#include <fstream.h>

int main( )
{
    ifstream in("testfile.cpp");
    ofstream out("testfile.out");
    out << in.rdbuf();  // copy file
    in.close();
    out.close();

    // open for reading and writing
    ifstream in2("testfile.out", ios::in|ios::out);
    ostream out2(in2.rdbuf());
    cout << in2.rdbuf();  // "get' pointer is initialized to the beginning
                          // of the file, print whole file
                          // however, "put" pointer is at the end of file
    out2 << "Where does this end up?";  // append to text
    out2.seekp(0, ios::beg); // "put" pointer is moved to beginning
                             // inserted text will overwrite existing text
    out2 << "And what about this? (overwrite existing text) ";

    in2.seekg(0, ios::beg);
    cout << in2.rdbuf(); // copy (overwrited) file

    getchar(); // to see the process from screen
}