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 blkcnt_t
31 Include: <sys/types.h>. Alternatively, <sys/stat.h>.
32 Used for file block counts. According to POSIX, it shall be a
34 signed integer type.
35 Conforming to: POSIX.1-2001 and later.
37 See also: stat(2)
39 blksize_t
41 Include: <sys/types.h>. Alternatively, <sys/stat.h>.
42 Used for file block sizes. According to POSIX, it shall be a
44 signed integer type.
45 Conforming to: POSIX.1-2001 and later.
47 See also: stat(2)
49 cc_t
51 Include: <termios.h>.
52 Used for terminal special characters. According to POSIX, it
54 shall be an unsigned integer type.
55 Conforming to: POSIX.1-2001 and later.
57 See also: termios(3)
59 clock_t
61 Include: <time.h> or <sys/types.h>. Alternatively,
62 <sys/time.h>.
63 Used for system time in clock ticks or CLOCKS_PER_SEC (defined
65 in <time.h>). According to POSIX, it shall be an integer type
66 or a real-floating type.
67 Conforming to: C99 and later; POSIX.1-2001 and later.
69 See also: times(2), clock(3)
71 clockid_t
73 Include: <sys/types.h>. Alternatively, <time.h>.
74 Used for clock ID type in the clock and timer functions. Ac‐
76 cording to POSIX, it shall be defined as an arithmetic type.
77 Conforming to: POSIX.1-2001 and later.
79 See also: clock_adjtime(2), clock_getres(2), clock_nanosleep(2),
81 timer_create(2), clock_getcpuclockid(3)
82 dev_t
84 Include: <sys/types.h>. Alternatively, <sys/stat.h>.
85 Used for device IDs. According to POSIX, it shall be an integer
87 type. For further details of this type, see makedev(3).
88 Conforming to: POSIX.1-2001 and later.
90 See also: mknod(2), stat(2)
92 div_t
94 Include: <stdlib.h>.
95 typedef struct {
97 int quot; /* Quotient */
98 int rem; /* Remainder */
99 } div_t;
100 It is the type of the value returned by the div(3) function.
102 Conforming to: C99 and later; POSIX.1-2001 and later.
104 See also: div(3)
106 double_t
108 Include: <math.h>.
109 The implementation's most efficient floating type at least as
111 wide as double. Its type depends on the value of the macro
112 FLT_EVAL_METHOD (defined in <float.h>):
113 0 double_t is double.
115 1 double_t is double.
117 2 double_t is long double.
119 For other values of FLT_EVAL_METHOD, the type of double_t is im‐
121 plementation-defined.
122 Conforming to: C99 and later; POSIX.1-2001 and later.
124 See also: the float_t type in this page.
126 fd_set
128 Include: <sys/select.h>. Alternatively, <sys/time.h>.
129 A structure type that can represent a set of file descriptors.
131 According to POSIX, the maximum number of file descriptors in an
132 fd_set structure is the value of the macro FD_SETSIZE.
133 Conforming to: POSIX.1-2001 and later.
135 See also: select(2)
137 fenv_t
139 Include: <fenv.h>.
140 This type represents the entire floating-point environment, in‐
142 cluding control modes and status flags; for further details, see
143 fenv(3).
144 Conforming to: C99 and later; POSIX.1-2001 and later.
146 See also: fenv(3)
148 fexcept_t
150 Include: <fenv.h>.
151 This type represents the floating-point status flags collec‐
153 tively; for further details see fenv(3).
154 Conforming to: C99 and later; POSIX.1-2001 and later.
156 See also: fenv(3)
158 FILE
160 Include: <stdio.h>. Alternatively, <wchar.h>.
161 An object type used for streams.
163 Conforming to: C99 and later; POSIX.1-2001 and later.
165 See also: fclose(3), flockfile(3), fopen(3), fprintf(3),
167 fread(3), fscanf(3), stdin(3), stdio(3)
168 float_t
170 Include: <math.h>.
171 The implementation's most efficient floating type at least as
173 wide as float. Its type depends on the value of the macro
174 FLT_EVAL_METHOD (defined in <float.h>):
175 0 float_t is float.
177 1 float_t is double.
179 2 float_t is long double.
181 For other values of FLT_EVAL_METHOD, the type of float_t is im‐
183 plementation-defined.
184 Conforming to: C99 and later; POSIX.1-2001 and later.
186 See also: the double_t type in this page.
188 gid_t
190 Include: <sys/types.h>. Alternatively, <grp.h>, <pwd.h>, <sig‐
191 nal.h>, <stropts.h>, <sys/ipc.h>, <sys/stat.h>, or <unistd.h>.
192 A type used to hold group IDs. According to POSIX, this shall
194 be an integer type.
195 Conforming to: POSIX.1-2001 and later.
197 See also: chown(2), getgid(2), getegid(2), getgroups(2), getres‐
199 gid(2), getgrnam(3), credentials(7)
200 id_t
202 Include: <sys/types.h>. Alternatively, <sys/resource.h>.
203 A type used to hold a general identifier. According to POSIX,
205 this shall be an integer type that can be used to contain a
206 pid_t, uid_t, or gid_t.
207 Conforming to: POSIX.1-2001 and later.
209 See also: getpriority(2), waitid(2)
211 imaxdiv_t
213 Include: <inttypes.h>.
214 typedef struct {
216 intmax_t quot; /* Quotient */
217 intmax_t rem; /* Remainder */
218 } imaxdiv_t;
219 It is the type of the value returned by the imaxdiv(3) function.
221 Conforming to: C99 and later; POSIX.1-2001 and later.
223 See also: imaxdiv(3)
225 intmax_t
227 Include: <stdint.h>. Alternatively, <inttypes.h>.
228 A signed integer type capable of representing any value of any
230 signed integer type supported by the implementation. According
231 to the C language standard, it shall be capable of storing val‐
232 ues in the range [INTMAX_MIN, INTMAX_MAX].
233 The macro INTMAX_C() expands its argument to an integer constant
235 of type intmax_t.
236 The length modifier for intmax_t for the printf(3) and the
238 scanf(3) families of functions is j; resulting commonly in %jd
239 or %ji for printing intmax_t values.
240 Conforming to: C99 and later; POSIX.1-2001 and later.
242 Bugs: intmax_t is not large enough to represent values of type
244 __int128 in implementations where __int128 is defined and long
245 long is less than 128 bits wide.
246 See also: the uintmax_t type in this page.
248 intN_t
250 Include: <stdint.h>. Alternatively, <inttypes.h>.
251 int8_t, int16_t, int32_t, int64_t
253 A signed integer type of a fixed width of exactly N bits, N be‐
255 ing the value specified in its type name. According to the C
256 language standard, they shall be capable of storing values in
257 the range [INTN_MIN, INTN_MAX], substituting N by the appropri‐
258 ate number.
259 According to POSIX, int8_t, int16_t, and int32_t are required;
261 int64_t is only required in implementations that provide integer
262 types with width 64; and all other types of this form are op‐
263 tional.
264 The length modifiers for the intN_t types for the printf(3) fam‐
266 ily of functions are expanded by macros of the forms PRIdN and
267 PRIiN (defined in <inttypes.h>); resulting for example in
268 %"PRId64" or %"PRIi64" for printing int64_t values. The length
269 modifiers for the intN_t types for the scanf(3) family of func‐
270 tions are expanded by macros of the forms SCNdN and SCNiN, (de‐
271 fined in <inttypes.h>); resulting for example in %"SCNd8" or
272 %"SCNi8" for scanning int8_t values.
273 Conforming to: C99 and later; POSIX.1-2001 and later.
275 See also: the intmax_t, uintN_t, and uintmax_t types in this
277 page.
278 intptr_t
280 Include: <stdint.h>. Alternatively, <inttypes.h>.
281 A signed integer type such that any valid (void *) value can be
283 converted to this type and back. According to the C language
284 standard, it shall be capable of storing values in the range
285 [INTPTR_MIN, INTPTR_MAX].
286 The length modifier for intptr_t for the printf(3) family of
288 functions is expanded by the macros PRIdPTR and PRIiPTR (defined
289 in <inttypes.h>); resulting commonly in %"PRIdPTR" or %"PRIiPTR"
290 for printing intptr_t values. The length modifier for intptr_t
291 for the scanf(3) family of functions is expanded by the macros
292 SCNdPTR and SCNiPTR, (defined in <inttypes.h>); resulting com‐
293 monly in %"SCNdPTR" or %"SCNiPTR" for scanning intptr_t values.
294 Conforming to: C99 and later; POSIX.1-2001 and later.
296 See also: the uintptr_t and void * types in this page.
298 lconv
300 Include: <locale.h>.
301 struct lconv { /* Values in the "C" locale: */
303 char *decimal_point; /* "." */
304 char *thousands_sep; /* "" */
305 char *grouping; /* "" */
306 char *mon_decimal_point; /* "" */
307 char *mon_thousands_sep; /* "" */
308 char *mon_grouping; /* "" */
309 char *positive_sign; /* "" */
310 char *negative_sign; /* "" */
311 char *currency_symbol; /* "" */
312 char frac_digits; /* CHAR_MAX */
313 char p_cs_precedes; /* CHAR_MAX */
314 char n_cs_precedes; /* CHAR_MAX */
315 char p_sep_by_space; /* CHAR_MAX */
316 char n_sep_by_space; /* CHAR_MAX */
317 char p_sign_posn; /* CHAR_MAX */
318 char n_sign_posn; /* CHAR_MAX */
319 char *int_curr_symbol; /* "" */
320 char int_frac_digits; /* CHAR_MAX */
321 char int_p_cs_precedes; /* CHAR_MAX */
322 char int_n_cs_precedes; /* CHAR_MAX */
323 char int_p_sep_by_space; /* CHAR_MAX */
324 char int_n_sep_by_space; /* CHAR_MAX */
325 char int_p_sign_posn; /* CHAR_MAX */
326 char int_n_sign_posn; /* CHAR_MAX */
327 };
328 Contains members related to the formatting of numeric values.
330 In the "C" locale, its members have the values shown in the com‐
331 ments above.
332 Conforming to: C11 and later; POSIX.1-2001 and later.
334 See also: setlocale(3), localeconv(3), charsets(7), locale(7)
336 ldiv_t
338 Include: <stdlib.h>.
339 typedef struct {
341 long quot; /* Quotient */
342 long rem; /* Remainder */
343 } ldiv_t;
344 It is the type of the value returned by the ldiv(3) function.
346 Conforming to: C99 and later; POSIX.1-2001 and later.
348 See also: ldiv(3)
350 lldiv_t
352 Include: <stdlib.h>.
353 typedef struct {
355 long long quot; /* Quotient */
356 long long rem; /* Remainder */
357 } lldiv_t;
358 It is the type of the value returned by the lldiv(3) function.
360 Conforming to: C99 and later; POSIX.1-2001 and later.
362 See also: lldiv(3)
364 mode_t
366 Include: <sys/types.h>. Alternatively, <fcntl.h>, <ndbm.h>,
367 <spawn.h>, <sys/ipc.h>, <sys/mman.h>, or <sys/stat.h>.
368 Used for some file attributes (e.g., file mode). According to
370 POSIX, it shall be an integer type.
371 Conforming to: POSIX.1-2001 and later.
373 See also: chmod(2), mkdir(2), open(2), stat(2), umask(2)
375 off64_t
377 Include: <sys/types.h>.
378 Used for file sizes. It is a 64-bit signed integer type.
380 Conforming to: Present in glibc. It is not standardized by the
382 C language standard nor POSIX.
383 Notes: The feature test macro _LARGEFILE64_SOURCE has to be de‐
385 fined for this type to be available.
386 See also: copy_file_range(2), readahead(2), sync_file_range(2),
388 lseek64(3), feature_test_macros(7)
389 See also the off_t type in this page.
391 off_t
393 Include: <sys/types.h>. Alternatively, <aio.h>, <fcntl.h>,
394 <stdio.h>, <sys/mman.h>, <sys/stat.h.h>, or <unistd.h>.
395 Used for file sizes. According to POSIX, this shall be a signed
397 integer type.
398 Versions: <aio.h> and <stdio.h> define off_t since POSIX.1-2008.
400 Conforming to: POSIX.1-2001 and later.
402 Notes: On some architectures, the width of this type can be con‐
404 trolled with the feature test macro _FILE_OFFSET_BITS.
405 See also: lseek(2), mmap(2), posix_fadvise(2), pread(2), trun‐
407 cate(2), fseeko(3), lockf(3), posix_fallocate(3), fea‐
408 ture_test_macros(7)
409 See also the off64_t type in this page.
411 pid_t
413 Include: <sys/types.h>. Alternatively, <fcntl.h>, <sched.h>,
414 <signal.h>, <spawn.h>, <sys/msg.h>, <sys/sem.h>, <sys/shm.h>,
415 <sys/wait.h>, <termios.h>, <time.h>, <unistd.h>, or <utmpx.h>.
416 This type is used for storing process IDs, process group IDs,
418 and session IDs. According to POSIX, it shall be a signed inte‐
419 ger type, and the implementation shall support one or more pro‐
420 gramming environments where the width of pid_t is no greater
421 than the width of the type long.
422 Conforming to: POSIX.1-2001 and later.
424 See also: fork(2), getpid(2), getppid(2), getsid(2), gettid(2),
426 getpgid(2), kill(2), pidfd_open(2), sched_setscheduler(2), wait‐
427 pid(2), sigqueue(3), credentials(7),
428 ptrdiff_t
430 Include: <stddef.h>.
431 Used for a count of elements, and array indices. It is the re‐
433 sult of subtracting two pointers. According to the C language
434 standard, it shall be a signed integer type capable of storing
435 values in the range [PTRDIFF_MIN, PTRDIFF_MAX].
436 The length modifier for ptrdiff_t for the printf(3) and the
438 scanf(3) families of functions is t; resulting commonly in %td
439 or %ti for printing ptrdiff_t values.
440 Conforming to: C99 and later; POSIX.1-2001 and later.
442 See also: the size_t and ssize_t types in this page.
444 regex_t
446 Include: <regex.h>.
447 typedef struct {
449 size_t re_nsub; /* Number of parenthesized subexpressions */
450 } regex_t;
451 This is a structure type used in regular expression matching.
453 It holds a compiled regular expression, compiled with reg‐
454 comp(3).
455 Conforming to: POSIX.1-2001 and later.
457 See also: regex(3)
459 regmatch_t
461 Include: <regex.h>.
462 typedef struct {
464 regoff_t rm_so; /* Byte offset from start of string
465 to start of substring */
466 regoff_t rm_eo; /* Byte offset from start of string of
467 the first character after the end of
468 substring */
469 } regmatch_t;
470 This is a structure type used in regular expression matching.
472 Conforming to: POSIX.1-2001 and later.
474 See also: regexec(3)
476 regoff_t
478 Include: <regex.h>.
479 According to POSIX, it shall be a signed integer type capable of
481 storing the largest value that can be stored in either a
482 ptrdiff_t type or a ssize_t type.
483 Versions: Prior to POSIX.1-2008, the type was capable of storing
485 the largest value that can be stored in either an off_t type or
486 a ssize_t type.
487 Conforming to: POSIX.1-2001 and later.
489 See also: the regmatch_t structure and the ptrdiff_t and ssize_t
491 types in this page.
492 sigevent
494 Include: <signal.h>. Alternatively, <aio.h>, <mqueue.h>, or
495 <time.h>.
496 struct sigevent {
498 int sigev_notify; /* Notification type */
499 int sigev_signo; /* Signal number */
500 union sigval sigev_value; /* Signal value */
501 void (*sigev_notify_function)(union sigval);
502 /* Notification function */
503 pthread_attr_t *sigev_notify_attributes;
504 /* Notification attributes */
505 };
506 For further details about this type, see sigevent(7).
508 Versions: <aio.h> and <time.h> define sigevent since
510 POSIX.1-2008.
511 Conforming to: POSIX.1-2001 and later.
513 See also: timer_create(2), getaddrinfo_a(3), lio_listio(3),
515 mq_notify(3)
516 See also the aiocb structure in this page.
518 siginfo_t
520 Include: <signal.h>. Alternatively, <sys/wait.h>.
521 typedef struct {
523 int si_signo; /* Signal number */
524 int si_code; /* Signal code */
525 pid_t si_pid; /* Sending process ID */
526 uid_t si_uid; /* Real user ID of sending process */
527 void *si_addr; /* Address of faulting instruction */
528 int si_status; /* Exit value or signal */
529 union sigval si_value; /* Signal value */
530 } siginfo_t;
531 Information associated with a signal. For further details on
533 this structure (including additional, Linux-specific fields),
534 see sigaction(2).
535 Conforming to: POSIX.1-2001 and later.
537 See also: pidfd_send_signal(2), rt_sigqueueinfo(2), sigac‐
539 tion(2), sigwaitinfo(2), psiginfo(3)
540 sigset_t
542 Include: <signal.h>. Alternatively, <spawn.h>, or <sys/se‐
543 lect.h>.
544 This is a type that represents a set of signals. According to
546 POSIX, this shall be an integer or structure type.
547 Conforming to: POSIX.1-2001 and later.
549 See also: epoll_pwait(2), ppoll(2), pselect(2), sigaction(2),
551 signalfd(2), sigpending(2), sigprocmask(2), sigsuspend(2), sig‐
552 waitinfo(2), signal(7)
553 sigval
555 Include: <signal.h>.
556 union sigval {
558 int sigval_int; /* Integer value */
559 void *sigval_ptr; /* Pointer value */
560 };
561 Data passed with a signal.
563 Conforming to: POSIX.1-2001 and later.
565 See also: pthread_sigqueue(3), sigqueue(3), sigevent(7)
567 See also the sigevent structure and the siginfo_t type in this
569 page.
570 size_t
572 Include: <stddef.h> or <sys/types.h>. Alternatively, <aio.h>,
573 <glob.h>, <grp.h>, <iconv.h>, <monetary.h>, <mqueue.h>,
574 <ndbm.h>, <pwd.h>, <regex.h>, <search.h>, <signal.h>, <stdio.h>,
575 <stdlib.h>, <string.h>, <strings.h>, <sys/mman.h>, <sys/msg.h>,
576 <sys/sem.h>, <sys/shm.h>, <sys/socket.h>, <sys/uio.h>, <time.h>,
577 <unistd.h>, <wchar.h>, or <wordexp.h>.
578 Used for a count of bytes. It is the result of the sizeof oper‐
580 ator. According to the C language standard, it shall be an un‐
581 signed integer type capable of storing values in the range [0,
582 SIZE_MAX]. According to POSIX, the implementation shall support
583 one or more programming environments where the width of size_t
584 is no greater than the width of the type long.
585 The length modifier for size_t for the printf(3) and the
587 scanf(3) families of functions is z; resulting commonly in %zu
588 or %zx for printing size_t values.
589 Versions: <aio.h>, <glob.h>, <grp.h>, <iconv.h>, <mqueue.h>,
591 <pwd.h>, <signal.h>, and <sys/socket.h> define size_t since
592 POSIX.1-2008.
593 Conforming to: C99 and later; POSIX.1-2001 and later.
595 See also: read(2), write(2), fread(3), fwrite(3), memcmp(3),
597 memcpy(3), memset(3), offsetof(3)
598 See also the ptrdiff_t and ssize_t types in this page.
600 sockaddr
602 Include: <sys/socket.h>.
603 struct sockaddr {
605 sa_family_t sa_family; /* Address family */
606 char sa_data[]; /* Socket address */
607 };
608 Describes a socket address.
610 Conforming to: POSIX.1-2001 and later.
612 See also: accept(2), getpeername(2), getsockname(2), socket(2)
614 socklen_t
616 Include: <sys/socket.h>. Alternatively, <netdb.h>.
617 Describes the length of a socket address. According to POSIX,
619 this shall be an integer type of at least 32 bits.
620 Conforming to: POSIX.1-2001 and later.
622 See also: accept(2), bind(2), connect(2), gethostbyaddr(2), get‐
624 nameinfo(2), socket(2)
625 See also the sockaddr structure in this page.
627 ssize_t
629 Include: <sys/types.h>. Alternatively, <aio.h>, <monetary.h>,
630 <mqueue.h>, <stdio.h>, <sys/msg.h>, <sys/socket.h>, <sys/uio.h>,
631 or <unistd.h>.
632 Used for a count of bytes or an error indication. According to
634 POSIX, it shall be a signed integer type capable of storing val‐
635 ues at least in the range [-1, SSIZE_MAX], and the implementa‐
636 tion shall support one or more programming environments where
637 the width of ssize_t is no greater than the width of the type
638 long.
639 Glibc and most other implementations provide a length modifier
641 for ssize_t for the printf(3) and the scanf(3) families of func‐
642 tions, which is z; resulting commonly in %zd or %zi for printing
643 ssize_t values. Although z works for ssize_t on most implemen‐
644 tations, portable POSIX programs should avoid using it—for exam‐
645 ple, by converting the value to intmax_t and using its length
646 modifier (j).
647 Conforming to: POSIX.1-2001 and later.
649 See also: read(2), readlink(2), readv(2), recv(2), send(2),
651 write(2)
652 See also the ptrdiff_t and size_t types in this page.
654 suseconds_t
656 Include: <sys/types.h>. Alternatively, <sys/select.h>, or
657 <sys/time.h>.
658 Used for time in microseconds. According to POSIX, it shall be
660 a signed integer type capable of storing values at least in the
661 range [-1, 1000000], and the implementation shall support one or
662 more programming environments where the width of suseconds_t is
663 no greater than the width of the type long.
664 Conforming to: POSIX.1-2001 and later.
666 See also: the timeval structure in this page.
668 time_t
670 Include: <time.h> or <sys/types.h>. Alternatively, <sched.h>,
671 <sys/msg.h>, <sys/select.h>, <sys/sem.h>, <sys/shm.h>,
672 <sys/stat.h>, <sys/time.h>, or <utime.h>.
673 Used for time in seconds. According to POSIX, it shall be an
675 integer type.
676 Versions: <sched.h> defines time_t since POSIX.1-2008.
678 Conforming to: C99 and later; POSIX.1-2001 and later.
680 See also: stime(2), time(2), ctime(3), difftime(3)
682 timer_t
684 Include: <sys/types.h>. Alternatively, <time.h>.
685 Used for timer ID returned by timer_create(2). According to
687 POSIX, there are no defined comparison or assignment operators
688 for this type.
689 Conforming to: POSIX.1-2001 and later.
691 See also: timer_create(2), timer_delete(2), timer_getoverrun(2),
693 timer_settime(2)
694 timespec
696 Include: <time.h>. Alternatively, <aio.h>, <mqueue.h>,
697 <sched.h>, <signal.h>, <sys/select.h>, or <sys/stat.h>.
698 struct timespec {
700 time_t tv_sec; /* Seconds */
701 long tv_nsec; /* Nanoseconds */
702 };
703 Describes times in seconds and nanoseconds.
705 Conforming to: C11 and later; POSIX.1-2001 and later.
707 See also: clock_gettime(2), clock_nanosleep(2), nanosleep(2),
709 timerfd_gettime(2), timer_gettime(2)
710 timeval
712 Include: <sys/time.h>. Alternatively, <sys/resource.h>,
713 <sys/select.h>, or <utmpx.h>.
714 struct timeval {
716 time_t tv_sec; /* Seconds */
717 suseconds_t tv_usec; /* Microseconds */
718 };
719 Describes times in seconds and microseconds.
721 Conforming to: POSIX.1-2001 and later.
723 See also: gettimeofday(2), select(2), utimes(2), adjtime(3), fu‐
725 times(3), timeradd(3)
726 uid_t
728 Include: <sys/types.h>. Alternatively, <pwd.h>, <signal.h>,
729 <stropts.h>, <sys/ipc.h>, <sys/stat.h>, or <unistd.h>.
730 A type used to hold user IDs. According to POSIX, this shall be
732 an integer type.
733 Conforming to: POSIX.1-2001 and later.
735 See also: chown(2), getuid(2), geteuid(2), getresuid(2), getpw‐
737 nam(3), credentials(7)
738 uintmax_t
740 Include: <stdint.h>. Alternatively, <inttypes.h>.
741 An unsigned integer type capable of representing any value of
743 any unsigned integer type supported by the implementation. Ac‐
744 cording to the C language standard, it shall be capable of stor‐
745 ing values in the range [0, UINTMAX_MAX].
746 The macro UINTMAX_C() expands its argument to an integer con‐
748 stant of type uintmax_t.
749 The length modifier for uintmax_t for the printf(3) and the
751 scanf(3) families of functions is j; resulting commonly in %ju
752 or %jx for printing uintmax_t values.
753 Conforming to: C99 and later; POSIX.1-2001 and later.
755 Bugs: uintmax_t is not large enough to represent values of type
757 unsigned __int128 in implementations where unsigned __int128 is
758 defined and unsigned long long is less than 128 bits wide.
759 See also: the intmax_t type in this page.
761 uintN_t
763 Include: <stdint.h>. Alternatively, <inttypes.h>.
764 uint8_t, uint16_t, uint32_t, uint64_t
766 An unsigned integer type of a fixed width of exactly N bits, N
768 being the value specified in its type name. According to the C
769 language standard, they shall be capable of storing values in
770 the range [0, UINTN_MAX], substituting N by the appropriate num‐
771 ber.
772 According to POSIX, uint8_t, uint16_t, and uint32_t are re‐
774 quired; uint64_t is only required in implementations that pro‐
775 vide integer types with width 64; and all other types of this
776 form are optional.
777 The length modifiers for the uintN_t types for the printf(3)
779 family of functions are expanded by macros of the forms PRIuN,
780 PRIoN, PRIxN, and PRIXN (defined in <inttypes.h>); resulting for
781 example in %"PRIu32" or %"PRIx32" for printing uint32_t values.
782 The length modifiers for the uintN_t types for the scanf(3) fam‐
783 ily of functions are expanded by macros of the forms SCNuN, SC‐
784 NoN, SCNxN, and SCNXN (defined in <inttypes.h>); resulting for
785 example in %"SCNu16" or %"SCNx16" for scanning uint16_t values.
786 Conforming to: C99 and later; POSIX.1-2001 and later.
788 See also: the intmax_t, intN_t, and uintmax_t types in this
790 page.
791 uintptr_t
793 Include: <stdint.h>. Alternatively, <inttypes.h>.
794 An unsigned integer type such that any valid (void *) value can
796 be converted to this type and back. According to the C language
797 standard, it shall be capable of storing values in the range [0,
798 UINTPTR_MAX].
799 The length modifier for uintptr_t for the printf(3) family of
801 functions is expanded by the macros PRIuPTR, PRIoPTR, PRIxPTR,
802 and PRIXPTR (defined in <inttypes.h>); resulting commonly in
803 %"PRIuPTR" or %"PRIxPTR" for printing uintptr_t values. The
804 length modifier for uintptr_t for the scanf(3) family of func‐
805 tions is expanded by the macros SCNuPTR, SCNoPTR, SCNxPTR, and
806 SCNXPTR (defined in <inttypes.h>); resulting commonly in %"SC‐
807 NuPTR" or %"SCNxPTR" for scanning uintptr_t values.
808 Conforming to: C99 and later; POSIX.1-2001 and later.
810 See also: the intptr_t and void * types in this page.
812 va_list
814 Include: <stdarg>. Alternatively, <stdio.h>, or <wchar.h>.
815 Used by functions with a varying number of arguments of varying
817 types. The function must declare an object of type va_list
818 which is used by the macros va_start(3), va_arg(3), va_copy(3),
819 and va_end(3) to traverse the list of arguments.
820 Conforming to: C99 and later; POSIX.1-2001 and later.
822 See also: va_start(3), va_arg(3), va_copy(3), va_end(3)
824 void *
826 According to the C language standard, a pointer to any object
827 type may be converted to a pointer to void and back. POSIX fur‐
828 ther requires that any pointer, including pointers to functions,
829 may be converted to a pointer to void and back.
830 Conversions from and to any other pointer type are done implic‐
832 itly, not requiring casts at all. Note that this feature pre‐
833 vents any kind of type checking: the programmer should be care‐
834 ful not to convert a void * value to a type incompatible to that
835 of the underlying data, because that would result in undefined
836 behavior.
837 This type is useful in function parameters and return value to
839 allow passing values of any type. The function will typically
840 use some mechanism to know the real type of the data being
841 passed via a pointer to void.
842 A value of this type can't be dereferenced, as it would give a
844 value of type void, which is not possible. Likewise, pointer
845 arithmetic is not possible with this type. However, in GNU C,
846 pointer arithmetic is allowed as an extension to the standard;
847 this is done by treating the size of a void or of a function as
848 1. A consequence of this is that sizeof is also allowed on void
849 and on function types, and returns 1.
850 The conversion specifier for void * for the printf(3) and the
852 scanf(3) families of functions is p.
853 Versions: The POSIX requirement about compatibility between void
855 * and function pointers was added in POSIX.1-2008 Technical Cor‐
856 rigendum 1 (2013).
857 Conforming to: C99 and later; POSIX.1-2001 and later.
859 See also: malloc(3), memcmp(3), memcpy(3), memset(3)
861 See also the intptr_t and uintptr_t types in this page.
863
865 The structures described in this manual page shall contain, at least,
866 the members shown in their definition, in no particular order.
867 Most of the integer types described in this page don't have a corre‐
869 sponding length modifier for the printf(3) and the scanf(3) families of
870 functions. To print a value of an integer type that doesn't have a
871 length modifier, it should be converted to intmax_t or uintmax_t by an
872 explicit cast. To scan into a variable of an integer type that doesn't
873 have a length modifier, an intermediate temporary variable of type int‐
874 max_t or uintmax_t should be used. When copying from the temporary
875 variable to the destination variable, the value could overflow. If the
876 type has upper and lower limits, the user should check that the value
877 is within those limits, before actually copying the value. The example
878 below shows how these conversions should be done.
879 Conventions used in this page
881 In "Conforming to" we only concern ourselves with C99 and later and
882 POSIX.1-2001 and later. Some types may be specified in earlier ver‐
883 sions of one of these standards, but in the interests of simplicity we
884 omit details from earlier standards.
885 In "Include", we first note the "primary" header(s) that define the
887 type according to either the C or POSIX.1 standards. Under "Alterna‐
888 tively", we note additional headers that the standards specify shall
889 define the type.
890
892 The program shown below scans from a string and prints a value stored
893 in a variable of an integer type that doesn't have a length modifier.
894 The appropriate conversions from and to intmax_t, and the appropriate
895 range checks, are used as explained in the notes section above.
896 #include <stdint.h>
898 #include <stdio.h>
899 #include <stdlib.h>
900 #include <sys/types.h>
901 int
903 main (void)
904 {
905 static const char *const str = "500000 us in half a second";
906 suseconds_t us;
907 intmax_t tmp;
908 /* Scan the number from the string into the temporary variable. */
910 sscanf(str, "%jd", &tmp);
912 /* Check that the value is within the valid range of suseconds_t. */
914 if (tmp < -1 || tmp > 1000000) {
916 fprintf(stderr, "Scanned value outside valid range!\n");
917 exit(EXIT_FAILURE);
918 }
919 /* Copy the value to the suseconds_t variable 'us'. */
921 us = tmp;
923 /* Even though suseconds_t can hold the value -1, this isn't
925 a sensible number of microseconds. */
926 if (us < 0) {
928 fprintf(stderr, "Scanned value shouldn't be negative!\n");
929 exit(EXIT_FAILURE);
930 }
931 /* Print the value. */
933 printf("There are %jd microseconds in half a second.\n",
935 (intmax_t) us);
936 exit(EXIT_SUCCESS);
938 }
939
941 feature_test_macros(7), standards(7)
942
944 This page is part of release 5.12 of the Linux man-pages project. A
945 description of the project, information about reporting bugs, and the
946 latest version of this page, can be found at
947 https://www.kernel.org/doc/man-pages/.
948Linux 2021-03-22 SYSTEM_DATA_TYPES(7)