c++ - 在一个指针上使用 "delete"会删除第二个指针(二叉搜索树)

Question

这是一项任务；我不能使用智能指针。这是我感觉正在发生的事情的直观表示:

使用 Main.cpp 中的 myTree.remove(4) 后调试器中的树:

当我在二进制搜索树的 removeRec 函数中调用 delete temp 时，BTNode* x 从正确指向 2 变为错误分配到随机内存，如 temp。显然，我希望 4 消失并让 BTNode* x 指向 2。这是我的构造函数/析构函数的问题吗？

独立 RemoveRec 函数:

bool BinarySearchTree::remove(int data){
    return removeRec(root, data);
}

bool BinarySearchTree::removeRec(BTNode* &x, int data){
    if (x == NULL){
        return false;
    }
    else {
        if (data < x->data){
            return removeRec(x->left, data);
        }
        else if (data > x->data){
            return removeRec(x->right, data);
        }
        else // Found item
        {
            BTNode* temp = x;
            if (x->left == NULL){
                x = x->right;
            }
            else if (x->right == NULL){
                x = x->left;
            }
            else {
                replaceParent(temp, temp->left);
            }
            delete temp;
            return true;
        }
    }
}

BinarySearchTree.h:

#pragma once
#include <cstddef>
using namespace std;

#ifndef BTNODE_H
#define BTNODE_H

struct BTNode{
    // Data Fields
    int data;
    BTNode* left;
    BTNode* right;

    // Constructor
    BTNode(const int& the_data,
        BTNode* left_val = NULL,
        BTNode* right_val = NULL) :
        data(the_data), left(left_val), right(right_val) {}

    // Destructor (to avoid warning message)
    ~BTNode() {
        if (this->left){
            delete this->left;
        }
        if (this->right){
            delete this->right;
        }
    }
};
#endif

#ifndef BINARY_SEARCH_TREE_H
#define BINARY_SEARCH_TREE_H

class BinarySearchTree
{
private:
    BTNode* root;

public:

    // BST Constructor / Deconstructor
    BinarySearchTree() : root(NULL){}

    BinarySearchTree(const int& the_data,
        const BinarySearchTree& left_child = BinarySearchTree(),
        const BinarySearchTree& right_child = BinarySearchTree()) :
        root(new BTNode(the_data, left_child.root, right_child.root)){}

    virtual ~BinarySearchTree(){}

    // Interface Functions ----------------------
    bool add(int data);
    bool remove(int data);
    void clear();

    // My Functions -----------------------------
    bool addRec(BTNode* &x, int data);
    bool removeRec(BTNode* &x, int data);
    bool Search(BTNode* root, int data);
    void replaceParent(BTNode* &old_root, BTNode* &local_root);
};
#endif

BinarySearchTree.cpp:

#pragma once
#include "BinarySearchTree.h"
#include <memory>
#include <thread>
#include <chrono>
#include <mutex>

// Interface Functions ----------------------
bool BinarySearchTree::add(int data){
    return addRec(root, data);
}

bool BinarySearchTree::addRec(BTNode* &x, int data){
    if (x == NULL){
        x = new BTNode(data);
        return true;
    }
    if (data == x->data){
        return false;
    }
    if (x != NULL){
        if (data < x->data){
            return addRec(x->left, data);
        }
        if (data > x->data){
            return addRec(x->right, data);
        }
    }
}

bool BinarySearchTree::remove(int data){
    return removeRec(root, data);
}

bool BinarySearchTree::removeRec(BTNode* &x, int data){
    if (x == NULL){
        return false;
    }
    else {
        if (data < x->data){
            return removeRec(x->left, data);
        }
        else if (data > x->data){
            return removeRec(x->right, data);
        }
        else // Found item
        {
            BTNode* temp = x;
            if (x->left == NULL){
                x = x->right;
            }
            else if (x->right == NULL){
                x = x->left;
            }
            else {
                replaceParent(temp, temp->left);
            }
            delete temp;
            return true;
        }
    }
}

void BinarySearchTree::replaceParent(BTNode* &old_root, BTNode* &local_root){
    if (local_root->right == NULL){
        replaceParent(old_root, local_root->right);
    }
    else{
        old_root->data = local_root->data;
        old_root = local_root;
        local_root = local_root->left;
    }
}

void BinarySearchTree::clear(){
    delete root;
    root = NULL;
}

// My Functions -----------------------------
bool BinarySearchTree::Search(BTNode* root, int data) {
    if (root == NULL) {
        return false;
    }
    else if (root->data == data) {
        return true;
    }
    else if (data < root->data) { // had <= instead
        return Search(root->left, data);
    }
    else if (data > root->data) { // had no "if"
        return Search(root->right, data);
    }
}

main.cpp

#include <stdio.h>
#include "BinarySearchTree.h"

using namespace std;

int main(){
    BinarySearchTree myTree;

    myTree.add(6);
    myTree.add(4);
    myTree.add(8);
    myTree.add(2);

    myTree.remove(4);
}

Answer 1

当一个节点从你的树中移除时，你重新分配指向它的节点现在指向一个 child 。在本例中，它从 6->4->2 变为 6->2。但是，当您删除节点 4 时，它仍然指向 2。然后 4 的析构函数杀死节点 2。

解决方案是在删除节点之前将节点中的 left 和 right 指针设置为 NULL。