// test_fileio.cc   open, read, change, write file

#include <iostream>
#include <fstream>       // file IO stuff in here
#include <string>
#include <strstream>
using namespace std;

int main()
{
  ifstream file_in;      // object  file_in  of type istream (like cin)
  ofstream file_out;     // object  file_out of type ostream (like cout)
  char in_line[255];     // hold one line at a time (old C string)
  string line;           // for manipulating line
  string char_val;       // ASCII character string value
  int val;               // binary value (integer)
  char out_val[6];       // reconverted ASCII string

  cout << "test_fileio expects a file named  junk.txt  to exists" << endl;
  // first just open file and read and print it
  file_in.open("junk.txt");
  if(!file_in) 
  {
    cout << "could not open file junk.txt" << endl;
    return 1;
  }

  while(!file_in.eof())   // loop to read the input file
  {
    file_in.getline(in_line, 255, '\n');
    line = string(in_line);
    cout << line << endl;
  }
  file_in.close();
  cout << " finished read and print of a file" << endl;


  // open again, now modify and write
  file_in.open("junk.txt");
  if(!file_in) 
  {
    cout << "could not open file junk.txt" << endl;
    return 1;
  }

  file_out.open("junk.out");
  if(!file_out) 
  {
    cout << "could not open file junk.out" << endl;
    return 1;
  }
  while(!file_in.eof())   // loop to read the input file
  {
    file_in.getline(in_line, 255, '\n');
    line = string(in_line);
    cout << line << endl;
    if(line.length() < 1) break; // can't do zero length lines
    if(line.substr(8,4)==string("good") && line.length()>=18)
    {
      line.replace(8, 4, string("OK  ")); // modify a field

      char_val = line.substr(12, 6); // extract a field
      istrstream buf(char_val.begin(), char_val.length());
      buf >> val;                    // convert to binary
      cout << val << endl;
      ostrstream conv(out_val, 6);
      conv << val/2 ;                // do some computation
      line.replace(12, 6, string(out_val));

    }
    file_out << line << endl;
  }
  file_in.close();
  file_out.close();

  cout << "test_fileio finished." << endl;  
  return 0;
}