php截取字符串,带中文,多余的省略号代替

function subtext($text, $length)
{
    if(mb_strlen($text, "utf8") > $length){
        return mb_substr($text, 0, $length, "utf8")."...";
    }
    else{
        return $text;
    }

}

$str="我们是family happy family";
echo subtext($str,5); //我们是fa...