templates and operator overloading

[adikid89]

What am I doing wrong? Here is some code:

friend ostream& operator<< <>(ostream& os, const binary_tree<T>& bt);

template<class T>
ostream& operator<<(ostream& os, const binary_tree<T>& bt)
{
	_print(os,bt.root);
	return os;
}

Here is the error output:

|error: `_print' was not declared in this scope|

I did this to fix it.. but can it be done without the temp?
I think I made some big mistakes somewhere...Not very used to working with templates.

template<class T>
ostream& operator<<(ostream& os, const binary_tree<T>& bt)
{
	binary_tree<T> temp;
	temp._print(os,bt.root);
	return os;
}

L.E:
This can't be right... cause it's not as efficient as using the print() function it the class, since it has to make a clone of the object I want to print, which is O(n), and another O(n) to print it. That can't be right.. why can't I make:

template<class T>
ostream& operator<<(ostream& os, const binary_tree<T>& bt)
{
	bt._print(os,bt.root);
	return os;
}

Even later edit:
This way it works.. though why? It's not like the function _print() modifies anything..

template<class T>
ostream& operator<<(ostream& os, binary_tree<T>& bt)
{
	bt._print(os,bt.root);
	return os;
}

Here is the _print() function:
template<class T>

void binary_tree<T>::_print(ostream& os, node* tree)
{
	if(tree==NULL) return;
	_print(os,tree->left);
		os << tree->data << ", ";
	_print(os,tree->right);
}

[Bazzy]

On the first code you didn't put bt. before _print

This way it works.. though why? It's not like the function _print() modifies anything..

You need to say this to the compiler:
void binary_tree<T>::_print(ostream& os, node* tree) const

[adikid89]

Thanks! It works. Good to know.