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:

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
controls whether prefix is used to indicate numeric base

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.