PROLOG | NAME | SYNOPSIS | DESCRIPTION | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

time.h(0P)                POSIX Programmer's Manual               time.h(0P)

PROLOG         top

       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.

NAME         top

       time.h — time types

SYNOPSIS         top

       #include <time.h>

DESCRIPTION         top

       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.1‐2008, 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.

APPLICATION USAGE         top

       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).

RATIONALE         top

       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.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       locale.h(0p), signal.h(0p), stddef.h(0p), sys_types.h(0p)

       The System Interfaces volume of POSIX.1‐2008, 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)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                          time.h(0P)