What is the virtual function?

Answer:

When derived class overrides the base class function by redefining the same function. If a client wants to access redefined the method from derived class through a pointer from the base class object, then you must define this function in the base class as a virtual function.

Let see an example, where the derived class function is called by base class pointer using virtual keyword.

#include<iostream>
using namespace std;
//Base class
class base
{
public:
    virtual void print()
    {
        cout << "print base class" << endl;
    }
};
//Child class
class derived: public base
{
public:
    void print()
    {
        cout << "print derived class" << endl;
    }
};
int main(void)
{
    //derive class object
    derived d;
    
    //Base class pointer
    base *b = &d;
    
    // virtual function, binded at runtime
    b->print();
    
    return 0;
}

Output:

print derived class