C++中序线索化二叉树

#include <iostream>
using namespace std;

typedef struct TBTNode
{
    char data;
    int ltag,rtag;
    struct TBTNode * lchild;
    struct TBTNode * rchild;
}TBTNode;

TBTNode * initTBTNode()
{
    TBTNode * p=(TBTNode*)malloc(sizeof(TBTNode));
    p->lchild=0;
    p->rchild=0;
    p->ltag=0;
    p->rtag=0;
    return p;
}

TBTNode * initTBTree(TBTNode * p)
{
    TBTNode * A=initTBTNode();
    TBTNode * B=initTBTNode();
    TBTNode * C=initTBTNode();
    TBTNode * D=initTBTNode();
    TBTNode * E=initTBTNode();

    A->data='A';
    B->data='B';
    C->data='C';
    D->data='D';
    E->data='E';

    A->lchild=B;
    A->rchild=C;
    B->rchild=D;
    C->lchild=E;

    p=A;

    return p;
}

void InThread(TBTNode *p,TBTNode *&pre)
{
    if(p!=0)
    {
        InThread(p->lchild,pre);
        if(p->lchild==0)
        {
            p->lchild=pre;
            p->ltag=1;
        }
        if(pre!=0&&pre->rchild==0)
        {
            pre->rchild=p;
            pre->rtag=1;
        }
        pre=p;
        InThread(p->rchild,pre);
    }
}

TBTNode * First(TBTNode * p)
{
    while(p->ltag==0)
        p=p->lchild;
    return p;
}

TBTNode * Next(TBTNode * p)
{
    if(p->rtag==0)
        return First(p->rchild);
    else
        return p->rchild;
}

void Inorder(TBTNode * root)
{
    for(TBTNode *p=First(root);p!=0;p=Next(p))
        cout << p->data << " ";
    cout << endl;
}

void createInThread(TBTNode * root)
{
    TBTNode * pre =initTBTNode();
    if(root!=0)
    {
        InThread(root,pre);
        pre->rchild=0;
        pre->rtag=1;
    }
}

int main(int argc, char* argv[])
{
    TBTNode *p=initTBTNode();
    p=initTBTree(p);
    TBTNode *pre=initTBTNode();
    createInThread(p);
    Inorder(p);
    return 0;
}