std::setw (3) - Linux Manuals

std::setw: std::setw


std::setw - std::setw


Defined in header <iomanip>
/*unspecified*/ setw( int n );

When used in an expression out << setw(n) or in >> setw(n), sets the width parameter of the stream out or in to exactly n.


n - new value for width

Return value

Returns an object of unspecified type such that if str is the name of an output stream of type std::basic_ostream<CharT, Traits> or std::basic_istream<CharT, Traits>, then the expression str << setw(n) or str >> setw(n) behaves as if the following code was executed:


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 1-7 of basic_ostream::operator<<() (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.


// Run this code

  #include <sstream>
  #include <iostream>
  #include <iomanip>

  int main()
      std::cout << "no setw:" << 42 << '\n'
                << "setw(6):" << std::setw(6) << 42 << '\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";


  no setw:42
  setw(6): 42
  setw(6), several elements: 89 1234
  Input from "hello, world" with setw(6) gave "hello"

See also

         manages field width
width (public member function of std::ios_base)
         changes the fill character
setfill (function template)

internal sets the placement of fill characters
left (function)