Beginner's Guide
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    Stream Input & OutputStream I/OStream I/O

    Custom I/O Custom

    Example: Point Coordinate I/O Example

    by overloading two functions with names operator<< and operator>>
    struct point { int x;  int y; };
    
    std::ostream& operator << (std::ostream& os, point const& p) {
      return os << '(' << p.x << ',' << p.y << ')';
    }
    
    std::istream& operator >> (std::istream& is, point& p) {
      return is >> p.x >> p.y;
    }
    
    point p {1,2}; cout << p << '\n'; // prints (1,2) cin >> p; // reads 2 ints into p.x and p.y

    Stream Operators Operators

    operator functions for stream input/output of objects of type T:
    std::ostream& operator << (std::ostream& os, T const& x) {
      // write to stream …
      return os;
    }
    
    std::istream& operator >> (std::istream& is, T& x) { // read from stream … return is; }

    Operators << and >> return a reference (to their stream parameter) to allow operator chaining:

    cin  >> x >> y; operator>>( operator>>(cin, x), y)
    cout << x << y; operator<<( operator<<(cout,x), y)

    There are no default stream operations in the standard library for containers like std::vector, because there are too many possible use cases:

    • just print values … separated by what?
    • format output as plain text / XML / …
    • (de-)serialize container

    (Some) Standard Library Stream Types (Some) Standard Stream Types Stream Types

    istream input stream reference istream& binds to any other kind of std:: input stream
    ostream output stream reference ostream& binds to any other kind of std:: output stream
    ifstream input file stream extracted data is read from a file
    ofstream output file stream inserted data is stored in a file
    ostringstream output string stream inserted data is stored in a string buffer
    istringstream input string stream extracted data is read from a string buffer

    Utilities

    Read Lines With getline getline

    std::getline(istream&, string&, stopat='\n')

    reads until the next stopat character (default = until end of line)

    string s;
    getline(cin, s);
    getline(cin, s, '\t');
    getline(cin, s, 'a');
     
    read entire line
    read until next tab
    read until next 'a'

    Skip Forward With ignore ignore

    std::istream::ignore(n, c)
    • forwards stream by n characters
    • until stop character c
    // skip next 8 characters
    cin.ignore(8);
    
    // skip by max. 10 characters or until after '=' cin.ignore(10, '=');
    // skip until after next newline character cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

    Formatting Manipulators Manipulators

    #include <iomanip>
    
    double d = 12.345678; double e = 2011; double f = 1e-10;
    cout << d << e << f
    << setprecision(4) << d << e << f
    << fixed << d << e << f
    << scientific << d << e << f
    << true <<' '<< false << boolalpha << true <<' '<< false;
    header 
    

    12.345678 2011 1e-010
    # of digits 12.35 2011 1e-010
    fixed # of decimals 12.3457 2011.0000 1.0000e-010
    scientific notation 1.2346e+001 2.0110e+003 1.0000e-010
    1 0 booleans as string true false