本文代码为C++实现线索二叉树，文中所有代码均经过测试。

#ifndef _THREAD_BIN_TREE_H
#define _THREAD_BIN_TREE_H

#include <iostream>
#include <stack>
#include <assert.h>
using namespace::std;

typedef enum{LINK, THREAD}Tag;

template<typename _T>
class _Thread_Bin_Tree;

template<typename _T>
class _Tree_Node{
	friend class _Thread_Bin_Tree<_T>;
public:
	_Tree_Node() :m_data(_T()), leftChild(NULL), rightChild(NULL), ltag(LINK), rtag(LINK)
	{}
	_Tree_Node(_T data, _Tree_Node<_T>* left = NULL, _Tree_Node<_T>* right = NULL) 
				:m_data(data), leftChild(left), rightChild(left), ltag(LINK), rtag(LINK)
	{}
public:
	Tag ltag;
	Tag rtag;
	_T m_data;
	_Tree_Node<_T>  *leftChild;
	_Tree_Node<_T>  *rightChild;
};

template<typename _T>
class _Thread_Bin_Tree{
	typedef _Tree_Node<_T> node_type;
public:
	_Thread_Bin_Tree() = default;
	_Thread_Bin_Tree(const _T& ref) :refval(ref)
	{}
	~_Thread_Bin_Tree() {}
public:
	void init_bin_tree(const char *&);
	void inorder_thread();

	void inorder_traverse()const;

	node_type* First()const;
	node_type* Last()const;
	node_type *Prev(node_type *)const;
	node_type *Next(node_type *)const;
	node_type *Parent(node_type *)const;
protected:
	void init_bin_tree(node_type *&, const char *&);
	void inorder_thread(node_type *&, node_type *&);

	void inorder_traverse(node_type *)const;

	node_type* First(node_type *)const;
	node_type* Last(node_type *)const;
	node_type *Prev(node_type *, node_type *)const;
	node_type *Next(node_type*, node_type *)const;
	node_type *Parent(node_type*, node_type *)const;
private:
	_T refval;
	node_type *root; 
};

/************************************public interface******************************************/

template<typename _T>
void _Thread_Bin_Tree<_T>::init_bin_tree(const char *&str)
{
	init_bin_tree(root, str);
}

template<typename _T>
void _Thread_Bin_Tree<_T>::inorder_thread()
{
	node_type *pre = NULL;
	inorder_thread(root, pre);
	pre->rtag = THREAD;
}

template<typename _T>
void _Thread_Bin_Tree<_T>::inorder_traverse()const
{
	inorder_traverse(root);
}

template<typename _T>
_Tree_Node<_T>* _Thread_Bin_Tree<_T>::First()const
{
	return First(root);
}

template<typename _T>
_Tree_Node<_T>* _Thread_Bin_Tree<_T>::Last()const
{
	return Last(root);
}

template<typename _T>
_Tree_Node<_T>* _Thread_Bin_Tree<_T>::Prev(node_type *cur)const
{
	return Prev(root, cur);
}

template<typename _T>
_Tree_Node<_T>* _Thread_Bin_Tree<_T>::Next(node_type *cur)const
{
	return Next(root, cur);
}

template<typename _T>
_Tree_Node<_T>* _Thread_Bin_Tree<_T>::Parent(node_type *cur)const
{
	return Parent(root, cur);
}

/************************************protected interface***************************************/

template<typename _T>
void _Thread_Bin_Tree<_T>::init_bin_tree(node_type *&pt, const char *&str)
{
	if(*str == refval){
		pt = NULL;	
	}
	else{
		pt = new node_type(*str);
		init_bin_tree(pt->leftChild, ++str);
		init_bin_tree(pt->rightChild, ++str);
	}
}

template<typename _T>
void _Thread_Bin_Tree<_T>::inorder_thread(node_type *&pt, node_type *&pre)
{
	if(pt == NULL)
		return ;
	
	inorder_thread(pt->leftChild, pre);

	if(pt->leftChild == NULL){
		pt->ltag = THREAD;
		pt->leftChild = pre;
	}

	if(pre != NULL && pre->rightChild == NULL){
		pre->rtag = THREAD;
		pre->rightChild = pt;
	}

	pre = pt;
	inorder_thread(pt->rightChild, pre);
}

template<typename _T>
void _Thread_Bin_Tree<_T>::inorder_traverse(node_type *pt)const
{
	if(pt != NULL){
		while(pt != NULL){
			pt = First(pt);
			cout << pt->m_data << " "; 
		
			while(pt->ltag == THREAD && pt->rightChild != NULL){
				pt = pt->rightChild;
				cout << pt->m_data << " ";
			}
			
			pt = pt->rightChild;
		}
	}
}

template<typename _T>
_Tree_Node<_T>* _Thread_Bin_Tree<_T>::First(node_type *pt)const
{
	assert(pt != NULL);
	
	while(pt->ltag == LINK)
		pt = pt->leftChild;
	return pt;
}

template<typename _T>
_Tree_Node<_T>* _Thread_Bin_Tree<_T>::Last(node_type *pt)const
{
	assert(pt != NULL);

	while(pt->rtag == LINK)
		pt = pt->rightChild;
	return pt;
}

template<typename _T>
_Tree_Node<_T>* _Thread_Bin_Tree<_T>::Prev(node_type *pt, node_type *cur)const
{
	assert(pt != NULL && cur != NULL && pt != cur);

	if(cur->ltag == THREAD)
		return cur->leftChild;
	else
		return Last(cur->leftChild);
}

template<typename _T>
_Tree_Node<_T>* _Thread_Bin_Tree<_T>::Next(node_type *pt, node_type *cur)const
{
	assert(pt != NULL && cur != NULL);

	if(cur->ltag == THREAD)
		return cur->rightChild;
	else
		return First(cur->rightChild);		
}

template<typename _T>
_Tree_Node<_T>* _Thread_Bin_Tree<_T>::Parent(node_type *pt, node_type *cur)const
{
	assert(pt != NULL && cur != NULL && pt != cur);

	if(cur->rtag == THREAD && cur->rightChild != NULL 
						   && cur->rightChild->leftChild == cur)
		return cur->rightChild;
	if(cur->ltag == THREAD && cur->leftChild->rightChild == cur)
		return cur->leftChild;

	node_type *tmp = Last(cur)->rightChild;
	if(tmp != NULL && tmp->leftChild->rightChild == cur)
		return tmp->leftChild;
	if(tmp != NULL && tmp->leftChild == cur)    //for B -> A
		return tmp;

	tmp = First(cur)->leftChild;
	if(tmp != NULL && tmp->rightChild == cur)
		return tmp;
}

#endif