NAME¶

std::bitset::operator[] - std::bitset::operator[]

Synopsis¶

bool operator[]( std::size_t pos ) const; (1) (constexpr since C++11)
reference operator[]( std::size_t pos ); (2) (constexpr since C++23)

Accesses the bit at position pos. The first version returns the value of the bit,
the second version returns an object of type std::bitset::reference that allows
modification of the value.

Unlike test(), does not throw exceptions: the behavior is undefined if pos is out of
bounds.

Parameters¶

pos - position of the bit to return

Return value¶

1) The value of the requested bit.
2) An object of type std::bitset::reference, which allows writing to the requested
bit.

Exceptions¶

(none)

Example¶

// Run this code

#include <bitset>
#include <cstddef>
#include <iostream>

int main()
{
std::bitset<8> b1{0b00101010}; // binary literal for 42

for (std::size_t i = 0; i < b1.size(); ++i)
std::cout << "b1[" << i << "]: " << b1[i] << '\n';
b1[0] = true; // modifies the first bit through bitset::reference

std::cout << "After setting bit 0, b1 holds " << b1 << '\n';
}

Output:¶

b1[0]: 0
b1[1]: 1
b1[2]: 0
b1[3]: 1
b1[4]: 0
b1[5]: 1
b1[6]: 0
b1[7]: 0
After setting bit 0, b1 holds 00101011

Defect reports

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

DR Applied to Behavior as published Correct behavior
1. the description was missing in the
LWG 11 C++98 C++ standard 1. description added
2. there was only the non-const 2. added the const overload
overload
the behavior of reading the bit at
LWG 907 C++98 pos was equivalent avoids mentioning test()
to that of test(pos), but test() may
throw exceptions

See also¶

test accesses specific bit
(public member function)