Assignment Operator Overload memory leak

[kim14im]

This is about linked list. I don't know why I have memory leak on ASSIGNMENT OPERATOR =. Can you just ignore the other and just focus on the ASSIGNMENT OPERATOR =.
ASSUME ALL THE FUNCTION AND VARIABLES HAVE DECLARED AND WORK PROPERLY.
Can someone help me with it ? thanks

struct node
{
	double value;
	node* next;
};

/**< Constructor  */
linkedlist::linkedlist()
{
    head = tail =  NULL;
}

/**< desconstructor   */
linkedlist::~linkedlist()
{
    node * tmp = head;

    while (tmp != NULL)
    {
        node * del = tmp;
        tmp = tmp->next;
        delete del;
    }
    head = tail = NULL;
}

/**< Assignment = */
linkedlist& linkedlist::operator=(const linkedlist& assign)
{
    head = NULL;
    node *tmp;
    tmp = assign.head;

    while (tmp->next != NULL)       //Point to next link not NULL
    {
        add_back(tmp->value);       //keeping adding link list
        tmp = tmp->next;            //move to the next element
    }

    add_back(tmp->value);           //add the last element
    return *this;
}

[jlb]

ASSUME ALL THE FUNCTION AND VARIABLES HAVE DECLARED AND WORK PROPERLY.

That's probably a very bad assumption to make, but whatever.

Look at the first line in your operator=, I suspect that is a big part of the problem.

[kim14im]

Sorry for the mess. everything works ok. But when I check cppcheck. it show my operator = has memory leak. Im thinking should i set something to NULL or delete something in there.

[jlb]

Without seeing what and where head is defined, I lean to the idea that setting it to NULL in that first line is where the leak is occurring.

[dhayden]

It looks to me like you're leaking the previous contents of the list.

Also, I suspect you aren't handling the case where assign is an empty list.

[kim14im]

Thanks all Guy!