CODEWITHSUNDEEP
c++templatesgenerics
whileone
whileone

Reputation: 2845

C++ LinkedList using template

I want to make my own linkedlist implementatin in c++ using templates. However, I run into several compiler errors. Here is the code:

template <class T>
class Node{
T datum;
Node _next = NULL;
 public:
 Node(T datum)
{
    this->datum = datum;
}
 void setNext(Node next)
 {
     _next = next;
 }
 Node getNext()
 {
     return _next;
 }
 T getDatum()
 {
     return datum;
 }          
};
template <class T>
class LinkedList{
Node<T> *node;
Node<T> *currPtr;
Node<T> *next_pointer;
int size;
public:
LinkedList(T datum)
  {
      node = new Node<T>(datum);
      currPtr = node;  //assignment between two pointers.
      size = 1;
  }
void add(T datum)
 {
   Node<T> *temp = new Node<T>(datum);
   (*currPtr).setNext((*temp));
   currPtr = temp;       
   size++;
 }
T next()
{
   next_pointer = node;
   T data = (*next_pointer).getDatum();
   next_pointer = (*next_pointer).getNext();
   return data;
}
int getSize()
{
   return size;
}   
};

when I try to instantiate this class, I got the following errors:

LinkedList.cpp: In instantiation of `Node<int>':
LinkedList.cpp:35:   instantiated from `LinkedList<T>::LinkedList(T) [with T = int]'
LinkedList.cpp:60:   instantiated from here
LinkedList.cpp:7: error: `Node<T>::_next' has incomplete type
LinkedList.cpp:5: error: declaration of `class Node<int>'
make[2]: *** [build/Debug/Cygwin-Windows/LinkedList.o] Error 1
make[1]: *** [.build-conf] Error 2
make: *** [.build-impl] Error 2

I'm using NetBeans IDE. Could anybody give me some suggestion to improve it? Thanks a lot!!

Upvotes: 0

Views: 2998

Answers (4)

crashmstr
crashmstr

Reputation: 28583

Just like when you do Node<T> *node; in the LinkedList, you need to also do the same in your Node class

template <class T>
class Node{
    T datum;
    Node<T> *_next;//template parameter
                   //also, need to make this a pointer and initialized in constructor
public:

//...
    void setNext(Node<T> next) //template parameter
    {
        _next = next;
    }
    Node<T> getNext() //template parameter
    {
        return _next;
    }
//...
};

Upvotes: 1

Matt K
Matt K

Reputation: 13892

It might just be this line:

Node _next = NULL;

You really need that to be a pointer (Node<T>* _next). If a class contained an instance of its own type, then THAT instance would have its own instance of that type and so on ad memorum exhaustum.

Upvotes: 1

Fr&#233;d&#233;ric Terrazzoni
Fr&#233;d&#233;ric Terrazzoni

Reputation: 2270

Your Node class should contain a pointer to the next Node, not a Node directly. Here you've a recursive type which is impossible to handle for the compiler.

Another mistake is that you cannot initialize a member like this. You must do that in the constructor.

So, replace Node _next = NULL; by Node *_next; and initialize the pointer _next to nullptr in your constructor.

Upvotes: 1

Luchian Grigore
Luchian Grigore

Reputation: 258698

Besides the syntax being wrong:

class Node{
T datum;
Node _next = NULL;
//....

you can't have a member of the same type as a member. You can use a pointer though:

template <class T>
class Node{
T datum;
Node<T>* _next;

and set it in the constructor (because =NULL wouldn't be legal there).

Related: Why is a class allowed to have a static member of itself, but not a non-static member?

Upvotes: 1

Related Questions