Thread: templates & linked list

if anyone explain me why this code is not working and where I'm making mistakes:

Code:

#include <iostream>
using namespace std;

template <class T>
struct Node
{
	T*data;
	struct Node *next;
};

template <class T>
class List
{
private:
	struct Node *head;
public:
	List():head(0){}
	~List(){/*appropriate clean up*/}
	void insert_new(T);
};
template <class T>
void List<T>::insert_new(T dat)
{
	Node *tmp=new Node;
	tmp->data=new T;
	*(tmp->data)=dat;
	if(!head)
	{
		head=tmp;
		return ;
	}
	tmp->next=head;
	head=tmp;
}

int main()
{
	List<int> Head;
	Head.insert_new(1);
}

Thanks very much!

Well, I'm trying to implement Linked list with any type of data, so I use template, but I got stuck on first function insert new element in the list. When I compile the code I get following error:

at line:

tmp->data=new T;
error
error C2440: '=' : cannot convert from 'int *' to ' *'
in line:

Node *tmp=new Node;

error:
error C2512: 'Node' : no appropriate default constructor available
in the same line:
error:
error C2955: 'Node' : use of class template requires template argument list

and so on. Compile by yourself and see.
I fix this with the following code:

Code:

#include <iostream>
using namespace std;
template <class T>
class List
{
private:
	struct Node //struct node in class
	{
		T*data;
		struct Node *next;
	}*head;
	
public:
	List():head(0){}
	~List(){/*appropriate clean up*/}
	void insert_new(T);
	void show(List &l);
};
template <class T>
void List<T>::insert_new(T dat)
{
	Node *tmp=new Node;
	tmp->data=new T;
	*(tmp->data)=dat;
	tmp->next=NULL;
	if(!head)
	{
		head=tmp;
		return ;
	}
	tmp->next=head;
	head=tmp;
}
template <class T>
void List<T>::show(List &l)
{
		Node*tmp=l.head;
		while(tmp !=NULL)
		{
			cout<<*(tmp->data)<<" ";
			tmp=tmp->next;
		}
}

int main()
{
	List<int> Head;
	Head.insert_new(1);
	Head.insert_new(2);
	Head.insert_new(4);
	Head.insert_new(2);
	Head.show(Head);
	return 0;
}

so just by moving struct Node in the class
why the other way is not working?

why the other way is not working?

Because Node is a templated struct so you must provide the type for instantiation.

Code:

Node *tmp=new Node;

should be

Code:

Node<T> *tmp=new Node<T>;

Otherwise, the compiler has no idea how you want to parameterize Node.

It works when you nest the Node struct inside your List class because Node just uses the type parameter from List.

Hope that helps.

-tf