///////////////////////////////////////////////////////////////
// readwrit.cpp - demonstrate read/write fstreams            //
//                with buffer location seeking               //
// Jim Fawcett, 24 Mar 96, modified 23 Mar 97                //
///////////////////////////////////////////////////////////////

#include <iostream>     // cout, <<
#include <fstream>      // ifstream(), <<, >>
#include <cstdlib>      // exit(1);
using namespace std;

void main(int argc, char *argv[]) {

  if(argc < 2) {
    cout << "please enter file name on command line\n";
    exit(1);
  }

///////////////////////////////////////////////////////////////
// file open modes:        in       out       app       ate  //
//                             nocreate noreplace     trunc  //
///////////////////////////////////////////////////////////////

// save input file as a temporary file for reading and writing
  ifstream masterin(argv[argc-1]);
  ofstream tempout("tmp.tmp");
  tempout << masterin.rdbuf();
  masterin.close();
  tempout.close();

// open temporary for processing
  ifstream in("tmp.tmp", ios::in|ios::out);
  if(!in.good()) {
    cout << "can't open file tmp.tmp" << endl;
    exit(1);
  }

// use input buffer for output too
  ostream out(in.rdbuf());

// now, try reading and writing
  cout << "\nthis is a test file for reading and writing:\n"
       <<   "============================================\n";
  cout << in.rdbuf();
  out << "this line is added to the end\n";

// how many bytes in file?
  streampos sp = out.tellp();
  out.seekp(-sp, ios::end);            // back up from end
  out << "this overwrites first\n";

// write it out to see what happened
  cout << "\n\nmodified file:\n"
       <<   "==============\n";
  in.seekg(ios::beg);                  // go to beginning
  cout << in.rdbuf();

}