<?php
$name=DateTimeZone::listIdentifiers(DateTimeZone::PER_COUNTRY, "US");
print_r($name);
?>
Working fine in localhost. But when i am trying it online i m getting error Fatal error: Undefined class constant 'PER_COUNTRY' on line 1
That is a PHP 5.3 or greater function. So your server version on your live server is not >= PHP 5.3
See here: http://www.php.net/manual/en/datetimezone.listidentifiers.php
Check your versions of PHP: PER_COUNTRY was added with 5.3.0