指针背后的值通过打印改变

Question

我想在 C++ 中使用指向左子节点和右子节点的每个节点的指针构建一个简单的二叉树。我手动设置树的根，然后我向树添加一个数字，但是通过在 main() 中打印它的值，指针后面的变量的值改变了它的值。

#include <stdlib.h>
#include <iostream>
using namespace std;

struct Node
{
    int data = 0;
    Node *leftNode = NULL;
    Node *rightNode = NULL;
};

void insertNode(Node *node, int newData)
{
    cout << "Testing Node: " << node -> data << " | " << &(node -> data) << endl;
    //smaller (or equal) or bigger
    if (newData > node -> data)
    {
        if (node -> rightNode == NULL)
        {
            Node newNode;
            newNode.data = newData;
            node -> rightNode = &newNode;
        }
        else
        {
            insertNode(node->rightNode, newData);
        }
    }
    else
    {
        if (node -> leftNode == NULL)
        {
            Node newNode;
            newNode.data = newData;
            node -> leftNode = &newNode;
            cout << "Added Node: " << (node -> leftNode) -> data << " AT " << &(node -> leftNode -> data) << endl;
        }
        else
        {
            insertNode(node -> leftNode, newData);
        }
    }
}

int main()
{
    Node firstnode;
    firstnode.data = 42;
    Node *pointer = &firstnode;
    //insert nodes
    /*for (int i = 0; i < 10; i++)
    {
        cout << "Inserting new Element: " << (10 + i) << endl;
        int newI = 10 + i;
        insertNode(&firstnode, newI);
    }*/
    cout << "Inserting new Element: " << (10) << endl;
    int newI = 10;
    insertNode(&firstnode, newI);
    cout << "in main " << firstnode.leftNode -> data << " | " << &(firstnode.leftNode -> data) << endl;
    cout << "in main2 " << firstnode.leftNode -> data << " | " << &(firstnode.leftNode -> data) << endl;

    return 0;
}

输出：

Inserting new Element: 10
Testing Node: 42 | 0x61feec
Added Node: 10 AT 0x61fea8
in main 10 | 0x61fea8
in main2 6422216 | 0x61fea8

你有什么解决办法吗？

Answer 1

您正在将指针分配给非静态局部变量。从函数返回时，非静态局部变量将无效。您应该动态地分配节点。

换句话说，你应该使用

Node* newNode = new Node;
newNode -> data = newData;
node -> rightNode = newNode;

而不是

Node newNode;
newNode.data = newData;
node -> rightNode = &newNode;

并且 node -> leftNode 也这样做。

指针背后的值通过打印改变

Value behind a pointer changes by printing it

c++

binary-tree

pointers