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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,  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.

       The *clock time stamp represents the time in seconds  since  1970-01-01
       00:00:00	 Coordinated  Universal	 Time  (UTC).  The POSIX standard says
       that time stamps must be nonnegative  and  must	ignore	leap  seconds.
       Many implementations extend POSIX by allowing negative time stamps, and
       can therefore represent time stamps that predate	 the  introduction  of
       UTC and are some other flavor of Universal Time (UT).  Some implementa‐
       tions support leap seconds, in contradiction to POSIX.

       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 UT 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 UT,
       with positive values  indicating	 east  of  the	Prime  Meridian.   The
       field's name is derived from Greenwich Mean Time, a precursor of UT.

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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