Explain the concept of virtual functions in C++ and how they are implemented?

Explanation of Virtual Functions in C++

Virtual functions in C++ allow a function in a base class to be overridden in a derived class, enabling runtime polymorphism. When a member function is declared as virtual in a base class, it is expected to be redefined in a derived class. This enables the compiler to determine the correct function to be called at runtime based on the actual object type rather than the pointer type.

Implementation of Virtual Functions

In order to use virtual functions in C++, the base class method that needs to be overridden in the derived class must be declared as virtual. The derived class method that overrides the base class virtual method should also be declared as virtual. This establishes the link between the base class method and the overridden method in the derived class.

Under the hood, virtual functions are typically implemented using a mechanism called the Virtual Method Table (VMT) or Virtual Function Table (VFT). Each class with virtual functions has its own VMT containing pointers to the virtual functions of that class. When an object is created, a pointer to its VMT is stored in the object. This pointer, known as the vptr (virtual pointer), allows the correct virtual function to be called at runtime based on the actual object type.

Overall, virtual functions in C++ are a powerful feature that enables polymorphism and dynamic binding, allowing for flexible and extensible code design.