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copied!<p>When you use a reference or a pointer to call a method, the compiler searches in the type of the pointer or reference at the declaration of the method (here it searches in <code>B</code> the declaration of some method with signature <code>f()</code>). When it finds one :</p> <ul> <li>if it is NOT marked as <code>virtual</code>, then it solves it as a call to the method defined for this class - this is a static binding.</li> <li>if it is marked as <code>virtual</code>, then the method called will be the appropriate one of the object referenced or pointed by - this is a dynamic binding.</li> </ul> <p>The next test would have been :</p> <pre><code>DD * dd = new DD(); D * d = dd; B * b = d; b->f(); d->f(); dd->f(); </code></pre> <p>One single object <code>new DD()</code> that is used/viewed differently... Each type can be thought as a kind of view you have on an object. If you see it as a <code>B</code> then <code>f()</code> does something but always the same thing, but if you see it as <code>D</code> or <code>DD</code>, <code>f()</code> does something different...</p> <p>If you meet someone in the street, the standard way for him to salute you is to say hello, but for the same person, when he meets a friend of him he can either say hi! or Yo! :</p> <pre><code>class Person { public: void salute() { cout << "Hello" << endl; } }; class Friend : public Person { public: virtual void salute() { cout << "Hi!" << endl; } }; class RoomMate : public Friend { public: virtual void salute() { cout << "Yo!" << endl; } }; void asACustomer(Person &p) { p.salute(); // static binding, we need the standard politeness } void asAFriend(Friend &f) { p.salute(); // dynamic binding, we want an appropriate message... } RoomMate joe; asCustomer(joe); asFriend(joe); </code></pre> <p>With static binding you know at compile time which method is called; with dynamic binding you cannot, you only know that an appropriate one will be. This is a key point in sub-typing polymorphism.</p> <p>In general, be careful when mixing static and dynamic binding for a method.</p>

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