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CTIME(3)							      CTIME(3)

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

SYNOPSIS
       #include <time.h>

       char *ctime(const time_t *timer);

       char *asctime(const struct tm *timeptr);

       struct tm *localtime(const time_t *timer);

       struct tm *gmtime(const time_t *timer);

       char *timezone(ing zone, int dst);

       time_t mktime(struct tm *timeptr);

       size_t strftime(char *s, size_t maxsize,
	    const char *format, const struct tm *timeptr);

       void tzset(void);

       extern char *tzname[2];

DESCRIPTION
       Tzset uses the value of the environment variable TZ to set up the  time
       conversion information used by localtime, ctime, strftime and mktime.

       If  TZ  does  not  appear  in  the  environment, the TZDEFAULT file (as
       defined in tzfile.h) is used.  If this file fails for any  reason,  the
       Greenwich Mean Time (GMT) offset as provided by the kernel is used.  In
       this case, DST is ignored, resulting in the  time  being	 incorrect  by
       some  amount  if	 DST  is  currently  in effect.	 If this fails for any
       reason, GMT is used.

       If TZ appears in the environment but its value is a null string, GMT is
       used; if TZ appears and begins with a slash, it is used as the absolute
       pathname of the tzfile(5)-format file  from  which  to  read  the  time
       conversion information; if TZ appears and begins with a character other
       than a slash, it's used as a  pathname  relative	 to  the  system  time
       conversion  information directory, defined as TZDIR in the include file
       tzfile.h.  If this file fails for any reason, GMT is used.

       Programs	 that  always  wish  to	 use  local  wall  clock  time	should
       explicitly remove the environmental variable TZ with unsetenv(3).

       Ctime converts the calendar time	 pointed to by timer, such as returned
       by time(2) into ASCII and returns a pointer to a 26-character string in
       the following form (all the fields have constant width):

	   Sun Sep 16 01:03:52 1973\n\0

       Asctime	converts  the  broken-down time in the structure pointed to by
       timeptr into a string as returned by ctime.

       Localtime and gmtime  return  pointers  to  structures  containing  the
       broken-down  time.   Localtime  corrects for the time zone and possible
       daylight savings time; gmtime converts directly to GMT,	which  is  the
       time UNIX uses.

       The tm structure declaration from the <time.h> file is:

	      struct tm {
		   int tm_sec;	  /* seconds after the minute (0-59) */
		   int tm_min;	  /* minutes after the hour (0-59) */
		   int tm_hour;	  /* hours since midnight (0-23) */
		   int tm_mday;	  /* day of the month (1-31) */
		   int tm_mon;	  /* months since January (0-11) */
		   int tm_year;	  /* years since 1900 */
		   int tm_wday;	  /* days since Sunday (0-6) */
		   int tm_yday;	  /* days since Jan. 1 (0-365) */
		   int tm_isdst;  /* flag; daylight savings time in effect */
		   long tm_gmtoff;	   /* offset from GMT in seconds */
		   char *tm_zone; /* abbreviation of timezone name */
	      };

       Tm_isdst is non-zero if a time zone adjustment such as Daylight Savings
       time is in effect.

       Tm_gmtoff is the offset (in seconds) of the time represented from  GMT,
       with positive values indicating East of Greenwich.

       Timezone	 remains  for  compatibility  reasons only; it's impossible to
       reliably map timezone's arguments (zone, a “minutes west of GMT”	 value
       and  dst,  a  “daylight	saving	time  in  effect” flag) to a time zone
       abbreviation.

       Mktime converts the broken-down time, expressed as local time,  in  the
       structure  pointed  to  by  timeptr into a calendar time value with the
       same encoding as that of the values returned by time(3).	 The  original
       values of the tm structure members tm_wday and tm_yday are ignored.  On
       successful completion of mktime these  values  are  set	appropriately.
       The  values  for	 the  tm_year,	tm_mon,	 tm_mday, tm_hour, tm_min, and
       tm_sec may be outside the ranges described above and will  be  adjusted
       appropriately to reflect the correct time.  For example,	 if tm_year is
       set to 1980 and tm_mon is set to -2  the	 return	 value	would  reflect
       November 1979.

       Strftime places characters into the array pointed to by s as controlled
       by the string pointed to by format.  The format string consists of zero
       or  more	 conversion  specifiers and ordinary characters.  A conversion
       specifier consists of a	%  character  followed	by  a  character  that
       determines  the	behavior  of  the  conversion specifier.  All ordinary
       characters  (including  the  terminating	 null  character)  are	copied
       unchanged  into	the  array.   Each conversion specifier is replaced by
       appropriate  characters	as  described  in  the	following  list.   The
       appropriate  characters	are  determined by the values contained in the
       structure pointed to  by	 timeptr.   Below  is  a  list	of  conversion
       specifiers:

	      %%     identical to %

	      %a     abbreviated weekday name

	      %A     full weekday name

	      %b     abbreviated month name

	      %B     full month name

	      %c     time  and date using the time and date representation for
		     the locale (%X %x)

	      %d     day of the month as a decimal number (01-31)

	      %H     hour based on a 24-hour clock as a decimal number (00-23)

	      %I     hour based on a 12-hour clock as a decimal number (01-12)

	      %j     day of the year as a decimal number (001-366)

	      %m     month as a decimal number (01-12)

	      %M     minute as a decimal number (00-59)

	      %p     AM/PM designation associated with a 12-hour clock

	      %S     second as a decimal number (00-61)

	      %w     weekday as a decimal number (0-6), where Sunday is 0

	      %x     date using the date representation for the locale

	      %X     time using the time representation for the locale

	      %y     year without century (00-99)

	      %Y     year with century (e.g. 1990)

	      %Z     time zone name or abbreviation, or no  characters	if  no
		     time zone is determinable.

RETURN VALUE
       Ctime  returns  the  pointer  returned by asctime with that broken-down
       time as argument.

       Asctime returns a pointer to a string.

       Localtime returns a pointer to a tm structure.

       Gmtime returns a pointer to a tm structure, or a null pointer if GMT is
       not available.

       Mktime  returns	the specified calendar time encoded as a value of type
       time_t.	 If  the  calendar  time  cannot  be  represented,  the	 value
       (time_t)-1 is returned.

       Strftime returns the number of characters placed into the array pointed
       to by s not including the  terminating  null  character	if  the	 total
       number of resulting characters including the terminating null character
       is not more than maxsize.  Otherwise, zero is returned.

NOTE
       The return values point to static data whose content 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).

SEE ALSO
       gettimeofday(2), getenv(3), time(3), tzfile(5), environ(7)

4th Berkeley Distribution	August 1, 1992			      CTIME(3)
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