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1 | @node System Configuration, Language Features, System Information, Top |
2 | @chapter System Configuration Parameters | |
3 | ||
4 | The functions and macros listed in this chapter give information about | |
5 | configuration parameters of the operating system---for example, capacity | |
6 | limits, presence of optional POSIX features, and the default path for | |
7 | executable files (@pxref{String Parameters}). | |
8 | ||
9 | @menu | |
10 | * General Limits:: Constants and functions that describe | |
11 | various process-related limits that have | |
12 | one uniform value for any given machine. | |
13 | * System Options:: Optional POSIX features. | |
14 | * Version Supported:: Version numbers of POSIX.1 and POSIX.2. | |
15 | * Sysconf:: Getting specific configuration values | |
16 | of general limits and system options. | |
17 | * Minimums:: Minimum values for general limits. | |
18 | ||
19 | * Limits for Files:: Size limitations that pertain to individual files. | |
20 | These can vary between file systems | |
21 | or even from file to file. | |
22 | * Options for Files:: Optional features that some files may support. | |
23 | * File Minimums:: Minimum values for file limits. | |
24 | * Pathconf:: Getting the limit values for a particular file. | |
25 | ||
26 | * Utility Limits:: Capacity limits of some POSIX.2 utility programs. | |
27 | * Utility Minimums:: Minimum allowable values of those limits. | |
28 | ||
29 | * String Parameters:: Getting the default search path. | |
30 | @end menu | |
31 | ||
32 | @node General Limits | |
33 | @section General Capacity Limits | |
34 | @cindex POSIX capacity limits | |
35 | @cindex limits, POSIX | |
36 | @cindex capacity limits, POSIX | |
37 | ||
38 | The POSIX.1 and POSIX.2 standards specify a number of parameters that | |
39 | describe capacity limitations of the system. These limits can be fixed | |
40 | constants for a given operating system, or they can vary from machine to | |
41 | machine. For example, some limit values may be configurable by the | |
42 | system administrator, either at run time or by rebuilding the kernel, | |
43 | and this should not require recompiling application programs. | |
44 | ||
45 | @pindex limits.h | |
46 | Each of the following limit parameters has a macro that is defined in | |
47 | @file{limits.h} only if the system has a fixed, uniform limit for the | |
48 | parameter in question. If the system allows different file systems or | |
49 | files to have different limits, then the macro is undefined; use | |
50 | @code{sysconf} to find out the limit that applies at a particular time | |
51 | on a particular machine. @xref{Sysconf}. | |
52 | ||
53 | Each of these parameters also has another macro, with a name starting | |
54 | with @samp{_POSIX}, which gives the lowest value that the limit is | |
55 | allowed to have on @emph{any} POSIX system. @xref{Minimums}. | |
56 | ||
57 | @cindex limits, program argument size | |
58 | @comment limits.h | |
59 | @comment POSIX.1 | |
60 | @deftypevr Macro int ARG_MAX | |
61 | If defined, the unvarying maximum combined length of the @var{argv} and | |
62 | @var{environ} arguments that can be passed to the @code{exec} functions. | |
63 | @end deftypevr | |
64 | ||
65 | @cindex limits, number of processes | |
66 | @comment limits.h | |
67 | @comment POSIX.1 | |
68 | @deftypevr Macro int CHILD_MAX | |
69 | If defined, the unvarying maximum number of processes that can exist | |
70 | with the same real user ID at any one time. In BSD and GNU, this is | |
71 | controlled by the @code{RLIMIT_NPROC} resource limit; @pxref{Limits on | |
72 | Resources}. | |
73 | @end deftypevr | |
74 | ||
75 | @cindex limits, number of open files | |
76 | @comment limits.h | |
77 | @comment POSIX.1 | |
78 | @deftypevr Macro int OPEN_MAX | |
79 | If defined, the unvarying maximum number of files that a single process | |
80 | can have open simultaneously. In BSD and GNU, this is controlled | |
81 | by the @code{RLIMIT_NOFILE} resource limit; @pxref{Limits on Resources}. | |
82 | @end deftypevr | |
83 | ||
84 | @comment limits.h | |
85 | @comment POSIX.1 | |
86 | @deftypevr Macro int STREAM_MAX | |
87 | If defined, the unvarying maximum number of streams that a single | |
88 | process can have open simultaneously. @xref{Opening Streams}. | |
89 | @end deftypevr | |
90 | ||
91 | @cindex limits, time zone name length | |
92 | @comment limits.h | |
93 | @comment POSIX.1 | |
94 | @deftypevr Macro int TZNAME_MAX | |
95 | If defined, the unvarying maximum length of a time zone name. | |
96 | @xref{Time Zone Functions}. | |
97 | @end deftypevr | |
98 | ||
99 | These limit macros are always defined in @file{limits.h}. | |
100 | ||
101 | @cindex limits, number of supplementary group IDs | |
102 | @comment limits.h | |
103 | @comment POSIX.1 | |
104 | @deftypevr Macro int NGROUPS_MAX | |
105 | The maximum number of supplementary group IDs that one process can have. | |
106 | ||
107 | The value of this macro is actually a lower bound for the maximum. That | |
108 | is, you can count on being able to have that many supplementary group | |
109 | IDs, but a particular machine might let you have even more. You can use | |
110 | @code{sysconf} to see whether a particular machine will let you have | |
111 | more (@pxref{Sysconf}). | |
112 | @end deftypevr | |
113 | ||
114 | @comment limits.h | |
115 | @comment POSIX.1 | |
116 | @deftypevr Macro int SSIZE_MAX | |
117 | The largest value that can fit in an object of type @code{ssize_t}. | |
118 | Effectively, this is the limit on the number of bytes that can be read | |
119 | or written in a single operation. | |
120 | ||
121 | This macro is defined in all POSIX systems because this limit is never | |
122 | configurable. | |
123 | @end deftypevr | |
124 | ||
125 | @comment limits.h | |
126 | @comment POSIX.2 | |
127 | @deftypevr Macro int RE_DUP_MAX | |
128 | The largest number of repetitions you are guaranteed is allowed in the | |
129 | construct @samp{\@{@var{min},@var{max}\@}} in a regular expression. | |
130 | ||
131 | The value of this macro is actually a lower bound for the maximum. That | |
132 | is, you can count on being able to have that many repetitions, but a | |
133 | particular machine might let you have even more. You can use | |
134 | @code{sysconf} to see whether a particular machine will let you have | |
135 | more (@pxref{Sysconf}). And even the value that @code{sysconf} tells | |
136 | you is just a lower bound---larger values might work. | |
137 | ||
138 | This macro is defined in all POSIX.2 systems, because POSIX.2 says it | |
139 | should always be defined even if there is no specific imposed limit. | |
140 | @end deftypevr | |
141 | ||
142 | @node System Options | |
143 | @section Overall System Options | |
144 | @cindex POSIX optional features | |
145 | @cindex optional POSIX features | |
146 | ||
147 | POSIX defines certain system-specific options that not all POSIX systems | |
148 | support. Since these options are provided in the kernel, not in the | |
149 | library, simply using the GNU C library does not guarantee any of these | |
150 | features is supported; it depends on the system you are using. | |
151 | ||
152 | @pindex unistd.h | |
153 | You can test for the availability of a given option using the macros in | |
154 | this section, together with the function @code{sysconf}. The macros are | |
155 | defined only if you include @file{unistd.h}. | |
156 | ||
157 | For the following macros, if the macro is defined in @file{unistd.h}, | |
158 | then the option is supported. Otherwise, the option may or may not be | |
159 | supported; use @code{sysconf} to find out. @xref{Sysconf}. | |
160 | ||
161 | @comment unistd.h | |
162 | @comment POSIX.1 | |
163 | @deftypevr Macro int _POSIX_JOB_CONTROL | |
164 | If this symbol is defined, it indicates that the system supports job | |
165 | control. Otherwise, the implementation behaves as if all processes | |
166 | within a session belong to a single process group. @xref{Job Control}. | |
167 | @end deftypevr | |
168 | ||
169 | @comment unistd.h | |
170 | @comment POSIX.1 | |
171 | @deftypevr Macro int _POSIX_SAVED_IDS | |
172 | If this symbol is defined, it indicates that the system remembers the | |
173 | effective user and group IDs of a process before it executes an | |
174 | executable file with the set-user-ID or set-group-ID bits set, and that | |
175 | explicitly changing the effective user or group IDs back to these values | |
176 | is permitted. If this option is not defined, then if a nonprivileged | |
177 | process changes its effective user or group ID to the real user or group | |
178 | ID of the process, it can't change it back again. @xref{Enable/Disable | |
179 | Setuid}. | |
180 | @end deftypevr | |
181 | ||
182 | For the following macros, if the macro is defined in @file{unistd.h}, | |
183 | then its value indicates whether the option is supported. A value of | |
184 | @code{-1} means no, and any other value means yes. If the macro is not | |
185 | defined, then the option may or may not be supported; use @code{sysconf} | |
186 | to find out. @xref{Sysconf}. | |
187 | ||
188 | @comment unistd.h | |
189 | @comment POSIX.2 | |
190 | @deftypevr Macro int _POSIX2_C_DEV | |
191 | If this symbol is defined, it indicates that the system has the POSIX.2 | |
192 | C compiler command, @code{c89}. The GNU C library always defines this | |
193 | as @code{1}, on the assumption that you would not have installed it if | |
194 | you didn't have a C compiler. | |
195 | @end deftypevr | |
196 | ||
197 | @comment unistd.h | |
198 | @comment POSIX.2 | |
199 | @deftypevr Macro int _POSIX2_FORT_DEV | |
200 | If this symbol is defined, it indicates that the system has the POSIX.2 | |
201 | Fortran compiler command, @code{fort77}. The GNU C library never | |
202 | defines this, because we don't know what the system has. | |
203 | @end deftypevr | |
204 | ||
205 | @comment unistd.h | |
206 | @comment POSIX.2 | |
207 | @deftypevr Macro int _POSIX2_FORT_RUN | |
208 | If this symbol is defined, it indicates that the system has the POSIX.2 | |
209 | @code{asa} command to interpret Fortran carriage control. The GNU C | |
210 | library never defines this, because we don't know what the system has. | |
211 | @end deftypevr | |
212 | ||
213 | @comment unistd.h | |
214 | @comment POSIX.2 | |
215 | @deftypevr Macro int _POSIX2_LOCALEDEF | |
216 | If this symbol is defined, it indicates that the system has the POSIX.2 | |
217 | @code{localedef} command. The GNU C library never defines this, because | |
218 | we don't know what the system has. | |
219 | @end deftypevr | |
220 | ||
221 | @comment unistd.h | |
222 | @comment POSIX.2 | |
223 | @deftypevr Macro int _POSIX2_SW_DEV | |
224 | If this symbol is defined, it indicates that the system has the POSIX.2 | |
225 | commands @code{ar}, @code{make}, and @code{strip}. The GNU C library | |
226 | always defines this as @code{1}, on the assumption that you had to have | |
227 | @code{ar} and @code{make} to install the library, and it's unlikely that | |
228 | @code{strip} would be absent when those are present. | |
229 | @end deftypevr | |
230 | ||
231 | @node Version Supported | |
232 | @section Which Version of POSIX is Supported | |
233 | ||
234 | @comment unistd.h | |
235 | @comment POSIX.1 | |
236 | @deftypevr Macro {long int} _POSIX_VERSION | |
237 | This constant represents the version of the POSIX.1 standard to which | |
238 | the implementation conforms. For an implementation conforming to the | |
dfd2257a | 239 | 1995 POSIX.1 standard, the value is the integer @code{199506L}. |
28f540f4 RM |
240 | |
241 | @code{_POSIX_VERSION} is always defined (in @file{unistd.h}) in any | |
242 | POSIX system. | |
243 | ||
244 | @strong{Usage Note:} Don't try to test whether the system supports POSIX | |
245 | by including @file{unistd.h} and then checking whether | |
246 | @code{_POSIX_VERSION} is defined. On a non-POSIX system, this will | |
247 | probably fail because there is no @file{unistd.h}. We do not know of | |
248 | @emph{any} way you can reliably test at compilation time whether your | |
249 | target system supports POSIX or whether @file{unistd.h} exists. | |
250 | ||
251 | The GNU C compiler predefines the symbol @code{__POSIX__} if the target | |
252 | system is a POSIX system. Provided you do not use any other compilers | |
253 | on POSIX systems, testing @code{defined (__POSIX__)} will reliably | |
254 | detect such systems. | |
255 | @end deftypevr | |
256 | ||
257 | @comment unistd.h | |
258 | @comment POSIX.2 | |
259 | @deftypevr Macro {long int} _POSIX2_C_VERSION | |
260 | This constant represents the version of the POSIX.2 standard which the | |
261 | library and system kernel support. We don't know what value this will | |
262 | be for the first version of the POSIX.2 standard, because the value is | |
263 | based on the year and month in which the standard is officially adopted. | |
264 | ||
265 | The value of this symbol says nothing about the utilities installed on | |
266 | the system. | |
267 | ||
268 | @strong{Usage Note:} You can use this macro to tell whether a POSIX.1 | |
269 | system library supports POSIX.2 as well. Any POSIX.1 system contains | |
270 | @file{unistd.h}, so include that file and then test @code{defined | |
271 | (_POSIX2_C_VERSION)}. | |
272 | @end deftypevr | |
273 | ||
274 | @node Sysconf | |
275 | @section Using @code{sysconf} | |
276 | ||
277 | When your system has configurable system limits, you can use the | |
278 | @code{sysconf} function to find out the value that applies to any | |
279 | particular machine. The function and the associated @var{parameter} | |
280 | constants are declared in the header file @file{unistd.h}. | |
281 | ||
282 | @menu | |
283 | * Sysconf Definition:: Detailed specifications of @code{sysconf}. | |
284 | * Constants for Sysconf:: The list of parameters @code{sysconf} can read. | |
285 | * Examples of Sysconf:: How to use @code{sysconf} and the parameter | |
286 | macros properly together. | |
287 | @end menu | |
288 | ||
289 | @node Sysconf Definition | |
290 | @subsection Definition of @code{sysconf} | |
291 | ||
292 | @comment unistd.h | |
293 | @comment POSIX.1 | |
294 | @deftypefun {long int} sysconf (int @var{parameter}) | |
295 | This function is used to inquire about runtime system parameters. The | |
296 | @var{parameter} argument should be one of the @samp{_SC_} symbols listed | |
297 | below. | |
298 | ||
299 | The normal return value from @code{sysconf} is the value you requested. | |
300 | A value of @code{-1} is returned both if the implementation does not | |
f65fd747 | 301 | impose a limit, and in case of an error. |
28f540f4 RM |
302 | |
303 | The following @code{errno} error conditions are defined for this function: | |
304 | ||
305 | @table @code | |
306 | @item EINVAL | |
307 | The value of the @var{parameter} is invalid. | |
308 | @end table | |
309 | @end deftypefun | |
310 | ||
311 | @node Constants for Sysconf | |
312 | @subsection Constants for @code{sysconf} Parameters | |
313 | ||
314 | Here are the symbolic constants for use as the @var{parameter} argument | |
315 | to @code{sysconf}. The values are all integer constants (more | |
316 | specifically, enumeration type values). | |
317 | ||
318 | @table @code | |
319 | @comment unistd.h | |
320 | @comment POSIX.1 | |
321 | @item _SC_ARG_MAX | |
322 | Inquire about the parameter corresponding to @code{ARG_MAX}. | |
323 | ||
324 | @comment unistd.h | |
325 | @comment POSIX.1 | |
326 | @item _SC_CHILD_MAX | |
327 | Inquire about the parameter corresponding to @code{CHILD_MAX}. | |
328 | ||
329 | @comment unistd.h | |
330 | @comment POSIX.1 | |
331 | @item _SC_OPEN_MAX | |
332 | Inquire about the parameter corresponding to @code{OPEN_MAX}. | |
333 | ||
334 | @comment unistd.h | |
335 | @comment POSIX.1 | |
336 | @item _SC_STREAM_MAX | |
337 | Inquire about the parameter corresponding to @code{STREAM_MAX}. | |
338 | ||
339 | @comment unistd.h | |
340 | @comment POSIX.1 | |
341 | @item _SC_TZNAME_MAX | |
342 | Inquire about the parameter corresponding to @code{TZNAME_MAX}. | |
343 | ||
344 | @comment unistd.h | |
345 | @comment POSIX.1 | |
346 | @item _SC_NGROUPS_MAX | |
347 | Inquire about the parameter corresponding to @code{NGROUPS_MAX}. | |
348 | ||
349 | @comment unistd.h | |
350 | @comment POSIX.1 | |
351 | @item _SC_JOB_CONTROL | |
352 | Inquire about the parameter corresponding to @code{_POSIX_JOB_CONTROL}. | |
353 | ||
354 | @comment unistd.h | |
355 | @comment POSIX.1 | |
356 | @item _SC_SAVED_IDS | |
357 | Inquire about the parameter corresponding to @code{_POSIX_SAVED_IDS}. | |
358 | ||
359 | @comment unistd.h | |
360 | @comment POSIX.1 | |
361 | @item _SC_VERSION | |
362 | Inquire about the parameter corresponding to @code{_POSIX_VERSION}. | |
363 | ||
364 | @comment unistd.h | |
365 | @comment POSIX.1 | |
366 | @item _SC_CLK_TCK | |
367 | Inquire about the parameter corresponding to @code{CLOCKS_PER_SEC}; | |
368 | @pxref{Basic CPU Time}. | |
369 | ||
dfd2257a UD |
370 | @comment unistd.h |
371 | @comment GNU | |
372 | @item _SC_CHARCLASS_NAME_MAX | |
373 | Inquire about the parameter corresponding to maximal length allowed for | |
374 | a character class name in an extended locale specification. These | |
375 | extensions are not yet standardized and so this option is not standardized | |
376 | as well. | |
377 | ||
378 | @comment unistdh.h | |
379 | @comment POSIX.1 | |
380 | @item _SC_REALTIME_SIGNALS | |
381 | Inquire about the parameter corresponding to @code{_POSIX_REALTIME_SIGNALS}. | |
382 | ||
383 | @comment unistd.h | |
384 | @comment POSIX.1 | |
385 | @item _SC_PRIORITY_SCHEDULING | |
386 | Inquire about the parameter corresponding to @code{_POSIX_PRIORITY_SCHEDULING}. | |
387 | ||
388 | @comment unistd.h | |
389 | @comment POSIX.1 | |
390 | @item _SC_TIMERS | |
391 | Inquire about the parameter corresponding to @code{_POSIX_TIMERS}. | |
392 | ||
393 | @comment unistd.h | |
394 | @comment POSIX.1 | |
395 | @item _SC_ASYNCHRONOUS_IO | |
396 | Inquire about the parameter corresponding to @code{_POSIX_ASYNCHRONOUS_IO}. | |
397 | ||
398 | @comment unistd.h | |
399 | @comment POSIX.1 | |
400 | @item _SC_PRIORITIZED_IO | |
401 | Inquire about the parameter corresponding to @code{_POSIX_PRIORITIZED_IO}. | |
402 | ||
403 | @comment unistd.h | |
404 | @comment POSIX.1 | |
405 | @item _SC_SYNCHRONIZED_IO | |
406 | Inquire about the parameter corresponding to @code{_POSIX_SYNCHRONIZED_IO}. | |
407 | ||
408 | @comment unistd.h | |
409 | @comment POSIX.1 | |
410 | @item _SC_FSYNC | |
411 | Inquire about the parameter corresponding to @code{_POSIX_FSYNC}. | |
412 | ||
413 | @comment unistd.h | |
414 | @comment POSIX.1 | |
415 | @item _SC_MAPPED_FILES | |
416 | Inquire about the parameter corresponding to @code{_POSIX_MAPPED_FILES}. | |
417 | ||
418 | @comment unistd.h | |
419 | @comment POSIX.1 | |
420 | @item _SC_MEMLOCK | |
421 | Inquire about the parameter corresponding to @code{_POSIX_MEMLOCK}. | |
422 | ||
423 | @comment unistd.h | |
424 | @comment POSIX.1 | |
425 | @item _SC_MEMLOCK_RANGE | |
426 | Inquire about the parameter corresponding to @code{_POSIX_MEMLOCK_RANGE}. | |
427 | ||
428 | @comment unistd.h | |
429 | @comment POSIX.1 | |
430 | @item _SC_MEMORY_PROTECTION | |
431 | Inquire about the parameter corresponding to @code{_POSIX_MEMORY_PROTECTION}. | |
432 | ||
433 | @comment unistd.h | |
434 | @comment POSIX.1 | |
435 | @item _SC_MESSAGE_PASSING | |
436 | Inquire about the parameter corresponding to @code{_POSIX_MESSAGE_PASSING}. | |
437 | ||
438 | @comment unistd.h | |
439 | @comment POSIX.1 | |
440 | @item _SC_SEMAPHORES | |
441 | Inquire about the parameter corresponding to @code{_POSIX_SEMAPHORES}. | |
442 | ||
443 | @comment unistd.h | |
444 | @comment POSIX.1 | |
445 | @item _SC_SHARED_MEMORY_OBJECTS | |
446 | Inquire about the parameter corresponding to | |
447 | @code{_POSIX_SHARED_MEMORY_OBJECTS}. | |
448 | ||
449 | @comment unistd.h | |
450 | @comment POSIX.1 | |
451 | @item _SC_AIO_LISTIO_MAX | |
452 | Inquire about the parameter corresponding to @code{_POSIX_AIO_LISTIO_MAX}. | |
453 | ||
454 | @comment unistd.h | |
455 | @comment POSIX.1 | |
456 | @item _SC_AIO_MAX | |
457 | Inquire about the parameter corresponding to @code{_POSIX_AIO_MAX}. | |
458 | ||
459 | @comment unistd.h | |
460 | @comment POSIX.1 | |
461 | @item _SC_AIO_PRIO_DELTA_MAX | |
462 | Inquire the value by which a process can decrease its asynchronous I/O | |
463 | priority level from its own scheduling priority. This corresponds to the | |
464 | run-time invariant value @code{AIO_PRIO_DELTA_MAX}. | |
465 | ||
466 | @comment unistd.h | |
467 | @comment POSIX.1 | |
468 | @item _SC_DELAYTIMER_MAX | |
469 | Inquire about the parameter corresponding to @code{_POSIX_DELAYTIMER_MAX}. | |
470 | ||
471 | @comment unistd.h | |
472 | @comment POSIX.1 | |
473 | @item _SC_MQ_OPEN_MAX | |
474 | Inquire about the parameter corresponding to @code{_POSIX_MQ_OPEN_MAX}. | |
475 | ||
476 | @comment unistd.h | |
477 | @comment POSIX.1 | |
478 | @item _SC_MQ_PRIO_MAX | |
479 | Inquire about the parameter corresponding to @code{_POSIX_MQ_PRIO_MAX}. | |
480 | ||
481 | @comment unistd.h | |
482 | @comment POSIX.1 | |
483 | @item _SC_RTSIG_MAX | |
484 | Inquire about the parameter corresponding to @code{_POSIX_RTSIG_MAX}. | |
485 | ||
486 | @comment unistd.h | |
487 | @comment POSIX.1 | |
488 | @item _SC_SEM_NSEMS_MAX | |
489 | Inquire about the parameter corresponding to @code{_POSIX_SEM_NSEMS_MAX}. | |
490 | ||
491 | @comment unistd.h | |
492 | @comment POSIX.1 | |
493 | @item _SC_SEM_VALUE_MAX | |
494 | Inquire about the parameter corresponding to @code{_POSIX_SEM_VALUE_MAX}. | |
495 | ||
496 | @comment unistd.h | |
497 | @comment POSIX.1 | |
498 | @item _SC_SIGQUEUE_MAX | |
499 | Inquire about the parameter corresponding to @code{_POSIX_SIGQUEUE_MAX}. | |
500 | ||
501 | @comment unistd.h | |
502 | @comment POSIX.1 | |
503 | @item _SC_TIMER_MAX | |
504 | Inquire about the parameter corresponding to @code{_POSIX_TIMER_MAX}. | |
505 | ||
506 | @comment unistd.h | |
507 | @comment POSIX.1g | |
508 | @item _SC_PII | |
509 | Inquire about the parameter corresponding to @code{_POSIX_PII}. | |
510 | ||
511 | @comment unistd.h | |
512 | @comment POSIX.1g | |
513 | @item _SC_PII_XTI | |
514 | Inquire about the parameter corresponding to @code{_POSIX_PII_XTI}. | |
515 | ||
516 | @comment unistd.h | |
517 | @comment POSIX.1g | |
518 | @item _SC_PII_SOCKET | |
519 | Inquire about the parameter corresponding to @code{_POSIX_PII_SOCKET}. | |
520 | ||
521 | @comment unistd.h | |
522 | @comment POSIX.1g | |
523 | @item _SC_PII_INTERNET | |
524 | Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET}. | |
525 | ||
526 | @comment unistd.h | |
527 | @comment POSIX.1g | |
528 | @item _SC_PII_OSI | |
529 | Inquire about the parameter corresponding to @code{_POSIX_PII_OSI}. | |
530 | ||
531 | @comment unistd.h | |
532 | @comment POSIX.1g | |
533 | @item _SC_SELECT | |
534 | Inquire about the parameter corresponding to @code{_POSIX_SELECT}. | |
535 | ||
536 | @comment unistd.h | |
537 | @comment POSIX.1g | |
538 | @item _SC_UIO_MAXIOV | |
539 | Inquire about the parameter corresponding to @code{_POSIX_UIO_MAXIOV}. | |
540 | ||
541 | @comment unistd.h | |
542 | @comment POSIX.1g | |
543 | @item _SC_PII_INTERNET_STREAM | |
544 | Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET_STREAM}. | |
545 | ||
546 | @comment unistd.h | |
547 | @comment POSIX.1g | |
548 | @item _SC_PII_INTERNET_DGRAM | |
549 | Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET_DGRAM}. | |
550 | ||
551 | @comment unistd.h | |
552 | @comment POSIX.1g | |
553 | @item _SC_PII_OSI_COTS | |
554 | Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_COTS}. | |
555 | ||
556 | @comment unistd.h | |
557 | @comment POSIX.1g | |
558 | @item _SC_PII_OSI_CLTS | |
559 | Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_CLTS}. | |
560 | ||
561 | @comment unistd.h | |
562 | @comment POSIX.1g | |
563 | @item _SC_PII_OSI_M | |
564 | Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_M}. | |
565 | ||
566 | @comment unistd.h | |
567 | @comment POSIX.1g | |
568 | @item _SC_T_IOV_MAX | |
569 | Inquire the value of the value associated with the @code{T_IOV_MAX} | |
570 | variable. | |
571 | ||
572 | @comment unistd.h | |
573 | @comment POSIX.1 | |
574 | @item _SC_THREADS | |
575 | Inquire about the parameter corresponding to @code{_POSIX_THREADS}. | |
576 | ||
577 | @comment unistd.h | |
578 | @comment POSIX.1 | |
579 | @item _SC_THREAD_SAFE_FUNCTIONS | |
580 | Inquire about the parameter corresponding to | |
581 | @code{_POSIX_THREAD_SAFE_FUNCTIONS}. | |
582 | ||
583 | @comment unistd.h | |
584 | @comment POSIX.1 | |
585 | @item _SC_GETGR_R_SIZE_MAX | |
586 | Inquire about the parameter corresponding to @code{_POSIX_GETGR_R_SIZE_MAX}. | |
587 | ||
588 | @comment unistd.h | |
589 | @comment POSIX.1 | |
590 | @item _SC_GETPW_R_SIZE_MAX | |
591 | Inquire about the parameter corresponding to @code{_POSIX_GETPW_R_SIZE_MAX}. | |
592 | ||
593 | @comment unistd.h | |
594 | @comment POSIX.1 | |
595 | @item _SC_LOGIN_NAME_MAX | |
596 | Inquire about the parameter corresponding to @code{_POSIX_LOGIN_NAME_MAX}. | |
597 | ||
598 | @comment unistd.h | |
599 | @comment POSIX.1 | |
600 | @item _SC_TTY_NAME_MAX | |
601 | Inquire about the parameter corresponding to @code{_POSIX_TTY_NAME_MAX}. | |
602 | ||
603 | @comment unistd.h | |
604 | @comment POSIX.1 | |
605 | @item _SC_THREAD_DESTRUCTOR_ITERATIONS | |
606 | Inquire about the parameter corresponding to | |
607 | @code{_POSIX_THREAD_DESTRUCTOR_ITERATIONS}. | |
608 | ||
609 | @comment unistd.h | |
610 | @comment POSIX.1 | |
611 | @item _SC_THREAD_KEYS_MAX | |
612 | Inquire about the parameter corresponding to @code{_POSIX_THREAD_KEYS_MAX}. | |
613 | ||
614 | @comment unistd.h | |
615 | @comment POSIX.1 | |
616 | @item _SC_THREAD_STACK_MIN | |
617 | Inquire about the parameter corresponding to @code{_POSIX_THREAD_STACK_MIN}. | |
618 | ||
619 | @comment unistd.h | |
620 | @comment POSIX.1 | |
621 | @item _SC_THREAD_THREADS_MAX | |
622 | Inquire about the parameter corresponding to @code{_POSIX_THREAD_THREADS_MAX}. | |
623 | ||
624 | @comment unistd.h | |
625 | @comment POSIX.1 | |
626 | @item _SC_THREAD_ATTR_STACKADDR | |
627 | Inquire about the parameter corresponding to | |
628 | @code{_POSIX_THREAD_ATTR_STACKADDR}. | |
629 | ||
630 | @comment unistd.h | |
631 | @comment POSIX.1 | |
632 | @item _SC_THREAD_ATTR_STACKSIZE | |
633 | Inquire about the parameter corresponding to | |
634 | @code{_POSIX_THREAD_ATTR_STACKSIZE}. | |
635 | ||
636 | @comment unistd.h | |
637 | @comment POSIX.1 | |
638 | @item _SC_THREAD_PRIORITY_SCHEDULING | |
639 | Inquire about the parameter corresponding to | |
640 | @code{_POSIX_THREAD_PRIORITY_SCHEDULING}. | |
641 | ||
642 | @comment unistd.h | |
643 | @comment POSIX.1 | |
644 | @item _SC_THREAD_PRIO_INHERIT | |
645 | Inquire about the parameter corresponding to @code{_POSIX_THREAD_PRIO_INHERIT}. | |
646 | ||
647 | @comment unistd.h | |
648 | @comment POSIX.1 | |
649 | @item _SC_THREAD_PRIO_PROTECT | |
650 | Inquire about the parameter corresponding to @code{_POSIX_THREAD_PRIO_PROTECT}. | |
651 | ||
652 | @comment unistd.h | |
653 | @comment POSIX.1 | |
654 | @item _SC_THREAD_PROCESS_SHARED | |
655 | Inquire about the parameter corresponding to | |
656 | @code{_POSIX_THREAD_PROCESS_SHARED}. | |
657 | ||
28f540f4 RM |
658 | @comment unistd.h |
659 | @comment POSIX.2 | |
660 | @item _SC_2_C_DEV | |
661 | Inquire about whether the system has the POSIX.2 C compiler command, | |
662 | @code{c89}. | |
663 | ||
664 | @comment unistd.h | |
665 | @comment POSIX.2 | |
666 | @item _SC_2_FORT_DEV | |
667 | Inquire about whether the system has the POSIX.2 Fortran compiler | |
668 | command, @code{fort77}. | |
669 | ||
670 | @comment unistd.h | |
671 | @comment POSIX.2 | |
672 | @item _SC_2_FORT_RUN | |
673 | Inquire about whether the system has the POSIX.2 @code{asa} command to | |
674 | interpret Fortran carriage control. | |
675 | ||
676 | @comment unistd.h | |
677 | @comment POSIX.2 | |
678 | @item _SC_2_LOCALEDEF | |
679 | Inquire about whether the system has the POSIX.2 @code{localedef} | |
680 | command. | |
681 | ||
682 | @comment unistd.h | |
683 | @comment POSIX.2 | |
684 | @item _SC_2_SW_DEV | |
685 | Inquire about whether the system has the POSIX.2 commands @code{ar}, | |
686 | @code{make}, and @code{strip}. | |
687 | ||
688 | @comment unistd.h | |
689 | @comment POSIX.2 | |
690 | @item _SC_BC_BASE_MAX | |
691 | Inquire about the maximum value of @code{obase} in the @code{bc} | |
692 | utility. | |
693 | ||
694 | @comment unistd.h | |
695 | @comment POSIX.2 | |
696 | @item _SC_BC_DIM_MAX | |
697 | Inquire about the maximum size of an array in the @code{bc} | |
698 | utility. | |
699 | ||
700 | @comment unistd.h | |
701 | @comment POSIX.2 | |
702 | @item _SC_BC_SCALE_MAX | |
703 | Inquire about the maximum value of @code{scale} in the @code{bc} | |
704 | utility. | |
705 | ||
706 | @comment unistd.h | |
707 | @comment POSIX.2 | |
708 | @item _SC_BC_STRING_MAX | |
709 | Inquire about the maximum size of a string constant in the | |
710 | @code{bc} utility. | |
711 | ||
712 | @comment unistd.h | |
713 | @comment POSIX.2 | |
714 | @item _SC_COLL_WEIGHTS_MAX | |
715 | Inquire about the maximum number of weights that can necessarily | |
716 | be used in defining the collating sequence for a locale. | |
717 | ||
718 | @comment unistd.h | |
719 | @comment POSIX.2 | |
720 | @item _SC_EXPR_NEST_MAX | |
721 | Inquire about the maximum number of expressions nested within | |
722 | parentheses when using the @code{expr} utility. | |
723 | ||
724 | @comment unistd.h | |
725 | @comment POSIX.2 | |
726 | @item _SC_LINE_MAX | |
727 | Inquire about the maximum size of a text line that the POSIX.2 text | |
728 | utilities can handle. | |
729 | ||
730 | @comment unistd.h | |
731 | @comment POSIX.2 | |
732 | @item _SC_EQUIV_CLASS_MAX | |
733 | Inquire about the maximum number of weights that can be assigned to an | |
734 | entry of the @code{LC_COLLATE} category @samp{order} keyword in a locale | |
735 | definition. The GNU C library does not presently support locale | |
736 | definitions. | |
737 | ||
738 | @comment unistd.h | |
739 | @comment POSIX.2 | |
740 | @item _SC_VERSION | |
741 | Inquire about the version number of POSIX.1 that the library and kernel | |
742 | support. | |
743 | ||
744 | @comment unistd.h | |
745 | @comment POSIX.2 | |
746 | @item _SC_2_VERSION | |
747 | Inquire about the version number of POSIX.2 that the system utilities | |
748 | support. | |
749 | ||
750 | @comment unistd.h | |
751 | @comment GNU | |
752 | @item _SC_PAGESIZE | |
753 | Inquire about the virtual memory page size of the machine. | |
754 | @code{getpagesize} returns the same value. | |
755 | @c @xref{XXX getpagesize}. !!! ??? | |
dfd2257a UD |
756 | |
757 | @comment unistd.h | |
758 | @comment GNU | |
759 | @item _SC_NPROCESSORS_CONF | |
760 | Inquire about number of configured processors. | |
761 | ||
762 | @comment unistd.h | |
763 | @comment GNU | |
764 | @item _SC_NPROCESSORS_ONLN | |
765 | Inquire about number of processors online. | |
766 | ||
767 | @comment unistd.h | |
768 | @comment GNU | |
769 | @item _SC_PHYS_PAGES | |
770 | Inquire about number of physical pages in the system. | |
771 | ||
772 | @comment unistd.h | |
773 | @comment GNU | |
774 | @item _SC_AVPHYS_PAGES | |
775 | Inquire about number of available physical pages in the system. | |
776 | ||
777 | @comment unistd.h | |
778 | @comment GNU | |
779 | @item _SC_ATEXIT_MAX | |
780 | Inquire about number of functions which can be registered as termination | |
781 | functions for @code{atexit}; @pxref{Cleanups on Exit}. | |
782 | ||
783 | @comment unistd.h | |
784 | @comment X/Open | |
785 | @item _SC_XOPEN_VERSION | |
786 | Inquire about the parameter corresponding to @code{_XOPEN_VERSION}. | |
787 | ||
788 | @comment unistd.h | |
789 | @comment X/Open | |
790 | @item _SC_XOPEN_XCU_VERSION | |
791 | Inquire about the parameter corresponding to @code{_XOPEN_XCU_VERSION}. | |
792 | ||
793 | @comment unistd.h | |
794 | @comment X/Open | |
795 | @item _SC_XOPEN_UNIX | |
796 | Inquire about the parameter corresponding to @code{_XOPEN_UNIX}. | |
797 | ||
798 | @comment unistd.h | |
799 | @comment X/Open | |
800 | @item _SC_XOPEN_CRYPT | |
801 | Inquire about the parameter corresponding to @code{_XOPEN_CRYPT}. | |
802 | ||
803 | @comment unistd.h | |
804 | @comment X/Open | |
805 | @item _SC_XOPEN_ENH_I18N | |
806 | Inquire about the parameter corresponding to @code{_XOPEN_ENH_I18N}. | |
807 | ||
808 | @comment unistd.h | |
809 | @comment X/Open | |
810 | @item _SC_XOPEN_SHM | |
811 | Inquire about the parameter corresponding to @code{_XOPEN_SHM}. | |
812 | ||
813 | @comment unistd.h | |
814 | @comment X/Open | |
815 | @item _SC_XOPEN_XPG2 | |
816 | Inquire about the parameter corresponding to @code{_XOPEN_XPG2}. | |
817 | ||
818 | @comment unistd.h | |
819 | @comment X/Open | |
820 | @item _SC_XOPEN_XPG3 | |
821 | Inquire about the parameter corresponding to @code{_XOPEN_XPG3}. | |
822 | ||
823 | @comment unistd.h | |
824 | @comment X/Open | |
825 | @item _SC_XOPEN_XPG4 | |
826 | Inquire about the parameter corresponding to @code{_XOPEN_XPG4}. | |
827 | ||
828 | @comment unistd.h | |
829 | @comment X/Open | |
830 | @item _SC_CHAR_BIT | |
831 | Inquire about number of bits in a variable of type @code{char}. | |
832 | ||
833 | @comment unistd.h | |
834 | @comment X/Open | |
835 | @item _SC_CHAR_MAX | |
836 | Inquire about maximum value which can be stored in a variable of type | |
837 | @code{char}. | |
838 | ||
839 | @comment unistd.h | |
840 | @comment X/Open | |
841 | @item _SC_CHAR_MIN | |
842 | Inquire about minimum value which can be stored in a variable of type | |
843 | @code{char}. | |
844 | ||
845 | @comment unistd.h | |
846 | @comment X/Open | |
847 | @item _SC_INT_MAX | |
848 | Inquire about maximum value which can be stored in a variable of type | |
849 | @code{int}. | |
850 | ||
851 | @comment unistd.h | |
852 | @comment X/Open | |
853 | @item _SC_INT_MIN | |
854 | Inquire about minimum value which can be stored in a variable of type | |
855 | @code{int}. | |
856 | ||
857 | @comment unistd.h | |
858 | @comment X/Open | |
859 | @item _SC_LONG_BIT | |
860 | Inquire about number of bits in a variable of type @code{long int}. | |
861 | ||
862 | @comment unistd.h | |
863 | @comment X/Open | |
864 | @item _SC_WORD_BIT | |
865 | Inquire about number of bits in a variable of a register word. | |
866 | ||
867 | @comment unistd.h | |
868 | @comment X/Open | |
869 | @item _SC_MB_LEN_MAX | |
870 | Inquire the maximum length of a multi-byte representation of a wide | |
871 | character value. | |
872 | ||
873 | @comment unistd.h | |
874 | @comment X/Open | |
875 | @item _SC_NZERO | |
876 | Inquire value used to internally represent the zero priority level for | |
877 | the process execution. | |
878 | ||
879 | @comment unistd.h | |
880 | @comment X/Open | |
881 | @item SC_SSIZE_MAX | |
882 | Inquire about maximum value which can be stored in a variable of type | |
883 | @code{ssize_t}. | |
884 | ||
885 | @comment unistd.h | |
886 | @comment X/Open | |
887 | @item _SC_SCHAR_MAX | |
888 | Inquire about maximum value which can be stored in a variable of type | |
889 | @code{signed char}. | |
890 | ||
891 | @comment unistd.h | |
892 | @comment X/Open | |
893 | @item _SC_SCHAR_MIN | |
894 | Inquire about minimum value which can be stored in a variable of type | |
895 | @code{signed char}. | |
896 | ||
897 | @comment unistd.h | |
898 | @comment X/Open | |
899 | @item _SC_SHRT_MAX | |
900 | Inquire about maximum value which can be stored in a variable of type | |
901 | @code{short int}. | |
902 | ||
903 | @comment unistd.h | |
904 | @comment X/Open | |
905 | @item _SC_SHRT_MIN | |
906 | Inquire about minimum value which can be stored in a variable of type | |
907 | @code{short int}. | |
908 | ||
909 | @comment unistd.h | |
910 | @comment X/Open | |
911 | @item _SC_UCHAR_MAX | |
912 | Inquire about maximum value which can be stored in a variable of type | |
913 | @code{unsigned char}. | |
914 | ||
915 | @comment unistd.h | |
916 | @comment X/Open | |
917 | @item _SC_UINT_MAX | |
918 | Inquire about maximum value which can be stored in a variable of type | |
919 | @code{unsigned int}. | |
920 | ||
921 | @comment unistd.h | |
922 | @comment X/Open | |
923 | @item _SC_ULONG_MAX | |
924 | Inquire about maximum value which can be stored in a variable of type | |
925 | @code{unsigned long int}. | |
926 | ||
927 | @comment unistd.h | |
928 | @comment X/Open | |
929 | @item _SC_USHRT_MAX | |
930 | Inquire about maximum value which can be stored in a variable of type | |
931 | @code{unsigned short int}. | |
932 | ||
933 | @comment unistd.h | |
934 | @comment X/Open | |
935 | @item _SC_NL_ARGMAX | |
936 | Inquire about the parameter corresponding to @code{NL_ARGMAX}. | |
937 | ||
938 | @comment unistd.h | |
939 | @comment X/Open | |
940 | @item _SC_NL_LANGMAX | |
941 | Inquire about the parameter corresponding to @code{NL_LANGMAX}. | |
942 | ||
943 | @comment unistd.h | |
944 | @comment X/Open | |
945 | @item _SC_NL_MSGMAX | |
946 | Inquire about the parameter corresponding to @code{NL_MSGMAX}. | |
947 | ||
948 | @comment unistd.h | |
949 | @comment X/Open | |
950 | @item _SC_NL_NMAX | |
951 | Inquire about the parameter corresponding to @code{NL_NMAX}. | |
952 | ||
953 | @comment unistd.h | |
954 | @comment X/Open | |
955 | @item _SC_NL_SETMAX | |
956 | Inquire about the parameter corresponding to @code{NL_SETMAX}. | |
957 | ||
958 | @comment unistd.h | |
959 | @comment X/Open | |
960 | @item _SC_NL_TEXTMAX | |
961 | Inquire about the parameter corresponding to @code{NL_TEXTMAX}. | |
28f540f4 RM |
962 | @end table |
963 | ||
f65fd747 | 964 | @node Examples of Sysconf |
28f540f4 RM |
965 | @subsection Examples of @code{sysconf} |
966 | ||
967 | We recommend that you first test for a macro definition for the | |
968 | parameter you are interested in, and call @code{sysconf} only if the | |
969 | macro is not defined. For example, here is how to test whether job | |
970 | control is supported: | |
971 | ||
972 | @smallexample | |
973 | @group | |
974 | int | |
975 | have_job_control (void) | |
976 | @{ | |
977 | #ifdef _POSIX_JOB_CONTROL | |
978 | return 1; | |
979 | #else | |
980 | int value = sysconf (_SC_JOB_CONTROL); | |
981 | if (value < 0) | |
982 | /* @r{If the system is that badly wedged,} | |
983 | @r{there's no use trying to go on.} */ | |
984 | fatal (strerror (errno)); | |
985 | return value; | |
986 | #endif | |
987 | @} | |
988 | @end group | |
989 | @end smallexample | |
990 | ||
991 | Here is how to get the value of a numeric limit: | |
992 | ||
993 | @smallexample | |
994 | int | |
995 | get_child_max () | |
996 | @{ | |
997 | #ifdef CHILD_MAX | |
998 | return CHILD_MAX; | |
999 | #else | |
1000 | int value = sysconf (_SC_CHILD_MAX); | |
1001 | if (value < 0) | |
1002 | fatal (strerror (errno)); | |
1003 | return value; | |
1004 | #endif | |
1005 | @} | |
1006 | @end smallexample | |
1007 | ||
1008 | @node Minimums | |
1009 | @section Minimum Values for General Capacity Limits | |
1010 | ||
1011 | Here are the names for the POSIX minimum upper bounds for the system | |
1012 | limit parameters. The significance of these values is that you can | |
1013 | safely push to these limits without checking whether the particular | |
1014 | system you are using can go that far. | |
1015 | ||
1016 | @table @code | |
dfd2257a UD |
1017 | @comment limits.h |
1018 | @comment POSIX.1 | |
1019 | @item _POSIX_AIO_LISTIO_MAX | |
1020 | The most restrictive limit permitted by POSIX for the maximum number of | |
1021 | I/O operations that can be specified in a list I/O call. The value of | |
1022 | this constant is @code{2}; thus you can add up to two new entries | |
1023 | of the list of outstandard operations. | |
1024 | ||
1025 | @comment limits.h | |
1026 | @comment POSIX.1 | |
1027 | @item _POSIX_AIO_MAX | |
1028 | The most restrictive limit permitted by POSIX for the maximum number of | |
1029 | outstanding asynchronous I/O operations. The value of this constant is | |
1030 | @code{1}. So you cannot expect that you can issue more than one | |
1031 | operation and immediately continue with the normal work, receiving the | |
1032 | notifications asynchronously. | |
1033 | ||
28f540f4 RM |
1034 | @comment limits.h |
1035 | @comment POSIX.1 | |
1036 | @item _POSIX_ARG_MAX | |
1037 | The value of this macro is the most restrictive limit permitted by POSIX | |
1038 | for the maximum combined length of the @var{argv} and @var{environ} | |
1039 | arguments that can be passed to the @code{exec} functions. | |
1040 | Its value is @code{4096}. | |
1041 | ||
1042 | @comment limits.h | |
1043 | @comment POSIX.1 | |
1044 | @item _POSIX_CHILD_MAX | |
1045 | The value of this macro is the most restrictive limit permitted by POSIX | |
1046 | for the maximum number of simultaneous processes per real user ID. Its | |
1047 | value is @code{6}. | |
1048 | ||
1049 | @comment limits.h | |
1050 | @comment POSIX.1 | |
1051 | @item _POSIX_NGROUPS_MAX | |
1052 | The value of this macro is the most restrictive limit permitted by POSIX | |
1053 | for the maximum number of supplementary group IDs per process. Its | |
1054 | value is @code{0}. | |
1055 | ||
1056 | @comment limits.h | |
1057 | @comment POSIX.1 | |
1058 | @item _POSIX_OPEN_MAX | |
1059 | The value of this macro is the most restrictive limit permitted by POSIX | |
1060 | for the maximum number of files that a single process can have open | |
1061 | simultaneously. Its value is @code{16}. | |
1062 | ||
1063 | @comment limits.h | |
1064 | @comment POSIX.1 | |
1065 | @item _POSIX_SSIZE_MAX | |
1066 | The value of this macro is the most restrictive limit permitted by POSIX | |
1067 | for the maximum value that can be stored in an object of type | |
1068 | @code{ssize_t}. Its value is @code{32767}. | |
1069 | ||
1070 | @comment limits.h | |
1071 | @comment POSIX.1 | |
1072 | @item _POSIX_STREAM_MAX | |
1073 | The value of this macro is the most restrictive limit permitted by POSIX | |
1074 | for the maximum number of streams that a single process can have open | |
1075 | simultaneously. Its value is @code{8}. | |
1076 | ||
1077 | @comment limits.h | |
1078 | @comment POSIX.1 | |
1079 | @item _POSIX_TZNAME_MAX | |
1080 | The value of this macro is the most restrictive limit permitted by POSIX | |
1081 | for the maximum length of a time zone name. Its value is @code{3}. | |
1082 | ||
1083 | @comment limits.h | |
1084 | @comment POSIX.2 | |
1085 | @item _POSIX2_RE_DUP_MAX | |
1086 | The value of this macro is the most restrictive limit permitted by POSIX | |
1087 | for the numbers used in the @samp{\@{@var{min},@var{max}\@}} construct | |
1088 | in a regular expression. Its value is @code{255}. | |
1089 | @end table | |
1090 | ||
1091 | @node Limits for Files | |
1092 | @section Limits on File System Capacity | |
1093 | ||
1094 | The POSIX.1 standard specifies a number of parameters that describe the | |
1095 | limitations of the file system. It's possible for the system to have a | |
1096 | fixed, uniform limit for a parameter, but this isn't the usual case. On | |
1097 | most systems, it's possible for different file systems (and, for some | |
1098 | parameters, even different files) to have different maximum limits. For | |
1099 | example, this is very likely if you use NFS to mount some of the file | |
1100 | systems from other machines. | |
1101 | ||
1102 | @pindex limits.h | |
1103 | Each of the following macros is defined in @file{limits.h} only if the | |
1104 | system has a fixed, uniform limit for the parameter in question. If the | |
1105 | system allows different file systems or files to have different limits, | |
1106 | then the macro is undefined; use @code{pathconf} or @code{fpathconf} to | |
1107 | find out the limit that applies to a particular file. @xref{Pathconf}. | |
1108 | ||
1109 | Each parameter also has another macro, with a name starting with | |
1110 | @samp{_POSIX}, which gives the lowest value that the limit is allowed to | |
1111 | have on @emph{any} POSIX system. @xref{File Minimums}. | |
1112 | ||
1113 | @cindex limits, link count of files | |
1114 | @comment limits.h | |
1115 | @comment POSIX.1 | |
1116 | @deftypevr Macro int LINK_MAX | |
1117 | The uniform system limit (if any) for the number of names for a given | |
1118 | file. @xref{Hard Links}. | |
1119 | @end deftypevr | |
1120 | ||
1121 | @cindex limits, terminal input queue | |
1122 | @comment limits.h | |
1123 | @comment POSIX.1 | |
1124 | @deftypevr Macro int MAX_CANON | |
1125 | The uniform system limit (if any) for the amount of text in a line of | |
1126 | input when input editing is enabled. @xref{Canonical or Not}. | |
1127 | @end deftypevr | |
1128 | ||
1129 | @comment limits.h | |
1130 | @comment POSIX.1 | |
1131 | @deftypevr Macro int MAX_INPUT | |
1132 | The uniform system limit (if any) for the total number of characters | |
1133 | typed ahead as input. @xref{I/O Queues}. | |
1134 | @end deftypevr | |
1135 | ||
1136 | @cindex limits, file name length | |
1137 | @comment limits.h | |
1138 | @comment POSIX.1 | |
1139 | @deftypevr Macro int NAME_MAX | |
1140 | The uniform system limit (if any) for the length of a file name component. | |
1141 | @end deftypevr | |
1142 | ||
1143 | @comment limits.h | |
1144 | @comment POSIX.1 | |
1145 | @deftypevr Macro int PATH_MAX | |
1146 | The uniform system limit (if any) for the length of an entire file name (that | |
1147 | is, the argument given to system calls such as @code{open}). | |
1148 | @end deftypevr | |
1149 | ||
1150 | @cindex limits, pipe buffer size | |
1151 | @comment limits.h | |
1152 | @comment POSIX.1 | |
1153 | @deftypevr Macro int PIPE_BUF | |
1154 | The uniform system limit (if any) for the number of bytes that can be | |
1155 | written atomically to a pipe. If multiple processes are writing to the | |
1156 | same pipe simultaneously, output from different processes might be | |
1157 | interleaved in chunks of this size. @xref{Pipes and FIFOs}. | |
1158 | @end deftypevr | |
1159 | ||
1160 | These are alternative macro names for some of the same information. | |
1161 | ||
1162 | @comment dirent.h | |
1163 | @comment BSD | |
1164 | @deftypevr Macro int MAXNAMLEN | |
1165 | This is the BSD name for @code{NAME_MAX}. It is defined in | |
1166 | @file{dirent.h}. | |
1167 | @end deftypevr | |
1168 | ||
1169 | @comment stdio.h | |
f65fd747 UD |
1170 | @comment ISO |
1171 | @deftypevr Macro int FILENAME_MAX | |
28f540f4 RM |
1172 | The value of this macro is an integer constant expression that |
1173 | represents the maximum length of a file name string. It is defined in | |
1174 | @file{stdio.h}. | |
1175 | ||
1176 | Unlike @code{PATH_MAX}, this macro is defined even if there is no actual | |
1177 | limit imposed. In such a case, its value is typically a very large | |
1178 | number. @strong{This is always the case on the GNU system.} | |
1179 | ||
1180 | @strong{Usage Note:} Don't use @code{FILENAME_MAX} as the size of an | |
1181 | array in which to store a file name! You can't possibly make an array | |
1182 | that big! Use dynamic allocation (@pxref{Memory Allocation}) instead. | |
1183 | @end deftypevr | |
1184 | ||
1185 | @node Options for Files | |
1186 | @section Optional Features in File Support | |
1187 | ||
1188 | POSIX defines certain system-specific options in the system calls for | |
1189 | operating on files. Some systems support these options and others do | |
1190 | not. Since these options are provided in the kernel, not in the | |
1191 | library, simply using the GNU C library does not guarantee any of these | |
1192 | features is supported; it depends on the system you are using. They can | |
1193 | also vary between file systems on a single machine. | |
1194 | ||
1195 | @pindex unistd.h | |
1196 | This section describes the macros you can test to determine whether a | |
1197 | particular option is supported on your machine. If a given macro is | |
1198 | defined in @file{unistd.h}, then its value says whether the | |
1199 | corresponding feature is supported. (A value of @code{-1} indicates no; | |
1200 | any other value indicates yes.) If the macro is undefined, it means | |
1201 | particular files may or may not support the feature. | |
1202 | ||
1203 | Since all the machines that support the GNU C library also support NFS, | |
1204 | one can never make a general statement about whether all file systems | |
1205 | support the @code{_POSIX_CHOWN_RESTRICTED} and @code{_POSIX_NO_TRUNC} | |
1206 | features. So these names are never defined as macros in the GNU C | |
1207 | library. | |
1208 | ||
1209 | @comment unistd.h | |
1210 | @comment POSIX.1 | |
1211 | @deftypevr Macro int _POSIX_CHOWN_RESTRICTED | |
1212 | If this option is in effect, the @code{chown} function is restricted so | |
f65fd747 | 1213 | that the only changes permitted to nonprivileged processes is to change |
28f540f4 RM |
1214 | the group owner of a file to either be the effective group ID of the |
1215 | process, or one of its supplementary group IDs. @xref{File Owner}. | |
1216 | @end deftypevr | |
1217 | ||
1218 | @comment unistd.h | |
1219 | @comment POSIX.1 | |
1220 | @deftypevr Macro int _POSIX_NO_TRUNC | |
1221 | If this option is in effect, file name components longer than | |
1222 | @code{NAME_MAX} generate an @code{ENAMETOOLONG} error. Otherwise, file | |
1223 | name components that are too long are silently truncated. | |
1224 | @end deftypevr | |
1225 | ||
1226 | @comment unistd.h | |
1227 | @comment POSIX.1 | |
1228 | @deftypevr Macro {unsigned char} _POSIX_VDISABLE | |
1229 | This option is only meaningful for files that are terminal devices. | |
1230 | If it is enabled, then handling for special control characters can | |
1231 | be disabled individually. @xref{Special Characters}. | |
1232 | @end deftypevr | |
1233 | ||
1234 | @pindex unistd.h | |
1235 | If one of these macros is undefined, that means that the option might be | |
1236 | in effect for some files and not for others. To inquire about a | |
1237 | particular file, call @code{pathconf} or @code{fpathconf}. | |
1238 | @xref{Pathconf}. | |
1239 | ||
1240 | @node File Minimums | |
1241 | @section Minimum Values for File System Limits | |
1242 | ||
1243 | Here are the names for the POSIX minimum upper bounds for some of the | |
1244 | above parameters. The significance of these values is that you can | |
1245 | safely push to these limits without checking whether the particular | |
dfd2257a UD |
1246 | system you are using can go that far. In most cases GNU systems do not |
1247 | have these strict limitations. The actual limit should be requested if | |
1248 | necessary. | |
28f540f4 RM |
1249 | |
1250 | @table @code | |
1251 | @comment limits.h | |
1252 | @comment POSIX.1 | |
1253 | @item _POSIX_LINK_MAX | |
1254 | The most restrictive limit permitted by POSIX for the maximum value of a | |
1255 | file's link count. The value of this constant is @code{8}; thus, you | |
1256 | can always make up to eight names for a file without running into a | |
1257 | system limit. | |
1258 | ||
1259 | @comment limits.h | |
1260 | @comment POSIX.1 | |
1261 | @item _POSIX_MAX_CANON | |
1262 | The most restrictive limit permitted by POSIX for the maximum number of | |
1263 | bytes in a canonical input line from a terminal device. The value of | |
1264 | this constant is @code{255}. | |
1265 | ||
1266 | @comment limits.h | |
1267 | @comment POSIX.1 | |
1268 | @item _POSIX_MAX_INPUT | |
1269 | The most restrictive limit permitted by POSIX for the maximum number of | |
1270 | bytes in a terminal device input queue (or typeahead buffer). | |
1271 | @xref{Input Modes}. The value of this constant is @code{255}. | |
1272 | ||
1273 | @comment limits.h | |
1274 | @comment POSIX.1 | |
1275 | @item _POSIX_NAME_MAX | |
1276 | The most restrictive limit permitted by POSIX for the maximum number of | |
1277 | bytes in a file name component. The value of this constant is | |
1278 | @code{14}. | |
1279 | ||
1280 | @comment limits.h | |
1281 | @comment POSIX.1 | |
1282 | @item _POSIX_PATH_MAX | |
1283 | The most restrictive limit permitted by POSIX for the maximum number of | |
1284 | bytes in a file name. The value of this constant is @code{255}. | |
1285 | ||
1286 | @comment limits.h | |
1287 | @comment POSIX.1 | |
1288 | @item _POSIX_PIPE_BUF | |
1289 | The most restrictive limit permitted by POSIX for the maximum number of | |
1290 | bytes that can be written atomically to a pipe. The value of this | |
1291 | constant is @code{512}. | |
1292 | @end table | |
1293 | ||
1294 | @node Pathconf | |
1295 | @section Using @code{pathconf} | |
1296 | ||
1297 | When your machine allows different files to have different values for a | |
1298 | file system parameter, you can use the functions in this section to find | |
1299 | out the value that applies to any particular file. | |
1300 | ||
1301 | These functions and the associated constants for the @var{parameter} | |
1302 | argument are declared in the header file @file{unistd.h}. | |
1303 | ||
1304 | @comment unistd.h | |
1305 | @comment POSIX.1 | |
1306 | @deftypefun {long int} pathconf (const char *@var{filename}, int @var{parameter}) | |
1307 | This function is used to inquire about the limits that apply to | |
1308 | the file named @var{filename}. | |
1309 | ||
1310 | The @var{parameter} argument should be one of the @samp{_PC_} constants | |
1311 | listed below. | |
1312 | ||
1313 | The normal return value from @code{pathconf} is the value you requested. | |
1314 | A value of @code{-1} is returned both if the implementation does not | |
1315 | impose a limit, and in case of an error. In the former case, | |
1316 | @code{errno} is not set, while in the latter case, @code{errno} is set | |
1317 | to indicate the cause of the problem. So the only way to use this | |
1318 | function robustly is to store @code{0} into @code{errno} just before | |
1319 | calling it. | |
1320 | ||
1321 | Besides the usual file name errors (@pxref{File Name Errors}), | |
1322 | the following error condition is defined for this function: | |
1323 | ||
1324 | @table @code | |
1325 | @item EINVAL | |
1326 | The value of @var{parameter} is invalid, or the implementation doesn't | |
1327 | support the @var{parameter} for the specific file. | |
1328 | @end table | |
1329 | @end deftypefun | |
1330 | ||
1331 | @comment unistd.h | |
1332 | @comment POSIX.1 | |
1333 | @deftypefun {long int} fpathconf (int @var{filedes}, int @var{parameter}) | |
1334 | This is just like @code{pathconf} except that an open file descriptor | |
1335 | is used to specify the file for which information is requested, instead | |
1336 | of a file name. | |
1337 | ||
1338 | The following @code{errno} error conditions are defined for this function: | |
1339 | ||
1340 | @table @code | |
1341 | @item EBADF | |
1342 | The @var{filedes} argument is not a valid file descriptor. | |
1343 | ||
1344 | @item EINVAL | |
1345 | The value of @var{parameter} is invalid, or the implementation doesn't | |
1346 | support the @var{parameter} for the specific file. | |
1347 | @end table | |
1348 | @end deftypefun | |
1349 | ||
1350 | Here are the symbolic constants that you can use as the @var{parameter} | |
1351 | argument to @code{pathconf} and @code{fpathconf}. The values are all | |
1352 | integer constants. | |
1353 | ||
1354 | @table @code | |
1355 | @comment unistd.h | |
1356 | @comment POSIX.1 | |
1357 | @item _PC_LINK_MAX | |
1358 | Inquire about the value of @code{LINK_MAX}. | |
1359 | ||
1360 | @comment unistd.h | |
1361 | @comment POSIX.1 | |
1362 | @item _PC_MAX_CANON | |
1363 | Inquire about the value of @code{MAX_CANON}. | |
1364 | ||
1365 | @comment unistd.h | |
1366 | @comment POSIX.1 | |
1367 | @item _PC_MAX_INPUT | |
1368 | Inquire about the value of @code{MAX_INPUT}. | |
1369 | ||
1370 | @comment unistd.h | |
1371 | @comment POSIX.1 | |
1372 | @item _PC_NAME_MAX | |
1373 | Inquire about the value of @code{NAME_MAX}. | |
1374 | ||
1375 | @comment unistd.h | |
1376 | @comment POSIX.1 | |
1377 | @item _PC_PATH_MAX | |
1378 | Inquire about the value of @code{PATH_MAX}. | |
1379 | ||
1380 | @comment unistd.h | |
1381 | @comment POSIX.1 | |
1382 | @item _PC_PIPE_BUF | |
1383 | Inquire about the value of @code{PIPE_BUF}. | |
1384 | ||
1385 | @comment unistd.h | |
1386 | @comment POSIX.1 | |
1387 | @item _PC_CHOWN_RESTRICTED | |
1388 | Inquire about the value of @code{_POSIX_CHOWN_RESTRICTED}. | |
1389 | ||
1390 | @comment unistd.h | |
1391 | @comment POSIX.1 | |
1392 | @item _PC_NO_TRUNC | |
1393 | Inquire about the value of @code{_POSIX_NO_TRUNC}. | |
1394 | ||
1395 | @comment unistd.h | |
1396 | @comment POSIX.1 | |
1397 | @item _PC_VDISABLE | |
1398 | Inquire about the value of @code{_POSIX_VDISABLE}. | |
dfd2257a UD |
1399 | |
1400 | @comment unistd.h | |
1401 | @comment POSIX.1 | |
1402 | @item _PC_SYNC_IO | |
1403 | Inquire about the value of @code{_POSIX_SYNC_IO}. | |
1404 | ||
1405 | @comment unistd.h | |
1406 | @comment POSIX.1 | |
1407 | @item _PC_ASYNC_IO | |
1408 | Inquire about the value of @code{_POSIX_ASYNC_IO}. | |
1409 | ||
1410 | @comment unistd.h | |
1411 | @comment POSIX.1 | |
1412 | @item _PC_PRIO_IO | |
1413 | Inquire about the value of @code{_POSIX_PRIO_IO}. | |
1414 | ||
1415 | @comment unistd.h | |
1416 | @comment POSIX.1g | |
1417 | @item _PC_SOCK_MAXBUF | |
1418 | Inquire about the value of @code{_POSIX_PIPE_BUF}. | |
28f540f4 RM |
1419 | @end table |
1420 | ||
1421 | @node Utility Limits | |
1422 | @section Utility Program Capacity Limits | |
1423 | ||
1424 | The POSIX.2 standard specifies certain system limits that you can access | |
1425 | through @code{sysconf} that apply to utility behavior rather than the | |
1426 | behavior of the library or the operating system. | |
1427 | ||
1428 | The GNU C library defines macros for these limits, and @code{sysconf} | |
1429 | returns values for them if you ask; but these values convey no | |
1430 | meaningful information. They are simply the smallest values that | |
1431 | POSIX.2 permits. | |
1432 | ||
1433 | @comment limits.h | |
1434 | @comment POSIX.2 | |
1435 | @deftypevr Macro int BC_BASE_MAX | |
1436 | The largest value of @code{obase} that the @code{bc} utility is | |
1437 | guaranteed to support. | |
1438 | @end deftypevr | |
1439 | ||
1440 | @comment limits.h | |
1441 | @comment POSIX.2 | |
1442 | @deftypevr Macro int BC_SCALE_MAX | |
1443 | The largest value of @code{scale} that the @code{bc} utility is | |
1444 | guaranteed to support. | |
1445 | @end deftypevr | |
1446 | ||
1447 | @comment limits.h | |
1448 | @comment POSIX.2 | |
1449 | @deftypevr Macro int BC_DIM_MAX | |
1450 | The largest number of elements in one array that the @code{bc} utility | |
1451 | is guaranteed to support. | |
1452 | @end deftypevr | |
1453 | ||
1454 | @comment limits.h | |
1455 | @comment POSIX.2 | |
1456 | @deftypevr Macro int BC_STRING_MAX | |
1457 | The largest number of characters in one string constant that the | |
1458 | @code{bc} utility is guaranteed to support. | |
1459 | @end deftypevr | |
1460 | ||
1461 | @comment limits.h | |
1462 | @comment POSIX.2 | |
1463 | @deftypevr Macro int BC_DIM_MAX | |
1464 | The largest number of elements in one array that the @code{bc} utility | |
1465 | is guaranteed to support. | |
1466 | @end deftypevr | |
1467 | ||
1468 | @comment limits.h | |
1469 | @comment POSIX.2 | |
1470 | @deftypevr Macro int COLL_WEIGHTS_MAX | |
1471 | The largest number of weights that can necessarily be used in defining | |
1472 | the collating sequence for a locale. | |
1473 | @end deftypevr | |
1474 | ||
1475 | @comment limits.h | |
1476 | @comment POSIX.2 | |
1477 | @deftypevr Macro int EXPR_NEST_MAX | |
1478 | The maximum number of expressions that can be nested within parenthesis | |
1479 | by the @code{expr} utility. | |
1480 | @end deftypevr | |
1481 | ||
1482 | @comment limits.h | |
1483 | @comment POSIX.2 | |
1484 | @deftypevr Macro int LINE_MAX | |
1485 | The largest text line that the text-oriented POSIX.2 utilities can | |
1486 | support. (If you are using the GNU versions of these utilities, then | |
1487 | there is no actual limit except that imposed by the available virtual | |
1488 | memory, but there is no way that the library can tell you this.) | |
1489 | @end deftypevr | |
1490 | ||
1491 | @comment limits.h | |
1492 | @comment POSIX.2 | |
1493 | @deftypevr Macro int EQUIV_CLASS_MAX | |
1494 | The maximum number of weights that can be assigned to an entry of the | |
1495 | @code{LC_COLLATE} category @samp{order} keyword in a locale definition. | |
1496 | The GNU C library does not presently support locale definitions. | |
1497 | @end deftypevr | |
1498 | ||
1499 | @node Utility Minimums | |
1500 | @section Minimum Values for Utility Limits | |
1501 | ||
1502 | @table @code | |
1503 | @comment limits.h | |
1504 | @comment POSIX.2 | |
1505 | @item _POSIX2_BC_BASE_MAX | |
1506 | The most restrictive limit permitted by POSIX.2 for the maximum value of | |
1507 | @code{obase} in the @code{bc} utility. Its value is @code{99}. | |
1508 | ||
1509 | @comment limits.h | |
1510 | @comment POSIX.2 | |
1511 | @item _POSIX2_BC_DIM_MAX | |
1512 | The most restrictive limit permitted by POSIX.2 for the maximum size of | |
1513 | an array in the @code{bc} utility. Its value is @code{2048}. | |
1514 | ||
1515 | @comment limits.h | |
1516 | @comment POSIX.2 | |
1517 | @item _POSIX2_BC_SCALE_MAX | |
1518 | The most restrictive limit permitted by POSIX.2 for the maximum value of | |
1519 | @code{scale} in the @code{bc} utility. Its value is @code{99}. | |
1520 | ||
1521 | @comment limits.h | |
1522 | @comment POSIX.2 | |
1523 | @item _POSIX2_BC_STRING_MAX | |
1524 | The most restrictive limit permitted by POSIX.2 for the maximum size of | |
1525 | a string constant in the @code{bc} utility. Its value is @code{1000}. | |
1526 | ||
1527 | @comment limits.h | |
1528 | @comment POSIX.2 | |
1529 | @item _POSIX2_COLL_WEIGHTS_MAX | |
1530 | The most restrictive limit permitted by POSIX.2 for the maximum number | |
1531 | of weights that can necessarily be used in defining the collating | |
1532 | sequence for a locale. Its value is @code{2}. | |
1533 | ||
1534 | @comment limits.h | |
1535 | @comment POSIX.2 | |
1536 | @item _POSIX2_EXPR_NEST_MAX | |
1537 | The most restrictive limit permitted by POSIX.2 for the maximum number | |
1538 | of expressions nested within parenthesis when using the @code{expr} utility. | |
1539 | Its value is @code{32}. | |
1540 | ||
1541 | @comment limits.h | |
1542 | @comment POSIX.2 | |
1543 | @item _POSIX2_LINE_MAX | |
1544 | The most restrictive limit permitted by POSIX.2 for the maximum size of | |
1545 | a text line that the text utilities can handle. Its value is | |
1546 | @code{2048}. | |
1547 | ||
1548 | @comment limits.h | |
1549 | @comment POSIX.2 | |
1550 | @item _POSIX2_EQUIV_CLASS_MAX | |
1551 | The most restrictive limit permitted by POSIX.2 for the maximum number | |
1552 | of weights that can be assigned to an entry of the @code{LC_COLLATE} | |
1553 | category @samp{order} keyword in a locale definition. Its value is | |
1554 | @code{2}. The GNU C library does not presently support locale | |
1555 | definitions. | |
1556 | @end table | |
1557 | ||
1558 | @node String Parameters | |
1559 | @section String-Valued Parameters | |
1560 | ||
1561 | POSIX.2 defines a way to get string-valued parameters from the operating | |
1562 | system with the function @code{confstr}: | |
1563 | ||
1564 | @comment unistd.h | |
1565 | @comment POSIX.2 | |
1566 | @deftypefun size_t confstr (int @var{parameter}, char *@var{buf}, size_t @var{len}) | |
1567 | This function reads the value of a string-valued system parameter, | |
1568 | storing the string into @var{len} bytes of memory space starting at | |
1569 | @var{buf}. The @var{parameter} argument should be one of the | |
1570 | @samp{_CS_} symbols listed below. | |
1571 | ||
1572 | The normal return value from @code{confstr} is the length of the string | |
1573 | value that you asked for. If you supply a null pointer for @var{buf}, | |
1574 | then @code{confstr} does not try to store the string; it just returns | |
1575 | its length. A value of @code{0} indicates an error. | |
1576 | ||
1577 | If the string you asked for is too long for the buffer (that is, longer | |
1578 | than @code{@var{len} - 1}), then @code{confstr} stores just that much | |
1579 | (leaving room for the terminating null character). You can tell that | |
1580 | this has happened because @code{confstr} returns a value greater than or | |
1581 | equal to @var{len}. | |
1582 | ||
1583 | The following @code{errno} error conditions are defined for this function: | |
1584 | ||
1585 | @table @code | |
1586 | @item EINVAL | |
1587 | The value of the @var{parameter} is invalid. | |
1588 | @end table | |
1589 | @end deftypefun | |
1590 | ||
1591 | Currently there is just one parameter you can read with @code{confstr}: | |
1592 | ||
1593 | @table @code | |
1594 | @comment unistd.h | |
1595 | @comment POSIX.2 | |
1596 | @item _CS_PATH | |
1597 | This parameter's value is the recommended default path for searching for | |
1598 | executable files. This is the path that a user has by default just | |
1599 | after logging in. | |
dfd2257a UD |
1600 | |
1601 | @comment unistd.h | |
1602 | @comment Unix98 | |
1603 | @item _CS_LFS_CFLAGS | |
f2ea0f5b | 1604 | The returned string specifies which additional flags must be given to |
dfd2257a UD |
1605 | the C compiler if a source is compiled using the |
1606 | @code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}. | |
1607 | ||
1608 | @comment unistd.h | |
1609 | @comment Unix98 | |
1610 | @item _CS_LFS_LDFLAGS | |
f2ea0f5b | 1611 | The returned string specifies which additional flags must be given to |
dfd2257a UD |
1612 | the linker if a source is compiled using the |
1613 | @code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}. | |
1614 | ||
1615 | @comment unistd.h | |
1616 | @comment Unix98 | |
1617 | @item _CS_LFS_LIBS | |
f2ea0f5b | 1618 | The returned string specifies which additional libraries must be linked |
dfd2257a UD |
1619 | to the application if a source is compiled using the |
1620 | @code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}. | |
1621 | ||
1622 | @comment unistd.h | |
1623 | @comment Unix98 | |
1624 | @item _CS_LFS_LINTFLAGS | |
f2ea0f5b | 1625 | The returned string specifies which additional flags must be given to |
dfd2257a UD |
1626 | the the lint tool if a source is compiled using the |
1627 | @code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}. | |
1628 | ||
1629 | @comment unistd.h | |
1630 | @comment Unix98 | |
1631 | @item _CS_LFS64_CFLAGS | |
f2ea0f5b | 1632 | The returned string specifies which additional flags must be given to |
dfd2257a UD |
1633 | the C compiler if a source is compiled using the |
1634 | @code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}. | |
1635 | ||
1636 | @comment unistd.h | |
1637 | @comment Unix98 | |
1638 | @item _CS_LFS64_LDFLAGS | |
f2ea0f5b | 1639 | The returned string specifies which additional flags must be given to |
dfd2257a UD |
1640 | the linker if a source is compiled using the |
1641 | @code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}. | |
1642 | ||
1643 | @comment unistd.h | |
1644 | @comment Unix98 | |
1645 | @item _CS_LFS64_LIBS | |
f2ea0f5b | 1646 | The returned string specifies which additional libraries must be linked |
dfd2257a UD |
1647 | to the application if a source is compiled using the |
1648 | @code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}. | |
1649 | ||
1650 | @comment unistd.h | |
1651 | @comment Unix98 | |
1652 | @item _CS_LFS64_LINTFLAGS | |
f2ea0f5b | 1653 | The returned string specifies which additional flags must be given to |
dfd2257a UD |
1654 | the the lint tool if a source is compiled using the |
1655 | @code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}. | |
28f540f4 RM |
1656 | @end table |
1657 | ||
1658 | The way to use @code{confstr} without any arbitrary limit on string size | |
1659 | is to call it twice: first call it to get the length, allocate the | |
1660 | buffer accordingly, and then call @code{confstr} again to fill the | |
1661 | buffer, like this: | |
1662 | ||
1663 | @smallexample | |
1664 | @group | |
1665 | char * | |
1666 | get_default_path (void) | |
1667 | @{ | |
1668 | size_t len = confstr (_CS_PATH, NULL, 0); | |
1669 | char *buffer = (char *) xmalloc (len); | |
1670 | ||
1671 | if (confstr (_CS_PATH, buf, len + 1) == 0) | |
1672 | @{ | |
1673 | free (buffer); | |
1674 | return NULL; | |
1675 | @} | |
1676 | ||
1677 | return buffer; | |
1678 | @} | |
1679 | @end group | |
1680 | @end smallexample |