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NAME

       time.h - time types

SYNOPSIS

       #include <time.h>

DESCRIPTION

       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 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 define the following symbolic names:

       NULL   Null pointer constant.

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

       CLOCK_PROCESS_CPUTIME_ID

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

       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 declare the structure timespec, which has 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
       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:

       CLOCK_REALTIME
              The identifier of the system-wide realtime clock.

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

       CLOCK_MONOTONIC

              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.

APPLICATION USAGE

       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

       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 previous versions of
       POSIX.

FUTURE DIRECTIONS

       None.

SEE ALSO

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

COPYRIGHT

       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 original Standard can be  obtained  online
       at http://www.opengroup.org/unix/online.html .