Question

How does the this pointer behaves when used inside a base class method:

class Base{
public:
   int a;
   Base() : a(5) {}
   void func(){
       std::cout << " value is : " << this->a << std::endl;
   }
};

class Derived : public Base{
private:
   int a;
public:
   Derived() : a(1){}
   void func1(){
       std::cout << " value is : " << this->a << std::endl;
   }
};

int main(){
   Derived d;
   d.func();
   d.func1();
}

the output of the code is :

value is : 5

value is : 1

As i am using the same object to call both the functions. So will the value of this pointer differ in methods for base and derived class ?

Answer 1

this->a is equivalent to a in that context, so it has nothing to do with the base pointer.

The member a is resolved statically, and the derived class hides the base class member, since they’re both named a.

To check the this pointer itself, you can print it directly:

std::cout << this;

It will be the same for both objects.

The main thing to take from this is that Base::a and Derived::a are different. Try the following in Derived:

void func1(){
    std::cout << "derived value is : " << a << std::endl;
    std::cout << "   base value is : " << Base::a << std::endl;
}