表达式树 [英] expression Tree

问题描述

我写了一个表达式树和遍历遍历，但这是行不通的.问题可能与指针(* left和* right)有关，但我没有发现任何错误.代码在这里；

I wrote a expression tree and preorder traversal , but this doesn''t work. The problem is probably related to pointers(*left and *right) But I haven''t found anything wrong. Code is here;

#include <iostream>
#include <string>
#include <vector>
#include "Node.h"


using namespace std;



void preorderTraversal(Node *root){
	if(root != NULL){
		cout << root->c;
		preorderTraversal(root->left);
		preorderTraversal(root->right);
	}
}


int main() {

	string s = "ab+cde+**";
	vector<Node> lst;
	Node *left ;
	Node *right ;

	for(int i = 0; i < s.size(); i++){

		bool b =((s[i]=='*') || (s[i]=='+') || (s[i]=='-') || (s[i]=='\\') || (s[i]=='^'));
		
		if(b){
			left = new Node();
			right = new Node();
			*right = lst.at(lst.size()-1);
			lst.pop_back();
			*left = lst.at(lst.size()-1);
			lst.pop_back();
			lst.push_back(Node(s[i],left,right));
			
			delete left;
			delete right;
			left = NULL;
			right = NULL;
		}else{
			lst.push_back(Node(s[i]));
		}
	}

	cout << lst.size()<<endl;
	preorderTraversal(&lst.back());

	return 0;
}

#define NODE_H_
using namespace std;
#include <iostream>
class Node {
public:
    Node();
    Node(char c, Node *left, Node *right);
    Node(char c);
    ~Node();
    char c;
    Node *left;
    Node *right;
private:
};
#endif /* NODE_H_ */

#include "Node.h"
Node::Node() {
    // TODO Auto-generated constructor stub
    this->c = NULL;
    left = NULL;
    right = NULL;

}
Node::Node(char c){
    this->c = c;
    left = NULL;
    right = NULL;
}
Node::Node(char c, Node *left, Node *right){
    this->c = c;
    this->left = left;
    this->right = right;
}
Node::~Node() {
    // TODO Auto-generated destructor stub
}

如果有人可以提供帮助，我将非常感激.

If anyone can help with this I would really appreciate it.

推荐答案

您确定要执行此操作吗?

Are you sure you want to do this?

delete left;
delete right;
left = NULL;
right = NULL;

我可能不明白您要在这里做什么，但是看起来您存储了一堆原始指针，然后删除了它们指向的对象.我会重写Node来执行所有内存管理，并将其保留在main之外.

干杯，

Ash

I may not understand what you''re trying to do here but it looks like you store a bunch of raw pointers then delete the objects they''re pointing to. I''d rewrite Node to do all the memory management and keep it out of main.

Cheers,

Ash

我想在if块中每次都在delete左右移动，因为我认为当new分配Node时，这堆指针可能会不必要地消耗内存.所以我以为我可以通过删除指针来保护这种消耗.我不知道很好地使用指针.这是我的想法(但这可能是错误的.我不明白这是怎么回事).

但是，当我删除此部分并尝试在for循环之后左右写delete时，它可以正常工作.

如何在Node中处理内存管理?

感谢您的帮助.

I wanted to delete left and right for every time in if block because I thought when a Node is allocated by new , this bunch of pointers may consume unnecessarily memory. So I thought I protected this consumption by deleting pointer. I don''t know to use pointers very well. This is my thought (But this is probably wrong. I don''t understand what is wrong with that).

But when I remove this part and try to write delete left and right after for loop, it works fine.

How can I handle memory management in Node?

Thanks for help.

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