Compiler error in declaring template friend class within a template class

Question

I have been trying to implement my own linked list class for didactic purposes.

I specified the \"List\" class as friend inside the Iterator declaration, but it doesn\'t

Answer 1

The problem is List has not been properly declared in Iterator.h. Instead, nest the Iterator class inside List (automagically making it a template), which you'll likely want to do anyway (to use List::Iterator instead of renaming it to ListIterator or IteratorForList, as you would to have more than one Iterator in a namespace).

template<class T>
struct List {
  //...
  struct Node {/*...*/};
  struct Iterator {
    // ...
  private:
    Iterator(Node*);
    friend class List; // still required
  };
  //...
};

Answer 2

try adding a forward declaration

template <class T> class List;

at the start of Iterator.h -- that might be what you need to allow the friend declaration inside the Iterator class to work.