/** * 生成随机字符串 * @author 宁佳兵 
     
       * @param int $length * @return string */function createNonceStr($length = 16) {    $chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";    $str = "";    for ($i = 0; $i < $length; $i++) {      $str .= substr($chars, mt_rand(0, strlen($chars) - 1), 1);    }    return $str;}