I have read about pointers to class members, but I have never seen them being used in any practical applications. Can someone explain what are the use cases of such pointers? Is it really necessary to have such pointers?

Eg.

class abc
{
public:
    int a;
    abc(int val) { a = val; }
};

 int main
{
   int abc::*data;
   abc obj(5);

   data = &abc::a;

   cout << "Value of a is " << obj.*data << endl;

   return 0;
}

In the above eg. why is the value of 'a' accessed in this manner? What is the advantage of using pointers to class members?