随机产生六位数密码

function randStr($len = 6, $format = 'ALL') {    switch ($format) {        case 'ALL':            $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-@#~';            break;        case 'CHAR':            $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-@#~';            break;        case 'NUMBER':            $chars = '0123456789';            break;        default :            $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-@#~';            break;    }    mt_srand((double)microtime() * 1000000 * getmypid());    $password = "";    while (strlen($password) < $len)        $password .= substr($chars, (mt_rand() % strlen($chars)), 1);    return $password;}