C++ Visibility Modes

VISIBILITY MODES

An important feature of Inheritance is to know which member of the base class will be acquired by the derived class. This is done by using visibility modes.

The accessibility of base class by the derived class is controlled by visibility modes. The three visibility modes are private, protected and public. The default visibility mode is private. Though visibility modes and access specifiers look similar, the main difference between them is Access specifiers control the accessibility of the members with in the class where as visibility modes control the access of inherited members with in the class.

Private visibility mode

When a base class is inherited with private visibility mode the public and protected members of the base class become ‘private’ members of the derived class

protected visibility mode

When a base class is inherited with protected visibility mode the protected and public members of the base class become ‘protected members ‘ of the derived class

public visibility mode

When a base class is inherited with public visibility mode , the protected members of the base class will be inherited as protected members of the derived class and the public members of the base class will be inherited as public members of the derived class.

Illustration 16.6 explains the significance of different visibility modes.

//Implementation of Single Inheritance using public visibility mode

#include <iostream>

using namespace std;

class Shape

{

private:

      int count;

protected:

      int width;

      int height;

public:

      void setWidth(int w)

      {

      width = w;

      }

 void setHeight(int h)

{

height = h;

}

};

class Rectangle: publicShape

{

public:

int getArea()

{

return (width * height);

}

};

int main()

{

Rectangle Rect;

Rect.setWidth(5);

Rect.setHeight(7);

// Print the area of theobject.

cout<< "Total area: "<<Rect.getArea() <<endl;

return 0;

}

Output

Total area: 35

The following table contain the members defined inside each class before inheritance

The following table contain the details of members defined after inheritance

Suppose the class rectangle is derived with protected visibility then the properties of class rectangle will change as follows

In case the class rectangle is derived with private visibility mode from its base class shape then the property of class rectangle will change as follows

When you derive the class from an existing base class,it may inherit the properties of the base class based on its visibility mode.So one must give appropriate visibility mode depends up on the need.

Private inheritance should be used when you want the features of the base class to be available to the derived class but not to the classes that are derived from the derived class.

Protected inheritance should be used when features of base class to be available only to the derived class members but not to the outside world.

Public inheritance can be used when features of base class to be available the derived class members and also to the outside world.