Question

What’s the difference between these two statements?

ob.A::ar[0] = 200;
ob.ar[0] = 200;

where ob is an object of class A

class A
{
    public:
        int *ar;
        A()
        {
            ar = new int[100];
        }
};

Answer 1

In this case there is no difference.

This notation:

obj.Class::member

is only to solve the ambiguities coming from inheritance:

class A {
public:
  int a;
}

class B {
public:
  int a;
}

class C : public A, B {
   void func() {
      // this objects holds 2 instance variables of name "a" inherited from A and B
      this->A::a = 1;
      this->B::a = 2;
   }

}