Need of virtual function? Why we use virtual function in c++?

Question

Anybody clear me about virtual function . Actually I am not understand why we use and how we use. please tell me somebody in detail.

Answer 1

Suppose you have a class :

class 3dObject
{
public:
virtual float Volume() { return 0.0f; }
};

and 2 classes that derive from it

class Cube : public 3dObject
{
float c;
public:
float Volume() { return c*c*c; }
};

class Sphere : public 3dObject
{
float radius;
public:
float Volume() { return radius; } // not correct volume but this is just an example
};

And you have object pointers defined like this:
Sphere s;
Cube c;

3dObject *o1 = &s;
3dObject *o2 = &c;

float v1 = o1->Volume();
float v2 = o2->Volume();

How will the program know which Volume() to call for o1 and o2? Since it is being called dynamically at run time using a pointer, the function needs to be declared virtual in 3dObject so that the right function be called.

Answer 2

By keeping what is called a vtable, a table that keeps track of the addresses of all the virtual functions.

Answer 3

still I am confused little bit.
when we declared same function virtual in base class. and two class inherit from it and both use Same function. but how virtual helping​ to identify which fiction call by main.🤔