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PROLOG | NAME | SYNOPSIS | DESCRIPTION | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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time.h(0P) POSIX Programmer's Manual time.h(0P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
time.h — time types
#include <time.h>
Some of the functionality described on this reference page
extends the ISO C standard. Applications shall define the
appropriate feature test macro (see the System Interfaces volume
of POSIX.1‐2017, Section 2.2, The Compilation Environment) to
enable the visibility of these symbols in this header.
The <time.h> header shall define the clock_t, size_t, time_t,
types as described in <sys/types.h>.
The <time.h> header shall define the clockid_t and timer_t types
as described in <sys/types.h>.
The <time.h> header shall define the locale_t type as described
in <locale.h>.
The <time.h> header shall define the pid_t type as described in
<sys/types.h>.
The tag sigevent shall be declared as naming an incomplete
structure type, the contents of which are described in the
<signal.h> header.
The <time.h> header shall declare the tm structure, which shall
include at least the following members:
int tm_sec Seconds [0,60].
int tm_min Minutes [0,59].
int tm_hour Hour [0,23].
int tm_mday Day of month [1,31].
int tm_mon Month of year [0,11].
int tm_year Years since 1900.
int tm_wday Day of week [0,6] (Sunday =0).
int tm_yday Day of year [0,365].
int tm_isdst Daylight Savings flag.
The value of tm_isdst shall be positive if Daylight Savings Time
is in effect, 0 if Daylight Savings Time is not in effect, and
negative if the information is not available.
The <time.h> header shall declare the timespec structure, which
shall include at least the following members:
time_t tv_sec Seconds.
long tv_nsec Nanoseconds.
The <time.h> header shall also declare the itimerspec structure,
which shall include at least the following members:
struct timespec it_interval Timer period.
struct timespec it_value Timer expiration.
The <time.h> header shall define the following macros:
NULL As described in <stddef.h>.
CLOCKS_PER_SEC
A number used to convert the value returned by the
clock() function into seconds. The value shall be
an expression with type clock_t. The value of
CLOCKS_PER_SEC shall be 1 million on XSI-conformant
systems. However, it may be variable on other
systems, and it should not be assumed that
CLOCKS_PER_SEC is a compile-time constant.
The <time.h> header shall define the following symbolic
constants. The values shall have a type that is assignment-
compatible with clockid_t.
CLOCK_MONOTONIC
The identifier for the system-wide monotonic clock,
which is defined as a clock measuring real time,
whose value cannot be set via clock_settime() and
which cannot have negative clock jumps. The maximum
possible clock jump shall be implementation-
defined.
CLOCK_PROCESS_CPUTIME_ID
The identifier of the CPU-time clock associated
with the process making a clock() or timer*()
function call.
CLOCK_REALTIME
The identifier of the system-wide clock measuring
real time.
CLOCK_THREAD_CPUTIME_ID
The identifier of the CPU-time clock associated
with the thread making a clock() or timer*()
function call.
The <time.h> header shall define the following symbolic constant:
TIMER_ABSTIME Flag indicating time is absolute. For functions
taking timer objects, this refers to the clock
associated with the timer.
The <time.h> header shall provide a declaration or definition for
getdate_err. The getdate_err symbol shall expand to an
expression of type int. It is unspecified whether getdate_err is
a macro or an identifier declared with external linkage, and
whether or not it is a modifiable lvalue. If a macro definition
is suppressed in order to access an actual object, or a program
defines an identifier with the name getdate_err, the behavior is
undefined.
The following shall be declared as functions and may also be
defined as macros. Function prototypes shall be provided.
char *asctime(const struct tm *);
char *asctime_r(const struct tm *restrict, char *restrict);
clock_t clock(void);
int clock_getcpuclockid(pid_t, clockid_t *);
int clock_getres(clockid_t, struct timespec *);
int clock_gettime(clockid_t, struct timespec *);
int clock_nanosleep(clockid_t, int, const struct timespec *,
struct timespec *);
int clock_settime(clockid_t, const struct timespec *);
char *ctime(const time_t *);
char *ctime_r(const time_t *, char *);
double difftime(time_t, time_t);
struct tm *getdate(const char *);
struct tm *gmtime(const time_t *);
struct tm *gmtime_r(const time_t *restrict, struct tm *restrict);
struct tm *localtime(const time_t *);
struct tm *localtime_r(const time_t *restrict, struct tm *restrict);
time_t mktime(struct tm *);
int nanosleep(const struct timespec *, struct timespec *);
size_t strftime(char *restrict, size_t, const char *restrict,
const struct tm *restrict);
size_t strftime_l(char *restrict, size_t, const char *restrict,
const struct tm *restrict, locale_t);
char *strptime(const char *restrict, const char *restrict,
struct tm *restrict);
time_t time(time_t *);
int timer_create(clockid_t, struct sigevent *restrict,
timer_t *restrict);
int timer_delete(timer_t);
int timer_getoverrun(timer_t);
int timer_gettime(timer_t, struct itimerspec *);
int timer_settime(timer_t, int, const struct itimerspec *restrict,
struct itimerspec *restrict);
void tzset(void);
The <time.h> header shall declare the following as variables:
extern int daylight;
extern long timezone;
extern char *tzname[];
Inclusion of the <time.h> header may make visible all symbols
from the <signal.h> header.
The following sections are informative.
The range [0,60] for tm_sec allows for the occasional leap
second.
tm_year is a signed value; therefore, years before 1900 may be
represented.
To obtain the number of clock ticks per second returned by the
times() function, applications should call sysconf(_SC_CLK_TCK).
The range [0,60] seconds allows for positive or negative leap
seconds. The formal definition of UTC does not permit double
leap seconds, so all mention of double leap seconds has been
removed, and the range shortened from the former [0,61] seconds
seen in earlier versions of this standard.
None.
locale.h(0p), signal.h(0p), stddef.h(0p), sys_types.h(0p)
The System Interfaces volume of POSIX.1‐2017, Section 2.2, The
Compilation Environment, asctime(3p), clock(3p),
clock_getcpuclockid(3p), clock_getres(3p), clock_nanosleep(3p),
ctime(3p), difftime(3p), getdate(3p), gmtime(3p), localtime(3p),
mktime(3p), mq_receive(3p), mq_send(3p), nanosleep(3p),
pthread_getcpuclockid(3p), pthread_mutex_timedlock(3p),
pthread_rwlock_timedrdlock(3p), pthread_rwlock_timedwrlock(3p),
sem_timedwait(3p), strftime(3p), strptime(3p), sysconf(3p),
time(3p), timer_create(3p), timer_delete(3p),
timer_getoverrun(3p), tzset(3p), utime(3p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The
Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be
obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 time.h(0P)
Pages that refer to this page: aio.h(0p), mqueue.h(0p), pthread.h(0p), sched.h(0p), semaphore.h(0p), signal.h(0p), sys_select.h(0p), sys_stat.h(0p), sys_types.h(0p), wchar.h(0p), wctype.h(0p), asctime(3p), clock(3p), clock_getcpuclockid(3p), clock_getres(3p), clock_nanosleep(3p), ctime(3p), difftime(3p), getdate(3p), gmtime(3p), localtime(3p), mktime(3p), mq_receive(3p), mq_send(3p), nanosleep(3p), posix_trace_attr_getclockres(3p), pthread_getcpuclockid(3p), pthread_mutex_timedlock(3p), pthread_rwlock_timedrdlock(3p), pthread_rwlock_timedwrlock(3p), sem_timedwait(3p), sigtimedwait(3p), sigwait(3p), strftime(3p), strptime(3p), time(3p), timer_create(3p), timer_delete(3p), timer_getoverrun(3p), tzset(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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