PHP / Mysql：Connexion与数据库一起使用mysqli，而不是PDO

I works on a android application, with a PHP server, linked to MySQL.

In my PHP server, I try to create a PDO.

try{
    $pdo = new PDO('mysql:host=localhost;dbname=quiz_android_db','root','****');
}
catch (PDOException $e){
    echo ('Erreur: ' . $e->getMessage());
}

But each Time, I have this error :

Erreur: SQLSTATE[HY000] [1045] Access denied for user 'root'@'localhost' (using password: YES)

I use the same username and the same password in a mysqli object and it works. Where could be the problem ?

I use windows 10, php 5.6.19 , mysql 5.17.11

EDIT : This is the way use mysqli

$mysqli = new mysqli("localhost","root","****","quiz_android_db");

    if ($mysqli->connect_errno) {
        echo "Echec lors de la connexion à MySQL : (" . $mysqli->connect_errno . ") " . $mysqli->connect_error;
        return null;
    }