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std::setw(3) C++ Standard Libary std::setw(3) NAME std::setw - std::setw Synopsis Defined in header <iomanip> /* 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. Parameters n - new value for width 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: void f(std::ios_base& str, int n) { // set width str.width(n); } Notes The width property of the stream will be reset to zero (meaning "un- specified") 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 be- tween the individual I/O functions and are described at each operator<< and operator>> overload page individually. Example // Run this code #include <iomanip> #include <iostream> #include <sstream> 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" Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior LWG 183 C++98 setw could only be used with streams of usable with any type std::ostream or std::istream character stream See also width manages field width (public member function of std::ios_base) setfill changes the fill character (function template) internal sets the placement of fill characters left (function) right showbase controls whether prefix is used to indicate numeric base noshowbase (function) http://cppreference.com 2024.06.10 std::setw(3)
NAME | Synopsis | Parameters | Return value | Notes | Example | Output: | See also
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