class prototype and template error

[hellochar]

I'm writing a linked list program, and I'm using templates to specify which type of data the linked list will hold. In order to let other programs use my linked list, I need a header for the classes and functions. I must be declaring the headers wrong or implementing them wrong, because my compiler is giving me a crapload of errors.

My header linkedlist.h looks something like this

#ifndef LINKEDLIST_H
#define LINKEDLIST_H

template <class E>
class Link;

template <class E>
class LinkedList;

template <class E> //retrieves first link
Link<E> LinkedList::first(void); //Gives me error: " 'template<class E> struct LinkedList' used without template parameters

template <class E> //add link to end of list
void LinkedList::add(Link<E> *l); //same error

...
...

#endif /* LINKEDLIST_H */

Here is my linkedlist.cpp

#include "linkedlist.h"

template <class E>
class Link {
    public:
    E *data;
    Link<E> *next;

    Link(void) {
    }

    Link(E *data) {
        this.data = data;
    }
};

template <class E>
class LinkedList {

    public:
    const Link<E> *const head ();
    Link<E> *const last;

    LinkedList(void) {
        last = head;
    }

    LinkedList(Link<E> l) {
        this();
        add(l);
    }

    LinkedList(E o) {
        this(new Link<E>(o));
    }

    Link<E>* first(void) {
        return head->next;
    }

    void add(Link<E> *l) {
        last->next = l;
        last = l;
    }

...
...

}

[dcs]

At that point Link and LinkedList are not yet defined. In order to return a value, of that type, it needs to know the definition (to know how big it is, among other things). I don't suppose you were trying to return pointers instead?

[hellochar]

Originally I was trying to return pointers, but the compiler gave me another error. For instance, when I had

*Link<E> LinkedList::first(void);

There was an error stating "expected constructor, destructor, or type conversion before "LinkedList"" Although that did remove the other error. But that doesn't really help to replace one error with another hehe

editops, turns out i wrote that wrong. Should have been

 Link<E> *LinkedList::first(void);

but when I do that, the original error comes back. so still no dice

[dcs]

[nm]

[hellochar]

Nevermind, I've figured it out. Had to use LinkedList<E>::LinkedList(). And I redeclared class LinkedList in my .cpp file, when I really just had to implement the prototypes.

[dargueta]

Just a helpful hint you don't really need - instead of using the old #ifndef/#define trick for forcing the file to include only once, just use #pragma once before any of your code in the header file.

[dcs]

Originally Posted by dargueta

Just a helpful hint you don't really need - instead of using the old #ifndef/#define trick for forcing the file to include only once, just use #pragma once before any of your code in the header file.

That's the less portable way.

[dargueta]

True, but if you're compiling on your own computer and not someone else's, it shouldn't really matter.