Node : Use of class template requires template argument list

Question

I have a node class which can store data of any type.

This is my code right now. I'm getting a error C2059: syntax error : '<' on friend class List;

template <typename T>
class Node{
protected:
    T info;
    Node *urm;
    Node *ant;
public:
    int get_info() { return info; }
    void set_info(T a) { info = a; }
    friend class List<T>;
};

template <typename T>
class List{
protected:
    Node<T> *p, *u;
public:
};

Also, don't edit the question and change the code dramatically, since the initial answers will look completely out of context. — vsoftco, May 17 '15 at 17:42

vsoftco · Accepted Answer · 2015-05-17T17:40:59.017

2

Node is a class template and it expects a template argument at instantiation. So you have to specify it, something like

Node<int> *p, *u; // Nodes of integers
    ^^^^^
    instantiate the template with int

Since your Node is a class template, I suggest making List a class template too, as otherwise List loses the ability of manipulating arbitrary types

template <typename T>    
class List{
protected:
    Node<T> *p, *u;
public:
};

UPDATE (but please do not change your code and question live, better ask a new one)

You should also provide a forward declaration of List, as otherwise it is not visible when declaring the friend in Node. In other words, put this line

template<typename T>
class List; // forward declaration

above the declaration of Node.

edited May 17 '15 at 17:40

answered May 17 '15 at 16:20

vsoftco

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Hi! I'm getting a `'List' : class template has already been declared as a non-class template` now. – Shury May 17 '15 at 16:31
1

Did you also change friendship declaration? – Maciej Dziuban May 17 '15 at 16:54
1

@Shury as Maciej mentioned, use `friend class List;` now – vsoftco May 17 '15 at 17:01
No, how should the friendship declaration be changed? – Shury May 17 '15 at 17:01
@Shury You should try finding a good C++ book and read a bit about templates. They are important and understanding how they work is fundamental. [Here is a good list.](http://stackoverflow.com/q/388242/3093378) – vsoftco May 17 '15 at 17:02
@Shury that's good of course, but it won't replace a good book, where you can quickly (and correctly) learn the fundamentals. – vsoftco May 17 '15 at 17:18
@Shury see the updated edit, you need to provide a forward declaration. – vsoftco May 17 '15 at 17:41

score 1 · Answer 2 · answered May 17 '15 at 16:56

1

Try this :

template<typename T>
class List{
    protected:
    Node<T> *p, *u;
    public:
};

You need to provide a template argument list to Node to create its objects.

answered May 17 '15 at 16:56

0x6773

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Node : Use of class template requires template argument list

2 Answers2