What are virtual functions and pure virtual functions in C++?

In C++, a virtual function is a function declared as virtual in a base class which can be redefined in derived classes, allowing the appropriate function to be called at runtime based on the actual type of the object. Using virtual functions can achieve runtime polymorphism.

A pure virtual function is a virtual function declared in a base class with no actual implementation, serving only as an interface. Derived classes must implement the pure virtual function in order to be instantiated. If a class contains a pure virtual function, it is considered an abstract class and cannot be instantiated. Pure virtual functions are commonly used to define interfaces and enforce specific method implementations in derived classes. In C++, pure virtual functions can be used to implement the concepts of interfaces and abstract classes.