Error Conditions with Streams

• So far, we have assumed that all stream operations have been successful; this is a dangerous assumption
• There are many potential errors when dealing with files
• Input files may not exist; output files may be read-only; disks can become full; users may not have read/write privileges with certain files
• We have seen 3 functions associated with streams: open(), close(), and eof().
• There are many others, some of which are used to detect errors; fail() is useful for error detection

  ifstream myIn;
  myIn.open("datafile.in", ios::in);

  // test to see if there was an error; if there was 
  // an error, it is not safe to proceed
  if ( myIn.fail() )
    cout << "Unable to open input file" << endl;
  else
  {
     while ( !myIn.eof() )
     {
        // process data in file
     }
     myIn.close();   // close the file here
  }