C++ redirect input

 #include<iostream>
 #include<string>
 #include<fstream>
 using namespace std;
 int main()
 {
 #ifndef ONLINE_JUDGE
    ifstream in("in.txt",ios::in);
    streambuf *backup,*file;
    backup=cin.rdbuf();
    file=in.rdbuf();
    cin.rdbuf(file);
 #endif
    string s;
    while(cin>>s)
    cout<<s<<endl;
 #ifndef ONLINE_JUDGE
    cin.rdbuf(backup);
    in.close();
 #endif
     ;
 }