Operator -> doesn't work as expected in C++

Question

I was practicing single linked list in c++ (practicing how to find the beginning node of the circular list), but found the use of operator -> very confusing. I'm using Visual studio 2010 C++ Express

This works perfectly: head->append(2)->append(3)->append(4)->append(5)

But this doesn't work (to create a circular linked list): head->append(2)->append(3)->append(4)->append(5)->append(head->next)

When I jump in this method and debug, it seems head->next is not passed correctly into the method.

But this works:

1. Node* tail=head->append(2)->append(3)->append(4)->append(5); tail->append(head->next);
2. Or after I change return c->next to return head in the two methods, head->append(2)->append(3)->append(4)->append(5)->append(head->next) also works.

What am I missing here? Thank you!

Details of my code is as follows:

void main(){
    Node* head=new Node(1);
    Node* tail=head->append(2)->append(3)->append(4)->append(5)->append(head->next);
    cin.get();
}

class Node{
public:
    Node* next;
    int data;
    bool marked;

    Node(int d){
        data=d;
        marked=false;
        next=NULL;
    }

    Node* append(int d){
        Node* c=this;
        while(c->next!=NULL){
            c=c->next;
        }
        c->next=new Node(d);
        return c->next;
    }

    Node* append(Node* n){
        Node* c=this;
        while(c->next!=NULL){
            c=c->next;
        }
        c->next=n;
        return c->next;
    }
};

Answer 1

You are experiencing undefined behavior.

The problem is that you are expecting head->next to be evaluated at a particular time (right before calling the last append(). But that is not guaranteed.

Answer 2

When you're passing head->next - its before changing it with head->append. I'm afraid you're confusing the order of writing with the order of execution.

In this case you're changing the value and reading it in the same execution statement, that's undefined behavior.