Q:

bindParam literate through private member variable of a class

I create a class called User with only private member variables and getter/setter functions 
class User {
   private $m_id;
   private $m_firstname;
   private $m_lastname;

   public function get_firstname() { return $this->m_firstnmae; }
   public function set_firstname($firstname) { $this->m_firstname = $firstname; }
   ...
}

so print_r($user)would give me something like this: 
User Object
(
   [m_id:User:private] => 2725
   [m_firstname:User:private] => Alan
   [m_lastname:User:private] => Turing
)

Now I am using PDO to insert the object into a database(I will skip the connection part, since it's working and not part of the problem). Here my function to insert the data:
function insert($user) 
{
    $insert_query = "insert into table (id,firstname,lastname) values (:id, :firstname, :lastname)";
    try
    {
        $stmt = $this->m_pdo->prepare($insert_query);
        $stmt->bindParam(':id', $user->get_id());
        $stmt->bindParam(':firstname', $user->get_firstname());
        $stmt->bindParam(':lastname', $user->get_lastname());

        $stmt->execute();
        return true;
    }
    catch (PDOException $ex)
    {
        echo $this->m_error_message = $ex->getMessage();
        return false;
    }
}

works as well. HOWEVER, when I change the php error_reporting to E_ALL | E_STRICT, which show runtime strict warning as well, the insert code produce the warning strict standards only variables should be passed by reference for the bindParam lines. After asking google, I found out that obviously I have to do this in 2 steps:
$id = $user->get_id()
$stmt->bindParam(':id', $id);

After converting them into the new format, everything works without any warning.
The thing is, my original User-class is much bigger with more then 20 private member variables and I have other classes like this as well. So I was thinking iterate through the variables and save them in an array and bindParam them as array. But then I face the problem that foreach only loop through the public variables but not the private ones... So my questions now:

is it possible to combine bindParam with a loop somehow?
if it is, how can I loop through private member variables and save them?

for convenience I use same naming-format everywhere. i.e. column in database with firstname would have the counterpart m_firstname in the User-class with get_firstname() and set_firstname($firstname) as getter/setter

A:

I think that you should use
public bool PDOStatement::bindValue ( mixed $parameter , mixed $value [, int $data_type = PDO::PARAM_STR ] ) 
Instead of bindParam() and keep your getters :)
moved from comment to answer

