pdo uri连接数据库问题

Warning:  PDO::__construct(file://D:\phpStudy\PHPTutorial\WWW\UserManager\pdo\dsn.txt): failed to open stream: No such file or directory in D:\phpStudy\PHPTutorial\WWW\UserManager\pdo\pdo_connectdburi.php on line 8
invalid data source URI

//通过URI形式连接数据库
try{
    $dsn='uri:file://D:\phpStudy\PHPTutorial\WWW\UserManager\pdo\dsn.txt';
    $username='root';
    $password='root';
    $pdo=new PDO($dsn,$username,$password);
    var_dump($pdo);
}catch (PDOException $e){
    echo $e->getMessage();
};

感觉书写问题啊