PHP timezone. Why offset is zero?

Question

I can't figure out how timezones work. Why this code produces zero as ouput? Shouldn't it return 10800 instead of 0?

$myZone   = new DateTimeZone('+0300');
$utcZone  = new DateTimeZone('+0000');

$dateA = new DateTime('now', $myZone);
var_dump($utcZone->getOffset($dateA)); // 0

$dateA->setTimezone($utcZone);
var_dump($utcZone->getOffset($dateA)); // 0

$dateA->modify('+ 3600 seconds');
var_dump($utcZone->getOffset($dateA)); // 0

It seems like $utcZone->getOffset(...) does not care about it's argument timezone and time diff at all. Where is the logic?

pr1nc3 · Accepted Answer · 2018-04-25 11:58:19Z

1

<?php

$myZone   = new DateTimeZone('+0300');
$utcZone  = new DateTimeZone('+0000');

$dateA = new DateTime('now', $myZone);


$timeOffset = $myZone->getOffset($dateA);
var_dump($timeOffset);

This one will return 10800 as you said. It was the other way around in getOffset.

output is : int(10800)

answered Apr 25, 2018 at 11:58

pr1nc3

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1 Comment

zim32 Over a year ago

It seems like $myZone->getOffset($dateA) does not care about $dateA timezone at all. What's point?

Guy · Accepted Answer · 2018-04-25 13:52:03Z

getOffset returns the offset used by the timezone at a specific moment.

Timezones can have more than one offset during history - the most common case is Daylight Saving Time, when the offset changes for a specified period. So depending on the time of the year, a certain timezone can have a different offset.

The datetime parameter defines the instant you want to check, and getOffset will check in the timezone's history and return the one used at that specific datetime - no matter what the datetime's timezone is. In the documentation you can find an example of that: http://php.net/manual/en/datetimezone.getoffset.php#refsect1-datetimezone.getoffset-examples

That said, when you use fixed offset values such as "+0000", this means that the DateTimeZone object will always have that offset, all the time - it never changes. That's why when you call $utcZone->getOffset, it always returns zero, no matter what datetime parameter you pass.

If you want the date's offset, call the getOffset method on the DateTime object.

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