public function verify()
{
    //生产验证码值
    $char_list = '1234567890';//所有可能的字符
    $list_lenght = strlen($char_list);
    $code_lenght = 6;//码值长度
    $verify = '';
    for ($i = 1; $i <= $code_lenght; ++$i) {
        $rend_index = mt_rand(0, $list_lenght - 1);
        $verify .= $char_list[$rend_index];//
    }
    return $verify;
}