Question

if i have the following node class

class Node {
 public:
Node() { next = NULL; prev = NULL; }
~Node() {}
 public :
Node *next;
Node *prev;
T data;
 };

how do i create an empty linked list in the function

LinkedList::LinkedList()

my linked list classs has the following functions

 void append(T item);
T get(int idx);
void insert(int idx, T item);
void map(T (*pf)(T item));
T remove(int index);
int size();
void unshift(T item);

Answer 1

Doubly linked lists usually have a reference to the first and (sometimes) last element in the list.

Node *first, *last;

In your constructor, just set these to NULL. Then make an isEmpty method which checks for this condition, and you’re done.

LinkedList::LinkedList()
{
    first = NULL;
    last = NULL;
}

bool LinkedList::isEmpty()
{
    return (first == NULL) && (last == NULL);
}