What's the difference between these two statements

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

There is no difference. The explicit namespace qualification of ar is redundant in this case.

It might not be redundant in cases where (multiple, nonvirtual) inheritance redefines the name ar. Sample (contrived):

#include <string>

class A 
{
    public:
        int *ar;
        A() { ar = new int[100]; }
        // unrelated, but prevent leaks: (Rule Of Three)
       ~A() { delete[] ar; }
    private:
        A(A const&);
        A& operator=(A const&);
};

class B : public A
{
    public:
        std::string ar[12];
};


int main()
{
    B ob;
    ob.A::ar[0] = 200;
    ob.ar[0] = "hello world";
}

See it on http://liveworkspace.org/code/d25889333ec378e1382cb5af5ad7c203