C++ constructor that deep copies a linked list - c++

Question

I am a noob to C++ and programming in general and am trying to make a constructor which will duplicate a linked list. The idea is that I can use
Individual* copyOfList = new Individual(originalList->getFirstBit());
to make a deep copy of the original list.
But my cose below seems not to be doing a deep copy. When I edit the copyOfList the originalList is affected as well. And I don't understand linked lists enough to make it deep copy. Can someone help me please.
Individual::Individual(BinaryNode * copyHead)
{
head = copyHead;
NodePtr last = NULL;
NodePtr temp = NULL;
curr = head;
while (curr != NULL)
{
temp = new BinaryNode(curr->data, NULL);
if (last != NULL)
{
last->next = temp;
}
last = temp;
if (head == NULL)
{
head = temp;
}
curr = curr->next;
}
}
Here is the BinaryNode code
class BinaryNode
{
public:
BinaryNode();
BinaryNode(bool the_data, BinaryNode *next_link);
bool data;
BinaryNode *next;
private:
};
This is the original list code. I think the order I populated it is adding to the head.
if(the_length > 0)
{
srand(time(NULL));
int randnumber;
NodePtr temp = new BinaryNode;
for(int i = 0; i < the_length; i++)
{
randnumber=(rand() % 2);
temp = new BinaryNode(randnumber,head);
head = temp;
}
}

Answer 1

head = copyHead;
With the above statement, head is pointing to the same memory location where copyHead is pointing to. Loop is not entered on an empty list. But in the loop -
if (head == NULL)
{
head = temp;
}
This can never be the case on an linked list to be copied that has childs. So, you are never updating the head of the linked list and instead it is still pointing to the starting node of the linked list to be copied. Try -
Individual::Individual(BinaryNode * copyHead)
{
if (NULL == copyHead)
{
// Empty list
return;
}
head = new BinaryNode(copyHead->data, NULL);
curr = head;
copyHead = copyHead->next;
while (NULL != copyHead)
{
// Copy the child node
curr->next = new BinaryNode(copyHead->data, NULL);
// Iterate to the next child element to be copied from.
copyHead = copyHead->next;
// Iterate to the next child element to be copied to.
curr = curr->next;
}
}
Hope it helps !

Answer 2

I'm assuming Individual is a class in your code and basically it's holding the head possition of the list. I mean:
class Individual{
private:
void* head;// may be anything*
public:
void* getHead()
{
return head;
}
// all the methods
}
Now c++ provide a special type of constructor i.e. Copy Constructor. If you don't define a one compiler provide a default copy of copy constructor which do a shallow copy of a object. To define your custom copy constructor:
Firstly add a new method in BinaryNode:
void link(BinaryNode& b)
{
b.next=this;
}
Individual::Individual(const Individual& args)
{
void* copyHead = args.getHead()
if ( copyHead==nullptr)
{
// Empty list
return;
}
head = new BinaryNode(copyHead->data, NULL);
curr = head->next;
copyHead = copyHead->next;
temp = head;
while (NULL != copyHead)
{
// Copied the child node
curr = new BinaryNode(copyHead->data, NULL);
curr.link(temp);
temp = curr;
// Iterate to the next child element to be copied from.
copyHead = copyHead->next;
// Iterate to the next child element to be copied to.
curr = curr->next;
}
}
Now as you want to to a deep copy You have to implement a code that will copy the whole list starting from the head pointer.