#include<iostream>
#include<iomanip>
#include<fstream>
#include<string>
#define _CRT_SECURE_NO_WARNINGS
using namespace std;
class CStudent
{
public:
    CStudent(const char* name,const char* id, float score = 0);
    void print();//输出
    friend ostream& operator<<(ostream& os, CStudent& stu);
    friend istream& operator>>(istream& is, CStudent& stu);
private:
    char strName[10];
    char strID[10];
    float fScore;
};
CStudent::CStudent(const char* name,const char* id,float score)
{
    strncpy_s(strName, name, strlen(strName)+1);
    strncpy_s(strID, id,strlen(strID)+1);
    fScore = score;
}
void CStudent::print()
{
    cout << endl << "学生信息如下：" << endl;
    cout << "姓名：" << strName << endl;
    cout << "学号：" << strID << endl;
    cout << "成绩：" << fScore << endl;
}
std::ostream& operator<<(ostream& os, CStudent& stu)
{
    //使用定长格式，使每一个类的数据长度为24个字节
    os.write(stu.strName, 10);
    os.write(stu.strID, 10);
    os.write((char*)& stu.fScore,4);//使float数据类型占4字节
        return os;
}
std::istream& operator>>(istream& is, CStudent& stu)
{
    char name[10], id[10];
    is.read(name, 10);
    is.read(id, 10);
    is.read((char*)&stu.fScore, 4);//读入4字节数据作为float类型
    strncpy_s(stu.strName, name, strlen(stu.strName)+1);
    strncpy_s(stu.strID, id, strlen(stu.strID)+1);
    return is;
}
void main()
{
    CStudent stu1("MaWenTao", "99001", 88);
    CStudent stu2("LiMing", "99002", 92);
    CStudent stu3("WangFang", "99003", 89);
    CStudent stu4("YangYang", "99004", 90);
    CStudent stu5("DingNing", "99005", 80);
    fstream file1;
    file1.open("student.dat", ios::out | ios::in | ios::binary);
    file1 << stu1 << stu2 << stu3 << stu4 << stu5;
    CStudent* one = new CStudent("","");
    const int size = 24;//每一个类的数据长度为24字节，与前呼应
    file1.seekp(size * 4);  file1 >> *one;  one->print();
    file1.seekp(size * 1);  file1 >> *one;  one->print();
    file1.seekp(size * 2, ios::cur);  file1 >> *one;  one->print();
    file1.close();
    delete one;
}