一个让我崩溃的错误

Binary_tree.h
C/C++ code

#ifndef Binary_Tree
#define Binary_Tree

//Node类
template <class Entry>
struct Binary_node 
{
    // data members:
    Entry data;
    Binary_node<Entry> *left;
    Binary_node<Entry> *right;
    // constructors:
    Binary_node( );
    Binary_node(const Entry &x);
};


//Binary_Tree类
template <class Entry>
class Binary_tree
{
public:
    Binary_tree();
    Binary_tree(const Binary_tree<Entry> &x);
    ~Binary_tree();
    Binary_tree & operator = (const Binary_tree<Entry> &original);
    bool empty() const;
    void preorder(void (*visit)(Entry &));
    void inorder(void (*visit)(Entry &));
    void postorder(void (*visit)(Entry &));
    int size( ) const;
    void clear( );
    int height( ) const;
    void insert(const Entry &);
protected:
    Binary_node<Entry> *root;
    void recursive_inorder(Binary_node<Entry> *sub_root,void (*visit)(Entry &));
    int recursive_size(Binary_node<Entry> *sub_root) const;
    int recursive_height(Binary_node<Entry> *sub_root) const;
    Binary_node<Entry> *recursive_copy(Binary_node<Entry> *sub_root);
};

#endif

Binary_tree.cpp
C/C++ code

#include "Binary_Tree.h"
#include "iostream"
using namespace std;

template <class Entry>
Binary_tree<Entry>::Binary_tree()
{
    root=NULL;
}

template <class Entry>
Binary_tree<Entry>::Binary_tree(const Binary_tree<Entry> &x)
{
    root=recursive_copy(x.root);
}

template <class Entry>
Binary_tree<Entry>::~Binary_tree()
{
    root=NULL;
}

template <class Entry>
bool Binary_tree<Entry> :: empty( ) const
{
    return root == NULL;
}

template <class Entry>
int Binary_tree<Entry>::size() const
{
    return recursive_size(root);
}

template <class Entry>
int Binary_tree<Entry>::height() const
{
    return recursive_height(root);
}

template <class Entry>
int Binary_tree<Entry> :: recursive_height(Binary_node<Entry> *sub_root) const
{
    if (sub_root == NULL) return 0;
    int l = recursive_height(sub_root->left);
    int r = recursive_height(sub_root->right);
    if (l > r) return 1 + l;
    else return 1 +r;
}

template <class Entry>
void Binary_tree<Entry> :: inorder(void (*visit)(Entry &))
{
    recursive_inorder(root, visit);
}

template <class Entry>
void Binary_tree<Entry> ::recursive_inorder(Binary_node<Entry> *sub_root,void (*visit)(Entry &))
{
    if (sub_root != NULL) 
    {
        recursive_inorder(sub_ root->left, visit);
        (*visit)(sub_root->data);
        recursive_inorder(sub_root->right, visit);
    }
}

template <class Entry>
int Binary_tree<Entry> :: recursive_size(Binary_node<Entry> *sub_root) const
{
    if (sub_root == NULL) return 0;
    return  1+recursive_size(sub_root->left)+ recursive_size(sub_root->right);
}

template <class Entry>
Binary_node<Entry> *Binary_tree<Entry> :: recursive_copy(Binary_node<Entry> *sub_root)
{
    cout << "执行了copy函数" << endl;
    if (sub_root == NULL) return NULL;
    Binary_node<Entry> *temp = new Binary_node<Entry>(sub_root->data);
    temp->left = recursive_copy(sub_root->left);
    temp->right = recursive_copy(sub_root->right);
    return temp;
}

Main.cpp
C/C++ code

#include "iostream"
#include "Binary_Tree.cpp"
using namespace std;


void main()
{
    Binary_tree<int> my;
    cout << my.size() << endl;

    Binary_tree<int> my1(my);
    cout << my1.size();

    Binary_tree<int> my2(my);
}

不是我自己写的代码，是老师PPt上拷贝的，同学拷贝的没有错误，我拷过来就有错误，错误如下：
Main.obj : error LNK2001: unresolved external symbol "public: __thiscall Binary_node<int>::Binary_node<int>(int const &)" (??0?$Binary_node@H@@QAE@ABH@Z)
Debug/Binary_tree.exe : fatal error LNK1120: 1 unresolved externals


大概是说我的那个重载的构造函数找不到，但是我将那个构造函数
template <class Entry>
Binary_tree<Entry>::Binary_tree(const Binary_tree<Entry> &x)
{
root=recursive_copy(x.root);
}
的哪一行 root=recursive_copy(x.root);屏蔽掉，然后编译，错误；删掉debug内容，编译，通过，运行，出错；恢复那一行，删掉debug，编译通过，运行出错；快崩溃了。换了一台电脑，用2010编译（之前是6.0），同样的错误。崩溃了……

C/C++ code

template <class Entry>
struct Binary_node 
{
    // data members:
    Entry data;
    Binary_node<Entry> *left;
    Binary_node<Entry> *right;
    // constructors:
    Binary_node( );
    Binary_node(const Entry &x);
};

把struct改为class，或者添加public：

#include "iostream"
#include "Binary_Tree.cpp"??? 
应该是 #include "Binary_Tree.h" 吧？