std::setw

 

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showpointnoshowpoint setprecision	fixedscientifichexfloatdefaultfloat (C++11)(C++11)
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setbase showbasenoshowbase	dechexoct
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boolalphanoboolalpha
Field width and fill control
setfill setw	internalleftright
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showposnoshowpos	uppercasenouppercase
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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.

Parameters

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:

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 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.

Example

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";
}

Output:

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

See also

width	manages field width (public member function of std::ios_base)
setfill	changes the fill character (function template)
internalleftright	sets the placement of fill characters (function)
showbasenoshowbase	controls whether prefix is used to indicate numeric base (function)