php convert utf-8 character encoding

php convert utf-8 character encoding

function strToUtf8($str){
    $encode = mb_detect_encoding($str, array("ASCII",'UTF-8',"GB2312","GBK",'BIG5'));
    if($encode == 'UTF-8'){
        return $str;
    }else{
        return mb_convert_encoding($str, 'UTF-8', $encode);
    }
}