php简单实现多字节字符串翻转的方法

<?php
function mb_strev ($string, $encoding = null) {
 if ($encoding === null) {
  $encoding = mb_detect_encoding($string);
 }
 $length = mb_strlen($string, $encoding);
 $reversed = '';
 while($length-- > 0) {
  $reversed .= mb_substring($string, $length, 1, $encoding);
 }
 return $reversed;
}