PHP如何转换时区？

<?php
function changeTimeZone($date_time, $format = &#39;Y-m-d H:i:s&#39;, $to = &#39;Europe/Rome&#39;, $from = &#39;Asia/Shanghai&#39;) {
    $datetime = new DateTime($date_time, new DateTimeZone($from));
    $datetime->setTimezone(new DateTimeZone($to));
    return $datetime->format($format);
}
 
$time = changeTimeZone(&#39;2018-12-19 00:00:00&#39;);
$t = changeTimeZone(&#39;2018-12-19 00:00:00&#39;, &#39;Y-m-d&#39;);
echo $time;
echo $t;