virtual-function-inheritance.cpp

// A typical example of inheritance and virtual function use.
// We would be mapping this code to equivalent C.
 
// Prototype graphics library function to draw a circle
void glib_draw_circle (int x, int y, int radius);
 
// Shape base class declaration
class Shape
{
protected:
  int m_x;    // X coordinate
  int m_y;  // Y coordinate
 
public:
  // Pure virtual function for drawing
  virtual void Draw() = 0; 
 
  // A regular virtual function
  virtual void MoveTo(int newX, int newY);
 
  // Regular method, not overridable.
  void Erase();
 
  // Constructor for Shape
  Shape(int x, int y);
 
  // Virtual destructor for Shape
  virtual ~Shape();
};
 
// Circle class declaration
class Circle : public Shape
{
private:
   int m_radius;    // Radius of the circle
 
public:
   // Override to draw a circle
   virtual void Draw();   
 
   // Constructor for Circle
   Circle(int x, int y, int radius);
 
   // Destructor for Circle
   virtual ~Circle();
};
 
// Shape constructor implementation
Shape::Shape(int x, int y)
{
   m_x = x;
   m_y = y;
}
 
// Shape destructor implementation
Shape::~Shape()
{
//...
}
 
// Circle constructor implementation
Circle::Circle(int x, int y, int radius) : Shape (x, y)
{
   m_radius = radius;
}
 
// Circle destructor implementation
Circle::~Circle()
{
//...
}
 
// Circle override of the pure virtual Draw method.
void Circle::Draw()
{
   glib_draw_circle(m_x, m_y, m_radius);
}
 
main()
{
  // Define a circle with a center at (50,100) and a radius of 25
  Shape *pShape = new Circle(50, 100, 25);
 
  // Define a circle with a center at (5,5) and a radius of 2
  Circle aCircle(5,5, 2);
 
  // Various operations on a Circle via a Shape pointer
  pShape->Draw();
  pShape->MoveTo(100, 100);
  pShape->Erase();
  delete pShape;
 
  // Invoking the Draw method directly
  aCircle.Draw();
}