关于#c++#的问题，请各位专家解答！

Question

class Student
{
public:
    void InputStudent(Date &birthday)
    {
        ofstream outfile("student.txt", ios::app);
        cout << "请输入学号：";
        cin >> num;
        cout << "请输入姓名：";
        cin >> name;
        birthday.SetDate();
        cout << "请输入性别：";
        cin >> gender;
        cout << "请输入3门课成绩：";
        cin >> score1 >> score2 >> score3;
        double average = (score1 + score2 + score3) / 3.0;
        int maxscore = max({score1, score2, score3});
        int minscore = min({score1, score2, score3});
        outfile << num << " " << name << " " << birthday.GetYear() << " " << birthday.GetMonth() 
        << " " << birthday.GetDay()<< " " << gender << " " << score1 << " " << score2 << " " << 
        score3 << " " << average << " " << maxscore << " " << minscore << endl;
        cout << "学生信息录入成功！" << endl;
        outfile.close();
    }
    //2.浏览学生全部信息
    void OutputStudents()
    {
        ifstream infile("student.txt");
        string line;
        while (getline(infile, line))
        {
            cout << line << endl;
        }
        infile.close();
    }
    //3.按学号查找学生记录
    void FindByNum(int findnum)
    {
        ifstream infile("student.txt");
        int num;
        string line;
        bool found = false;
        while (infile >> num)
        {
            if (num == findnum)
            {
                getline(infile, line);
                cout << num << " " << line << endl;
                found = true;
                break;
            }
            getline(infile, line);
        }
        infile.close();
        if (!found)
        {
            cout << "未找到学号为 " << findnum << " 的学生" << endl;
        }
    }
        //4.按学号删除学生记录
       void DeleteByID(int findnum)
        {
        fstream file("student.txt");
        ofstream temp("temp.txt");
        string line;
        int num;
        bool found = false;
        while (file >> num)
         {
            getline(file, line);
            if (num != findnum) 
            {
                temp << num << " " << line << endl;
            } 
            else 
            {
                found = true; 
            }
        }
        file.close();
        temp.close();
        if (found) 
        {
            remove("student.txt");
            rename("temp.txt", "student.txt");
            cout << "已成功删除学号为 " << findnum << " 的学生记录！" << endl;
        } 
        else 
        {
            cout << "未找到学号为 " << findnum << " 的学生记录。" << endl;
        }
    }
    //5.按学号修改出生日期
    void AlterDateByNum(int findnum)
    {
    fstream file("student.txt");
    ofstream temp("temp.txt");
    int num;
    string name, gender, line;
    int year, month, day, score1, score2, score3;
    double average;
    bool found = false;
    while (file >> num >> name >> year >> month >> day >> gender >> score1 >> score2 >> score3 >> average)
    {
        if (num == findnum)
        {
            Date newDate;
            newDate.SetDate();
            temp << num << " " << name << " " << newDate.GetYear() << " " << newDate.GetMonth() << " " << newDate.GetDay()
                 << " " << gender << " " << score1 << " " << score2 << " " << score3 << " " << average << endl;
            found = true;
            cout << "已成功修改学号为 " << num << " 的学生的出生日期！" << endl;
        }
        else
        {
            temp << num << " " << name << " " << year << " " << month << " " << day << " " << gender << " "
                 << score1 << " " << score2 << " " << score3 << " " << average << endl;
        }
    }
    file.close();
    temp.close();
    remove("student.txt");
    rename("temp.txt", "student.txt");
    if (!found)
    {
        cout << "未找到学号为 " << findnum << " 的学生" << endl;
    }
    }
    //6. 按学号修改学生成
    void AlterScoreByNum(int findnum)
    {
    fstream file("student.txt");
    ofstream temp("temp.txt");
    int num;
    string name, gender, line;
    int year, month, day, score1, score2, score3;
    double average;
    bool found = false;
    while (file >> num >> name >> year >> month >> day >> gender >> score1 >> score2 >> score3 >> average)
    {
        if (num == findnum)
        {
            int newScore1, newScore2, newScore3;
            cout << "请输入新的三门课成绩: ";
            cin >> newScore1 >> newScore2 >> newScore3;
            double newAverage = (newScore1 + newScore2 + newScore3) / 3.0;
            int newMax = max({newScore1, newScore2, newScore3});
            int newMin = min({newScore1, newScore2, newScore3});

            temp << num << " " << name << " " << year << " " << month << " " << day << " " << gender << " "
                 << newScore1 << " " << newScore2 << " " << newScore3 << " " <<
                  newAverage << " " << newMax << " " << newMin << endl;

            found = true;
            cout << "已成功修改学号为 " << num << " 的学生成绩！" << endl;
        }
        else
        {
            temp << num << " " << name << " " << year << " " << month << " " << day << " " << gender << " "
                 << score1 << " " << score2 << " " << score3 << " " << average << endl;
        }
    }
    file.close();
    temp.close();
    remove("student.txt");
    rename("temp.txt", "student.txt");
    if (!found)
    {
        cout << "未找到学号为 " << findnum << " 的学生" << endl;
    }
    }
private:
    int num;
    string name;
    string gender;
    int score1, score2, score3;
};

每一行代码的注释，特别是关于文件部分的

Answer 1

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对于你提供的C++代码，下面是对每段与文件操作相关代码的详细解释及注释：

// 定义Student类的InputStudent方法，用于输入学生信息并将其写入到"student.txt"文件中
void InputStudent(Date &birthday)
{
    ofstream outfile("student.txt", ios::app); // 创建一个ofstream对象outfile，打开"student.txt"文件，并以追加模式（ios::app）打开
    // 下面的代码从标准输入读取数据
    cout << "请输入学号：";
    cin >> num;
    cout << "请输入姓名：";
    cin >> name;
    // 设置生日日期，这里假设Date类有SetDate()成员函数
    birthday.SetDate();
    cout << "请输入性别：";
    cin >> gender;
    cout << "请输入3门课成绩：";
    cin >> score1 >> score2 >> score3;
    
    // 计算平均分、最高分和最低分
    double average = (score1 + score2 + score3) / 3.0;
    int maxscore = max({score1, score2, score3});
    int minscore = min({score1, score2, score3});

    // 将数据写入文件
    outfile << num << " " << name << " " << birthday.GetYear() << " " << birthday.GetMonth() 
            << " " << birthday.GetDay() << " " << gender << " " << score1 << " " << score2 << " " 
            << score3 << " " << average << " " << maxscore << " " << minscore << endl;
    
    // 输出确认信息
    cout << "学生信息录入成功！" << endl;
    outfile.close(); // 关闭文件
}

// 定义OutputStudents方法，用于输出所有学生的信息
void OutputStudents()
{
    ifstream infile("student.txt"); // 创建ifstream对象infile，打开"student.txt"文件
    string line;
    // 循环读取文件中的每一行，并输出到控制台
    while (getline(infile, line))
    {
        cout << line << endl;
    }
    infile.close(); // 关闭文件
}

// 定义FindByNum方法，用于按学号查找学生记录
void FindByNum(int findnum)
{
    ifstream infile("student.txt"); // 打开"student.txt"文件
    int num;
    string line;
    bool found = false; // 初始化标志变量，表示是否找到学号
    // 循环读取文件中的每个学号
    while (infile >> num)
    {
        if (num == findnum) // 如果找到匹配的学号
        {
            getline(infile, line); // 读取包含学号的整行
            cout << num << " " << line << endl; // 输出学号及其对应的信息
            found = true; // 标记找到
            break; // 结束循环
        }
        getline(infile, line); // 读取当前行的剩余部分，以便下一次循环继续读取下一个学号
    }
    infile.close(); // 关闭文件
    if (!found) // 如果没有找到学号
    {
        cout << "未找到学号为 " << findnum << " 的学生" << endl; // 输出未找到信息
    }
}

// 定义DeleteByID方法，用于按学号删除学生记录
void DeleteByID(int findnum)
{
    fstream file("student.txt"); // 打开"student.txt"文件，读写模式
    ofstream temp("temp.txt"); // 创建临时文件"temp.txt"
    string line;
    int num;
    bool found = false; // 是否找到学号的标志
    // 遍历文件中的每条记录
    while (file >> num)
    {
        getline(file, line); // 读取整行
        if (num != findnum) // 如果学号不等于要删除的学号
        {
            temp << num << " " << line << endl; // 将该行写入临时文件
        }
        else
        {
            found = true; // 找到了要删除的学号
        }
    }
    file.close(); // 关闭原文件
    temp.close(); // 关闭临时文件
    if (found) // 如果找到了学号
    {
        remove("student.txt"); // 删除原文件
        rename("temp.txt", "student.txt"); // 将临时文件重命名为原文件名
        cout << "已成功删除学号为 " << findnum << " 的学生记录！" << endl; // 输出删除成功信息
    }
    else // 如果没有找到学号
    {
        cout << "未找到学号为 " << findnum << " 的学生记录。" << endl; // 输出未找到信息
    }
}

// 定义AlterDateByNum方法，用于按学号修改学生的出生日期
void AlterDateByNum(int findnum)
{
    fstream file("student.txt"); // 打开"student.txt"文件，读写模式
    ofstream temp("temp.txt"); // 创建临时文件"temp.txt"
    int num;
    string name, gender, line;
    int year, month, day, score1, score2, score3;
    double average;
    bool found = false; // 是否找到学号的标志
    // 遍历文件中的每条记录
    while (file >> num >> name >> year >> month >> day >> gender >> score1 >> score2 >> score3 >> average)
    {
        if (num == findnum) // 如果找到要修改的学号
        {
            Date newDate; // 创建新的Date对象
            newDate.SetDate(); // 设置新日期
            // 将更新后的日期写入临时文件
            temp << num << " " << name << " " << newDate.GetYear() << " " << newDate.GetMonth() << " " << newDate.GetDay()
                 << " " << gender << " " << score1 << " " << score2 << " " << score3 << " " << average << endl;
            found = true; // 标记找到
            cout << "已成功修改学号为 " << num << " 的学生的出生日期！" << endl; // 输出修改成功信息
        }
        else
        {
            // 如果不是要修改的学号，则将原有数据写入临时文件
            temp << num << " " << name << " " << year << " " << month << " " << day << " " << gender << " "
                 << score1 << " " << score2 << " " << score3 << " " << average << endl;
        }
    }
    file.close(); // 关闭原文件
    temp.close(); // 关闭临时文件
    remove("student.txt"); // 删除原文件
    rename("temp.txt", "student.txt"); // 将临时文件重命名为原文件名
    if (!found) // 如果没有找到学号
    {
        cout << "未找到学号为 " << findnum << " 的学生" << endl; // 输出未找到信息
    }
}

// 定义AlterScoreByNum方法，用于按学号修改学生的成绩
void AlterScoreByNum(int findnum)
{
    fstream file("student.txt"); // 打开"student.txt"文件，读写模式
    ofstream temp("temp.txt"); // 创建临时文件"temp.txt"
    int num;
    string name, gender, line;
    int year, month, day, score1, score2, score3;
    double average;
    bool found = false; // 是否找到学号的标志
    // 遍历文件中的每条记录
    while (file >> num >> name >> year >> month >> day >> gender >> score1 >> score2 >> score3 >> average)
    {
        if (num == findnum) // 如果找到要修改的学号
        {
            int newScore1, newScore2, newScore3; // 新的成绩
            cout << "请输入新的三门课成绩: ";
            cin >> newScore1 >> newScore2 >> newScore3; // 输入新成绩
            double newAverage = (newScore1 + newScore2 + newScore3) / 3.0; // 计算新的平均分
            int newMax = max({newScore1, newScore2, newScore3}); // 计算最大值
            int newMin = min({newScore1, newScore2, newScore3}); // 计算最小值
            // 将更新后的成绩写入临时文件
            temp << num << " " << name << " " << year << " " << month << " " << day << " " << gender << " "
                 << newScore1 << " " << newScore2 << " " << newScore3 << " " << newAverage << " " << newMax << " " << newMin << endl;
            found = true; // 标记找到
            cout << "已成功修改学号为 " << num << " 的学生成绩！" << endl; // 输出修改成功信息
        }
        else
        {
            // 如果不是要修改的学号，则将原有数据写入临时文件
            temp << num << " " << name << " " << year << " " << month << " " << day << " " << gender << " "
                 << score1 << " " << score2 << " " << score3 << " " << average << endl;
        }
    }
    file.close(); // 关闭原文件
    temp.close(); // 关闭临时文件
    remove("student.txt"); // 删除原文件
    rename("temp.txt", "student.txt"); // 将临时文件重命名为原文件名
    if (!found) // 如果没有找到学号
    {
        cout << "未找到学号为 " << findnum << " 的学生" << endl; // 输出未找到信息
    }
}

以上代码展示了如何在C++中使用文件流（fstream, ifstream, ofstream）进行文件的读写操作，包括添加、查找、删除和修改文件中的记录。在这些方法中，使用了临时文件策略来实现记录的删除和修改，这是一种常见的文件处理技巧，可以避免直接修改源文件时可能产生的数据丢失风险。