Object Oriented Programming Using C++ Unit 7th Semester 4th
Importance of virtual function, function call binding, virtual functions, implementing late binding,
need for virtual functions, abstract base classes and pure virtual functions, virtual destructors
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Importance of virtual function: A virtual function is a member function that is declared within a
base class and redefined by a derived class. To create virtual function, precede the function’s
declaration in the base class with the keyword virtual. When a class containing virtual function is
inherited, the derived class redefines the virtual function to suit its own needs.
Virtual Functions are used to support "Run time Polymorphism". You can make a function virtual
by preceding its declaration within the class by keyword 'virtual'. When a Base Class has a virtual
member function, any class that inherits from the Base Class can redefine the function with exactly
the same prototype i.e. only functionality can be redefined, not the interface of the function.
A Base class pointer can be used to point to Base Class Object as well as Derived Class
Object. When the virtual function is called by using a Base Class Pointer, the Compiler decides at
Runtime which version of the function i.e. Base Class version or the overridden Derived Class
version is to be called. This is called Run time Polymorphism.
What is Virtual Function?
A virtual function is a member function within the base class that we redefine in a derived class. It
is declared using the virtual keyword. When a class containing virtual function is inherited, the
derived class redefines the virtual function to suit its own needs.
Virtual Function is a member function of the base class which is overridden in the derived class.
The compiler performs late binding on this function.
To make a function virtual, we write the keyword virtual before the function definition.
A virtual function is a member function that you expect to be redefined in derived classes. When
you refer to a derived class object using a pointer or a reference to the base class, you can call a
virtual function for that object and execute the derived class's version of the function.
Virtual functions ensure that the correct function is called for an object, regardless of the
expression used to make the function call. Functions in derived classes override virtual functions in
base classes only if their type is the same.
Rules for Virtual Function in C++
1. Virtual functions must be members of some class.
2. Virtual functions cannot be static members.
3. They are accessed through object pointers.
4. They can be a friend of another class.
5. A virtual function must be defined in the base class, even though it is not used..
What is binding?
Binding for functions means that wherever there is a function call, the compiler needs to know
which function definition it should be matched to. This depends upon the signature of each
