c++二进制文件输入输出

#include <fstream>
#include <iostream>
using namespace std;
struct student
{int num;
  char name[20];
  float score;
};
int main( )
{  int i;
 student stud[5]={1001,"Li",85,1002,"Fun",97.5,1004,"Wang",54,
                   1006,"Tan",76.5,1010,"ling",96};
  fstream iofile("stud.dat",ios::in|ios::out|ios::binary);    
//用fstream类定义输入输出二进制文件流对象iofile
  if(!iofile)
   {cerr<<"open error!"<<endl;
    abort( );
   }
  for(i=0;i<5;i++)//向磁盘文件输出个学生的数据
    iofile.write((char *)&stud[i],sizeof(stud[i]));    
  student stud1[5];                                    //用来存放从磁盘文件读入的数据
  for(i=0;i<5;i=i+2)
    {iofile.seekg(i*sizeof(stud[i]),ios::beg);    //定位于第,2,4学生数据开头
     iofile.read((char *)&stud1[i/2],sizeof(stud1[0]));  
//先后读入个学生的数据,存放在stud1[0],stud[1]和stud[2]中
     cout<<stud1[i/2].num<<" "<<stud1[i/2].name<<" "<<stud1[i/2].score<<endl;
//输出stud1[0],stud[1]和stud[2]各成员的值
}
  cout<<endl;  
  stud[2].num=1012;                                                  //修改第个学生(序号为)的数据
  strcpy(stud[2].name,"Wu");
  stud[2].score=60;
  iofile.seekp(2*sizeof(stud[0]),ios::beg);      //定位于第个学生数据的开头
  iofile.write((char *)&stud[2],sizeof(stud[2])); //更新第3个学生数据
  iofile.seekg(0,ios::beg);                                              //重新定位于文件开头
  for(i=0;i<5;i++)
    {iofile.read((char *)&stud[i],sizeof(stud[i]));    //读入5个学生的数据
     cout<<stud[i].num<<" "<<stud[i].name<<" "<<stud[i].score<<endl;
    }
  iofile.close( );
return 0;
}