C++ Program to Create an Interface

Interfaces are a feature of Java that allows us to define an abstract type that defines the behaviour of a class. In C++, there is no concept of interfaces, but we can create an interface-like structure using pure abstract classes. In this article, we will learn how to create interface-like structure in C++.

Implementation of Interface in C++

To create an interface, first we need to understand the rules that governs the behaviour of interface:

• Interface only contains the declaration of the methods not definition.
• Interface methods must be declared public.
• Any class can implement/inherit any interface.
• The implementing class must provide the definition of the methods.
• Instance of interface cannot be created.

All of these rules can be followed by C++ pure abstract class that only contains the pure virtual functions. Following are the rules that governs the behaviour of pure abstract class:

• All methods of pure abstract class are only declared but not defined (pure virtual methods).
• Its methods can be defined either public, protected or private.
• Any class can inherit pure abstract class.
• The implementing class must provide the definition of the methods otherwise it will become abstract class.
• Instance of pure virtual class cannot be created.

As we can see, we can almost perfectly simulate the Java Interfaces with C++ Pure Abstract Classes.

Example

GFG
GeeksforGeeks

Explanation: The class I acts as an interface, declaring the pure virtual function getName() which must be implemented by any class that inherits from it. Classes B and C inherit from I and provide their own specific implementations of the getName() function, returning different strings.