Calling base class virtual method by derived class virtual method

Question

In C++ - take a case where derived class deriving from a base class and there is a virtual method in base class which the derived class is overriding. Could someone tell me a real life scenario where the derived class version of the virtual function might require to call the base class version of the virtual function?

Example,

class Base
{
public:
    Base() {}
    virtual ~Base() {}
    virtual void display() { cout << "Base version" << endl; }
};

class Derived : public Base
{
public:
    Derived() {}
    virtual ~Derived() {}
    void display();
};

void Derived::display()
{
    Base::display();  // a scenario which would require to call like this?
    cout << "Derived version" << endl;
}

Answer 1

You do that every time when you also need base class behavior but don't want (or can't) reimplement it.

One common example is serialization:

void Derived::Serialize( Container& where )
{
    Base::Serialize( where );
    // now serialize Derived fields

}

you don't care how base class is serialized, but you definitely want it to serialize (otherwise you lose some data), so you call the base class method.

Answer 2

You can find lots of real-life examples in MFC. For. e.g

CSomeDialog::OnInitDialog()
{
  CDialogEx::OnInitDialog(); //The base class function is called.
  ----
  ----- 
}