std::setw - cppreference.com (original) (raw)

| | | | | ---------------------------------- | | | | /* unspecified */ setw( int n ); | | |

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

Some operations reset the width to zero (see below), so std::setw may need to be repeatedly called to set the width for multiple operations.

[edit] Parameters

[edit] Return value

An object of unspecified type such that

if out is an object of type std::basic_ostream<CharT, Traits>, the expression out << setw(n)
- has type std::basic_ostream<CharT, Traits>&
- has value out
- behaves as if it called f(out, n)
if in is an object of type std::basic_istream<CharT, Traits>, the expression in >> setw(n)
- has type std::basic_istream<CharT, Traits>&
- has value in
- behaves as if it called f(in, n)

where the function f is defined as:

[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_istream&, char*)
Output
Overloads of basic_ostream::operator<<() that take arithmetic types or void pointers (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

#include #include #include int main() { std::cout << "no setw: [" << 42 << "]\n" << "setw(6): [" << std::setw(6) << 42 << "]\n" << "no setw, several elements: [" << 89 << 12 << 34 << "]\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] no setw, several elements: [891234] setw(6), several elements: [89 1234] Input from "hello, world" with setw(6) gave "hello"

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.