DateTime object not associated with timestamp?

Question

Is the object DateTime not tied to its timestamp? Or does getTimestamp () have some kind of side effect when used when changing DST?

Details
When setting the time stamp of an object DateTimethat is on DST(which means that formatting time exists both before and after changing the clock), the returned time stamp is different from the set time stamp.

$ php --version
PHP 7.1.3 (cli) (built: Mar 17 2017 16:59:59) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.1.0, Copyright (c) 1998-2017 Zend Technologies

Playback
Consider the following phpscript:

date_default_timezone_set('Europe/Berlin');

$date = new DateTime();
$set_timestamp = 1319932800;
$date->setTimestamp($set_timestamp);
$get_timestamp = $date->getTimestamp();

fwrite(STDERR, $set_timestamp . "\n");  // 1319932800
fwrite(STDERR, $get_timestamp . "\n");  // 1319936400 **(WHY IS THIS DIFFERENT?)**

Why are printed values not equal?

Answer 1

, unix UTC, DST.

DateTime ( "" , DateTime).

, DST, +00: 00 UTC.

:

1. DateTime

+00: 00, ( @) :

$set_timestamp = 1319932800;
$date = new DateTime('@' . $set_timestamp);

print($set_timestamp . "\n");
print($date->getTimestamp() . "\n");

: .

2. setTimestamp()

setTimezone() DateTimeZone('+00:00') DateTimeZone('UTC') setTimestamp():

$set_timestamp = 1319932800;
$date = new DateTime();
$date->setTimezone(new DateTimeZone('UTC'));
$date->setTimestamp($set_timestamp);

print($set_timestamp . "\n");
print($date->getTimestamp() . "\n");

, :

1319932800
1319932800

---

date_default_timezone_set(), .

, $date (, unix ), .

Answer 2

\DateTime , , getter .

, DST , 1319932800..1319936400 1319936400..1319940000 :
https://www.epochconverter.com/timezones?q=1319936399&tz=Europe%2FBerlin https://www.epochconverter.com/timezones?q=1319939999&tz=Europe%2FBerlin