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读写二进制文件。 

Class 用法.

将map存进二进制文件，高速读写。

#include <fstream>
#include <string>
#include <map>
#include <iostream>
using namespace std;

class STUDENT{
   public:
      string name;
      int age;
};
int main()
{
   map<int,STUDENT> obm, VM;
   int num;
   STUDENT stu;
   num = 23;
   stu.name = "张山";
   stu.age = 55;
   obm.insert(make_pair(num, stu));
   num = 24;
   stu.name = "王五";
   stu.age = 55;
   obm.insert(make_pair(num, stu));
   num = 25;
   stu.name = "什么";
   stu.age = 55;
   obm.insert(make_pair(num, stu));
   num = 26;
   stu.name = "哎呀";
   stu.age = 55;
   obm.insert(make_pair(num, stu));
//显示
   cout << "学号\t姓名\t年龄" << endl;
   map<int,STUDENT>::iterator iter = obm.begin();
   while (iter != obm.end()){
      cout << iter->first << "\t" << iter->second.name << "\t" << iter->second.age << endl; iter++; //保存
   }
   ofstream out("22.txt",ios::binary);
   if (!out.is_open()) {
      cout << "File is open fail!" << endl;
   }
   iter = obm.begin();
   while (iter != obm.end()) {
      out.write((char*)&iter->first,sizeof(int));
      out.write((char*)&iter->second,sizeof(stu));
      iter++;
   }
   out.close(); //读取
   ifstream in("22.txt",ios::binary);
   if (!in.is_open()) {
      cout << "File is open fail!" << endl;
   }
   while (!in.eof()) {
      in.read((char*)&num,sizeof(int));
      in.read((char*)&stu,sizeof(stu));
      VM.insert(make_pair(num,stu));
   }
   in.close(); //显示
   iter = VM.begin();
   while (iter != VM.end()) {
      cout << iter->first << " " << iter->second.name << " " << iter->second.age << endl; iter++;
   }
   return 0;
}