c++ class template return value error - c++

Question

I was using eclipse to code up a queue, one function called getFirst is defined as:
template<class T>
T getFirst(){
return head->data;
}
in the main, after declaring the queue Q and input some valid data like:
Queue<int> Q;
Q.add(2);
cout << Q.getFirst() << endl;
The output is 2, which is just what I desired;
But!!! If I change the code to:
Queue<int> Q;
Q.add(2);
cout << Q.getFirst() << endl;
cout << Q.getFirst() << endl;
the output is not:
2
2
but something like:
2
2657382
after a few thoughts, I modified the code to:
Queue<int> Q;
Q.add(2);
cout << Q.getFirst();
cout << Q.getFirst() << endl;
this time it worked!! Just fine!! the output is 22, which make sense.
Can anybody kindly explain to me the problem here?
The definition of Node and Queue is generic and general :
template<typename T>
class Node{
public:
Node(T data, Node* left = 0, Node* right = 0): _data(data), _left(left), _right(right){
if(left)
left->_right = this;
if(right)
right->_left = this;
}
Node(): _right(0){}
private:
T _data;
Node<T>* _left;
Node<T>* _right;
friend class Queque<T>;
};
template<typename T>
class Queque{
public:
Queque(): _first(new Node<T>), _size(0){
_first->_right = _first;
_first->_left = _first;
}
void addFirst(T item){
Node<T>(item, _first, _first->_right);
_size++;
}
T examineFirst(){
return _first->_right->_data;
}
private:
Node<T>* const _first;
int _size;
};

Answer 1

void addFirst(T item){
Node<T>(item, _first, _first->_right);
_size++;
}
Node is a stack variable, and it's constructor will change _first, and first->_right to be pointing to some stack address, which will lead for unpredicted results, in your example usage << endl; modified stack, leading to some garbage output. To fix this you need to use new for new nodes allocation and, of course free them later with delete.