PHP OOP - Passing object to function is not working - php

Question

I have a problem here on PHP OOP. I try to do something that I always do in .NET - pass the whole object to the function. Unfortunately, the script didn't appear to work and when I try to debug (using Netbeans) it stopped here:
$ud = new userdetails($fullname, $email, $contact, $username, $password, $password2);
Can somebody tell me what did I do wrongly? Thanks in advance!
My script:
<?php
include 'class/registration.php';
$fullname = $_POST['fullname'];
$email = $_POST['email'];
$contact = $_POST['contact'];
$username = $_POST['username'];
$password = $_POST['password'];
$password2 = $_POST['password2'];
$ud = new userdetails($fullname, $email, $contact, $username, $password, $password2);
if (registration::checkEmptyField($ud)==true){
$error = "Please don't leave any field empty";
}
userdetail class:
<?php
class userdetails {
protected $_fullname;
protected $_email;
protected $_contact;
protected $_username;
protected $_password;
protected $_password2;
public function __construct($fullname,$email,$contact,$username,$password,$password2) {
$this->_fullname = $fullname;
$this->_email = $email;
$this->_contact = $contact;
$this->_username = $username;
$this->_password = $password;
$this->_password2 = $password2;
}
public function get_fullname() {
return $this->_fullname;
}
public function get_email() {
return $this->_email;
}
public function get_contact() {
return $this->_contact;
}
public function get_username() {
return $this->_username;
}
public function get_password() {
return $this->_password;
}
public function get_password2() {
return $this->_password2;
}
}
registration class:
<?php
class registration {
function checkEmptyField(&$userdetails){
if ($userdetails-> get_fullname == ''){
return true;
}
elseif ($userdetails->get_email == ''){
return true;
}
elseif ($userdetails->get_contact == ''){
return true;
}
elseif ($userdetails->get_username == ''){
return true;
}
elseif ($userdetails->get_password == ''){
return true;
}
elseif ($userdetails->get_password2 == ''){
return true;
}
}
}

Answer 1

You ask for a property, not a method here: $userdetails-> get_fullname
Correct way: $userdetails-> get_fullname()
You should always turn on the error reporting, because this should have been reported by php.

Answer 2

The way you call registration::checkEmptyField() requires it to be declared as static.
<?php
class registration {
static function checkEmptyField(userdetails $userdetails) {
...
}
}
There is no need to prepend $userdetails with &, in PHP the objects are always passed by reference. It's better to use type hinting: prepend the parameter name ($userdetails) with its expected type (class userdetails in this case).