
calling `free'.
If `malloc' fails in a noninteractive program, make that a fatal
error. In an interactive program (one that reads commands from the
user), it is better to abort the command and return to the command
reader loop. This allows the user to kill other processes to free up
virtual memory, and then try the command again.
Use `getopt_long' to decode arguments, unless the argument syntax
makes this unreasonable.
When static storage is to be written in during program execution, use
explicit C code to initialize it. Reserve C initialized declarations
for data that will not be changed.
Try to avoid low-level interfaces to obscure Unix data structures
(such as file directories, utmp, or the layout of kernel memory), since
these are less likely to work compatibly. If you need to find all the
files in a directory, use `readdir' or some other high-level interface.
These are supported compatibly by GNU.
The preferred signal handling facilities are the BSD variant of
`signal', and the POSIX `sigaction' function; the alternative USG
`signal' interface is an inferior design.
Nowadays, using the POSIX signal functions may be the easiest way to
make a program portable. If you use `signal', then on GNU/Linux
systems running GNU libc version 1, you should include `bsd/signal.h'
instead of `signal.h', so as to get BSD behavior. It is up to you
whether to support systems where `signal' has only the USG behavior, or
give up on them.
In error checks that detect "impossible" conditions, just abort.
There is usually no point in printing any message. These checks
indicate the existence of bugs. Whoever wants to fix the bugs will have
to read the source code and run a debugger. So explain the problem with
comments in the source. The relevant data will be in variables, which
are easy to examine with the debugger, so there is no point moving them
elsewhere.
Do not use a count of errors as the exit status for a program.
_That does not work_, because exit status values are limited to 8 bits
(0 through 255). A single run of the program might have 256 errors; if
you try to return 256 as the exit status, the parent process will see 0
as the status, and it will appear that the program succeeded.
If you make temporary files, check the `TMPDIR' environment
variable; if that variable is defined, use the specified directory
instead of `/tmp'.
In addition, be aware that there is a possible security problem when
creating temporary files in world-writable directories. In C, you can
avoid this problem by creating temporary files in this manner:
fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0600);
or by using the `mkstemps' function from libiberty.
In bash, use `set -C' to avoid this problem.
File: standards.info, Node: Libraries, Next: Errors, Prev: Semantics, Up: Program Behavior
4.3 Library Behavior
====================
Try to make library functions reentrant. If they need to do dynamic
storage allocation, at least try to avoid any nonreentrancy aside from
that of `malloc' itself.
Here are certain name conventions for libraries, to avoid name
conflicts.
Choose a name prefix for the library, more than two characters long.
All external function and variable names should start with this prefix.
In addition, there should only be one of these in any given library
member. This usually means putting each one in a separate source file.
An exception can be made when two external symbols are always used
together, so that no reasonable program could use one without the
other; then they can both go in the same file.
External symbols that are not documented entry points for the user
should have names beginning with `_'. The `_' should be followed by
the chosen name prefix for the library, to prevent collisions with
other libraries. These can go in the same files with user entry points
if you like.
Static functions and variables can be used as you like and need not
fit any naming convention.
File: standards.info, Node: Errors, Next: User Interfaces, Prev: Libraries, Up: Program Behavior
4.4 Formatting Error Messages
=============================
Error messages from compilers should look like this:
SOURCE-FILE-NAME:LINENO: MESSAGE
If you want to mention the column number, use one of these formats:
SOURCE-FILE-NAME:LINENO:COLUMN: MESSAGE
SOURCE-FILE-NAME:LINENO.COLUMN: MESSAGE
Line numbers should start from 1 at the beginning of the file, and
column numbers should start from 1 at the beginning of the line. (Both
of these conventions are chosen for compatibility.) Calculate column
numbers assuming that space and all ASCII printing characters have
equal width, and assuming tab stops every 8 columns.
The error message can also give both the starting and ending
positions of the erroneous text. There are several formats so that you
can avoid redundant information such as a duplicate line number. Here
are the possible formats:
SOURCE-FILE-NAME:LINENO-1.COLUMN-1-LINENO-2.COLUMN-2: MESSAGE
SOURCE-FILE-NAME:LINENO-1.COLUMN-1-COLUMN-2: MESSAGE
SOURCE-FILE-NAME:LINENO-1-LINENO-2: MESSAGE
When an error is spread over several files, you can use this format:
FILE-1:LINENO-1.COLUMN-1-FILE-2:LINENO-2.COLUMN-2: MESSAGE
Error messages from other noninteractive programs should look like
this:
PROGRAM:SOURCE-FILE-NAME:LINENO: MESSAGE
when there is an appropriate source file, or like this:
PROGRAM: MESSAGE
when there is no relevant source file.
If you want to mention the column number, use this format:
PROGRAM:SOURCE-FILE-NAME:LINENO:COLUMN: MESSAGE
In an interactive program (one that is reading commands from a
terminal), it is better not to include the program name in an error
message. The place to indicate which program is running is in the
prompt or with the screen layout. (When the same program runs with
input from a source other than a terminal, it is not interactive and
would do best to print error messages using the noninteractive style.)
The string MESSAGE should not begin with a capital letter when it
follows a program name and/or file name, because that isn't the
beginning of a sentence. (The sentence conceptually starts at the
beginning of the line.) Also, it should not end with a period.
Error messages from interactive programs, and other messages such as
usage messages, should start with a capital letter. But they should not
end with a period.
File: standards.info, Node: User Interfaces, Next: Graphical Interfaces, Prev: Errors, Up: Program Behavior
4.5 Standards for Interfaces Generally
======================================
Please don't make the behavior of a utility depend on the name used to
invoke it. It is useful sometimes to make a link to a utility with a
different name, and that should not change what it does.
Instead, use a run time option or a compilation switch or both to
select among the alternate behaviors.
Likewise, please don't make the behavior of the program depend on the
type of output device it is used with. Device independence is an
important principle of the system's design; do not compromise it merely
to save someone from typing an option now and then. (Variation in error
message syntax when using a terminal is ok, because that is a side issue
that people do not depend on.)
If you think one behavior is most useful when the output is to a
terminal, and another is most useful when the output is a file or a
pipe, then it is usually best to make the default behavior the one that
is useful with output to a terminal, and have an option for the other
behavior.
Compatibility requires certain programs to depend on the type of
output device. It would be disastrous if `ls' or `sh' did not do so in
the way all users expect. In some of these cases, we supplement the
program with a preferred alternate version that does not depend on the
output device type. For example, we provide a `dir' program much like
`ls' except that its default output format is always multi-column
format.
File: standards.info, Node: Graphical Interfaces, Next: Command-Line Interfaces, Prev: User Interfaces, Up: Program Behavior
4.6 Standards for Graphical Interfaces
======================================
When you write a program that provides a graphical user interface,
please make it work with X Windows and the GTK+ toolkit unless the
functionality specifically requires some alternative (for example,
"displaying jpeg images while in console mode").
In addition, please provide a command-line interface to control the
functionality. (In many cases, the graphical user interface can be a
separate program which invokes the command-line program.) This is so
that the same jobs can be done from scripts.
Please also consider providing a CORBA interface (for use from
GNOME), a library interface (for use from C), and perhaps a
keyboard-driven console interface (for use by users from console mode).
Once you are doing the work to provide the functionality and the
graphical interface, these won't be much extra work.
File: standards.info, Node: Command-Line Interfaces, Next: Option Table, Prev: Graphical Interfaces, Up: Program Behavior
4.7 Standards for Command Line Interfaces
=========================================
It is a good idea to follow the POSIX guidelines for the command-line
options of a program. The easiest way to do this is to use `getopt' to
parse them. Note that the GNU version of `getopt' will normally permit
options anywhere among the arguments unless the special argument `--'
is used. This is not what POSIX specifies; it is a GNU extension.
Please define long-named options that are equivalent to the
single-letter Unix-style options. We hope to make GNU more user
friendly this way. This is easy to do with the GNU function
`getopt_long'.
One of the advantages of long-named options is that they can be
consistent from program to program. For example, users should be able
to expect the "verbose" option of any GNU program which has one, to be
spelled precisely `--verbose'. To achieve this uniformity, look at the
table of common long-option names when you choose the option names for
your program (*note Option Table::).
It is usually a good idea for file names given as ordinary arguments
to be input files only; any output files would be specified using
options (preferably `-o' or `--output'). Even if you allow an output
file name as an ordinary argument for compatibility, try to provide an
option as another way to specify it. This will lead to more consistency
among GNU utilities, and fewer idiosyncrasies for users to remember.
All programs should support two standard options: `--version' and
`--help'. CGI programs should accept these as command-line options,
and also if given as the `PATH_INFO'; for instance, visiting
`http://example.org/p.cgi/--help' in a browser should output the same
information as invoking `p.cgi --help' from the command line.
* Menu:
* --version:: The standard output for --version.
* --help:: The standard output for --help.
File: standards.info, Node: --version, Next: --help, Up: Command-Line Interfaces
4.7.1 `--version'
-----------------
The standard `--version' option should direct the program to print
information about its name, version, origin and legal status, all on
standard output, and then exit successfully. Other options and
arguments should be ignored once this is seen, and the program should
not perform its normal function.
The first line is meant to be easy for a program to parse; the
version number proper starts after the last space. In addition, it
contains the canonical name for this program, in this format:
GNU Emacs 19.30
The program's name should be a constant string; _don't_ compute it from
`argv[0]'. The idea is to state the standard or canonical name for the
program, not its file name. There are other ways to find out the
precise file name where a command is found in `PATH'.
If the program is a subsidiary part of a larger package, mention the
package name in parentheses, like this:
emacsserver (GNU Emacs) 19.30
If the package has a version number which is different from this
program's version number, you can mention the package version number
just before the close-parenthesis.
If you _need_ to mention the version numbers of libraries which are
distributed separately from the package which contains this program,
you can do so by printing an additional line of version info for each
library you want to mention. Use the same format for these lines as for
the first line.
Please do not mention all of the libraries that the program uses
"just for completeness"--that would produce a lot of unhelpful clutter.
Please mention library version numbers only if you find in practice that
they are very important to you in debugging.
The following line, after the version number line or lines, should
be a copyright notice. If more than one copyright notice is called
for, put each on a separate line.
Next should follow a line stating the license, preferably using one
of abbrevations below, and a brief statement that the program is free
software, and that users are free to copy and change it. Also mention
that there is no warranty, to the extent permitted by law. See
recommended wording below.
It is ok to finish the output with a list of the major authors of the
program, as a way of giving credit.
Here's an example of output that follows these rules:
GNU hello 2.3
Copyright (C) 2007 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
You should adapt this to your program, of course, filling in the
proper year, copyright holder, name of program, and the references to
distribution terms, and changing the rest of the wording as necessary.
This copyright notice only needs to mention the most recent year in
which changes were made--there's no need to list the years for previous
versions' changes. You don't have to mention the name of the program in
these notices, if that is inconvenient, since it appeared in the first
line. (The rules are different for copyright notices in source files;
*note Copyright Notices: (maintain)Copyright Notices.)
Translations of the above lines must preserve the validity of the
copyright notices (*note Internationalization::). If the translation's
character set supports it, the `(C)' should be replaced with the
copyright symbol, as follows:
(the official copyright symbol, which is the letter C in a circle);
Write the word "Copyright" exactly like that, in English. Do not
translate it into another language. International treaties recognize
the English word "Copyright"; translations into other languages do not
have legal significance.
Finally, here is the table of our suggested license abbreviations.
Any abbreviation can be followed by `vVERSION[+]', meaning that
particular version, or later versions with the `+', as shown above.
In the case of exceptions for extra permissions with the GPL, we use
`/' for a separator; the version number can follow the license
abbreviation as usual, as in the examples below.
GPL
GNU General Public License, `http://www.gnu.org/licenses/gpl.html'.
LGPL
GNU Lesser General Public License,
`http://www.gnu.org/licenses/lgpl.html'.
GPL/Guile
GNU GPL with the exception for Guile; for example, GPLv3+/Guile
means the GNU GPL version 3 or later, with the extra exception for
Guile.
GPL/Ada
GNU GPL with the exception for Ada.
Apache
The Apache Software Foundation license,
`http://www.apache.org/licenses'.
Artistic
The Artistic license used for Perl,
`http://www.perlfoundation.org/legal'.
Expat
The Expat license, `http://www.jclark.com/xml/copying.txt'.
MPL
The Mozilla Public License, `http://www.mozilla.org/MPL/'.
OBSD
The original (4-clause) BSD license, incompatible with the GNU GPL
`http://www.xfree86.org/3.3.6/COPYRIGHT2.html#6'.
PHP
The license used for PHP, `http://www.php.net/license/'.
public domain
The non-license that is being in the public domain,
`http://www.gnu.org/licenses/license-list.html#PublicDomain'.
Python
The license for Python, `http://www.python.org/2.0.1/license.html'.
RBSD
The revised (3-clause) BSD, compatible with the GNU GPL,
`http://www.xfree86.org/3.3.6/COPYRIGHT2.html#5'.
X11
The simple non-copyleft license used for most versions of the X
Window system, `http://www.xfree86.org/3.3.6/COPYRIGHT2.html#3'.
Zlib
The license for Zlib, `http://www.gzip.org/zlib/zlib_license.html'.
More information about these licenses and many more are on the GNU
licensing web pages, `http://www.gnu.org/licenses/license-list.html'.
File: standards.info, Node: --help, Prev: --version, Up: Command-Line Interfaces
4.7.2 `--help'
--------------
The standard `--help' option should output brief documentation for how
to invoke the program, on standard output, then exit successfully.