1SYSTEM_DATA_TYPES(7) Linux Programmer's Manual SYSTEM_DATA_TYPES(7)
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6 system_data_types - overview of system data types
7
9 aiocb
10 Include: <aio.h>.
11 struct aiocb {
13 int aio_fildes; /* File descriptor */
14 off_t aio_offset; /* File offset */
15 volatile void *aio_buf; /* Location of buffer */
16 size_t aio_nbytes; /* Length of transfer */
17 int aio_reqprio; /* Request priority offset */
18 struct sigevent aio_sigevent; /* Signal number and value */
19 int aio_lio_opcode;/* Operation to be performed */
20 };
21 For further information about this structure, see aio(7).
23 Conforming to: POSIX.1-2001 and later.
25 See also: aio_cancel(3), aio_error(3), aio_fsync(3),
27 aio_read(3), aio_return(3), aio_suspend(3), aio_write(3),
28 lio_listio(3)
29 clock_t
31 Include: <time.h> or <sys/types.h>. Alternatively,
32 <sys/time.h>.
33 Used for system time in clock ticks or CLOCKS_PER_SEC (defined
35 in <time.h>). According to POSIX, it shall be an integer type
36 or a real-floating type.
37 Conforming to: C99 and later; POSIX.1-2001 and later.
39 See also: times(2), clock(3)
41 clockid_t
43 Include: <sys/types.h>. Alternatively, <time.h>.
44 Used for clock ID type in the clock and timer functions. Ac‐
46 cording to POSIX, it shall be defined as an arithmetic type.
47 Conforming to: POSIX.1-2001 and later.
49 See also: clock_adjtime(2), clock_getres(2), clock_nanosleep(2),
51 timer_create(2), clock_getcpuclockid(3)
52 dev_t
54 Include: <sys/types.h>. Alternatively, <sys/stat.h>.
55 Used for device IDs. According to POSIX, it shall be an integer
57 type. For further details of this type, see makedev(3).
58 Conforming to: POSIX.1-2001 and later.
60 See also: mknod(2), stat(2)
62 div_t
64 Include: <stdlib.h>.
65 typedef struct {
67 int quot; /* Quotient */
68 int rem; /* Remainder */
69 } div_t;
70 It is the type of the value returned by the div(3) function.
72 Conforming to: C99 and later; POSIX.1-2001 and later.
74 See also: div(3)
76 double_t
78 Include: <math.h>.
79 The implementation's most efficient floating type at least as
81 wide as double. Its type depends on the value of the macro
82 FLT_EVAL_METHOD (defined in <float.h>):
83 0 double_t is double.
85 1 double_t is double.
87 2 double_t is long double.
89 For other values of FLT_EVAL_METHOD, the type of double_t is im‐
91 plementation-defined.
92 Conforming to: C99 and later; POSIX.1-2001 and later.
94 See also: the float_t type in this page.
96 fd_set
98 Include: <sys/select.h>. Alternatively, <sys/time.h>.
99 A structure type that can represent a set of file descriptors.
101 According to POSIX, the maximum number of file descriptors in an
102 fd_set structure is the value of the macro FD_SETSIZE.
103 Conforming to: POSIX.1-2001 and later.
105 See also: select(2)
107 fenv_t
109 Include: <fenv.h>.
110 This type represents the entire floating-point environment, in‐
112 cluding control modes and status flags; for further details, see
113 fenv(3).
114 Conforming to: C99 and later; POSIX.1-2001 and later.
116 See also: fenv(3)
118 fexcept_t
120 Include: <fenv.h>.
121 This type represents the floating-point status flags collec‐
123 tively; for further details see fenv(3).
124 Conforming to: C99 and later; POSIX.1-2001 and later.
126 See also: fenv(3)
128 FILE
130 Include: <stdio.h>. Alternatively, <wchar.h>.
131 An object type used for streams.
133 Conforming to: C99 and later; POSIX.1-2001 and later.
135 See also: fclose(3), flockfile(3), fopen(3), fprintf(3),
137 fread(3), fscanf(3), stdin(3), stdio(3)
138 float_t
140 Include: <math.h>.
141 The implementation's most efficient floating type at least as
143 wide as float. Its type depends on the value of the macro
144 FLT_EVAL_METHOD (defined in <float.h>):
145 0 float_t is float.
147 1 float_t is double.
149 2 float_t is long double.
151 For other values of FLT_EVAL_METHOD, the type of float_t is im‐
153 plementation-defined.
154 Conforming to: C99 and later; POSIX.1-2001 and later.
156 See also: the double_t type in this page.
158 gid_t
160 Include: <sys/types.h>. Alternatively, <grp.h>, <pwd.h>, <sig‐
161 nal.h>, <stropts.h>, <sys/ipc.h>, <sys/stat.h>, or <unistd.h>.
162 A type used to hold group IDs. According to POSIX, this shall
164 be an integer type.
165 Conforming to: POSIX.1-2001 and later.
167 See also: chown(2), getgid(2), getegid(2), getgroups(2), getres‐
169 gid(2), getgrnam(2), credentials(7)
170 id_t
172 Include: <sys/types.h>. Alternatively, <sys/resource.h>.
173 A type used to hold a general identifier. According to POSIX,
175 this shall be an integer type that can be used to contain a
176 pid_t, uid_t, or gid_t.
177 Conforming to: POSIX.1-2001 and later.
179 See also: getpriority(2), waitid(2)
181 imaxdiv_t
183 Include: <inttypes.h>.
184 typedef struct {
186 intmax_t quot; /* Quotient */
187 intmax_t rem; /* Remainder */
188 } imaxdiv_t;
189 It is the type of the value returned by the imaxdiv(3) function.
191 Conforming to: C99 and later; POSIX.1-2001 and later.
193 See also: imaxdiv(3)
195 intmax_t
197 Include: <stdint.h>. Alternatively, <inttypes.h>.
198 A signed integer type capable of representing any value of any
200 signed integer type supported by the implementation. According
201 to the C language standard, it shall be capable of storing val‐
202 ues in the range [INTMAX_MIN, INTMAX_MAX].
203 The macro INTMAX_C() expands its argument to an integer constant
205 of type intmax_t.
206 The length modifier for intmax_t for the printf(3) and the
208 scanf(3) families of functions is j; resulting commonly in %jd
209 or %ji for printing intmax_t values.
210 Conforming to: C99 and later; POSIX.1-2001 and later.
212 Bugs: intmax_t is not large enough to represent values of type
214 __int128 in implementations where __int128 is defined and long
215 long is less than 128 bits wide.
216 See also: the uintmax_t type in this page.
218 intN_t
220 Include: <stdint.h>. Alternatively, <inttypes.h>.
221 int8_t, int16_t, int32_t, int64_t
223 A signed integer type of a fixed width of exactly N bits, N be‐
225 ing the value specified in its type name. According to the C
226 language standard, they shall be capable of storing values in
227 the range [INTN_MIN, INTN_MAX], substituting N by the appropri‐
228 ate number.
229 According to POSIX, int8_t, int16_t, and int32_t are required;
231 int64_t is only required in implementations that provide integer
232 types with width 64; and all other types of this form are op‐
233 tional.
234 The length modifiers for the intN_t types for the printf(3) fam‐
236 ily of functions are expanded by macros of the forms PRIdN and
237 PRIiN (defined in <inttypes.h>); resulting for example in
238 %"PRId64" or %"PRIi64" for printing int64_t values. The length
239 modifiers for the intN_t types for the scanf(3) family of func‐
240 tions are expanded by macros of the forms SCNdN and SCNiN, (de‐
241 fined in <inttypes.h>); resulting for example in %"SCNd8" or
242 %"SCNi8" for scanning int8_t values.
243 Conforming to: C99 and later; POSIX.1-2001 and later.
245 See also: the intmax_t, uintN_t, and uintmax_t types in this
247 page.
248 intptr_t
250 Include: <stdint.h>. Alternatively, <inttypes.h>.
251 A signed integer type such that any valid (void *) value can be
253 converted to this type and back. According to the C language
254 standard, it shall be capable of storing values in the range
255 [INTPTR_MIN, INTPTR_MAX].
256 The length modifier for intptr_t for the printf(3) family of
258 functions is expanded by the macros PRIdPTR and PRIiPTR (defined
259 in <inttypes.h>); resulting commonly in %"PRIdPTR" or %"PRIiPTR"
260 for printing intptr_t values. The length modifier for intptr_t
261 for the scanf(3) family of functions is expanded by the macros
262 SCNdPTR and SCNiPTR, (defined in <inttypes.h>); resulting com‐
263 monly in %"SCNdPTR" or %"SCNiPTR" for scanning intptr_t values.
264 Conforming to: C99 and later; POSIX.1-2001 and later.
266 See also: the uintptr_t and void * types in this page.
268 lconv
270 Include: <locale.h>.
271 struct lconv { /* Values in the "C" locale: */
273 char *decimal_point; /* "." */
274 char *thousands_sep; /* "" */
275 char *grouping; /* "" */
276 char *mon_decimal_point; /* "" */
277 char *mon_thousands_sep; /* "" */
278 char *mon_grouping; /* "" */
279 char *positive_sign; /* "" */
280 char *negative_sign; /* "" */
281 char *currency_symbol; /* "" */
282 char frac_digits; /* CHAR_MAX */
283 char p_cs_precedes; /* CHAR_MAX */
284 char n_cs_precedes; /* CHAR_MAX */
285 char p_sep_by_space; /* CHAR_MAX */
286 char n_sep_by_space; /* CHAR_MAX */
287 char p_sign_posn; /* CHAR_MAX */
288 char n_sign_posn; /* CHAR_MAX */
289 char *int_curr_symbol; /* "" */
290 char int_frac_digits; /* CHAR_MAX */
291 char int_p_cs_precedes; /* CHAR_MAX */
292 char int_n_cs_precedes; /* CHAR_MAX */
293 char int_p_sep_by_space; /* CHAR_MAX */
294 char int_n_sep_by_space; /* CHAR_MAX */
295 char int_p_sign_posn; /* CHAR_MAX */
296 char int_n_sign_posn; /* CHAR_MAX */
297 };
298 Contains members related to the formatting of numeric values.
300 In the "C" locale, its members have the values shown in the com‐
301 ments above.
302 Conforming to: C11 and later; POSIX.1-2001 and later.
304 See also: setlocale(3), localeconv(3), charsets(5), locale(7)
306 ldiv_t
308 Include: <stdlib.h>.
309 typedef struct {
311 long quot; /* Quotient */
312 long rem; /* Remainder */
313 } ldiv_t;
314 It is the type of the value returned by the ldiv(3) function.
316 Conforming to: C99 and later; POSIX.1-2001 and later.
318 See also: ldiv(3)
320 lldiv_t
322 Include: <stdlib.h>.
323 typedef struct {
325 long long quot; /* Quotient */
326 long long rem; /* Remainder */
327 } lldiv_t;
328 It is the type of the value returned by the lldiv(3) function.
330 Conforming to: C99 and later; POSIX.1-2001 and later.
332 See also: lldiv(3)
334 off_t
336 Include: <sys/types.h>. Alternatively, <aio.h>, <fcntl.h>,
337 <stdio.h>, <sys/mman.h>, <sys/stat.h.h>, or <unistd.h>.
338 Used for file sizes. According to POSIX, this shall be a signed
340 integer type.
341 Versions: <aio.h> and <stdio.h> define off_t since POSIX.1-2008.
343 Conforming to: POSIX.1-2001 and later.
345 Notes: On some architectures, the width of this type can be con‐
347 trolled with the feature test macro _FILE_OFFSET_BITS.
348 See also: lseek(2), mmap(2), posix_fadvise(2), pread(2), trun‐
350 cate(2), fseeko(3), lockf(3), posix_fallocate(3), fea‐
351 ture_test_macros(7)
352 pid_t
354 Include: <sys/types.h>. Alternatively, <fcntl.h>, <sched.h>,
355 <signal.h>, <spawn.h>, <sys/msg.h>, <sys/sem.h>, <sys/shm.h>,
356 <sys/wait.h>, <termios.h>, <time.h>, <unistd.h>, or <utmpx.h>.
357 This type is used for storing process IDs, process group IDs,
359 and session IDs. According to POSIX, it shall be a signed inte‐
360 ger type, and the implementation shall support one or more pro‐
361 gramming environments where the width of pid_t is no greater
362 than the width of the type long.
363 Conforming to: POSIX.1-2001 and later.
365 See also: fork(2), getpid(2), getppid(2), getsid(2), gettid(2),
367 getpgid(2), kill(2), pidfd_open(2), sched_setscheduler(2), wait‐
368 pid(2), sigqueue(3), credentials(7),
369 ptrdiff_t
371 Include: <stddef.h>.
372 Used for a count of elements, and array indices. It is the re‐
374 sult of subtracting two pointers. According to the C language
375 standard, it shall be a signed integer type capable of storing
376 values in the range [PTRDIFF_MIN, PTRDIFF_MAX].
377 The length modifier for ptrdiff_t for the printf(3) and the
379 scanf(3) families of functions is t; resulting commonly in %td
380 or %ti for printing ptrdiff_t values.
381 Conforming to: C99 and later; POSIX.1-2001 and later.
383 See also: the size_t and ssize_t types in this page.
385 regex_t
387 Include: <regex.h>.
388 typedef struct {
390 size_t re_nsub; /* Number of parenthesized subexpressions. */
391 } regex_t;
392 This is a structure type used in regular expression matching.
394 It holds a compiled regular expression, compiled with reg‐
395 comp(3).
396 Conforming to: POSIX.1-2001 and later.
398 See also: regex(3)
400 regmatch_t
402 Include: <regex.h>.
403 typedef struct {
405 regoff_t rm_so; /* Byte offset from start of string
406 to start of substring */
407 regoff_t rm_eo; /* Byte offset from start of string of
408 the first character after the end of
409 substring */
410 } regmatch_t;
411 This is a structure type used in regular expression matching.
413 Conforming to: POSIX.1-2001 and later.
415 See also: regexec(3)
417 regoff_t
419 Include: <regex.h>.
420 According to POSIX, it shall be a signed integer type capable of
422 storing the largest value that can be stored in either a
423 ptrdiff_t type or a ssize_t type.
424 Versions: Prior to POSIX.1-2008, the type was capable of storing
426 the largest value that can be stored in either an off_t type or
427 a ssize_t type.
428 Conforming to: POSIX.1-2001 and later.
430 See also: the regmatch_t structure and the ptrdiff_t and ssize_t
432 types in this page.
433 sigevent
435 Include: <signal.h>. Alternatively, <aio.h>, <mqueue.h>, or
436 <time.h>.
437 struct sigevent {
439 int sigev_notify; /* Notification type */
440 int sigev_signo; /* Signal number */
441 union sigval sigev_value; /* Signal value */
442 void (*sigev_notify_function)(union sigval);
443 /* Notification function */
444 pthread_attr_t *sigev_notify_attributes;
445 /* Notification attributes */
446 };
447 For further details about this type, see sigevent(7).
449 Versions: <aio.h> and <time.h> define sigevent since
451 POSIX.1-2008.
452 Conforming to: POSIX.1-2001 and later.
454 See also: timer_create(2), getaddrinfo_a(3), lio_listio(3),
456 mq_notify(3)
457 See also the aiocb structure in this page.
459 siginfo_t
461 Include: <signal.h>. Alternatively, <sys/wait.h>.
462 typedef struct {
464 int si_signo; /* Signal number */
465 int si_code; /* Signal code */
466 pid_t si_pid; /* Sending process ID */
467 uid_t si_uid; /* Real user ID of sending process */
468 void *si_addr; /* Address of faulting instruction */
469 int si_status; /* Exit value or signal */
470 union sigval si_value; /* Signal value */
471 } siginfo_t;
472 Information associated with a signal. For further details on
474 this structure (including additional, Linux-specific fields),
475 see sigaction(2).
476 Conforming to: POSIX.1-2001 and later.
478 See also: pidfd_send_signal(2), rt_sigqueueinfo(2), sigac‐
480 tion(2), sigwaitinfo(2), psiginfo(3)
481 sigset_t
483 Include: <signal.h>. Alternatively, <spawn.h>, or <sys/se‐
484 lect.h>.
485 This is a type that represents a set of signals. According to
487 POSIX, this shall be an integer or structure type.
488 Conforming to: POSIX.1-2001 and later.
490 See also: epoll_pwait(2), ppoll(2), pselect(2), sigaction(2),
492 signalfd(2), sigpending(2), sigprocmask(2), sigsuspend(2), sig‐
493 waitinfo(2), signal(7)
494 sigval
496 Include: <signal.h>.
497 union sigval {
499 int sigval_int; /* Integer value */
500 void *sigval_ptr; /* Pointer value */
501 };
502 Data passed with a signal.
504 Conforming to: POSIX.1-2001 and later.
506 See also: pthread_sigqueue(3), sigqueue(3), sigevent(7)
508 See also the sigevent structure and the siginfo_t type in this
510 page.
511 size_t
513 Include: <stddef.h> or <sys/types.h>. Alternatively, <aio.h>,
514 <glob.h>, <grp.h>, <iconv.h>, <monetary.h>, <mqueue.h>,
515 <ndbm.h>, <pwd.h>, <regex.h>, <search.h>, <signal.h>, <stdio.h>,
516 <stdlib.h>, <string.h>, <strings.h>, <sys/mman.h>, <sys/msg.h>,
517 <sys/sem.h>, <sys/shm.h>, <sys/socket.h>, <sys/uio.h>, <time.h>,
518 <unistd.h>, <wchar.h>, or <wordexp.h>.
519 Used for a count of bytes. It is the result of the sizeof oper‐
521 ator. According to the C language standard, it shall be an un‐
522 signed integer type capable of storing values in the range [0,
523 SIZE_MAX]. According to POSIX, the implementation shall support
524 one or more programming environments where the width of size_t
525 is no greater than the width of the type long.
526 The length modifier for size_t for the printf(3) and the
528 scanf(3) families of functions is z; resulting commonly in %zu
529 or %zx for printing size_t values.
530 Versions: <aio.h>, <glob.h>, <grp.h>, <iconv.h>, <mqueue.h>,
532 <pwd.h>, <signal.h>, and <sys/socket.h> define size_t since
533 POSIX.1-2008.
534 Conforming to: C99 and later; POSIX.1-2001 and later.
536 See also: read(2), write(2), fread(3), fwrite(3), memcmp(3),
538 memcpy(3), memset(3), offsetof(3)
539 See also the ptrdiff_t and ssize_t types in this page.
541 ssize_t
543 Include: <sys/types.h>. Alternatively, <aio.h>, <monetary.h>,
544 <mqueue.h>, <stdio.h>, <sys/msg.h>, <sys/socket.h>, <sys/uio.h>,
545 or <unistd.h>.
546 Used for a count of bytes or an error indication. According to
548 POSIX, it shall be a signed integer type capable of storing val‐
549 ues at least in the range [-1, SSIZE_MAX], and the implementa‐
550 tion shall support one or more programming environments where
551 the width of ssize_t is no greater than the width of the type
552 long.
553 Glibc and most other implementations provide a length modifier
555 for ssize_t for the printf(3) and the scanf(3) families of func‐
556 tions, which is z; resulting commonly in %zd or %zi for printing
557 ssize_t values. Although z works for ssize_t on most implemen‐
558 tations, portable POSIX programs should avoid using it—for exam‐
559 ple, by converting the value to intmax_t and using its length
560 modifier (j).
561 Conforming to: POSIX.1-2001 and later.
563 See also: read(2), readlink(2), readv(2), recv(2), send(2),
565 write(2)
566 See also the ptrdiff_t and size_t types in this page.
568 suseconds_t
570 Include: <sys/types.h>. Alternatively, <sys/select.h>, or
571 <sys/time.h>.
572 Used for time in microseconds. According to POSIX, it shall be
574 a signed integer type capable of storing values at least in the
575 range [-1, 1000000], and the implementation shall support one or
576 more programming environments where the width of suseconds_t is
577 no greater than the width of the type long.
578 Conforming to: POSIX.1-2001 and later.
580 See also: the timeval structure in this page.
582 time_t
584 Include: <time.h> or <sys/types.h>. Alternatively, <sched.h>,
585 <sys/msg.h>, <sys/select.h>, <sys/sem.h>, <sys/shm.h>,
586 <sys/stat.h>, <sys/time.h>, or <utime.h>.
587 Used for time in seconds. According to POSIX, it shall be an
589 integer type.
590 Versions: <sched.h> defines time_t since POSIX.1-2008.
592 Conforming to: C99 and later; POSIX.1-2001 and later.
594 See also: stime(2), time(2), ctime(3), difftime(3)
596 timer_t
598 Include: <sys/types.h>. Alternatively, <time.h>.
599 Used for timer ID returned by timer_create(2). According to
601 POSIX, there are no defined comparison or assignment operators
602 for this type.
603 Conforming to: POSIX.1-2001 and later.
605 See also: timer_create(2), timer_delete(2), timer_getoverrun(2),
607 timer_settime(2)
608 timespec
610 Include: <time.h>. Alternatively, <aio.h>, <mqueue.h>,
611 <sched.h>, <signal.h>, <sys/select.h>, or <sys/stat.h>.
612 struct timespec {
614 time_t tv_sec; /* Seconds */
615 long tv_nsec; /* Nanoseconds */
616 };
617 Describes times in seconds and nanoseconds.
619 Conforming to: C11 and later; POSIX.1-2001 and later.
621 See also: clock_gettime(2), clock_nanosleep(2), nanosleep(2),
623 timerfd_gettime(2), timer_gettime(2)
624 timeval
626 Include: <sys/time.h>. Alternatively, <sys/resource.h>,
627 <sys/select.h>, or <utmpx.h>.
628 struct timeval {
630 time_t tv_sec; /* Seconds */
631 suseconds_t tv_usec; /* Microseconds */
632 };
633 Describes times in seconds and microseconds.
635 Conforming to: POSIX.1-2001 and later.
637 See also: gettimeofday(2), select(2), utimes(2), adjtime(3), fu‐
639 times(3), timeradd(3)
640 uid_t
642 Include: <sys/types.h>. Alternatively, <pwd.h>, <signal.h>,
643 <stropts.h>, <sys/ipc.h>, <sys/stat.h>, or <unistd.h>.
644 A type used to hold user IDs. According to POSIX, this shall be
646 an integer type.
647 Conforming to: POSIX.1-2001 and later.
649 See also: chown(2), getuid(2), geteuid(2), getresuid(2), getpw‐
651 nam(2), credentials(7)
652 uintmax_t
654 Include: <stdint.h>. Alternatively, <inttypes.h>.
655 An unsigned integer type capable of representing any value of
657 any unsigned integer type supported by the implementation. Ac‐
658 cording to the C language standard, it shall be capable of stor‐
659 ing values in the range [0, UINTMAX_MAX].
660 The macro UINTMAX_C() expands its argument to an integer con‐
662 stant of type uintmax_t.
663 The length modifier for uintmax_t for the printf(3) and the
665 scanf(3) families of functions is j; resulting commonly in %ju
666 or %jx for printing uintmax_t values.
667 Conforming to: C99 and later; POSIX.1-2001 and later.
669 Bugs: uintmax_t is not large enough to represent values of type
671 unsigned __int128 in implementations where unsigned __int128 is
672 defined and unsigned long long is less than 128 bits wide.
673 See also: the intmax_t type in this page.
675 uintN_t
677 Include: <stdint.h>. Alternatively, <inttypes.h>.
678 uint8_t, uint16_t, uint32_t, uint64_t
680 An unsigned integer type of a fixed width of exactly N bits, N
682 being the value specified in its type name. According to the C
683 language standard, they shall be capable of storing values in
684 the range [0, UINTN_MAX], substituting N by the appropriate num‐
685 ber.
686 According to POSIX, uint8_t, uint16_t, and uint32_t are re‐
688 quired; uint64_t is only required in implementations that pro‐
689 vide integer types with width 64; and all other types of this
690 form are optional.
691 The length modifiers for the uintN_t types for the printf(3)
693 family of functions are expanded by macros of the forms PRIuN,
694 PRIoN, PRIxN, and PRIXN (defined in <inttypes.h>); resulting for
695 example in %"PRIu32" or %"PRIx32" for printing uint32_t values.
696 The length modifiers for the uintN_t types for the scanf(3) fam‐
697 ily of functions are expanded by macros of the forms SCNuN, SC‐
698 NoN, SCNxN, and SCNXN (defined in <inttypes.h>); resulting for
699 example in %"SCNu16" or %"SCNx16" for scanning uint16_t values.
700 Conforming to: C99 and later; POSIX.1-2001 and later.
702 See also: the intmax_t, intN_t, and uintmax_t types in this
704 page.
705 uintptr_t
707 Include: <stdint.h>. Alternatively, <inttypes.h>.
708 An unsigned integer type such that any valid (void *) value can
710 be converted to this type and back. According to the C language
711 standard, it shall be capable of storing values in the range [0,
712 UINTPTR_MAX].
713 The length modifier for uintptr_t for the printf(3) family of
715 functions is expanded by the macros PRIuPTR, PRIoPTR, PRIxPTR,
716 and PRIXPTR (defined in <inttypes.h>); resulting commonly in
717 %"PRIuPTR" or %"PRIxPTR" for printing uintptr_t values. The
718 length modifier for uintptr_t for the scanf(3) family of func‐
719 tions is expanded by the macros SCNuPTR, SCNoPTR, SCNxPTR, and
720 SCNXPTR (defined in <inttypes.h>); resulting commonly in %"SC‐
721 NuPTR" or %"SCNxPTR" for scanning uintptr_t values.
722 Conforming to: C99 and later; POSIX.1-2001 and later.
724 See also: the intptr_t and void * types in this page.
726 va_list
728 Include: <stdarg>. Alternatively, <stdio.h>, or <wchar.h>.
729 Used by functions with a varying number of arguments of varying
731 types. The function must declare an object of type va_list
732 which is used by the macros va_start(3), va_arg(3), va_copy(3),
733 and va_end(3) to traverse the list of arguments.
734 Conforming to: C99 and later; POSIX.1-2001 and later.
736 See also: va_start(3), va_arg(3), va_copy(3), va_end(3)
738 void *
740 According to the C language standard, a pointer to any object
741 type may be converted to a pointer to void and back. POSIX fur‐
742 ther requires that any pointer, including pointers to functions,
743 may be converted to a pointer to void and back.
744 Conversions from and to any other pointer type are done implic‐
746 itly, not requiring casts at all. Note that this feature pre‐
747 vents any kind of type checking: the programmer should be care‐
748 ful not to convert a void * value to a type incompatible to that
749 of the underlying data, because that would result in undefined
750 behavior.
751 This type is useful in function parameters and return value to
753 allow passing values of any type. The function will typically
754 use some mechanism to know the real type of the data being
755 passed via a pointer to void.
756 A value of this type can't be dereferenced, as it would give a
758 value of type void, which is not possible. Likewise, pointer
759 arithmetic is not possible with this type. However, in GNU C,
760 pointer arithmetic is allowed as an extension to the standard;
761 this is done by treating the size of a void or of a function as
762 1. A consequence of this is that sizeof is also allowed on void
763 and on function types, and returns 1.
764 The conversion specifier for void * for the printf(3) and the
766 scanf(3) families of functions is p.
767 Versions: The POSIX requirement about compatibility between void
769 * and function pointers was added in POSIX.1-2008 Technical Cor‐
770 rigendum 1 (2013).
771 Conforming to: C99 and later; POSIX.1-2001 and later.
773 See also: malloc(3), memcmp(3), memcpy(3), memset(3)
775 See also the intptr_t and uintptr_t types in this page.
777
779 The structures described in this manual page shall contain, at least,
780 the members shown in their definition, in no particular order.
781 Most of the integer types described in this page don't have a corre‐
783 sponding length modifier for the printf(3) and the scanf(3) families of
784 functions. To print a value of an integer type that doesn't have a
785 length modifier, it should be converted to intmax_t or uintmax_t by an
786 explicit cast. To scan into a variable of an integer type that doesn't
787 have a length modifier, an intermediate temporary variable of type int‐
788 max_t or uintmax_t should be used. When copying from the temporary
789 variable to the destination variable, the value could overflow. If the
790 type has upper and lower limits, the user should check that the value
791 is within those limits, before actually copying the value. The example
792 below shows how these conversions should be done.
793 Conventions used in this page
795 In "Conforming to" we only concern ourselves with C99 and later and
796 POSIX.1-2001 and later. Some types may be specified in earlier ver‐
797 sions of one of these standards, but in the interests of simplicity we
798 omit details from earlier standards.
799 In "Include", we first note the "primary" header(s) that define the
801 type according to either the C or POSIX.1 standards. Under "Alterna‐
802 tively", we note additional headers that the standards specify shall
803 define the type.
804
806 The program shown below scans from a string and prints a value stored
807 in a variable of an integer type that doesn't have a length modifier.
808 The appropriate conversions from and to intmax_t, and the appropriate
809 range checks, are used as explained in the notes section above.
810 #include <stdint.h>
812 #include <stdio.h>
813 #include <stdlib.h>
814 #include <sys/types.h>
815 int
817 main (void)
818 {
819 static const char *const str = "500000 us in half a second";
820 suseconds_t us;
821 intmax_t tmp;
822 /* Scan the number from the string into the temporary variable */
824 sscanf(str, "%jd", &tmp);
826 /* Check that the value is within the valid range of suseconds_t */
828 if (tmp < -1 || tmp > 1000000) {
830 fprintf(stderr, "Scanned value outside valid range!\n");
831 exit(EXIT_FAILURE);
832 }
833 /* Copy the value to the suseconds_t variable 'us' */
835 us = tmp;
837 /* Even though suseconds_t can hold the value -1, this isn't
839 a sensible number of microseconds */
840 if (us < 0) {
842 fprintf(stderr, "Scanned value shouldn't be negative!\n");
843 exit(EXIT_FAILURE);
844 }
845 /* Print the value */
847 printf("There are %jd microseconds in half a second.\n",
849 (intmax_t) us);
850 exit(EXIT_SUCCESS);
852 }
853
855 feature_test_macros(7), standards(7)
856
858 This page is part of release 5.10 of the Linux man-pages project. A
859 description of the project, information about reporting bugs, and the
860 latest version of this page, can be found at
861 https://www.kernel.org/doc/man-pages/.
862Linux 2020-12-21 SYSTEM_DATA_TYPES(7)