Add attribute to an object in PHP

How do you add an attribute to an Object in PHP?

Well, the general way to add arbitrary properties to an object is:

$object->attributename = value;

You can, much cleaner, pre-define attributes in your class (PHP 5+ specific, in PHP 4 you would use the old var $attributename)

class baseclass
 { 

  public $attributename;   // can be set from outside

  private $attributename;  // can be set only from within this specific class

  protected $attributename;  // can be set only from within this class and 
                             // inherited classes

this is highly recommended, because you can also document the properties in your class definition.

You can also define getter and setter methods that get called whenever you try to modify an object's property.