二叉树非递归中序遍历(借用stack)

递归的中序遍历,

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);
   }
}

根据递归调用函数时栈的情况, 自己手动操作栈,
于是有

#include < stack >
using   namespace  std;

template  < class  Entry >
void  Binary_tree < Entry > ::NonRecursiveInorder( void  ( * visit)(Entry))
... {
    Binary_node<Entry> *go=root;
    stack <Binary_node<Entry>* > stk;
    while(!stk.empty() || go!=NULL)
    ...{
        if(go!=NULL)
        ...{
            stk.push(go);
            go=go->left;
        }
        else
        ...{
            go=stk.top();
            stk.pop();
            (*visit)(go->data);
            go=go->right;
        }
    }   
}