包含配置文件的php中未定义的变量

Question

    <?php

    class Login
    {

    private $dbh = null;
    private $dsn ,$host, $username , $password= null;

    public $errors = array();

    public $messages = array();


    public function __construct()
    {

    session_start();
    require_once 'dbconfig.php';
    if (isset($_GET["logout"])) {
        $this->doLogout();
    }
    elseif (isset($_POST["login"])) {
        $this->dologinWithPostData();
    }
    }


    private function dologinWithPostData()
    {

    if (empty($_POST['user_name'])) {
        $this->errors[] = "Username field was empty.";
    } 
    elseif (empty($_POST['user_password'])) {
    $this->errors[] = "Password field was empty.";
    } 
    elseif (!empty($_POST['user_name']) && !empty($_POST['user_password'])) {
        $this->$dsn = "mysql:host=$host;dbname=$dbname"; // $dbname is empdb as in dbconfig.php
        $this->$dbh = new PDO($dsn, $username, $password);
        $this->$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);





    if (!$this->dbh->set_charset("utf8")) {
    $this->errors[] = $this->dbh->error;
    }
    if (!$this->dbh->connect_errno) {
        $user_name = $this->dbh->real_escape_string($_POST['user_name']);
        $sql = "SELECT user_name, user_email, user_password_hash
        FROM users
        WHERE user_name = '" . $user_name . "' OR user_email = '" . $user_name . "';";
        $result_of_login_check = $this->db_connection->query($sql);

        if ($result_of_login_check->num_rows == 1) {
        $result_row = $result_of_login_check->fetch_object();
        if (password_verify($_POST['user_password'], $result_row->user_password_hash)) {

        $_SESSION['user_name'] = $result_row->user_name;
        $_SESSION['user_email'] = $result_row->user_email;
        $_SESSION['user_login_status'] = 1;

        }
    else {
        $this->errors[] = "Wrong password. Try again.";
        }
    }
    else {
        $this->errors[] = "This user does not exist.";
        }
    } 
    else {
        $this->errors[] = "Database connection problem.";
    }
    }
    }

    public function doLogout()
    {

    $_SESSION = array();
    session_destroy();

    $this->messages[] = "You have been logged out.";
    }


    public function isUserLoggedIn()
    {
        if (isset($_SESSION['user_login_status']) AND $_SESSION['user_login_status'] == 1) {
        return true;
    }
    // default return
    return false;
    }

我一直在尝试使用php中的会话创建一个php登录页面。但是在我输入登录页面的值后，我得到的错误如下：

Undefined variable: host in www\proj\Login.php on line 38

Undefined variable: dbname in \www\proj\Login.php on line 38

Undefined variable: dsn in \www\proj\Login.php on line 38

Cannot access empty property in \www\proj\Login.php on line 38

是导致问题的查询还是我错误地包含了db.config。我已经包含 dbconfig.php 文件，该文件已初始化所有这些变量。