PHP 日期函数 gmstrftime()

<?php
   setlocale(LC_TIME, 'en_US');

   echo strftime("%b %d %Y %H:%M:%S", mktime(20, 0, 0, 12, 31, 2015)) . "\n";
   echo gmstrftime("%b %d %Y %H:%M:%S", mktime(20, 0, 0, 12, 31, 2015)) . "\n";
?>