C++课设，在删除最后一个人的信息时会出现访问冲突的报错。

Question

如图

这里是全部代码

#include <cstdlib>
#include <iostream>
#include <string>
#include <windows.h>
#include <conio.h>
#include <fstream>
using namespace std;
#define null NULL
class student
{
private:
    int flag;
    friend class studentMessage;
    student* next; //节点指针
    string name; //学生姓名
    string address;  //家庭住址
    string age; //出生日期
    long long id; //学号
    string sex;
    char grade;
    double chinese, math, english;  //语文 ， 数学 ， 英语
    double pe, science;     //体育  科学
    string major; long long int TL;     //  专业  ，  电话

public:
    static int num_total;  //总数

    //学生初始化
    student(long long _id, string _name, string _sex, string _age,char _science, char _pe, double _chinese, double _math, double _english)
    {
        name = _name;
        pe = _pe;
        science = _science;
        age = _age;
        sex = _sex;
        id = _id;

        chinese = _chinese;
        math = _math;
        english = _english;
        next = NULL;
    }
    //构造函数
    student() //为studentMessage初始化头结点用
    {
        name = "null";
        sex = "null";
        address = "null";
        age = "null";
        id = 0;
        chinese = 0;
        math = 0;
        english = 0;
        grade = '0';
        science = 0;
        pe = 0;
        major = "null";
        TL = 0;
        next = NULL;
    }
    ~student() {}
    void swap(student*);
};
int student::num_total = 0;

void student::swap(student* q)
{
    string _name, _sex, _address, _age;
    long long _id;
    double _chinese, _math, _english;  //语文 ， 数学 ， 英语
    double _pe, _science;     //体育 科学
    string _major; long long int _TL;     //  专业  ，  电话

    _chinese = chinese;
    chinese = q->chinese;
    q->chinese = _chinese;

    _math = math;
    math = q->math;
    q->math = _math;

    _english = english;
    english = q->english;
    q->english = _english;

    _pe = pe;
    pe = q->pe;
    q->pe = _pe;

    _science = science;
    science = q->science;
    q->science = _science;

    _major = major;
    major = q->major;
    q->major = _major;

    _TL = TL;
    TL = q->TL;
    q->TL = _TL;

    _name = name;
    name = q->name;
    q->name = _name;

    _sex = sex;
    sex = q->sex;
    q->sex = _sex;

    _address = address;
    address = q->address;
    q->address = _address;

    _age = age;
    age = q->age;
    q->age = _age;

    _id = id;
    id = q->id;
    q->id = _id;
}
class studentMessage
{
private:
    student* first; //头指针
    int num; //信息中的学生人数
public:
    studentMessage()
    {
        num = 0; //初始化学生人数为0
        first = new student;  //初始化头结点
    }
    ~studentMessage() { delete first; }

    /*管理系统常规操作*/
    void Insret(void); //插入
    void Display(void); //显示
    void Delete(void); //删除
    void Search(void); //搜索
    void Change(void); //改动
    void SearchByid(void); //按照学号查找
    void SearchByname(void); //按照姓名查找
    int menu(void); //初始的菜单
    void clear(void); //清空列表
    void tongji(void);  //统计学生人数
    void save(void);
    void duplicate(void);
    void read(void);
};


int studentMessage::menu(void)
{
    system("cls");
    int ch;
    cout << endl; cout << endl; cout << endl; cout << endl;
    cout << "**********************************************************************" << endl;
    cout << "======================================================================" << endl;
    cout << "***************************学生信息管理系统***************************" << endl; cout << endl;
    cout << endl;
    cout << "                         1.添加学生个人信息" << endl;
    cout << "                         2.查询学生个人信息" << endl;
    cout << "                         3.显示学生个人信息" << endl;
    cout << "                         4.编辑学生个人信息" << endl;
    cout << "                         5.删除学生个人信息" << endl;
    cout << "                         6.统计学生数量" << endl;
    cout << "                         7.保存" << endl;
    cout << "                         8.清除全部信息" << endl;
    cout << "                         9.读取已保存信息" << endl;
    cout << "                         0.退出系统" << endl; cout << endl;
    cout << endl;
    cout << "***********************************************************************" << endl;
    cout << "=======================================================================" << endl;
    cout << "***********************************************************************" << endl;
    cout << endl; cout << endl; cout << endl; cout << endl; cout << endl; cout << endl;
    cin >> ch;
    cout << "\n\n\n" << endl;
    return ch;
}

void studentMessage::save(void)
{
    system("cls");
    fstream f("student.txt", ios::out);
    int i;
    if (!f)
    {
        cout << endl; cout << endl; cout << endl;
        cout << "文件保存失败!！！！按任意键返回" << endl;
        if (i = _getch()) return;
    }

    if (student::num_total == 0)
    {
        cout << "当前记录中无学生" << endl;
    }

    else
    {
        student* p = first->next;
        while (p != null)
        {
            f << "学号:" << p->id << "  " << endl;
            f << "姓名:" << p->name << endl;
            f << "性别(boy/girl):" << p->sex << endl;
            f << "出生日期:" << p->age << endl;
            f << "科学成绩：" << p->science << endl;
            f << "体育成绩：" << p->pe << endl;
            f << "语文成绩：" << p->chinese << endl;
            f << "数学成绩：" << p->math << endl;
            f << "英语成绩：" << p->english << endl;
            f << "------------------------------------------------" << endl;
            p = p->next;
        }
    }
    f.close();

    cout << endl; cout << endl; cout << endl;
    cout << "学生信息文件已创建，按任意键继续" << endl;
    i = _getch();
}
void studentMessage::duplicate(void)
{
    system("cls");
    fstream f("duplicate.txt", ios::out);
    int i;
    if (!f)
    {
        cout << endl; cout << endl; cout << endl;
        cout << "副本保存失败!！！！按任意键返回" << endl;
        if (i = _getch()) return;
    }

    if (student::num_total == 0)
    {
        f << "当前记录中无学生" << endl;
    }

    else
    {
        student* p = first->next;
        while (p != null)
        {
            f << p->id << "  " << endl;
            f << p->name << endl;
            f << p->sex << endl;
            f << p->age << endl;
            f << p->science << endl;
            f << p->pe << endl;
            f << p->chinese << endl;
            f << p->math << endl;
            f << p->english << endl;
            p = p->next;
        }
    }
    f.close();

    cout << endl; cout << endl; cout << endl;
    cout << "学生信息文件已创建，按任意键继续" << endl;
    i = _getch();
}

void studentMessage::read(void)
{
    system("cls");
    string name;
    string age;
    long long id;
    string sex;
    double chinese, math, english;  //语文 ， 数学 ， 英语
    double pe, science;     //体育 科学
    int i;
    long long ch;
    ifstream f("duplicate.txt");
    while (1)
    {
        f >> ch;
        if (f.eof())
        {
            cout << "读取完毕" << endl;
            if (i = _getch()) return;
        }
        id=ch;
        f >> name;
        f >> sex;
        f >> age;
        f >> science;
        f >> pe;
        f >> chinese;
        f >> math;
        f >> english;
        student::num_total++;
        student* newstu = new student();
        newstu = new student(id,name,sex,age,science,pe, chinese, math, english);
        student* p = first;
        while (p->next != NULL)
        {
            p = p->next;
        }
        p->next = newstu;
        newstu->next = null;
    }
}
void studentMessage::tongji(void)
{
    system("cls");
    cout << "学生人数一共为：" << student::num_total << endl;
    int i;
    cout << endl; cout << endl; cout << endl;
    cout << "按任意键继续" << endl;
    i = _getch();
}


//插入
void studentMessage::Insret(void)
{
    system("cls");//
    string name;
    string age;
    long long id;
    char grade;
    string sex, address;
    double chinese, math, english;  //语文 ， 数学 ， 英语
    double pe, science;     //体育 科学
    string major; long long int TL;     //  专业  ，  电话

    cout << "请输入学生姓名: ";
    cin >> name;
    cout << "请输入学生性别(boy/girl): ";
    cin >> sex;
    cout << "请输入学生出生日期: ";
    cin >> age;
    cout << "请输入学生学号: ";
    cin >> id;
    cout << "请输入科学成绩：" << endl;
    cin >> science;
    cout << "请输入体育成绩：" << endl;
    cin >> pe;
    cout << "请输入语文成绩：" << endl;
    cin >> chinese;
    cout << "请输入数学成绩：" << endl;
    cin >> math;
    cout << "请输入英语成绩：" << endl;
    cin >> english;
    student::num_total++;
    student* newstu = new student();
    newstu = new student(id, name, sex, age, science, pe,chinese, math ,english);

    student* p = first;
    while (p->next != NULL)
    {
        p = p->next;
    }
    p->next = newstu;
    newstu->next = null;
}
//00000000000000000000000/
void studentMessage::Display(void)
{
    system("cls");
    if (student::num_total == 0)
    {
        cout << "当前记录中无学生" << endl;
    }

    else
    {
        student* p = first->next;
        while (p != null)
        {
            cout << "学号:" << p->id << "  " << endl;
            cout << "姓名:" << p->name << endl;
            cout << "性别(boy/girl):" << p->sex << endl;
            cout << "出生日期:" << p->age << endl;
            cout << "科学成绩：" << p->science << endl;
            cout << "体育成绩：" << p->pe << endl;
            cout << "语文成绩：" << p->chinese << endl;
            cout << "数学成绩：" << p->math << endl;
            cout << "英语成绩：" << p->english << endl;
            cout << "------------------------------------------------" << endl;
            p = p->next;
        }
    }
    int i;
    cout << endl; cout << endl; cout << endl;
    cout << "按任意键继续" << endl;
    i = _getch();
}

//删除功能~~~~~~~~~~~~~~~~
void studentMessage::Delete(void)
{
    string _name;
    system("cls");
    cout << "请输入需要删除的同学姓名：" << endl;
    cin >> _name;
    int k = 0;
    student* p = first;
    student* pre = first;
    while (p->next)      //这里是报错的位置
    {
        pre = p->next;
        if (pre->name == _name)
        {
            p->next = pre->next;
            k = 1;
            delete pre;
        }
        p = p->next;
    }
    if (k == 0 && p->name != _name)   cout << "记录为空!" << endl;
    else
    {
        student::num_total--;
    }


    int i;
    cout << endl; cout << endl; cout << endl;
    cout << "按任意键继续" << endl;
    i = _getch();
}


void studentMessage::Search(void)
{
    system("cls");
        int temp = 0;
    cout << "请输入查找的条件，有如下选项" << endl;
    cout << "按照学号查找（请输入【1】） 按照姓名查找（请输入【2】） " << endl;
    cout << " 退出（请输入【666】）" << endl;
    cin >> temp;
    switch (temp)
    {
    case 1: SearchByid(); break;
    case 2: SearchByname(); break;
    case 666: return;
    default: cout << "输入有误" << endl;
    }
}

void studentMessage::SearchByid(void)
{
    system("cls");//
    long long _id;
    int flag = 0;
    cout << "请输入待查找学生的学号：";
    cin >> _id;
    student* p = first->next;
    while (p != null)
    {
        if (p->id == _id)
        {
            flag = 1;
            cout << "下面是查找匹配结果：" << endl;
            cout << endl; cout << endl; cout << endl;
            cout << "学号:" << p->id << "  " << endl;
            cout << "姓名:" << p->name << endl;
            cout << "性别(boy/girl):" << p->sex << endl;
            cout << "出生日期:" << p->age << endl;
            cout << "科学成绩：" << p->science << endl;
            cout << "体育成绩：" << p->pe << endl;
            cout << "语文成绩：" << p->chinese << endl;
            cout << "数学成绩：" << p->math << endl;
            cout << "英语成绩：" << p->english << endl;
        }
        p = p->next;
    }
    if (flag == 0)
    {
        cout << "未找到匹配项" << endl;
    }
    int i;
    cout << endl; cout << endl; cout << endl;
    cout << "按任意键继续" << endl;
    i = _getch();
}

void studentMessage::SearchByname(void)
{
    system("cls");
        string _name;
    int flag = 0;
    cout << "请输入待查找的学生姓名: ";
    cin >> _name;
    student* p = first->next;
    while (p != null)
    {
        if (p->name == _name)
        {
            cout << "下面是查找匹配结果：" << endl;
            cout << endl; cout << endl; cout << endl;

            cout << "学号:" << p->id << "  " << endl;
            cout << "姓名:" << p->name << endl;
            cout << "性别(boy/girl):" << p->sex << endl;
            cout << "出生日期:" << p->age << endl;
            cout << "科学成绩：" << p->science << endl;
            cout << "体育成绩：" << p->pe << endl;
            cout << "语文成绩：" << p->chinese << endl;
            cout << "数学成绩：" << p->math << endl;
            cout << "英语成绩：" << p->english << endl;
        }
        p = p->next;
    }

    if (flag == 0)
    {
        cout << "未找到匹配项" << endl;
    }
    int i;
    cout << endl; cout << endl; cout << endl;
    cout << "按任意键继续" << endl;
    i = _getch();
}

void studentMessage::Change(void)
{
    system("cls");
    string _name, _sex, _address, _major, _age;
    char _grade; long long int _TL;
    double _chinese, _math, _english;  //语文 ， 数学 ， 英语
    double _pe, _science;     //体育 科学

    int flag = 0, temp;
    long long _id;
    int course = 0;
    cout << "请输入需要改动信息的学生的姓名: ";
    cin >> _name;
    student* p = first->next;
    while (p != null)
    {
        if (p->name == _name)
        {
            flag = 1;
            cout << "该学生当前信息如下：" << endl;
            cout << "学号:" << p->id << "  " << endl;
            cout << "姓名:" << p->name << endl;
            cout << "性别(boy/girl):" << p->sex << endl;
            cout << "出生日期:" << p->age << endl;
            cout << "科学成绩：" << p->science << endl;
            cout << "体育成绩：" << p->pe << endl;
            cout << "语文成绩：" << p->chinese << endl;
            cout << "数学成绩：" << p->math << endl;
            cout << "英语成绩：" << p->english << endl;
            cout << "请指明哪一项需要修改" << endl;
            cout << "修改学号（输入【1】） 修改出生日期（输入【2】）修改性别（输入【3】）修改成绩信息（输入【4】） " << endl;
            cout << " 退出（输入【123】）" << endl;
            cin >> temp;
            switch (temp)
            {
            case 1:
            {
                cout << "请输入新的学号：" << endl; cin >> _id;
                p->id = _id;
            }
            break;
            case 2:
            {
                cout << "请输入新的出生日期：" << endl;; cin >> _age;
                p->age = _age;
            }
            break;
            case 3:
            {
                cout << "请输入性别：" << endl;
                cin >> _sex;
                p->sex = _sex;
            }
            break;
            case 4:
            {
                cout << "请输入科学成绩：" << endl;
                cin >> _science;
                p->science = _science;
                cout << "请输入体育成绩：" << endl;
                cin >> _pe;
                p->pe = _pe;
                cout << "请输入语文成绩：" << endl;
                cin >> _chinese;
                p->chinese = _chinese;
                cout << "请输入数学成绩：" << endl;
                cin >> _math;
                p->math = _math;
                cout << "请输入英语成绩：" << endl;
                cin >> _english;
                p->english = _english;
            }
            break;
            case 123: return;
                cout << "修改后的信息如下： " << endl;
                cout << "姓名:" << p->name << "  " << endl;
                cout << "性别:" << p->sex << "  " << endl;
                cout << "出生日期:" << p->age << "  " << endl;
                cout << "学号:" << p->id << "  " << endl;
                cout << "科学成绩:" << p->science << "  " << endl;
                cout << "体育成绩:" << p->pe << "  " << endl;
                cout << "语文成绩:" << p->chinese << "  " << endl;
                cout << "数学成绩:" << p->math << "  " << endl;
                cout << "英语成绩:" << p->english << "  " << endl;

            default:  cout << "输入有误" << endl;
            }
        }
        p = p->next;
    }
    if (flag == 0)
        cout << "当前记录中没有此学生" << endl;
}

void studentMessage::clear(void)
{
    student::num_total = 0;
    student* p = first->next;
    while (p != null)
    {
        first->next = p->next;
        p->next = null;
        delete p;
        p = first->next;
    }
}

int main()
{
    studentMessage stulist;
    int ch;
    while (ch = stulist.menu())
    {
        switch (ch)
        {

        case 1: stulist.Insret();  break;
        case 2: stulist.Search();  break;
        case 3: stulist.Display(); break;
        case 4: stulist.Change();  break;
        case 5: stulist.Delete();  break;
        case 6: stulist.tongji();  break;
        case 7: 
            stulist.save();  
            stulist.duplicate();
            break;
        case 8: stulist.clear();   break;
        case 9: stulist.read();   break;
        case 0: return 0;
        default: cout << "请按要求输入" << endl;
        }
    }
    return 0;
}

究竟是哪里出了问题？

Answer 1

410之前加个else就行了
因为删除元素的代码中已经修改了p的next指向了，就不需要再次p=p->next了