Hello,
how can I overload << with templates, please?

Qt Code: 
  1. template <class T = int, size_t N = 100>
  2. class Stack {
  3. 	T _data[N];
  4. 	size_t _index;
  5.  
  6. public:
  7. 	Stack() : _index(0) { }
  8. 	void push(const T& value) {
  9. 		if ( _index != N) _data[_index] = value;
  10. 		else printf("stack full\n");
  11. 	}
  12.  
  13.  
  14. 	friend std::ostream& operator<<(std::ostream& os, const Stack<T>& stack) {
  15. 		for (int i=0; i < N; ++i)
  16. 			os << _data[i] << "  ";
  17. 		return os;
  18. 	}
  19. };
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Qt Code: 
  1. error C2597: illegal reference to non-static member 'Stack<>::_data'
  2. .....and others.....
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