Is is possible to have a single pointer that can point to an object of
type A, B, and C ?
I assume you mean "that can either point to an A object or to B object or to a C object", right?
Yes, you can have such a pointer.
How would I define that pointer?
A*
A base-class pointer can point to objects of derived classes.
Secondly, how would I call methods of the object if the pointer can
point to A/B/C classes?
You define a virtual function in A and override it in B and C. Then, when you call the method through your A*, the language will perform dynamic dispatch, i.e. it will automatically call the right method depending on whether your A* points to an A, to a B or to a C.
Do I need to cast them before calling the methods?
No. That would pretty much defeat the purpose of virtual functions.
Here is a complete example:
#include <iostream>
class A
{
public:
virtual ~A() {} // not really needed in this program,
// but almost always needed in real code
// when a class has a virtual function
virtual void method() { std::cout << "A::method\n"; }
};
class B : public A
{
public:
virtual void method() override { std::cout << "B::method\n"; }
};
class C : public A
{
public:
virtual void method() override { std::cout << "C::method\n"; }
};
int main()
{
A a;
B b;
C c;
A* ptr = &a;
ptr->method();
ptr = &b;
ptr->method();
ptr = &c;
ptr->method();
}
Output:
A::method
B::method
C::method
