What are Virtual functions in C++ ?

• Virtual function is a member function which is re-defined by a derived class and declared within a base class.
• When you refer to a derived class object using a reference or pointer to the base class, you can call a virtual function for that object and execute the derived class’s version of the function.
• It ensures that the correct function is called for an object, regardless of the type of reference used for function call.
• It is mainly used to achieve Run-time polymorphism.
• In base class functions are declared with a virtual. At run time the resolving of function call is done.

Sample Code

using namespace std;
 
class base {
public:
    virtual void print()
    {
        cout << "print base class\n";
    }
 
    void show()
    {
        cout << "show base class\n";
    }
};
 
class derived : public base {
public:
    void print()
    {
        cout << "print derived class\n";
    }
 
    void show()
    {
        cout << "show derived class\n";
    }
};
 
int main()
{
    base *bptr;
    derived d;
    bptr = &d;
 
    // Virtual function, binded at runtime
    bptr->print();
 
    // Non-virtual function, binded at compile time
    bptr->show();
   
    return 0;
}

Output