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Variants

std::bitset<N>:: set

From cppreference.net
C++
Utilities library
std::bitset
bitset & set ( ) ;
(1) (noexcept since C++11)
(constexpr since C++23)
bitset & set ( std:: size_t pos, bool value = true ) ;
(2) (constexpr since C++23)

Sets all bits to true or sets one bit to specified value.

1) Sets all bits to true .
2) Sets the bit at position pos to the value value .

Contents

Parameters

pos - the position (counting from ​ 0 ​ , i.e. from least significant to most significant) of the bit to set
value - the value to set the bit to

Return value

* this

Exceptions

2) Throws std::out_of_range if pos does not correspond to a valid bit position.

Example

Run this code 
#include <bitset>
#include <cstddef>
#include <iostream>
int main()
{
    std::bitset<8> b;
    std::cout << b << '\n';
    std::cout << b.set() << '\n';
    std::cout << b.reset() << '\n';
    for (std::size_t i = 1; i < b.size(); i += 2)
        b.set(i);
    std::cout << b << '\n';
}

Output: 

00000000
11111111
00000000
10101010

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 186 C++98 the type of value was int corrected to bool
LWG 2250 C++98 the behavior was undefined if pos does
not correspond to a valid bit position 		always throws an
exception in this case

See also

sets bits to false
(public member function)
toggles the values of bits
(public member function)