std::setw - cppreference.com

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# std::setw

From cppreference.com
< cpp‎ | io‎ | manip

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`.

### [edit] Parameters

n | - | new value for width

### [edit] 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);

### [edit] 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_ostream&, 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.

### [edit] 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"

### [edit] See also

width | manages field width (public member function of `std::ios_base`) [edit]
setfill | changes the fill character (function template) [edit]
internalleftright | sets the placement of fill characters (function) [edit]

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