hmm

//dbc.php
<?php
class Connection{

    private $servername = "localhost", $username = "root", $password = "", $dbname = "sbhotel";
    protected $conn = "", $row = "", $result = "", $sql = "", $validator=false;

    function __construct(){
        $this->conn = new mysqli($this->servername, $this->username, $this->password, $this->dbname);
    }

    function __destruct(){
        $this->conn->close();
    }
}

$db = new Connection();

?>
//sigUp.php
<?php
include_once($_SERVER['DOCUMENT_ROOT']."\sbhotel\components\php\connection\dbc.php");

class SignUp extends Connection{

    protected $userName = $_POST['userName'];
    protected $password = $_POST['password'];
    protected $passwordVerification = $_POST['passwordVerification'];
    protected $email= $_POST['email'];

    protected function __construct($userName, $password, $passwordVerification, $email) {
        $this->conn->real_escape_string($userName) = $userName;
        $this->conn->real_escape_string($password) = $password;
        $this->conn->real_escape_string($passwordVerification) = $passwordVerification;
        $this->conn->real_escape_string($email) = $email;

    }

    public function SignUpInputEmpty() {
         if (empty($this->userName) or empty($this->password) or empty($this->passwordVerification) or empty($this->email)) {
            echo "empty";
            //validator=false;
         }
         else {
            echo "set";
            //validator=true;
         }
        }
}
$me = new SignUp();
    echo $me->SignUpInputEmpty();
?>
//modal elem ahol használnám

<div class="modal fade" id="modalSign" tabindex="-1" role="dialog" aria-labelledby="modalLabel" aria-hidden="true">
    <div class="modal-dialog" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title" id="modalLabel">Regisztráció</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <form method="post">
                <div class="modal-body mx-3">
                    <div class="md-form mb-2">
                        <label for="userName">Felhasználónév:*</label>
                        <input type="text" class="form-control" name="userName" placeholder="Felhasználónév">
                    </div>
                    <div class="md-form mb-2">
                        <label for="password">Jelszó:*</label>
                        <input type="password" class="form-control" name="password" placeholder="Jelszó">
                    </div>
                    <div class="md-form mb-2">
                        <label for="passwordVerification">Jelszó megerősítése:*</label>
                        <input type="password" class="form-control" name="passwordVerification" placeholder="Jelszó megerősítése">
                    </div>
                    <div class="md-form mb-2">
                        <label for="email">Email:*</label>
                        <input type="email" class="form-control" name="email" placeholder="Pelda@pelda.hu">
                    </div>
                </div>
                <div class="modal-footer">
                    <input type="hidden" name="action" value="signUp">
                    <input type="submit" name="signUpButton" value="Regisztráció" class="btn btn-primary">
                    <button type="button" class="btn btn-secondary" data-dismiss="modal">Mégse</button>
                </div>
            </form>
        </div>
    </div>
</div>