stream I/O


concept of a stream (slide G-5)
  sequence of characters


streams are objects
  iostream classes 
    istream
    ostream
  fstream classes (iostreams specialized for files)
    ifstream (input file stream)
    ofstream (output file stream)

  special predefined istream/ostream instances
    cin for standard input (keyboard)                       
    cout for standard output (screen)
    cerr for standard error (also screen, but usu. for error msgs.)
  member functions
    e.g. istream::getline(...), ostream::put(...)


operators*
  insertion, <<
    e.g. cout << "stuff to display on screen";
  extraction, <<
    e.g. cin >> userInputValue1 >> userInputValue2;

*Which is which?  Think from the program's point of view;
 "become the program."  If you want to send text to the
 screen, you do so by sending it through the cout stream
 object, so you must "insert" the text into cout.


istream extraction, breaking at whitespace (slide G-10)
  see also, method istream::getline(char [], int)


checking for a valid istream
  general method:  just use stream object itself, e.g.

    while (cin) {
      cin >> anotherValue;
      // do something w/ the inputted value
    }
       
  more specific:  check for failure of a particular extraction

    while (cin >> anotherValue) {
      // do something w/ the inputted value
    }

  In the example above, if the user input does not match the
  type of variable anotherValue, the loop condition (cin
  expression) evaluates to false.


file streams 
  opening a file for reading by creating an instance of
  ifstream associated w/ the file:

    ifstream inputStream("inputFilename", ios::nocreate);

  Now, extracting from object inputStream reads from the
  file sequentially:
    
    inputStream >> firstValue >> secondValue;

  opening a file for writing by creating an instance of
  ofstream associated w/ the file:

    ofstream outputStream("outputFilename");
  
  Now, inserting to object outputStream writes to the file
  sequentially:

    outputStream << "This string is 29 bytes long.";