C++ template class' inner class access - c++

Question

I have a class like this:
#include <iostream>
template <class T>
class LL
{
using size_t = unsigned int;
class Node
{
T m_data;
Node* m_next;
Node(const T& data) :m_data{ data }, m_next{ nullptr }{}
friend std::ostream& operator<<(std::ostream& out, const Node& node)
{
out << node.m_data;
return out;
}
friend std::ostream& operator<<(std::ostream& out, const LL& ll);
friend class LL;
};
Node* m_first{ nullptr };
size_t m_size{ 0 };
Node* newNode(const T& data)
{
return new Node{ data };
}
public:
void push(const T& data)
{
Node* temp = newNode(data);
temp->m_next = m_first;
m_first = temp;
++m_size;
}
Node* head()
{
return m_first;
}
size_t size() const
{
return m_size;
}
~LL()
{
if (m_first)
{
Node* trav = m_first->m_next;
Node* foll = m_first;
while (trav)
{
delete foll;
foll = trav;
trav = trav->m_next;
}
delete foll;
}
}
friend std::ostream& operator<<(std::ostream& out, const LL& ll)
{
Node* trav = ll.m_first;
while (trav)
{
out << *trav << ' ';
trav = trav->m_next;
}
return out;
}
};
I also have a function template somewhere else below this class in the same file that tries to access Node and looks like this with two compiler errors:
template <typename T>
int getSize(LL<T>::Node* node) //C2065: node is undeclared, C3861: node is not found
{
if (node)
{
return 1 + getSize(node->m_next);
}
return 0;
} //does not compile
After sometime I tried this, again with two compiler:
template <typename T>
int getSize(LL<T>::Node<T>* node) //C2065 like before, C7510: use of dependent template name must be prefixed with 'template'
{
if (node)
{
return 1 + getSize(node->m_next);
}
return 0;
} //does not compile
After sometime again, I tried the below which compiled fine.
template <typename T>
int getSize(typename LL<T>::template Node<T>* node)
{
if (node)
{
return 1 + getSize(node->m_next);
}
return 0;
}
Now, when I tried to call this function from my driver function, I got compiler errors again:
int main()
{
LL<int> ll;
std::cout << getSize(ll.head()); //E0304, C2672 and C2783
//E0304: no instance of the function template "getSize" matches the argument list
//C2672: no matching overload function found
//C2783: could not deduce template argument for 'T'
}
I tried everything that I possible could and couldn't sort this problem out. Could someone please explain me what is going on?
Note: All codes that I've mentioned here are in the same file.

Answer 1

getSize(ll.head()) fails because of non-deduced context; template parameter T can't be deduced automatically.
If a template parameter is used only in non-deduced contexts and is not explicitly specified, template argument deduction fails.
1) The nested-name-specifier (everything to the left of the scope resolution operator ::) of a type that was specified using a qualified-id:
The declaration should be
template <typename T>
int getSize(typename LL<T>::Node* node) // using class instead of typename works for OP (MSVC)
{
//some code
}
And since Node is not a template you don't need to use template keyword.
LIVE
See Where and why do I have to put the “template” and “typename” keywords? about why use the keyword typename and template.