iostream/file_with_class.cpp

#include <iostream>
#include <fstream>
#include <string>
using std::cin, std::cout, std::string;

class Student
{
    string name;          // 学生姓名
    int course_num;       // 学生课程数
    int *score;           // 指向动态分配成绩数组
    const char *filename; // 用来处理读写文件的名字

public:
    Student(string _name, int _course_num, const char *_filename)
        : name{_name}, course_num{_course_num}, filename{_filename}
    {
        score = new int[course_num]{};
        cout << "请依次输入" << course_num << "门课的成绩：";
        for (int i = 0; i < course_num; ++i)
            std::cin >> score[i];
    }

    Student(const char *_filename) : filename{_filename}
    {
        std::ifstream infile(filename, std::ios::in | std::ios::binary);
        if (infile)
        {
            int len{};
            infile.read(reinterpret_cast<char *>(&len), sizeof(int));
            char *buffer = new char[len + 1]{};
            infile.read(buffer, len);
            name = buffer;
            delete[] buffer;
            infile.read(reinterpret_cast<char *>(&course_num), sizeof(course_num));
            score = new int[course_num]{};
            infile.read(reinterpret_cast<char *>(score), course_num * sizeof(int));
            infile.close();
        }
    }
    ~Student()
    {
        std::ofstream ofile(filename, std::ios::out | std::ios::binary);
        {
            int len{static_cast<int>(name.size())};
            ofile.write(reinterpret_cast<char *>(&len), sizeof(len));
            ofile.write(name.c_str(), len);
            ofile.write(reinterpret_cast<char *>(&course_num), sizeof(course_num));
            ofile.write(reinterpret_cast<char *>(score), course_num * sizeof(int));
            ofile.close();
            delete[] score;
        }
    }
    friend std::ostream &operator<<(std::ostream &os, Student &s)
    {
        os << "姓名：" << s.name << " 成绩：";
        for (int i{0}; i < s.course_num; ++i)
            os << s.score[i] << '\t';
        return os << '\n';
    }
};

int main()
{
    Student s1{"TOM", 5, "s1.dat"};
    // Student s1{"s1.dat"}; 这句话和上面的语句分两次运行即可
    cout << s1;
}