Converting a C++ class to a template class - c++

Question

I just finished creating my binary tree class only to realise that I was supposed to make it as a template. I've spent hours now trying to get to convert it to a template, but I keep getting a multitude of errors ranging from "invalid use of template-name" to "extra qualification of a member". I am new to the concept of templates but I have an idea of what I'm trying to achieve.
BTree.cpp
#include <iostream>
#include <string>
#include "BTree.h"
using namespace std;
BTree::BTree(board startboard, string startplayer)
{
treeboard = startboard;
player = startplayer;
root = new BTNode(treeboard, player,-1,-1);
}
BTree::~BTree()
{
delete root;
}
int BTree::sumtree()
{
if (root->getvalue(-1) > root->getvalue(1))
return root->getchildposition(-1);
else
return root->getchildposition(1);
}
BTree.h
#include <string>
#include "BTNode.h"
#include "board.h"
using namespace std;
class BTree
{
public:
BTree(board startboard, string startplayer);
~BTree();
int sumtree();
private:
string player;
board treeboard;
BTNode *root;
};
'startplayer' is currently a string, I would like this to be the generic template type.
What should my process be for turning this into a single template file?

Answer 1

Well, let's first look what errors or other deficits your code has:
Your BTree has a custom dtor, because it holds resources. But you are violating the rule-of-3:
You need to define or delete, at minimum, your assignment-operator and copy-ctor.
As an alternative (preferable), change BTNode *root; to use std::unique_ptr.
The first thing included in the implementation-file should always be its own header, to find broken dependencies in the header.
The header should include everything neccessary to use it, and not one bit more.
Now, there are good reasons why templates are usually header-only:
The compiler needs the definition to instantiate it.
Use the opportunity to move some of the functions into the class.
Next, you define a template like this:
template<class T> class BTree {
int BTree::sumtree();
};
And non-inline members like this:
template<class T> int BTree<T>::sumtree() {
return //...
}
In the template, you can use the type-argument like a normal type.
A note on BTNode: It's an implementation-detail of BTree, so put its definition into the class (which makes templating it the same and using it easier as well.)
Alternatively, if you don't actually need all the template-arguments for BTNode as well (or want to share its implementation), template it separately.
Don't forget to change all references from BTree though.

Answer 2

First of all to use templates in C++ all of your executable code NEEDS to be in the .h file so it is available at compile time.
Then to template your class, the usual way is to make it like :
template<class T>
class BTree
{
Btree(T startPlayer)
{
player = startPlayer;
}
// ... snip ...
T player;
}