how to overload operator++ in linked list

Question

Help me, please, realize overload operator++ in doubly linked list. I have a two classes A and B.

class A {
private:
    int h;
    int a;
public:
    A *next, *prev;

friend A operator ++(A &, int);
};

A operator ++(A &t, int) {
    A temp = t;
    temp.h++;
    temp.a++;
    return temp;
}


class B {
private:
    A *head, *tail;
public:
    void incValue();
};

void B::incValue() {
    while(head != nullptr) {
        head++;
        head = head -> next;
    }
}

After execution method incValue() head = NULL I don't understand why this don't work.

P.S. This code must be eq. head++

head -> setH(head -> getH() + 1);
head -> setA(head -> getA() + 1);

Answer 1

To overload operator ++ you need to support some data member of the linked list that will define the current position in the list. Also you need a member function that will reset the current position in the linked list.

Answer 2

If you want to call the overloaded operator++ for A you need to call (*head)++ in your B::incValue method.

Answer 3

First. You overloading operator to use first parameter as a class -> you don't need to make operator friend.

class A {
private:
    int h;
    int a;
public:
    A *next;
    A *prev;
    void operator ++ ( int ); 
};

This overloaded operator will work with object of class A. So to use it just write:

A a;
a++;

And realization of this operator will be:

void A::operator ++ ( int )
{
  h++;
  a++;
}

You realization will work only like:

A a;
a = a++;

Because operator ++ return new copy of A object, but incremented h and a members.

Second. About walking in list: Your while will stop when head == NULL, so after execution while loop head pointer will be equal to 0. So, that loop statement head++ will be executed for every object.