1time.h(0P) POSIX Programmer's Manual time.h(0P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 time.h — time types
13
15 #include <time.h>
16
18 Some of the functionality described on this reference page extends the
19 ISO C standard. Applications shall define the appropriate feature test
20 macro (see the System Interfaces volume of POSIX.1‐2017, Section 2.2,
21 The Compilation Environment) to enable the visibility of these symbols
22 in this header.
23 The <time.h> header shall define the clock_t, size_t, time_t, types as
25 described in <sys/types.h>.
26 The <time.h> header shall define the clockid_t and timer_t types as
28 described in <sys/types.h>.
29 The <time.h> header shall define the locale_t type as described in
31 <locale.h>.
32 The <time.h> header shall define the pid_t type as described in
34 <sys/types.h>.
35 The tag sigevent shall be declared as naming an incomplete structure
37 type, the contents of which are described in the <signal.h> header.
38 The <time.h> header shall declare the tm structure, which shall include
40 at least the following members:
41 int tm_sec Seconds [0,60].
44 int tm_min Minutes [0,59].
45 int tm_hour Hour [0,23].
46 int tm_mday Day of month [1,31].
47 int tm_mon Month of year [0,11].
48 int tm_year Years since 1900.
49 int tm_wday Day of week [0,6] (Sunday =0).
50 int tm_yday Day of year [0,365].
51 int tm_isdst Daylight Savings flag.
52 The value of tm_isdst shall be positive if Daylight Savings Time is in
54 effect, 0 if Daylight Savings Time is not in effect, and negative if
55 the information is not available.
56 The <time.h> header shall declare the timespec structure, which shall
58 include at least the following members:
59 time_t tv_sec Seconds.
62 long tv_nsec Nanoseconds.
63 The <time.h> header shall also declare the itimerspec structure, which
65 shall include at least the following members:
66 struct timespec it_interval Timer period.
69 struct timespec it_value Timer expiration.
70 The <time.h> header shall define the following macros:
72 NULL As described in <stddef.h>.
74 CLOCKS_PER_SEC
76 A number used to convert the value returned by the
77 clock() function into seconds. The value shall be an
78 expression with type clock_t. The value of
79 CLOCKS_PER_SEC shall be 1 million on XSI-conformant sys‐
80 tems. However, it may be variable on other systems, and
81 it should not be assumed that CLOCKS_PER_SEC is a com‐
82 pile-time constant.
83 The <time.h> header shall define the following symbolic constants. The
85 values shall have a type that is assignment-compatible with clockid_t.
86 CLOCK_MONOTONIC
88 The identifier for the system-wide monotonic clock, which
89 is defined as a clock measuring real time, whose value
90 cannot be set via clock_settime() and which cannot have
91 negative clock jumps. The maximum possible clock jump
92 shall be implementation-defined.
93 CLOCK_PROCESS_CPUTIME_ID
95 The identifier of the CPU-time clock associated with the
96 process making a clock() or timer*() function call.
97 CLOCK_REALTIME
99 The identifier of the system-wide clock measuring real
100 time.
101 CLOCK_THREAD_CPUTIME_ID
103 The identifier of the CPU-time clock associated with the
104 thread making a clock() or timer*() function call.
105 The <time.h> header shall define the following symbolic constant:
107 TIMER_ABSTIME Flag indicating time is absolute. For functions taking
109 timer objects, this refers to the clock associated with
110 the timer.
111 The <time.h> header shall provide a declaration or definition for get‐
113 date_err. The getdate_err symbol shall expand to an expression of type
114 int. It is unspecified whether getdate_err is a macro or an identifier
115 declared with external linkage, and whether or not it is a modifiable
116 lvalue. If a macro definition is suppressed in order to access an
117 actual object, or a program defines an identifier with the name get‐
118 date_err, the behavior is undefined.
119 The following shall be declared as functions and may also be defined as
121 macros. Function prototypes shall be provided.
122 char *asctime(const struct tm *);
125 char *asctime_r(const struct tm *restrict, char *restrict);
126 clock_t clock(void);
127 int clock_getcpuclockid(pid_t, clockid_t *);
128 int clock_getres(clockid_t, struct timespec *);
129 int clock_gettime(clockid_t, struct timespec *);
130 int clock_nanosleep(clockid_t, int, const struct timespec *,
131 struct timespec *);
132 int clock_settime(clockid_t, const struct timespec *);
133 char *ctime(const time_t *);
134 char *ctime_r(const time_t *, char *);
135 double difftime(time_t, time_t);
136 struct tm *getdate(const char *);
137 struct tm *gmtime(const time_t *);
138 struct tm *gmtime_r(const time_t *restrict, struct tm *restrict);
139 struct tm *localtime(const time_t *);
140 struct tm *localtime_r(const time_t *restrict, struct tm *restrict);
141 time_t mktime(struct tm *);
142 int nanosleep(const struct timespec *, struct timespec *);
143 size_t strftime(char *restrict, size_t, const char *restrict,
144 const struct tm *restrict);
145 size_t strftime_l(char *restrict, size_t, const char *restrict,
146 const struct tm *restrict, locale_t);
147 char *strptime(const char *restrict, const char *restrict,
148 struct tm *restrict);
149 time_t time(time_t *);
150 int timer_create(clockid_t, struct sigevent *restrict,
151 timer_t *restrict);
152 int timer_delete(timer_t);
153 int timer_getoverrun(timer_t);
154 int timer_gettime(timer_t, struct itimerspec *);
155 int timer_settime(timer_t, int, const struct itimerspec *restrict,
156 struct itimerspec *restrict);
157 void tzset(void);
158 The <time.h> header shall declare the following as variables:
160 extern int daylight;
163 extern long timezone;
164 extern char *tzname[];
165 Inclusion of the <time.h> header may make visible all symbols from the
167 <signal.h> header.
168 The following sections are informative.
170
172 The range [0,60] for tm_sec allows for the occasional leap second.
173 tm_year is a signed value; therefore, years before 1900 may be repre‐
175 sented.
176 To obtain the number of clock ticks per second returned by the times()
178 function, applications should call sysconf(_SC_CLK_TCK).
179
181 The range [0,60] seconds allows for positive or negative leap seconds.
182 The formal definition of UTC does not permit double leap seconds, so
183 all mention of double leap seconds has been removed, and the range
184 shortened from the former [0,61] seconds seen in earlier versions of
185 this standard.
186
188 None.
189
191 <locale.h>, <signal.h>, <stddef.h>, <sys_types.h>
192 The System Interfaces volume of POSIX.1‐2017, Section 2.2, The Compila‐
194 tion Environment, asctime(), clock(), clock_getcpuclockid(),
195 clock_getres(), clock_nanosleep(), ctime(), difftime(), getdate(),
196 gmtime(), localtime(), mktime(), mq_receive(), mq_send(), nanosleep(),
197 pthread_getcpuclockid(), pthread_mutex_timedlock(),
198 pthread_rwlock_timedrdlock(), pthread_rwlock_timedwrlock(), sem_timed‐
199 wait(), strftime(), strptime(), sysconf(), time(), timer_create(),
200 timer_delete(), timer_getoverrun(), tzset(), utime()
201
203 Portions of this text are reprinted and reproduced in electronic form
204 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
205 table Operating System Interface (POSIX), The Open Group Base Specifi‐
206 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
207 Electrical and Electronics Engineers, Inc and The Open Group. In the
208 event of any discrepancy between this version and the original IEEE and
209 The Open Group Standard, the original IEEE and The Open Group Standard
210 is the referee document. The original Standard can be obtained online
211 at http://www.opengroup.org/unix/online.html .
212 Any typographical or formatting errors that appear in this page are
214 most likely to have been introduced during the conversion of the source
215 files to man page format. To report such errors, see https://www.ker‐
216 nel.org/doc/man-pages/reporting_bugs.html .
217IEEE/The Open Group 2017 time.h(0P)