定义一个学生类, 包含学生的学号、 姓名和年龄等基本信息, 将学生信息写入二进 制文件 student. dat 中, 实现对学生信息的显示、 查询和删除等基本功能。用c++

下面是一个示例的学生类定义和实现：

#include <iostream>
#include <fstream>
#include <cstring>

using namespace std;

const int MAX_NAME_LEN = 20;

struct Student {
    int id;
    char name[MAX_NAME_LEN];
    int age;
};

class StudentManager {
public:
    void addStudent(int id, const char* name, int age);
    void displayAllStudents();
    void findStudentById(int id);
    void removeStudentById(int id);
private:
    fstream file;
    void writeStudentToFile(const Student& student);
    Student readStudentFromFile();
    bool matchById(const Student& student, int id);
};

void StudentManager::addStudent(int id, const char* name, int age) {
    Student student = {id};
    strncpy(student.name, name, MAX_NAME_LEN - 1);
    student.age = age;
    writeStudentToFile(student);
}

void StudentManager::displayAllStudents() {
    file.open("student.dat", ios::in | ios::binary);
    Student student;
    while (file.read(reinterpret_cast<char*>(&student), sizeof(Student))) {
        cout << "id: " << student.id << ", name: " << student.name << ", age: " << student.age << endl;
    }
    file.close();
}

void StudentManager::findStudentById(int id) {
    file.open("student.dat", ios::in | ios::binary);
    Student student;
    bool found = false;
    while (file.read(reinterpret_cast<char*>(&student), sizeof(Student))) {
        if (matchById(student, id)) {
            cout << "id: " << student.id << ", name: " << student.name << ", age: " << student.age << endl;
            found = true;
            break;
        }
    }
    if (!found) {
        cout << "Student with id " << id << " not found" << endl;
    }
    file.close();
}

void StudentManager::removeStudentById(int id) {
    file.open("student.dat", ios::in | ios::out | ios::binary);
    Student student;
    int pos = 0;
    while (file.read(reinterpret_cast<char*>(&student), sizeof(Student))) {
        if (matchById(student, id)) {
            file.seekp(pos);
            Student emptyStudent = {0};
            file.write(reinterpret_cast<char*>(&emptyStudent), sizeof(Student));
            cout << "Student with id " << id << " removed" << endl;
            break;
        }
        pos = file.tellg();
    }
    if (file.eof()) {
        cout << "Student with id " << id << " not found" << endl;
    }
    file.close();
}

void StudentManager::writeStudentToFile(const Student& student) {
    file.open("student.dat", ios::out | ios::app | ios::binary);
    file.write(reinterpret_cast<const char*>(&student), sizeof(Student));
    file.close();
}

Student StudentManager::readStudentFromFile() {
    Student student;
    file.read(reinterpret_cast<char*>(&student), sizeof(Student));
    return student;
}

bool StudentManager::matchById(const Student& student, int id) {
    return student.id == id;
}

在这个实现中，我们使用了 `fstream` 类来读写二进制文件。具体来说，对于写入操作，我们使用了 `ios::out` 和 `ios::app` 模式打开文件，以便在文件末尾添加新的学生信息；对于读取操作，我们使用了 `ios::in` 模式打开文件。在读写操作中，我们使用了 `reinterpret_cast` 来进行指针类型的转换，以便正确地读写二进制数据。

另外，我们还实现了一些基本的功能，比如添加学生、显示所有学生、按照学号查找学生和按照学号删除学生。在查找和删除操作中，我们使用了一个辅助函数 `matchById` 来判断学生信息是否与给定的学号匹配。

最后，我们可以在 `main` 函数中测试我们的实现：

int main() {
    StudentManager manager;
    manager.addStudent(1, "Alice", 20);
    manager.addStudent(2, "Bob", 21);
    manager.addStudent(3, "Charlie", 22);
    cout << "All students:" << endl;
    manager.displayAllStudents();
    cout << "Find student with id 2:" << endl;
    manager.findStudentById(2);
    cout << "Remove student with id 3:" << endl;
    manager.removeStudentById(3);
    cout << "All students after removal:" << endl;
    manager.displayAllStudents();
    return 0;
}

输出结果应该为：

All students:
id: 1, name: Alice, age: 20
id: 2, name: Bob, age: 21
id: 3, name: Charlie, age: 22
Find student with id 2:
id: 2, name: Bob, age: 21
Remove student with id 3:
Student with id 3 removed
All students after removal:
id: 1, name: Alice, age: 20
id: 2, name: Bob, age: 21