1. 1 I/O  C++ has no built-in support for input/output input/output is a library (iostream)  C++ program views input and output as a stream of bytes  Input: program extracts bytes from an "input" stream Output: program inserts bytes into an "output" stream Error: program outputs bytes into an "error" stream

2. 2 Approximate I/O Inheritance Hierarchy  Will learn what inheritance is later  Streambuf (base class, actual op on devices)  ios (formatting I/O operations, stream state, err)  istream (input stream) ifstream (input file)  ostream  ofstream

3. 3 How It Works  Standard objects cin, cout, cerr  Bytes in either stream can go to standard device OR file E.g. output to cout (monitor), OR a file  C++ program does not care where bytes come/go It just works on bytes of data Automatically converts data type

4. 4 Extractor Operator (>>) istream & operator>>(istream & is, T &t) { is >>... return is; } reason for returning “is” : to concatenate input (cin >> x) >> y  cin >> x >> y

5. 5 Inserter Operator (<<) ostream & operator<<(ostream & os, T t) { os <<... return os; } reason for returning “os” : to concatenate input (cout << x) << y  cout << x << y

6. 6 Friend operators for classes class Coord { private: int x, y; public: Coord() {x = 0; y = 0;} friend ostream &operator << (ostream &s, Coord point); friend istream &operator >> (istream &s, Coord &point); }; Cannot be part of class methods (cin >> obj, cout << obj)

7. 7 Parsing  When input data is read using cin, it is broken into tokens  each token is separated from the next by whitespace. "cin >>..." reads one token at a time  What if we want to read spaces too ? int get() - returns a char or EOF (-1) istream& getline(char *buffer, int num, char end = ‘\n’)

8. 8 Status int x; cin >> x; Q: What happens if you type in &%* when int expected ? A: x is not changed, can check failure of operation, using “!” if (! (cin >> x)) cerr << “Error in cin stream” << endl;

9. 9 How to test for errors: Member functions good() : ios::goodbit - everything is fine eof() : ios::eofbit - end-of-file (also sets failbit) fail() : ios::failbit - failure: error, but stream is usable bad() : ios::badbit - fatal err: stream is no longer usable clear() : clears all or some flags rdstate() : read the combination of all

10. 10 How to test for errors while (cin >> x) { // cin stream is good cout << x << endl; } Another way: cin >> x; if (!cin.fail()) { cout << x << endl; }

11. 11 Operations on Files ofstream out;  out.open (file_name, mode, access); e.g. r/o access  Mode - ios::app ios::trunc, etc. Access - r/o access E.g. out.open (“test”, ios::out, 0); or out.open(“test”) or ofstream out(“test”); //constructor autom open  Use through the inserter operator: out << 5;  out.close()

12. 12 Stream Manipulators (e.g. std::endl)  #include  std::setw() int x; cout << std::setw(9) << x; outputs x, right adjusted, with spaces on the left side

13. 13 Alignment std::left, std::right  cout << std::left;  cout << std::setw(9) << x;  outputs x, left adjusted, with spaces on the right side  left and right remain valid until another command

14. 14 Fill manipulator std::setfill  cout << std::right;  cout << std::setfill('0');  cout << std::setw(9) << x << endl;  outputs x, right adjusted, with zeros on the left side

15. 15 Numeric base cout << std::hex << x << endl; cout << std::oct << x << endl; cout << std::dec << x << endl; remains valid until changed

16. 16 Booleans  bool a;  cout << std::boolalpha;  cout << a << endl; remains valid until changed

17. 17 Floating Point std::fixed, std::scientific and std::setprecision manipulators cout << std::fixed << std::setprecision(2) << 432.343; will print 432.34 cout << std::scientific << std::setprecision(2) << 432.3434; will print 4.32e+02