php字符串转成字符数组(包含汉字)

<?php
   //字符串转成字符数组(包含汉字)
   function mbStrSplit ($string, $len=1) {
      $start = 0;
      $strlen = mb_strlen($string);
      while ($strlen) {
         $array[] = mb_substr($string,$start,$len,"utf8");
         $string = mb_substr($string, $len, $strlen,"utf8");
         $strlen = mb_strlen($string);
      }
      return $array;
   }
   $astr = "ab你好c8？=-9898d";
   $out = mbStrSplit($astr);
   var_dump($out);die;
?>