php : 警告:为 foreach(） 提供的参数无效

我只是想不通......但是当我抛出异常消息时，我有一种感觉问题就在那里。我在注册课上得到了几乎相同的代码。只需给错误数组正常消息，例如$this->errors[] ="一些错误"。

<?php

class class_login 
{
    private $id;
    private $username;
    private $password;
    private $passmd5;
    private $errors;
    private $access;
    private $login;
    private $ltoken;
    public function __cunstruct()
    {
        $this->errors = array();
        $this->login  = isset($_POST['login'])? 1:0;
        $this->access = 0;
        $this->ltoken  = $_POST['ltoken'];
        $this->id     = 0;
        $this->username = ($this->login)? $this->filter($_POST['lusername']) : $_SESSION['username'];
        $this->password = ($this->login)? $this->filter($_POST['lpassword']) : '';
        $this->passmd5 = ($this->login)? md5($this->password) : $_SESSION['password'];
    }
    public function isLoggedIn()
    {
        ($this->login)? $this->verifyPost() : $this->verifySession();
        return $this->access;
    }
    public function filter($var)
    {
        return preg_replace('/[^a-zA-Z0-9]/','',$var);
    }
    public function verifyPost()
    {
        try
        {
            if(!$this->tokenValid())
                throw new Exception('Invalid Form Submission!');
            if(!$this->isDataValid())
                throw new Exception('Ivalid Form Data!');
            if(!$this->verifyDatabase())
                throw new Exception('Invalid Username/Password!');
            $this->access = 1;
            $this->registerSession();
        }
        catch(Exception $e)
        {
            $this->errors[] = $e->getMessage();
        }
    }
    public function verifySession()
    {
        if($this->sessionExist() && $this->verifyDatabase())
        $this->access = 1;
    }
    public function verifyDatabase()
    {
        include('db_connect.php');
        $data = mysql_query("SELECT ID FROM users WHERE username = '($this->username)' AND password = '($this->passmd5)'");
        if (mysql_num_rows($data))
        {
            list($this->id) = @array_values(mysql_fetch_assoc($data));
            return true;
        }
        else
            return false;
       }
    public function isDataValid()
    {
        return (preg_match('/[^a-zA-Z0-9](5,12)$/',  $this->username) && preg_match('/[^a-zA-Z0-9](5,12)$/',  $this->password))? 1:0;
    }
    public function tokenValid()
    {
        return (!isset($_SESSION['ltoken']) || $this->ltoken != $_SESSION['ltoken'])? 0 : 1;
    }
    public function registerSession()
    {
        $_SESSION['ID']       = $this->id;
        $_SESSION['username'] = $this->username;
        $_SESSION['password'] = $this->passmd5;
    }
    public function sessionExist()
    {
        return (isset($_SESSION['username']) && isset($_SESSION['password']))? 1 : 0;
    }
    public function show_errors()
    {
        foreach($this->errors as $key=>$value)
            echo $value."</br>";
    }

}
?>