What is the purpose of a pure virtual function in C++?

A pure virtual function in C++ refers to a virtual function defined in a base class that has no implementation, serving as an interface for subclasses to implement specific functionalities. Subclasses must implement the pure virtual function from the base class; otherwise, the subclass will also become an abstract class and cannot be instantiated.

The purpose of a pure virtual function includes:

1. Define interface: By using pure virtual functions, a parent class can define an interface that specifies the methods that subclasses must implement, ensuring consistency and predictability of the subclasses.
2. Achieving polymorphism: By utilizing the features of pure virtual functions and virtual functions, polymorphism can be achieved, allowing for the invocation of corresponding methods based on the actual object’s type at runtime.
3. Implementing an abstract class: A class containing pure virtual functions is an abstract class, which cannot be instantiated and can only be used as an interface to be inherited and implemented. This design can enhance the flexibility and scalability of the code.