One of the most important concepts in object-oriented programming is that of inheritance. Inheritance allows us to define a class in terms of another class, which makes it easier to create and maintain an application. This also provides an opportunity to reuse the code functionality and fast implementation time.
When creating a class, instead of writing completely new data members and member functions, the programmer can designate that the new class should inherit the members of an existing class. This existing class is called the base class, and the new class is referred to as the derived class.
How to make a Private Member Inheritable
The private member is not inheritable. If we modify the visibility mode by making it public, but this takes away the advantage of data hiding.
C++ introduces a third visibility modifier, i.e., protected. The member which is declared as protected will be accessible to all the member functions within the class as well as the class immediately derived from it.
Visibility modes can be classified into three categories:
- Public: When the member is declared as public, it is accessible to all the functions of the program.
- Private: When the member is declared as private, it is accessible within the class only.
- Protected: When the member is declared as protected, it is accessible within its own class as well as the class immediately derived from it.
Visibility of Inherited Members
| Base class visibility | Derived class visibility | ||
|---|---|---|---|
| Public | Private | Protected | |
| Private | Not Inherited | Not Inherited | Not Inherited |
| Protected | Protected | Private | Protected |
| Public | Public | Private | Protected |
Base and Derived Classes
A class can be derived from more than one class, which means it can inherit data and functions from multiple base classes. To define a derived class, we use a class derivation list to specify the base class(es). A class derivation list names one or more base classes and has the form −
class derived-class: access-specifier base-class
Where access-specifier is one of public, protected, or private, and base-class is the name of a previously defined class. If the access-specifier is not used, then it is private by default.
How to make a Private Member Inheritable
The private member is not inheritable. If we modify the visibility mode by making it public, but this takes away the advantage of data hiding.
C++ introduces a third visibility modifier, i.e., protected. The member which is declared as protected will be accessible to all the member functions within the class as well as the class immediately derived from it.
Visibility modes can be classified into three categories:
- Public: When the member is declared as public, it is accessible to all the functions of the program.
- Private: When the member is declared as private, it is accessible within the class only.
- Protected: When the member is declared as protected, it is accessible within its own class as well as the class immediately derived from it.
Visibility of Inherited Members
| Base Class Visibility | Derived class visibility | ||
| Public | Private | Protected | |
| Private | Not Inherited | Not Inherited | Not Inherited |
| Protected | Protected | Private | Protected |
| Public | Public | Private | Protected |
Advantage of C++ Inheritance
Code reusability: Now you can reuse the members of your parent class. So, there is no need to define the member again. So less code is required in the class.
Types Of Inheritance
C++ supports five types of inheritance:
- Single inheritance
- Multiple inheritance
- Hierarchical inheritance
- Multilevel inheritance
- Hybrid inheritance
