public function register($username = "", $password = "", $confirmpassword = "", $email = "") {
        global $link;
        $error = array('success' => false, 'messages' => array());

        if(strlen($username) < 3 || strlen($username) > 32) {
            array_push($error["messages"], array('message' => 'Nome de utilizador com tamanho inválido.'));
        } else if(preg_match('/\s/',$username)) {
            array_push($error["messages"], array('message' => 'Nome de utilizador com formato inválido.'));
        } else {
            $username = mysql_real_escape_string($username);
            $numRows = mysql_query("SELECT id FROM users WHERE username = '$username'", $link);
            if(mysql_num_rows($numRows) > 0) {
                array_push($error["messages"], array('message' => 'Nome de utilizador já existe.'));
            }
        }

        if(strlen($password) < 6) {
            array_push($error["messages"], array('message' => 'Palavra-passe muito curta.'));
        } else if($password != $confirmpassword) {
            array_push($error["messages"], array('message' => 'Palavras-passe não correspondem.'));
        } else {
            $password = mysql_real_escape_string($password);
            $password = md5($password);
        }

        if(!filter_var($email, FILTER_VALIDATE_EMAIL)) {
            array_push($error["messages"], array('message' => 'Email com formato inválido.'));
        } else {
            $email = mysql_real_escape_string($email);
            $numRows = mysql_query("SELECT id FROM users WHERE email = '$email'", $link);
            if(mysql_num_rows($numRows) > 0) {
                array_push($error["messages"], array('message' => 'Email já existe.'));
            }
        }

        if(sizeof($error["messages"]) > 0) {
            #mysql_close($link);
            return $error;
        } else {
            if (!empty($_SERVER['HTTP_CLIENT_IP'])) {
                $ip = $_SERVER['HTTP_CLIENT_IP'];
            } elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {
                $ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
            } else {
                $ip = $_SERVER['REMOTE_ADDR'];
            }

            $resRegister = mysql_query("INSERT INTO users (username, password, email, registerip, userpic) VALUES ('" . $username . "','" . $password. "','" . $email. "','" . $ip. "', '')", $link);
            if(mysql_affected_rows() > 0) {
                #mysql_close($link);
                return array('success' => true, 'message' => "Conta criada com sucesso.");
            } else {
                #mysql_close($link);
                return array('success' => false, 'message' => "Ocorreu um erro ao registar.<br />Contacte o adminitrador.");
            }
        }
    }