Timezone conversion in PHP with DateTime - php

Question

I found some solutions recently and decided to go with this one so I created following method within one of my classes:
public static function date($format, $time = false, $from_timezone = false, $to_timezone = false) {
if (!$time) {
$time = time();
}
if (($from_timezone === $to_timezone) || (!$from_timezone || !$to_timezone)) {
return date($format, $time);
}
$from_tz = new DateTimeZone($from_timezone);
$to_tz = new DateTimeZone($to_timezone);
$dt = new DateTime();
$dt->setTimezone($from_tz);
$dt->setTimestamp($time);
$offset = $to_tz->getOffset($dt);
return date($format, $dt->format('U') + $offset);
}
Then I did a simple test - I converted datetime to some other timezone, and then convert the result back to the original timezone with expectations to get the original datetime.
$format = 'Y-m-d H:i:s';
$initialtime = '2013-06-13 12:00:00';
echo $initialtime;
echo '<br/>';
$convtime = TimezoneLib::date($format, strtotime($initialtime), 'Canada/Atlantic', 'Europe/Prague');
echo $convtime;
echo '<br/>';
echo TimezoneLib::date($format, strtotime($convtime), 'Europe/Prague', 'Canada/Atlantic');
die();
This is the output
2013-06-13 12:00:00 // Original
2013-06-13 14:00:00 // Converted
2013-06-13 11:00:00 // Converted to original timezone
Why dont they match? What am I missing? Thank you.
UPDATE
I am still unable to get matching dates even after removing strtotime. I found out that default timezone also affected DateTime objects. I came up with this:
<?php
class TimezoneLib {
public static $defaultSystemTimezone;
public static function init() {
self::$defaultSystemTimezone = date_default_timezone_get();
}
public static function date($format, $time = false, $from_timezone = false, $to_timezone = false) {
self::switchSystemTimezone($from_timezone);
if (!$time) {
$time = time();
}
if (($from_timezone === $to_timezone) || (!$from_timezone || !$to_timezone)) {
return date($format, $time);
}
$from_tz = new DateTimeZone($from_timezone);
$to_tz = new DateTimeZone($to_timezone);
$dt = new DateTime($time, $from_tz);
self::switchSystemTimezone($to_timezone);
$offset = $to_tz->getOffset($dt);
$convertedDate = date($format, $dt->format('U') + $offset);
self::restoreSystemTimezone();
return $convertedDate;
}
public static function switchSystemTimezone($timezone_identifier) {
return date_default_timezone_set($timezone_identifier);
}
public static function restoreSystemTimezone() {
return date_default_timezone_set(self::$defaultSystemTimezone);
}
}
TimezoneLib::init();
$format = 'Y-m-d H:i:s';
$initialtime = '2013-06-13 12:00:00';
echo $initialtime;
echo '<br/>';
$convtime = TimezoneLib::date($format, $initialtime, 'Canada/Atlantic', 'Europe/Prague');
echo $convtime;
echo '<br/>';
echo TimezoneLib::date($format, $convtime, 'Europe/Prague', 'Canada/Atlantic');
die();
With following output
2013-06-13 12:00:00
2013-06-13 19:00:00
2013-06-13 11:00:00

Answer 1

Create a new DateTime object instead than using strtotime:
$date = new DateTime('your_date_here', DateTimeZone object here);