What is the purpose of virtual functions in C++?

Virtual functions in C++ are a special type of function used to implement polymorphism.

Polymorphism refers to the concept in object-oriented programming where the same function name can have multiple different implementations, depending on the type of object calling it. The role of virtual functions is to allow declaring a function in a base class and then redefining its behavior in derived classes as needed. By using virtual functions, one can call functions in derived classes through a base class pointer or reference, achieving runtime polymorphism.

The format of defining a virtual function is to add the “virtual” keyword before the function declaration. A function declared as virtual in a base class can be overridden in a derived class, meaning that the behavior of the function can be redefined. When calling a virtual function through a base class pointer or reference, the implementation of the virtual function for the specific object pointed to or referenced is determined based on the type of the object.

Using virtual functions can achieve more flexible program design. By declaring a function as virtual, it is possible to redefine the behavior of the program by deriving classes without modifying existing code. This feature can be used to implement a common interface for the base class, with specific implementations defined by the derived classes. At the same time, virtual functions provide a foundation for runtime polymorphism, allowing functions in derived classes to be called through a base class pointer or reference, achieving dynamic binding.