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NEWCTIME(3)							   NEWCTIME(3)

NAME
       asctime,	 ctime, difftime, gmtime, localtime, mktime - convert date and
       time to ASCII

SYNOPSIS
       extern char *tzname[2];

       void tzset()

       #include <sys/types.h>

       char *ctime(clock)
       const time_t *clock;

       double difftime(time1, time0)
       time_t time1;
       time_t time0;

       #include <time.h>

       char *asctime(tm)
       const struct tm *tm;

       struct tm *localtime(clock)
       const time_t *clock;

       struct tm *gmtime(clock)
       const time_t *clock;

       time_t mktime(tm)
       struct tm *tm;

       cc ... -ltz

DESCRIPTION
       Ctime converts a long integer, pointed to by  clock,  representing  the
       time  in	 seconds since 00:00:00 UTC, 1970-01-01, and returns a pointer
       to a string of the form
			    Thu Nov 24 18:22:48 1986\n\0
       Years requiring fewer than four	characters  are	 padded	 with  leading
       zeroes.	 For  years  longer than four characters, the string is of the
       form
			  Thu Nov 24 18:22:48	  81986\n\0
       with five spaces before the year.  These unusual formats	 are  designed
       to  make	 it  less  likely  that older software that expects exactly 26
       bytes of output will mistakenly output misleading  values  for  out-of-
       range years.

       Localtime  and  gmtime  return pointers to ``tm'' structures, described
       below.  Localtime corrects for the time zone and any time zone  adjust‐
       ments (such as Daylight Saving Time in the United States).  After fill‐
       ing in the ``tm'' structure, localtime sets the tm_isdst'th element  of
       tzname  to  a pointer to an ASCII string that's the time zone abbrevia‐
       tion to be used with localtime's return value.

       Gmtime converts to Coordinated Universal Time.

       Asctime converts a time value contained in  a  ``tm''  structure	 to  a
       string,	as  shown  in  the above example, and returns a pointer to the
       string.

       Mktime converts the broken-down time, expressed as local time,  in  the
       structure  pointed  to  by  tm into a calendar time value with the same
       encoding as that of the values returned	by  the	 time  function.   The
       original	 values of the tm_wday and tm_yday components of the structure
       are ignored, and the original values of the other  components  are  not
       restricted  to  their  normal  ranges.	(A  positive or zero value for
       tm_isdst causes mktime to presume initially that summer time (for exam‐
       ple, Daylight Saving Time in the U.S.A.)	 respectively, is or is not in
       effect for the specified time.  A negative value	 for  tm_isdst	causes
       the  mktime  function  to  attempt  to divine whether summer time is in
       effect for the specified time; in this case it does not use  a  consis‐
       tent rule and may give a different answer when later presented with the
       same argument.)	On successful completion, the values  of  the  tm_wday
       and  tm_yday components of the structure are set appropriately, and the
       other components are set to represent the specified calendar time,  but
       with  their  values  forced  to their normal ranges; the final value of
       tm_mday is not set until tm_mon and  tm_year  are  determined.	Mktime
       returns	the  specified	calendar  time; If the calendar time cannot be
       represented, it returns -1.

       Difftime returns the difference between two calendar  times,  (time1  -
       time0), expressed in seconds.

       Declarations  of all the functions and externals, and the ``tm'' struc‐
       ture, are in the <time.h> header file.  The structure (of type)	struct
       tm includes the following fields:

		   int tm_sec;	    /∗ seconds (0 - 60) ∗/
		   int tm_min;	    /∗ minutes (0 - 59) ∗/
		   int tm_hour;	    /∗ hours (0 - 23) ∗/
		   int tm_mday;	    /∗ day of month (1 - 31) ∗/
		   int tm_mon;	    /∗ month of year (0 - 11) ∗/
		   int tm_year;	    /∗ year - 1900 ∗/
		   int tm_wday;	    /∗ day of week (Sunday = 0) ∗/
		   int tm_yday;	    /∗ day of year (0 - 365) ∗/
		   int tm_isdst;    /∗ is summer time in effect? ∗/
		   char ∗tm_zone;   /∗ abbreviation of timezone name ∗/
		   long tm_gmtoff;  /∗ offset from UTC in seconds ∗/

       The  tm_zone  and  tm_gmtoff  fields  exist, and are filled in, only if
       arrangements to do so were made when the library containing these func‐
       tions  was  created.  There is no guarantee that these fields will con‐
       tinue to exist in this form in future releases of this code.

       Tm_isdst is non-zero if summer time is in effect.

       Tm_gmtoff is the offset (in seconds) of the time represented from  UTC,
       with positive values indicating east of the Prime Meridian.

FILES
       /usr/local/etc/zoneinfo		   time zone information directory
       /usr/local/etc/zoneinfo/localtime   local time zone file
       /usr/local/etc/zoneinfo/posixrules  used with POSIX-style TZ's
       /usr/local/etc/zoneinfo/GMT	   for UTC leap seconds

       If  /usr/local/etc/zoneinfo/GMT	is absent, UTC leap seconds are loaded
       from /usr/local/etc/zoneinfo/posixrules.

SEE ALSO
       getenv(3), newstrftime(3), newtzset(3), time(2), tzfile(5)

NOTES
       The return values point to static data; the data is overwritten by each
       call.   The  tm_zone  field  of a returned struct tm points to a static
       array of characters, which will also be overwritten at  the  next  call
       (and by calls to tzset).

       Asctime and ctime behave strangely for years before 1000 or after 9999.
       The 1989 and 1999 editions of the C Standard say that  years  from  -99
       through 999 are converted without extra spaces, but this conflicts with
       longstanding  tradition	and  with  this	 implementation.   Traditional
       implementations	of  these two functions are restricted to years in the
       range 1900 through 2099.	 To avoid this portability mess, new  programs
       should use strftime instead.

       Avoid  using out-of-range values with mktime when setting up lunch with
       promptness sticklers in Riyadh.

								   NEWCTIME(3)
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