C++ In a Nutshell

<iomanip>

The <iomanip> header declares several I/O manipulators. An I/O manipulator is a function object that can be used in a sequence of input or output operators to manipulate the I/O stream. The manipulators are simple wrappers for functionality that is available as member functions of the ios_base class, but manipulators are simpler to use in some situations.

For example, to print formatted output, the following two code fragments are equivalent:

// Using manipulators
std::cout << std::setw(16) << std::setprecision(12) << x;
   
// Without manipulators
std::cout.width(16);
std::cout.precision(12);
std::cout << x;

At a basic level, manipulators are easy to use. If you want to understand exactly how they work, perhaps to write your own, see Chapter 9 for a thorough discussion of I/O, including manipulators.

The return type of each manipulator is implementation-defined. For the following function descriptions, this type is shown as manip_t.

Use a manipulator by applying it to a stream—that is, out << manip, in which out is an instance of basic_ostream, or in >> manip, in which in is an instance of basic_istream. In the following function descriptions, stream refers to the input or output stream to which the manipulator is being applied.