// Eg12-12.cpp
#include <cstring>
#include <fstream>
#include <iostream>
using namespace std;
class Employee {
private:
  int number, age;
  char name[20];
  double sal;

public:
  Employee() {}
  Employee(int num, char *Name, int Age, double Salary) {
    number = num;
    strcpy(name, Name);
    age = Age;
    sal = Salary;
  }
  void display() {
    cout << number << "\t" << name << "\t" << age << "\t" << sal << endl;
  }
};

int main() {
  ofstream out("D:/Employee.dat", ios::out); //定义随机输出文件
  Employee e1(1, "张三", 23, 2320);
  Employee e2(2, "李四", 32, 3210);
  Employee e3(3, "王五", 34, 2220);
  Employee e4(4, "刘六", 27, 1220);
  out.write((char *)&e1, sizeof(e1)); //按e1,e2,e3,e4顺序写入文件
  out.write((char *)&e2, sizeof(e2));
  out.write((char *)&e3, sizeof(e3));
  out.write((char *)&e4, sizeof(e4));

  //下面的代码将e3（即王五）的年龄改为40岁
  Employee e5(3, "王五", 40, 2220);
  out.seekp(
      2 *
      sizeof(
          e1)); //指针定位到第3（起始为0）个数据块，这里写错了应该是2*sizeof（e1）
  out.write((char *)&e5, sizeof(e5)); //将e5写到第3个数据块位置，覆盖e3
  out.close();                        //关闭文件
  
}