c++ - 为 LinkedList 调用 delete 时，变量被分配不同的内存

Question

我正在使用链表来存储二进制位的信息。度数表示整数 2 的幂次方。

问题出现在我的 set_bit 方法中。一旦找到“目标”节点指针，就应该删除节点指针“currentSet”。然而，不是将“currentSet”设置为空/释放内存，而是为 currentSet 提供了一个不同的、较低的内存地址。为什么是这样？我究竟做错了什么？当我明确地将 currentSet 出售给 nullptr 但不应该删除 currentSet 时，该程序可以正常工作吗？

这里是header的实现

//file is "binary.cpp"
#include <iostream>
#include "binary.h"

//using std::cout;

Binary::Binary(int x) {
    firstTerm = nullptr;

    while (x > 0) {
        unsigned int degree = (unsigned int) (log(float(x)) / log(float(2)));
        set_bit(1, degree);
        x -= (int) pow(float(2), float(degree));
    }
}

Binary::~Binary() {
    BinaryNode *temp;

    while (firstTerm != nullptr) {
        temp = firstTerm->next;
        delete firstTerm;
        firstTerm = temp;
    }
}

void Binary::set_bit(int bit, int degree) {
    BinaryNode *currentSet = firstTerm;
    BinaryNode *target;
    std::cout << "get_bit returns " << get_bit(degree) << std::endl;

    if (bit == 0 && get_bit(degree)) {
        std::cout << "bit = 0 " << std::endl;
        std::cout << "currentSet->degree " << currentSet->degree << std::endl;
        if (currentSet->degree == degree) {
            std::cout << "in if" << std::endl;
            firstTerm = currentSet->next;
            delete currentSet;
            std::cout << "end if" << std::endl;
        }
        else {
            target = currentSet;
            std::cout << "in else" << std::endl;
            while (currentSet != nullptr) {
                if (currentSet->degree == degree) {
                    std::cout << "in nested if" << std::endl;
                    //std::cout << "currentSet->degree = " << currentSet->degree << std::endl;
                    target->next = currentSet->next;
                    std::cout << "currentSet before delete " << currentSet << std::endl;
                    delete currentSet;
                    std::cout << "currentSet " << currentSet << "\nend nested if" << std::endl;
                }
                else {
                    std::cout << "in nested else" << std::endl;
                    std::cout << "firstTerm->next = " << firstTerm->next << std::endl;
                    std::cout << "currentSet->next = " << currentSet->next << std::endl;
                    target = currentSet;
                    currentSet = currentSet->next;
                    std::cout << "currentSet->next = " << currentSet->next << std::endl;
                    std::cout << "end nested else\n";
                }
            }
        }
    }

    else if (bit == 1 && get_bit(degree) == 0) {
        std::cout << "bit = 1" << std::endl;
        firstTerm = new BinaryNode(degree, firstTerm);
        /*if (firstTerm->next  nullptr) {
            currentSet = firstTerm;
        }*/
        std::cout << "firstTerm = " << firstTerm << std::endl;
        std::cout << "firstTerm->degree = " << firstTerm->degree << std::endl;
        std::cout << "firstTerm->next = " << firstTerm->next << std::endl;
    }
}

int Binary::get_bit(int degree) const {
    BinaryNode *currentGet = firstTerm;
    while (currentGet != nullptr) {
        //std::cout << "currentGet != nullptr";
        if (currentGet->degree == degree) {
            return 1;
        }
        currentGet = currentGet->next;
    }
    return 0;
}

这是标题

//file is "binary.h"
#ifndef _BINARY_H_
#define _BINARY_H_
#include <iostream>

class Binary {
private:
    struct BinaryNode {
        int degree;
        BinaryNode* next;
        BinaryNode(int d, BinaryNode* n): degree(d),next(n) {}
    };
    BinaryNode *firstTerm;

public:
    // default constructor
    Binary() {
       firstTerm = nullptr;
    }

void set_bit(int b, int d);

int get_bit(int d) const;
#endif

这是测试文件

//file is "binary_main.cpp
#include <iostream>
#include "binary.h"

using namespace std;

int main (void)
{
    cout << "\nTESTING GET AND SET METHODS" << endl;
    b1.set_bit(1, 2);
    b1.set_bit(1, 5);
    b1.set_bit(1, 0);
    b1.set_bit(0, 2);
}

已编辑

Answer 1

显式设置 currentSet 为 nullptr，使用来自 n.m. 的信息找到了答案。