void readfile() { vector<student> stu; ifstream in("user.txt"); int num; string name; while (in >> num >> name) { student s = { num, name }; stu.push_back(s); } in.close(); for (int i = 0; i < stu.size(); i++) { cout << stu[i].xuehao << " " << stu[i].name << endl; 这段代码什么意思 } }

这段代码是一个从文件中读取学生信息并输出到控制台的函数。具体来说，它打开名为"user.txt"的文件，逐行读取该文件中的学生信息（学号和姓名），将学生信息存储在一个名为stu的vector中，最后遍历该vector并输出学生信息（学号和姓名）到控制台。函数中的student是一个自定义的结构体，包含了学号和姓名两个成员变量。

相关问题

Task 2. Create a list of students by reading from student_hobbies.txt and display the list. // - You will also need to create a Student class, which has at least // two data fields: student name and an ArrayList of hobbies (String-type).优化以下代码private static ArrayList<Student> readFile(String string) throws IOException{ ArrayList<Student> studentlist=new ArrayList<Student>(); File file = new File("student_hobbies_JU.txt"); Scanner scanner = new Scanner(file); while (scanner.hasNextLine()) { String line = scanner.nextLine(); String[] data = line.split(", "); System.out.println(data); String name = data[0]; ArrayList<String> hobbies = new ArrayList<String>(); for(int i=0;i<data.length;i++){ hobbies.add(data[i]); } Student student = new Student(name, hobbies); studentlist.add(student); System.out.println(student); } scanner.close(); return studentlist; }//end readFile

下面是优化后的代码，其中将文件名作为参数传入函数中，使函数更加通用：

private static ArrayList<Student> readFile(String fileName) throws IOException {
    ArrayList<Student> studentList = new ArrayList<Student>();
    File file = new File(fileName);
    Scanner scanner = new Scanner(file);
    while (scanner.hasNextLine()) {
        String line = scanner.nextLine();
        String[] data = line.split(", ");
        String name = data[0];
        ArrayList<String> hobbies = new ArrayList<String>();
        for (int i = 1; i < data.length; i++) { // 从第二个元素开始，将所有的兴趣爱好添加到hobbies列表中
            hobbies.add(data[i]);
        }
        Student student = new Student(name, hobbies);
        studentList.add(student);
    }
    scanner.close();
    return studentList;
}

该函数将指定文件中的内容读取到一个ArrayList<Student>中，并返回该列表。下面是Student类的代码：

public class Student {
    private String name;
    private ArrayList<String> hobbies;

    public Student(String name, ArrayList<String> hobbies) {
        this.name = name;
        this.hobbies = hobbies;
    }

    public String getName() {
        return name;
    }

    public ArrayList<String> getHobbies() {
        return hobbies;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setHobbies(ArrayList<String> hobbies) {
        this.hobbies = hobbies;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", hobbies=" + hobbies +
                '}';
    }
}

该类包含两个数据字段：name和hobbies，分别表示学生的姓名和兴趣爱好列表。该类还包含构造函数、getter和setter方法以及toString方法，用于打印学生对象的信息。可以使用以下代码调用readFile函数并打印学生列表：

try {
    ArrayList<Student> studentList = readFile("student_hobbies.txt");
    for (Student student : studentList) {
        System.out.println(student);
    }
} catch (IOException e) {
    e.printStackTrace();
}

class Person {public: Person(char name[]="XXX", char sex='M',int age=18) { strcpy(this->name,name); this->sex =sex; this->age = age; } virtual void input() { cout << "Enter name:"; cin>> name; cout << "Enter sex:"; cin >> sex; cout << "Enter age:"; cin >> age; } virtual void output() { cout << "name:"<<name << "\t"; cout << "sex:"<< sex << "\t"; cout << "age:"<< sex << age <<endl; } protected: char name[21]; char sex; int age; }; 由Person类派生出如下的派生类Student： class Student:public Person {public: Student(char name[]="XXX", char sex='M',int age=18,char num[]="000000",char class_name[]="XXXXXX"); void input(); void output(); private: char num[10]; //学号 char class_name[21];//班级 }; void writeFile(string filename,Student stud[],int); void readFile(string filename,Student stud[],int); 要求： （1）写出Student类的构造函数、input函数、output函数的类外定义。 （2）写出把一组Student类对象写入文件的writeFile函数的函数体。 （3）写出从文件中读取所有Student类对象的readFile函数的函数体。

(1) Student类的构造函数、input函数、output函数的类外定义如下：

Student::Student(char name[], char sex, int age, char num[], char class_name[]) : Person(name, sex, age) {
    strcpy(this->num, num);
    strcpy(this->class_name, class_name);
}

void Student::input() {
    Person::input();
    cout << "Enter student number:";
    cin >> num;
    cout << "Enter class name:";
    cin >> class_name;
}

void Student::output() {
    Person::output();
    cout << "student number:" << num << "\t";
    cout << "class name:" << class_name << endl;
}

(2) 把一组Student类对象写入文件的writeFile函数的函数体如下：

void writeFile(string filename, Student stud[], int n) {
    ofstream out(filename, ios::out | ios::binary);
    if (!out) {
        cout << "Cannot open file!" << endl;
        return;
    }
    out.write(reinterpret_cast<char*>(&n), sizeof(int));
    for (int i = 0; i < n; i++) {
        out.write(reinterpret_cast<char*>(&stud[i]), sizeof(Student));
    }
    out.close();
}

(3) 从文件中读取所有Student类对象的readFile函数的函数体如下：

void readFile(string filename, Student stud[], int n) {
    ifstream in(filename, ios::in | ios::binary);
    if (!in) {
        cout << "Cannot open file!" << endl;
        return;
    }
    int count;
    in.read(reinterpret_cast<char*>(&count), sizeof(int));
    if (count != n) {
        cout << "The number of records in the file does not match the input!" << endl;
        in.close();
        return;
    }
    for (int i = 0; i < n; i++) {
        in.read(reinterpret_cast<char*>(&stud[i]), sizeof(Student));
    }
    in.close();
}