PHP生成随机字符串

<?php

  /**
  ** $length : the length of the result String
  **/
  function getRandChar($length){
     $str = null;
     $strPol = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz";//大小写字母以及数字
     $max = strlen($strPol)-1;
     
     for($i=0;$i<$length;$i++){
        $str.=$strPol[rand(0,$max)];
     }
     return $str;
  }
 
  echo getRandChar(10);
?>