Operator<< in C++ with custom Data Structures - c++

Question

I'm trying to make a custom set of header files to use a generic List and use operator<< to make it print into a ostream object
There are a couple of errors which I cannot resolve.
I'm trying to make a generic List class using a generic Node class. The generic List should be printed using the operator<< . However I'm getting a lot of errors.
#include <iostream>
using std::cout;
using std::ostream;
class List;
template<class T>
class Node
{
friend class List<Node>;
private:
T data_;
Node *next_;
public:
Node(T data);
T get_data();
};
template<typename T>
Node<T>::Node(T data)
{
data_ = data;
next_ = 0;
}
template<typename T>
T Node<T>::get_data()
{
return data_;
}
template<typename T>
class Node;
template<typename T>
class List
{
template<typename T>
friend ostream& operator<<(ostream& o , const List<T> head);
private:
Node<T> *start_;
bool is_empty();
public:
List();
~List();
void insert(T data);
void remove();
};
template<typename T>
bool List<T>::is_empty()
{
if(start_ == 0)
return true;
return false;
}
template<typename T>
List<T>::List()
{
start_ = 0;
}
template<typename T>
List<T>::~List()
{
if( !is_empty())
{
Node<T> *current = start_;
Node<T> *temp;
while(current != 0)
{
temp = current;
current = current->next_;
delete temp;
}
}
}
template<typename T>
void List<T>::insert(T data)
{
if(is_empty())
{
Node<T> *temp = new Node<T>(data);
start_ = temp;
}
else
{
Node<T> *temp = start_;
while(temp->next_ != 0)
{
temp = temp->next_;
}
temp->next_ = new Node<T>(data);
}
}
template<typename T>
void List<T>::remove()
{
if(start_->next_ == 0)
{
Node<T> *temp = start_->next_;
start_->next_ = 0;
delete temp;
}
else if(!is_empty())
{
Node<T> *stay = start_;
Node<T> *remove = stay->next_;
while(remove->next_ != 0)
{
stay = remove;
remove = remove->next_;
}
stay->next_ = 0;
delete remove;
}
}
// Experimental Stuff out here
template<typename T>
ostream& operator<<(ostream& o , const List<T> *head)
{
Node<T> *temp = head->start_;
if(!is_empty<T>())
{
while(temp->next_ != 0)
{
o << temp.get_data() << "\t";
o << "\n";
temp = temp->next_;
}
}
return o;
}
// End of Experimental Stuff

Answer 1

Assuming clients of your class instantiate it like this:
List<int> my_list;
You need to define your operator << overload like this:
template <typename T>
std::ostream& operator << (std::ostream& os, const List<T>& list)
{
// I'm gonna assume you have C++11
auto node = list.start_;
while (node != nullptr)
{
os << '\t' << node->get_data() << '\n';
node = node->next_;
}
return os;
}
Additionally, there are loads of errors in your code regarding templates, so please fix them first.