Writing a copy constructor with singly linked lists? - c++

Question

I'm writing a copy constructor that copies for example S to R; Set R(S);. S is a sorted singly linked list containing some ints (with a dummy node in the beginning).
Set::Set (const Set &source)
{
Node* sourceNode = source.head->next;
head = new Node(0, nullptr);
Node* nodeHead = source.head->next;
Node* p;
if (!sourceNode) {
std::cout << "Empty !" << endl;
}
else{
while (nodeHead) {
for (p=sourceNode; p->next; p=p->next) {
;
}
head->next = new Node(nodeHead->value,nullptr);
head = head->next;
nodeHead = nodeHead->next;
}
}
}
Right now it crashes and if i remove head = head->next; it will set S to { 5 }.
This is the constructor:
class Node
{
public:
Node (int, Node*);
private:
int value;
Node* next;
};
Why doesn't this work? This is my first experience with pointers so keep that in mind please.

Answer 1

Let's assume you have a function that adds to the end of the linked list. The copy constructor in this case would be very simple:
Set::Set (const Set &source) : head(0)
{
Node* sourceNode = source.head;
while (sourceNode != NULL )
{
addToList(sourceNode->value);
sourceNode = sourceNode->next;
}
}
The addToList would be the function that adds a node to the back of the list. All the copy constructor has to do is start off with an empty list, and in a loop, add items from the source list until the number of items in the source list is exhausted. This method, given that the addToList function is coded correctly, is guaranteed to work, and avoids code duplication.
This is the easiest way to implement the copy constructor. If you have no function that adds to the back of the list, now would be the good time to add it since you will need to to have such a function in any event.

Answer 2

Here is some code
LinkList(LinkList const & temp) // Copy constructor
{
this->head = 0; // calling list head
Node* tempHead = temp.head; /*For temprory store of head of link list*/
while (tempHead != 0)
{
this->insertAtEnd(tempHead->data);
tempHead = tempHead->next;
}
}
void insertAtEnd(int val)
{
Node* temp = new Node;
temp->data = val;
temp->next = 0;
Node* curr = this->head;
if (curr != 0)
{
while (curr->next != 0)
{
curr = curr->next;
}
curr->next = temp;
}
else
{
this->head = temp;
}
}