Date, Time, DSL and Timezone information handling

Question

Timezone and Daylight Savings information can change without notice. A simple piece of legislation could alter DSL for an area and render datetime information useless for a certain area on the globe, suddenly impacting code dependent on a server's or client's local time. And, timezones only loosely reflect actual sunset/sunrise times anyway.

There are several PHP userland libraries which this unpredictable definition of "time" could affect, including DateTime, date, and others. Outside of userland, there may be internal code which relies on timezone conversions.

How does PHP's libraries account for the ever changing definitions of dates, times, and timezones?

Keeping the used timezone database up to date is the admin's job. — CBroe, Mar 17 '13 at 02:55
@CBroe: "There is no installation needed to use these functions; they are part of the PHP core." But it also suggestes getting the latest from pecl. Your link provides conflicting instructions. Mind you this is an internals question, so I'm asking about how this tz data is maintained. — bob-the-destroyer, Mar 17 '13 at 03:08
http://en.wikipedia.org/wiki/Tz_database, http://www.iana.org/time-zones — CBroe, Mar 17 '13 at 03:14
@Cbroe: I almost choked on the 2011 lawsuit section. But despite that, is this information PHP relies on internally? — bob-the-destroyer, Mar 17 '13 at 03:16
@CBroe: thanks. You should add an answer about using iana.org. I'm still interested in the laughable lawsuit, but maybe that's not meant for this site. — bob-the-destroyer, Mar 17 '13 at 03:30

score 2 · Accepted Answer · answered Mar 17 '13 at 03:33

PHP uses the tz database, also called the zoneinfo database, IANA Time Zone Database or Olson database internally. (Although it is possible to feed it timezone data from another database of course.)

More info can be found here: http://en.wikipedia.org/wiki/Tz_database and here: http://www.iana.org/time-zones

Date, Time, DSL and Timezone information handling

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