|o||Years greater than 999 are interpreted as being the actual year, rather than the offset from 1900. Thus, 1964 would indicate the year Martin Luther King won the Nobel prize, not the year 3864.|
|o||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).|
|o||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.|
On perl versions older than 5.12.0, the range of dates that can be actually be handled depends on the size of time_t (usually a signed integer) on the 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.
As of version 5.12.0, perl has stopped using the underlying time library of the operating system its running on and has its own implementation of those routines with a safe range of at least +/ 2**52 (about 142 million years).
Because of DST changes, there are many time zones where the same local time occurs for two different GMT times on the same day. For example, in the Europe/Paris time zone, the local time of 2001-10-28 02:30:00 can represent either 2001-10-28 00:30:00 GMT, <B>orB> 2001-10-28 01:30:00 GMT.
When given an ambiguous local time, the timelocal() function should always return the epoch for the earlier of the two possible GMT times.
When a DST change causes a locale clock to skip one hour forward, there will be an hours worth of local times that dont exist. Again, for the Europe/Paris time zone, the local clock jumped from 2001-03-25 01:59:59 to 2001-03-25 03:00:00.
If the timelocal() function is given a non-existent local time, it will simply return an epoch value for the time one hour later.
On perl version 5.12.0 and newer, negative epoch values are fully supported.
On older versions of perl, negative epoch (time_t) values, which are not officially supported by the POSIX standards, are known not to work on some systems. These include MacOS (pre-OSX) and Win32.
On systems which do support negative epoch values, this module should be able to cope with dates before the start of the epoch, down the minimum value of time_t for the system.
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 weve seen before. If we know the start time of the month, we can always calculate any time within the month. The start times are calculated using a mathematical formula. Unlike other algorithms that do multiple calls to gmtime().
The timelocal() function is implemented using the same cache. We just assume that were translating a GMT time, and then fudge it when were 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 whole scheme for interpreting two-digit years can be considered a bug.
Support for this module is provided via the email@example.com email list. See http://lists.perl.org/ for more details.
Copyright (c) 1997-2003 Graham Barr, 2003-2007 David Rolsky. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
The full text of the license can be found in the LICENSE file included with this module.
This module is based on a Perl 4 library, timelocal.pl, that was included with Perl 4.036, and was most likely written by Tom Christiansen.
The current version was written by Graham Barr.
It is now being maintained separately from the Perl core by Dave Rolsky, <firstname.lastname@example.org>.
|perl v5.20.3||TIME::LOCAL (3)||2012-07-20|