//AB类，重载<<,  >>提供输入，并把输入内容放到文件里面,并输出到屏幕上(main里面可以写除函数外的代码）
#include"iostream.h"
#include"fstream.h"
#include"stdio.h"
class AB
  {  public:
       AB(){}
     friend ifstream& operator >>(ifstream& in,AB& a);
     friend ofstream& operator <<(ofstream& in,AB& a);
     private:
      char ch[100];
  };
main()
{    ifstream in;
    ofstream out;
     AB a(in);
    out.open("abc.txt");
    if(!out.fail())
   {  cout<<"error!"<<endl;
       exit(1);
    }
    in>>a;
    out<<a<<endl;
    out.close();
}
ifstream& operator >>(ifstream& in,AB& a)
{    in>>a.ch;
  return in;
}
ofstream& operator <<(ofstream& out,AB& a)
{    out<<a.ch;
    return out;
}