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    Beginner's Guide
    First Steps
    Input & Output
    Custom Types – Part 1
    Diagnostics
    Standard Library – Part 1
    Function Objects
    Standard Library – Part 2
    Code Organization
    Custom Types – Part 2
    Generic Programming
    Memory Management
    Software Design Basics

    Stream Input & Output Stream I/O Stream 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
    File I/O
    Beginner's Guide / Input&Output
    Input Errors

    Related …

    Last updated: 2019-11-09

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