External member functions of class template

Question

I have a Binary-Tree class template with several public and private member functions. When the member functions are both defined and implemented inside the class template, it compiles correctly and functions as expected. However, when I move those functions outside of the main class template, I get a multiplicity of errors.

• According to this reference, class template functions cannot be made external because the templates are compiled at run-time. http://www.codeguru.com/forum/archive/index.php/t-333284.html

• However this MSDN article suggests that "member templates can also be defined outside of a class." http://msdn.microsoft.com/en-us/library/swta9c6e(v=vs.80).aspx

Is there something I am missing here?

template <class type>
class BinaryTree{
private:
    Node<type>* root;
    void internalTraverse(Node<type>* n){}
    ......
public:
    ......
};

template <class type>
void BinaryTree<type>::internalTraverse(Node<type>* n){
    if (n == NULL){
        return;
    }
    internalTraverse(n->left);          //  <- This declaration has no storage type or identifier
    cout << "Node: " << n->data << endl;//  Ditto
    internalTraverse(n->right);         //  Ditto
};
......

For full disclosure: This is part of a homework assignment. However, its not directly related to the purpose of the assignment -- more of a tangential problem

Answer 1

You defined the member function both inline and out-of-line, so that's multiple. The following compiles:

#include <iostream>

template <typename> class Node;

template <class type>
class BinaryTree{
private:
  Node<type>* root;
  void internalTraverse(Node<type>* n);  // <--- no definition!
};

template <class type>
void BinaryTree<type>::internalTraverse(Node<type>* n){
  if (n == NULL){
    return;
  }
  internalTraverse(n->left);identifier
  std::cout << "Node: " << n->data << std::endl;
  internalTraverse(n->right);
}