Linked List ostream overload weird values - c++

Question

I'm realitively new to using linked lists. I'm trying to overload the ostream opperator for a doubly linked list with decleration :
template <class T>
class DynamicList;
template <class T>
template <class T>
class DynamicList
{
private:
Node<T> *head;
public:
class Node
{
public:
T* value;
Node<T> *next;
Node<T> *prev;
Node(T val)
{
next = nullptr;
prev = nullptr;
value = &val;
}
};
DynamicList();
~DynamicList();
void operator+=(const T);
friend std::ostream & operator<< <>(std::ostream &, const DynamicList<T> &);
};
and function defenition:
template <class T>
ostream& operator << (ostream & out , const DynamicList<T> & rhs)
{
Node<T>* nodePtr = rhs.head;
Node<T>* nptr = nodePtr->next;
while(nodePtr != NULL)
{
cout<<*(nodePtr->value)<<" ";
nodePtr = nodePtr->next;
}
out<<endl;
return out;
}
template <class T>
void DynamicList<T>:: operator +=(const T val)
{
Node<T>* nodePtr = nullptr;
T vall = val;
Node<T>* newNode = new Node<T>(vall);
if(!head)
{
head = newNode;
}
else
{
nodePtr = head;
while((nodePtr->next))
{
nodePtr = nodePtr->next;
}
nodePtr->next = newNode;
newNode->prev = nodePtr;
}
Every time I'm calling the opperator it gives a weird output for example using:
for(int i = 1; i <= 3; i++)
{
list += i;
}
cout<<list;
It would give an output like 135727363 135727383 135727383 ,I'd just like to know what I'm doing wrong and possibly how I could solve it

Answer 1

Your problem is here:
T* value;
You are storing the address of a value.
The problem is that you are storing the address of a variable that has gone out of scope.
T vall = val;
Node<T>* newNode = new Node<T>(vall);
The variable vall is local to the function operator += which means after it exists it no longer exists (and can contain anything).
To fix change the node to store the value.
class Node
{
public:
T value; // Notice no star here.
Node<T> *next;
Node<T> *prev;
Node(T const& val) // Add `const&` here to avoid a copy.
{
next = nullptr;
prev = nullptr;
value = val; // Notice no and `&` here
}
};