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POSIX 1003.1 - man page for time.h (posix section 0p)

<time.h>(P)			    POSIX Programmer's Manual			      <time.h>(P)

       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  IEEE Std 1003.1-2001,  Section 2.2, The Compilation Environment) to enable the
       visibility of these symbols in this header.

       The <time.h> header shall declare the structure tm, which shall include at least the  fol-
       lowing 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 Day-
       light Savings Time is not in effect, and negative if the information is not available.

       The <time.h> header shall define the following symbolic names:

       NULL   Null pointer constant.

	      A number used to convert the value returned by the clock() function into seconds.


	      The identifier of the CPU-time clock associated with the process making  a  clock()
	      or timer*() function call.


	      The identifier of the CPU-time clock associated with the thread making a clock() or
	      timer*() function call.

       The <time.h> header shall declare the structure timespec, which has at least the following

	      time_t  tv_sec	Seconds.
	      long    tv_nsec	Nanoseconds.

       The  <time.h>  header  shall also declare the itimerspec structure, which has at least the
       following members:

	      struct timespec  it_interval  Timer period.
	      struct timespec  it_value     Timer expiration.

       The following manifest constants shall be defined:

	      The identifier of the system-wide realtime clock.

	      Flag indicating time is absolute. For functions taking timer objects,  this  refers
	      to the clock associated with the timer.


	      The  identifier  for  the  system-wide monotonic clock, which is defined as a clock
	      whose value cannot be set via clock_settime() and which cannot have backward  clock
	      jumps. The maximum possible clock jump shall be implementation-defined.

       The clock_t, size_t, time_t,   clockid_t, and timer_t  types shall be defined as described
       in <sys/types.h> .

       Although the value of CLOCKS_PER_SEC is required to be 1  million  on  all  XSI-conformant
       systems,  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 provide a declaration for getdate_err.

       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);

	      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_gettime(timer_t, struct itimerspec *);
	      int	 timer_getoverrun(timer_t);
	      int	 timer_settime(timer_t, int, const struct itimerspec *restrict,
			     struct itimerspec *restrict);

	      void	 tzset(void);

       The following shall be declared 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, applica-
       tions should call sysconf(_SC_CLK_TCK).

       The range [0,60] seconds allows for positive or negative leap seconds.  The formal defini-
       tion 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 previous ver-
       sions of POSIX.


       <signal.h>  ,  <sys/types.h>  , the System Interfaces volume of IEEE Std 1003.1-2001, asc-
       time(), clock(), clock_getcpuclockid(), clock_getres(), clock_nanosleep(), ctime(),  diff-
       time(),	getdate(),  gmtime(), localtime(), mktime(), nanosleep(), strftime(), strptime(),
       sysconf(), time(), timer_create(), timer_delete(),  timer_getoverrun(),	tzname,  tzset(),

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable	Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				      <time.h>(P)

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