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Time::Local(3)


NAME

  Time::Local - efficiently compute time from local and GMT time


SYNOPSIS

      $time = timelocal($sec,$min,$hours,$mday,$mon,$year);
      $time = timegm($sec,$min,$hours,$mday,$mon,$year);


DESCRIPTION

  These routines are the inverse of built-in perl fuctions localtime() and
  gmtime().  They accept a date as a six-element array, and return the
  corresponding time(2) value in seconds since the Epoch (Midnight, January
  1, 1970).  This value can be positive or negative.

  It is worth drawing particular attention to the expected ranges for the
  values provided.  While the day of the month is expected to be in the range
  1..31, the month should be in the range 0..11. This is consistent with the
  values returned from localtime() and gmtime().

  The timelocal() and timegm() functions perform range checking on the input
  $sec, $min, $hours, $mday, and $mon values by default.  If you'd rather
  they didn't, you can explicitly import the timelocal_nocheck() and
  timegm_nocheck() functions.

	  use Time::Local 'timelocal_nocheck';

	  {
	      # The 365th day of 1999
	      print scalar localtime timelocal_nocheck 0,0,0,365,0,99;

	      # The twenty thousandth day since 1970
	      print scalar localtime timelocal_nocheck 0,0,0,20000,0,70;

	      # And even the 10,000,000th second since 1999!
	      print scalar localtime timelocal_nocheck 10000000,0,0,1,0,99;
	  }

  Your mileage may vary when trying these with minutes and hours, and it
  doesn't work at all for months.

  Strictly speaking, the year should also be specified in a form consistent
  with localtime(), i.e. the offset from 1900.	In order to make the
  interpretation of the year easier for humans, however, who are more
  accustomed to seeing years as two-digit or four-digit values, the following
  conventions are followed:

  ·   Years greater than 999 are interpreted as being the actual year, rather
      than the offset from 1900.  Thus, 1963 would indicate the year Martin
      Luther King won the Nobel prize, not the year 2863.

  ·   Years in the range 100..999 are interpreted as offset from 1900, so
      that 112 indicates 2012.	This rule also applies to years less than
      zero (but see note below regarding date range).

  ·   Years in the range 0..99 are interpreted as shorthand for years in the
      rolling "current century," defined as 50 years on either side of the
      current year.  Thus, today, in 1999, 0 would refer to 2000, and 45 to
      2045, but 55 would refer to 1955.	 Twenty years from now, 55 would
      instead refer to 2055.  This is messy, but matches the way people
      currently think about two digit dates.  Whenever possible, use an
      absolute four digit year instead.

  The scheme above allows interpretation of a wide range of dates,
  particularly if 4-digit years are used.

  Please note, however, that the range of dates that can be actually be
  handled depends on the size of an integer (time_t) on a given platform.
  Currently, this is 32 bits for most systems, yielding an approximate range
  from Dec 1901 to Jan 2038.

  Both timelocal() and timegm() croak if given dates outside the supported
  range.


IMPLEMENTATION

  These routines are quite efficient and yet are always guaranteed to agree
  with localtime() and gmtime().  We manage this by caching the start times
  of any months we've seen before.  If we know the start time of the month,
  we can always calculate any time within the month.  The start times
  themselves are guessed by successive approximation starting at the current
  time, since most dates seen in practice are close to the current date.
  Unlike algorithms that do a binary search (calling gmtime once for each bit
  of the time value, resulting in 32 calls), this algorithm calls it at most
  6 times, and usually only once or twice.  If you hit the month cache, of
  course, it doesn't call it at all.

  timelocal() is implemented using the same cache.  We just assume that we're
  translating a GMT time, and then fudge it when we're done for the timezone
  and daylight savings arguments.  Note that the timezone is evaluated for
  each date because countries occasionally change their official timezones.
  Assuming that localtime() corrects for these changes, this routine will
  also be correct.  The daylight savings offset is currently assumed to be
  one hour.


BUGS

  The whole scheme for interpreting two-digit years can be considered a bug.

  Note that the cache currently handles only years from 1900 through 2155.

  The proclivity to croak() is probably a bug.

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