A virtual function in C++ is a member function declared within a base class that can be redefined (overridden) by a derived class. When referring to a derived class object using a pointer or a reference to the base class, a virtual function can be called for that object, and the derived classs version of the method will be executed. This ensures that the correct function is called for an object, regardless of the type of reference used for the function call, and it is mainly used to achieve runtime polymorphism. Virtual functions are declared with the virtual keyword in a base class, and the resolving of a function call is done at runtime. Some rules for virtual functions in C++ include that they cannot be static, they should be accessed using a pointer or reference of the base class type to achieve runtime polymorphism, and if a virtual function is created in the base class and overridden in the derived class, the virtual keyword is not needed in the derived class, as functions are automatically considered virtual functions in the derived class.
In summary, virtual functions in C++ allow for dynamic dispatch and enable polymorphism, ensuring that the correct function is called for an object, regardless of the type of reference used for the function call.
