< cpp‎ | io‎ | manip
Input/output library
I/O manipulators
C-style I/O
(deprecated in C++98)
File I/O
String I/O
Array I/O
(deprecated in C++98)
(deprecated in C++98)
(deprecated in C++98)
Synchronized Output
Error category interface
Input/output manipulators
Floating-point formatting
Integer formatting
Boolean formatting
Field width and fill control
Other formatting
Whitespace processing
Output flushing
Status flags manipulation
Time and money I/O
Quoted manipulator
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
  • Output

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.


#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
(public member function of std::ios_base)
changes the fill character
(function template)
sets the placement of fill characters