用 C++编写代码，设计一个学生管理系统，具有添加、修改、删除、排序、查找、显示和保存功能

以下是一个简单的学生管理系统的C++代码示例：

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

struct Student {
    string name;
    int age;
    string major;
};

vector<Student> students;

void addStudent() {
    Student student;
    cout << "请输入学生姓名：";
    cin >> student.name;
    cout << "请输入学生年龄：";
    cin >> student.age;
    cout << "请输入学生专业：";
    cin >> student.major;
    students.push_back(student);
    cout << "添加成功！" << endl;
}

void displayStudent(const Student& student) {
    cout << "姓名：" << student.name << endl;
    cout << "年龄：" << student.age << endl;
    cout << "专业：" << student.major << endl;
}

void displayAllStudents() {
    if (students.empty()) {
        cout << "暂无学生信息！" << endl;
        return;
    }
    for (const auto& student : students) {
        displayStudent(student);
        cout << "-----------------------" << endl;
    }
}

void searchStudent() {
    string name;
    cout << "请输入要查找的学生姓名：";
    cin >> name;
    for (const auto& student : students) {
        if (student.name == name) {
            displayStudent(student);
            return;
        }
    }
    cout << "未找到该学生！" << endl;
}

void deleteStudent() {
    string name;
    cout << "请输入要删除的学生姓名：";
    cin >> name;
    for (auto it = students.begin(); it != students.end(); ++it) {
        if (it->name == name) {
            students.erase(it);
            cout << "删除成功！" << endl;
            return;
        }
    }
    cout << "未找到该学生！" << endl;
}

bool compareByName(const Student& s1, const Student& s2) {
    return s1.name < s2.name;
}

void sortStudentsByName() {
    sort(students.begin(), students.end(), compareByName);
    cout << "按姓名排序成功！" << endl;
}

void saveToFile() {
    ofstream file("students.txt");
    for (const auto& student : students) {
        file << "姓名：" << student.name << endl;
        file << "年龄：" << student.age << endl;
        file << "专业：" << student.major << endl;
        file << "-----------------------" << endl;
    }
    file.close();
    cout << "保存成功！" << endl;
}

int main() {
    int choice;

    while (true) {
        cout << "1. 添加学生信息" << endl;
        cout << "2. 修改学生信息" << endl; // 根据需要自行实现
        cout << "3. 删除学生信息" << endl;
        cout << "4. 按姓名排序" << endl;
        cout << "5. 查找学生信息" << endl;
        cout << "6. 显示所有学生信息" << endl;
        cout << "7. 保存学生信息到文件" << endl;
        cout << "0. 退出程序" << endl;
        cout << "请输入您的选择：";
        cin >> choice;

        switch (choice) {
            case 1:
                addStudent();
                break;
            case 2:
                // 实现修改学生信息的功能
                break;
            case 3:
                deleteStudent();
                break;
            case 4:
                sortStudentsByName();
                break;
            case 5:
                searchStudent();
                break;
            case 6:
                displayAllStudents();
                break;
            case 7:
                saveToFile();
                break;
            case 0:
                cout << "程序已退出！" << endl;
                return 0;
            default:
                cout << "无效选择！" << endl;
        }
    }

    return 0;
}

以上代码是一个简单的学生管理系统，实现了添加、删除、按姓名排序、查找、显示和保存学生信息的功能。根据需要，还可以进一步完善代码，实现修改学生信息的功能等。