Virtual function is a member function  in base class, which is redefined in the derived class.

Virtual function is declared by using the keyword virtual.

Syntax of virtual function:

class main_Class  // denotes the base class of virtual function 
{
public:
   virtual void pure_virtual() = 0;  // denotes a pure virtual function in c++
   // note that there is no function body	 
};

By using declaresdisplay() in parent class, we can generate the appearance of that function but it can't be called.

For making the function virtual , we have to add the virtual keyword before the function.

Virtual function resolves at run-time(dynamic binding).

E.g of virtual function:-

class Base
{
 public:
 virtual void show()
 {
  cout << "Base class";
 }
};
class Derived:public Base
{
 public:
 void show()
 {
  cout << "Derived Class";
 }
}

int main()
{
 Base* a;       //Base class pointer
 Derived b;     //Derived class object
 a = &b;
 a->show();     //Late Binding Ocuurs
}

In above code the dynamic binding will occur because virtual keyword is used before the base class, so derived version of function will be called. So the output will be:

E.g without using the virtual keyword:-

class Base
{
 public:
 void show()
 {
  cout << "Base class";
 }
};
class Derived:public Base
{
 public:
 void show()
 {
  cout << "Derived Class";
 }
}

int main()
{
 Base* a;       //Base class pointer
 Derived b;     //Derived class object
 a = &b;
 a->show();     //Early Binding Ocuurs
}

When using the base class pointer, it will always call the base version of the function.

so output will be: