取不到错误信息，怎么搞？

一个简单基础的类： class s{
public $fwq,$yhm,$mm,$km,$error=3,$err='';

public function __construct($fwq="mysql3.000webhost.com",$yhm="*******",$mm=" ******* ",$km=" ******* ")
{
$this->fwq=$fwq;
$this->yhm=$yhm;
$this->mm=$mm;
$this->km=$km;

$this->si= new MySQLI($this->fwq,$this->yhm,$this->mm,$this->km);

if($this->si->connect_error)
{
$this->err=$this->si->connect_error;
return $this->error=0;

}
后面省略~~~



连接错误时取不到连接失败的错误信息怎么搞，我$y=new s(),然后if($y->error==0)
{echo "连接失败".$y->err;}怎么取不到呢？？？

然而我直接 $my= new MySQLI("mysql3.000webhost.com","********","*******","*****");

if($my->connect_error)
{
echo "失败".$my->connect_error;
}
却能取到怎么回事？？？？？？