std::setw(3)

NAME
std::setw - std::setw

Synopsis
   Defined in header <iomanip>
   /* unspecified */ setw( int n );
   When used in an expression out << std::setw(n) or in >> std::setw(n), sets the width
   parameter of the stream out or in to exactly n.
   Some operations reset the width to zero (see below), so std::setw may need to be
   repeatedly called to set the width for multiple operations.

Parameters
   n - new value for width

Return value
   An object of unspecified type such that
     * if out is an object of type std::basic_ostream<CharT, Traits>, the expression
       out << setw(n)
          * has type std::basic_ostream<CharT, Traits>&
          * has value out
          * behaves as if it called f(out, n)
     * if in is an object of type std::basic_istream<CharT, Traits>, the expression in
       >> setw(n)
          * has type std::basic_istream<CharT, Traits>&
          * has value in
          * behaves as if it called f(in, n)
   where the function f is defined as:
 void f(std::ios_base& str, int n)
 {
     // set width
     str.width(n);
 }

Notes
   The width property of the stream will be reset to zero (meaning "unspecified") if
   any of the following functions are called:
     * Input
     * operator>>(basic_istream&, basic_string&)
     * operator>>(basic_istream&, char*)
     * Output
     * Overloads of basic_ostream::operator<<() that take arithmetic types or void
       pointers (at Stage 3 of num_put::put())
     * operator<<(basic_ostream&, char) and operator<<(basic_ostream&, char*)
     * operator<<(basic_ostream&, basic_string&)
     * std::put_money (inside money_put::put())
     * std::quoted (when used with an output stream)
   The exact effects this modifier has on the input and output vary between the
   individual I/O functions and are described at each operator<< and operator>>
   overload page individually.

Example
// Run this code
 #include <iomanip>
 #include <iostream>
 #include <sstream>
 int main()
 {
     std::cout << "no setw: [" << 42 << "]\n"
               << "setw(6): [" << std::setw(6) << 42 << "]\n"
               << "no setw, several elements: [" << 89 << 12 << 34 << "]\n"
               << "setw(6), several elements: [" << 89 << std::setw(6) << 12 << 34 << "]\n";
     std::istringstream is("hello, world");
     char arr[10];
     is >> std::setw(6) >> arr;
     std::cout << "Input from \"" << is.str() << "\" with setw(6) gave \""
               << arr << "\"\n";
 }

Output:
 no setw: [42]
 setw(6): [ 42]
 no setw, several elements: [891234]
 setw(6), several elements: [89 1234]
 Input from "hello, world" with setw(6) gave "hello"
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
     DR Applied to Behavior as published Correct behavior
   LWG 183 C++98 setw could only be used with streams of usable with any
                      type std::ostream or std::istream character stream

See also
   width manages field width
              (public member function of std::ios_base)
   setfill changes the fill character
              (function template)
   internal sets the placement of fill characters
   left (function)
   right
   showbase controls whether prefix is used to indicate numeric base
   noshowbase (function)