Question

So I want to copy a whole linked list classes, I have trouble figuring it out how to do so,

class list{
   public:
  list(const list &t);
private:
  struct Node{
    int x;
    Node *next;
  }*p;

I started with something like this:

list::list(const list &t){
  Node* q;
  q=new Node;
  while (p!=NULL){
    q->x= p->x;}
}

but I’m not sure if I am on the right track or what. I also have trouble how should I test such a copy constructor? For example I have list l1, then i insert couple integers into a list and then how I can copy it?

Answer 1

In your example it never will work if you initialized p or will work forever if p != NULL. You must allocate new nodes while traversing through t list:

  p = NULL;
  Node* copy = l.p;
  Node* insert = p;
  Node* inserted_el = NULL;
  while (copy){
     insert = new Node(); 
     insert->x = copy->x; 
     insert->next = NULL;
     if (inserted_el) {
         inserted_el->next = insert; //copy memory pointer to next element
     } else {
         p = insert; //copy memory pointer to list head
     }
     copy = copy->next;
     inserted_el = insert;
  }

This is basic idea. Also don’t forget to implement assign operator and destructor.
Usage:

list t1;
//insert nodes
list t2(t1);