C++ Virtual Functions Question:

A pure virtual function is a function which has no definition in the base class. Its definition lies only in the derived class ie it is compulsory for the derived class to provide definition of a pure virtual function. Since there is no definition in the base class, these functions can be equated to zero.

The general form of pure virtual function is:

virtual type func-name(parameter-list) = 0;

Consider following example of base class Shape and classes derived from it viz Circle, Rectangle, Triangle etc.

class Shape
{
int x, y;
public:
virtual void draw() = 0;
};

class Circle: public Shape
{
public:
draw()
{
//Code for drawing a circle
}
};

class Rectangle: public Shape
{
Public:
void draw()
{
//Code for drawing a rectangle
}
};

class Triangle: public Shape
{
Public:
void draw()
{
//Code for drawing a triangle
}
};

Thus, base class Shape has pure virtual function draw(); which is overridden by all the derived classes.