Question

I’ve been struggling quite a while with PHP’s DateTime classes. My understanding is that a UNIX-timstamp is always in UTC, regardless of the timezone.

That’s why I am quite confused with this code sample.

$date1 = new DateTime("@1351382400"); // Sun Oct 28 2012 02:00:00 GMT+2 (DST)
var_dump($date1->getTimestamp()); //prints: 1351382400
$date1->setTimezone(new DateTimeZone("Europe/Stockholm"););
var_dump($date1->getTimestamp()); //prints: 1351386000

As you can see setTimezone() changes the result of getTimestamp().

Is it expected that setTimezone() affects getTimestamp()?

Answer 1

The amount that you’re off is 3600 seconds, or 1 hour.

I think that what you’re seeing is because the date you picked is the end of Daylight Savings Time in Stockholm. If you use a different date, you don’t get that effect:

$now = time();
echo "            now: $now\n";

$date1 = new DateTime("@{$now}");
echo "     date1 here: {$date1->getTimestamp()}\n";
$date1->setTimezone(new DateTimeZone("Europe/Stockholm"));
echo "date1 Stockholm: {$date1->getTimestamp()}\n";

Output:

            now: 1352321491
     date1 here: 1352321491
date1 Stockholm: 1352321491

I’m not sure if this is a bug or not, but it doesn’t happen if you don’t pick a date on which DST is changing.