1SYSTEM_DATA_TYPES(7)       Linux Programmer's Manual      SYSTEM_DATA_TYPES(7)
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NAME

6       system_data_types - overview of system data types
7

DESCRIPTION

9       aiocb
10              Include: <aio.h>.
11
12              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
22              For further information about this structure, see aio(7).
23
24              Conforming to: POSIX.1-2001 and later.
25
26              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
30       blkcnt_t
31              Include: <sys/types.h>.  Alternatively, <sys/stat.h>.
32
33              Used  for  file block counts.  According to POSIX, it shall be a
34              signed integer type.
35
36              Conforming to: POSIX.1-2001 and later.
37
38              See also: stat(2)
39
40       blksize_t
41              Include: <sys/types.h>.  Alternatively, <sys/stat.h>.
42
43              Used for file block sizes.  According to POSIX, it  shall  be  a
44              signed integer type.
45
46              Conforming to: POSIX.1-2001 and later.
47
48              See also: stat(2)
49
50       cc_t
51              Include: <termios.h>.
52
53              Used  for  terminal  special characters.  According to POSIX, it
54              shall be an unsigned integer type.
55
56              Conforming to: POSIX.1-2001 and later.
57
58              See also: termios(3)
59
60       clock_t
61              Include:    <time.h>    or    <sys/types.h>.      Alternatively,
62              <sys/time.h>.
63
64              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
68              Conforming to: C99 and later; POSIX.1-2001 and later.
69
70              See also: times(2), clock(3)
71
72       clockid_t
73              Include: <sys/types.h>.  Alternatively, <time.h>.
74
75              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
78              Conforming to: POSIX.1-2001 and later.
79
80              See also: clock_adjtime(2), clock_getres(2), clock_nanosleep(2),
81              timer_create(2), clock_getcpuclockid(3)
82
83       dev_t
84              Include: <sys/types.h>.  Alternatively, <sys/stat.h>.
85
86              Used for device IDs.  According to POSIX, it shall be an integer
87              type.  For further details of this type, see makedev(3).
88
89              Conforming to: POSIX.1-2001 and later.
90
91              See also: mknod(2), stat(2)
92
93       div_t
94              Include: <stdlib.h>.
95
96              typedef struct {
97                  int quot; /* Quotient */
98                  int rem;  /* Remainder */
99              } div_t;
100
101              It is the type of the value returned by the div(3) function.
102
103              Conforming to: C99 and later; POSIX.1-2001 and later.
104
105              See also: div(3)
106
107       double_t
108              Include: <math.h>.
109
110              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
114              0      double_t is double.
115
116              1      double_t is double.
117
118              2      double_t is long double.
119
120              For other values of FLT_EVAL_METHOD, the type of double_t is im‐
121              plementation-defined.
122
123              Conforming to: C99 and later; POSIX.1-2001 and later.
124
125              See also: the float_t type in this page.
126
127       fd_set
128              Include: <sys/select.h>.  Alternatively, <sys/time.h>.
129
130              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
134              Conforming to: POSIX.1-2001 and later.
135
136              See also: select(2)
137
138       fenv_t
139              Include: <fenv.h>.
140
141              This  type represents the entire floating-point environment, in‐
142              cluding control modes and status flags; for further details, see
143              fenv(3).
144
145              Conforming to: C99 and later; POSIX.1-2001 and later.
146
147              See also: fenv(3)
148
149       fexcept_t
150              Include: <fenv.h>.
151
152              This  type  represents  the  floating-point status flags collec‐
153              tively; for further details see fenv(3).
154
155              Conforming to: C99 and later; POSIX.1-2001 and later.
156
157              See also: fenv(3)
158
159       FILE
160              Include: <stdio.h>.  Alternatively, <wchar.h>.
161
162              An object type used for streams.
163
164              Conforming to: C99 and later; POSIX.1-2001 and later.
165
166              See  also:  fclose(3),   flockfile(3),   fopen(3),   fprintf(3),
167              fread(3), fscanf(3), stdin(3), stdio(3)
168
169       float_t
170              Include: <math.h>.
171
172              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
176              0      float_t is float.
177
178              1      float_t is double.
179
180              2      float_t is long double.
181
182              For  other values of FLT_EVAL_METHOD, the type of float_t is im‐
183              plementation-defined.
184
185              Conforming to: C99 and later; POSIX.1-2001 and later.
186
187              See also: the double_t type in this page.
188
189       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
193              A  type  used to hold group IDs.  According to POSIX, this shall
194              be an integer type.
195
196              Conforming to: POSIX.1-2001 and later.
197
198              See also: chown(2), getgid(2), getegid(2), getgroups(2), getres‐
199              gid(2), getgrnam(3), credentials(7)
200
201       id_t
202              Include: <sys/types.h>.  Alternatively, <sys/resource.h>.
203
204              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
208              Conforming to: POSIX.1-2001 and later.
209
210              See also: getpriority(2), waitid(2)
211
212       imaxdiv_t
213              Include: <inttypes.h>.
214
215              typedef struct {
216                  intmax_t    quot; /* Quotient */
217                  intmax_t    rem;  /* Remainder */
218              } imaxdiv_t;
219
220              It is the type of the value returned by the imaxdiv(3) function.
221
222              Conforming to: C99 and later; POSIX.1-2001 and later.
223
224              See also: imaxdiv(3)
225
226       intmax_t
227              Include: <stdint.h>.  Alternatively, <inttypes.h>.
228
229              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
234              The macro INTMAX_C() expands its argument to an integer constant
235              of type intmax_t.
236
237              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
241              Conforming to: C99 and later; POSIX.1-2001 and later.
242
243              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
247              See also: the uintmax_t type in this page.
248
249       intN_t
250              Include: <stdint.h>.  Alternatively, <inttypes.h>.
251
252              int8_t, int16_t, int32_t, int64_t
253
254              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
260              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
265              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
274              Conforming to: C99 and later; POSIX.1-2001 and later.
275
276              See  also:  the  intmax_t,  uintN_t, and uintmax_t types in this
277              page.
278
279       intptr_t
280              Include: <stdint.h>.  Alternatively, <inttypes.h>.
281
282              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
287              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
295              Conforming to: C99 and later; POSIX.1-2001 and later.
296
297              See also: the uintptr_t and void * types in this page.
298
299       lconv
300              Include: <locale.h>.
301
302              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
329              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
333              Conforming to: C11 and later; POSIX.1-2001 and later.
334
335              See also: setlocale(3), localeconv(3), charsets(7), locale(7)
336
337       ldiv_t
338              Include: <stdlib.h>.
339
340              typedef struct {
341                  long    quot; /* Quotient */
342                  long    rem;  /* Remainder */
343              } ldiv_t;
344
345              It is the type of the value returned by the ldiv(3) function.
346
347              Conforming to: C99 and later; POSIX.1-2001 and later.
348
349              See also: ldiv(3)
350
351       lldiv_t
352              Include: <stdlib.h>.
353
354              typedef struct {
355                  long long   quot; /* Quotient */
356                  long long   rem;  /* Remainder */
357              } lldiv_t;
358
359              It is the type of the value returned by the lldiv(3) function.
360
361              Conforming to: C99 and later; POSIX.1-2001 and later.
362
363              See also: lldiv(3)
364
365       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
369              Used for some file attributes (e.g., file mode).   According  to
370              POSIX, it shall be an integer type.
371
372              Conforming to: POSIX.1-2001 and later.
373
374              See also: chmod(2), mkdir(2), open(2), stat(2), umask(2)
375
376       off64_t
377              Include: <sys/types.h>.
378
379              Used for file sizes.  It is a 64-bit signed integer type.
380
381              Conforming  to: Present in glibc.  It is not standardized by the
382              C language standard nor POSIX.
383
384              Notes: The feature test macro _LARGEFILE64_SOURCE has to be  de‐
385              fined for this type to be available.
386
387              See  also: copy_file_range(2), readahead(2), sync_file_range(2),
388              lseek64(3), feature_test_macros(7)
389
390              See also the off_t type in this page.
391
392       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
396              Used for file sizes.  According to POSIX, this shall be a signed
397              integer type.
398
399              Versions: <aio.h> and <stdio.h> define off_t since POSIX.1-2008.
400
401              Conforming to: POSIX.1-2001 and later.
402
403              Notes: On some architectures, the width of this type can be con‐
404              trolled with the feature test macro _FILE_OFFSET_BITS.
405
406              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
410              See also the off64_t type in this page.
411
412       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
417              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
423              Conforming to: POSIX.1-2001 and later.
424
425              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
429       ptrdiff_t
430              Include: <stddef.h>.
431
432              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
437              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
441              Conforming to: C99 and later; POSIX.1-2001 and later.
442
443              See also: the size_t and ssize_t types in this page.
444
445       regex_t
446              Include: <regex.h>.
447
448              typedef struct {
449                  size_t  re_nsub; /* Number of parenthesized subexpressions */
450              } regex_t;
451
452              This is a structure type used in  regular  expression  matching.
453              It  holds  a  compiled  regular  expression,  compiled with reg‐
454              comp(3).
455
456              Conforming to: POSIX.1-2001 and later.
457
458              See also: regex(3)
459
460       regmatch_t
461              Include: <regex.h>.
462
463              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
471              This is a structure type used in regular expression matching.
472
473              Conforming to: POSIX.1-2001 and later.
474
475              See also: regexec(3)
476
477       regoff_t
478              Include: <regex.h>.
479
480              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
484              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
488              Conforming to: POSIX.1-2001 and later.
489
490              See also: the regmatch_t structure and the ptrdiff_t and ssize_t
491              types in this page.
492
493       sigevent
494              Include:  <signal.h>.   Alternatively,  <aio.h>,  <mqueue.h>, or
495              <time.h>.
496
497              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
507              For further details about this type, see sigevent(7).
508
509              Versions:   <aio.h>   and   <time.h>   define   sigevent   since
510              POSIX.1-2008.
511
512              Conforming to: POSIX.1-2001 and later.
513
514              See   also:  timer_create(2),  getaddrinfo_a(3),  lio_listio(3),
515              mq_notify(3)
516
517              See also the aiocb structure in this page.
518
519       siginfo_t
520              Include: <signal.h>.  Alternatively, <sys/wait.h>.
521
522              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
532              Information associated with a signal.  For  further  details  on
533              this  structure  (including  additional, Linux-specific fields),
534              see sigaction(2).
535
536              Conforming to: POSIX.1-2001 and later.
537
538              See  also:  pidfd_send_signal(2),   rt_sigqueueinfo(2),   sigac‐
539              tion(2), sigwaitinfo(2), psiginfo(3)
540
541       sigset_t
542              Include:  <signal.h>.   Alternatively,  <spawn.h>,  or  <sys/se‐
543              lect.h>.
544
545              This is a type that represents a set of signals.   According  to
546              POSIX, this shall be an integer or structure type.
547
548              Conforming to: POSIX.1-2001 and later.
549
550              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
554       sigval
555              Include: <signal.h>.
556
557              union sigval {
558                  int     sigval_int; /* Integer value */
559                  void   *sigval_ptr; /* Pointer value */
560              };
561
562              Data passed with a signal.
563
564              Conforming to: POSIX.1-2001 and later.
565
566              See also: pthread_sigqueue(3), sigqueue(3), sigevent(7)
567
568              See  also  the sigevent structure and the siginfo_t type in this
569              page.
570
571       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
579              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
586              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
590              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
594              Conforming to: C99 and later; POSIX.1-2001 and later.
595
596              See also: read(2),  write(2),  fread(3),  fwrite(3),  memcmp(3),
597              memcpy(3), memset(3), offsetof(3)
598
599              See also the ptrdiff_t and ssize_t types in this page.
600
601       sockaddr
602              Include: <sys/socket.h>.
603
604              struct sockaddr {
605                  sa_family_t sa_family; /* Address family */
606                  char        sa_data[]; /* Socket address */
607              };
608
609              Describes a socket address.
610
611              Conforming to: POSIX.1-2001 and later.
612
613              See also: accept(2), getpeername(2), getsockname(2), socket(2)
614
615       socklen_t
616              Include: <sys/socket.h>.  Alternatively, <netdb.h>.
617
618              Describes  the  length of a socket address.  According to POSIX,
619              this shall be an integer type of at least 32 bits.
620
621              Conforming to: POSIX.1-2001 and later.
622
623              See also: accept(2), bind(2), connect(2), gethostbyaddr(2), get‐
624              nameinfo(2), socket(2)
625
626              See also the sockaddr structure in this page.
627
628       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
633              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
640              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
648              Conforming to: POSIX.1-2001 and later.
649
650              See also:  read(2),  readlink(2),  readv(2),  recv(2),  send(2),
651              write(2)
652
653              See also the ptrdiff_t and size_t types in this page.
654
655       suseconds_t
656              Include:   <sys/types.h>.    Alternatively,  <sys/select.h>,  or
657              <sys/time.h>.
658
659              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
665              Conforming to: POSIX.1-2001 and later.
666
667              See also: the timeval structure in this page.
668
669       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
674              Used for time in seconds.  According to POSIX, it  shall  be  an
675              integer type.
676
677              Versions: <sched.h> defines time_t since POSIX.1-2008.
678
679              Conforming to: C99 and later; POSIX.1-2001 and later.
680
681              See also: stime(2), time(2), ctime(3), difftime(3)
682
683       timer_t
684              Include: <sys/types.h>.  Alternatively, <time.h>.
685
686              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
690              Conforming to: POSIX.1-2001 and later.
691
692              See also: timer_create(2), timer_delete(2), timer_getoverrun(2),
693              timer_settime(2)
694
695       timespec
696              Include:   <time.h>.    Alternatively,   <aio.h>,    <mqueue.h>,
697              <sched.h>, <signal.h>, <sys/select.h>, or <sys/stat.h>.
698
699              struct timespec {
700                  time_t  tv_sec;  /* Seconds */
701                  long    tv_nsec; /* Nanoseconds */
702              };
703
704              Describes times in seconds and nanoseconds.
705
706              Conforming to: C11 and later; POSIX.1-2001 and later.
707
708              See  also:  clock_gettime(2),  clock_nanosleep(2), nanosleep(2),
709              timerfd_gettime(2), timer_gettime(2)
710
711       timeval
712              Include:   <sys/time.h>.     Alternatively,    <sys/resource.h>,
713              <sys/select.h>, or <utmpx.h>.
714
715              struct timeval {
716                  time_t      tv_sec;  /* Seconds */
717                  suseconds_t tv_usec; /* Microseconds */
718              };
719
720              Describes times in seconds and microseconds.
721
722              Conforming to: POSIX.1-2001 and later.
723
724              See also: gettimeofday(2), select(2), utimes(2), adjtime(3), fu‐
725              times(3), timeradd(3)
726
727       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
731              A type used to hold user IDs.  According to POSIX, this shall be
732              an integer type.
733
734              Conforming to: POSIX.1-2001 and later.
735
736              See also: chown(2), getuid(2), geteuid(2), getresuid(2),  getpw‐
737              nam(3), credentials(7)
738
739       uintmax_t
740              Include: <stdint.h>.  Alternatively, <inttypes.h>.
741
742              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
747              The macro UINTMAX_C() expands its argument to  an  integer  con‐
748              stant of type uintmax_t.
749
750              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
754              Conforming to: C99 and later; POSIX.1-2001 and later.
755
756              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
760              See also: the intmax_t type in this page.
761
762       uintN_t
763              Include: <stdint.h>.  Alternatively, <inttypes.h>.
764
765              uint8_t, uint16_t, uint32_t, uint64_t
766
767              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
773              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
778              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
787              Conforming to: C99 and later; POSIX.1-2001 and later.
788
789              See  also:  the  intmax_t,  intN_t,  and uintmax_t types in this
790              page.
791
792       uintptr_t
793              Include: <stdint.h>.  Alternatively, <inttypes.h>.
794
795              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
800              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
809              Conforming to: C99 and later; POSIX.1-2001 and later.
810
811              See also: the intptr_t and void * types in this page.
812
813       va_list
814              Include: <stdarg>.  Alternatively, <stdio.h>, or <wchar.h>.
815
816              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
821              Conforming to: C99 and later; POSIX.1-2001 and later.
822
823              See also: va_start(3), va_arg(3), va_copy(3), va_end(3)
824
825       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
831              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
838              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
843              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
851              The conversion specifier for void * for the  printf(3)  and  the
852              scanf(3) families of functions is p.
853
854              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
858              Conforming to: C99 and later; POSIX.1-2001 and later.
859
860              See also: malloc(3), memcmp(3), memcpy(3), memset(3)
861
862              See also the intptr_t and uintptr_t types in this page.
863

NOTES

865       The  structures  described in this manual page shall contain, at least,
866       the members shown in their definition, in no particular order.
867
868       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
880   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
886       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

EXAMPLES

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
897       #include <stdint.h>
898       #include <stdio.h>
899       #include <stdlib.h>
900       #include <sys/types.h>
901
902       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
909           /* Scan the number from the string into the temporary variable. */
910
911           sscanf(str, "%jd", &tmp);
912
913           /* Check that the value is within the valid range of suseconds_t. */
914
915           if (tmp < -1 || tmp > 1000000) {
916               fprintf(stderr, "Scanned value outside valid range!\n");
917               exit(EXIT_FAILURE);
918           }
919
920           /* Copy the value to the suseconds_t variable 'us'. */
921
922           us = tmp;
923
924           /* Even though suseconds_t can hold the value -1, this isn't
925              a sensible number of microseconds. */
926
927           if (us < 0) {
928               fprintf(stderr, "Scanned value shouldn't be negative!\n");
929               exit(EXIT_FAILURE);
930           }
931
932           /* Print the value. */
933
934           printf("There are %jd microseconds in half a second.\n",
935                   (intmax_t) us);
936
937           exit(EXIT_SUCCESS);
938       }
939

SEE ALSO

941       feature_test_macros(7), standards(7)
942

COLOPHON

944       This  page  is  part of release 5.13 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/.
948
949
950
951Linux                             2021-03-22              SYSTEM_DATA_TYPES(7)
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