how to set default timezone in php?

<?php

date_default_timezone_set('Europe/London');

echo date('Y-m-d H:i:s');

?>

how to fetch all supported timezones in PHP?

<?php

$timezone_offsets = array();

foreach(timezone_identifiers_list() as $timezone_identifier)

{

$date_time_zone = new DateTimeZone($timezone_identifier);

$date_time = new DateTime('now', $date_time_zone);

$timezone_offsets[$timezone_identifier] = $date_time_zone->getOffset($date_time);

}

echo "<pre>";

print_r($timezone_offsets);

?>