有如下定义的基类Person： 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：

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：

void writeFile(string filename, Student stud[], int n)
{
    ofstream ofs(filename, ios::binary);
    if (!ofs)
    {
        cerr << "Failed to open the file!" << endl;
        exit(1);
    }
    for (int i = 0; i < n; i++)
    {
        ofs.write((char*)&stud[i], sizeof(Student));
    }
    ofs.close();
}

（3）从文件中读取所有Student类对象的readFile函数的函数体：

void readFile(string filename, Student stud[], int n)
{
    ifstream ifs(filename, ios::binary);
    if (!ifs)
    {
        cerr << "Failed to open the file!" << endl;
        exit(1);
    }
    for (int i = 0; i < n; i++)
    {
        ifs.read((char*)&stud[i], sizeof(Student));
    }
    ifs.close();
}