For which class is the instance created and what is the derived class doing in this code?

Question

What is the derived class doing in this code like:

class Base
{
public:
       virtual std::string Name(){ return "Base Class"}

};
class Derived : public Base
{
 public:
        std::string Name() {return "Derived Class"}
}

int main()
{
   Base* object = new Derived();
   return 0;
}

I was following a tutorial but didn't understand What does Derived class in The instantiation of Base Class was doing in the above code.

Answer 1

The goal is to implement polymorphism, it's a OOP concept which allows you, among other things, to make derived class methods override the base class.

Consider the following:

class Base {
public:
    //virtual keyword allows method to be overriden
    virtual std::string Name() { return "Base Class"; }
    //virtual destructor needed for polymorphism otherwise it can lead to undefined behavior
    virtual ~Base(){} 
};

class Derived : public Base {
public:
    //optional keyword override signal the method has been overriden
    std::string Name() override { return "Derived Class"; }
};

class Derived2 : public Base {
public:
    std::string Name() override { return "Derived Class 2"; }
};

int main() {

    Base *object = new Derived();
    Base *object2 = new Derived2();
    Base *object3 = new Base();
    //collection of objects of type Base* which can hold any class of the family
    Base *collection[] = {object, object2, object3};

    for (auto &obj : collection) {//test print
        std::cout << obj->Name() << std::endl;
    }
}

As the comments explain, I can have a collection of different objects of the same family and when you call Name() the method call will deppend on the object.

Output:

Derived Class
Derived Class 2
Base Class