std::bitset<N>::operator[]

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.

1) Returns the value of the bit.

2) Returns an object of type std::bitset::reference that allows modification of the value.

If pos < size() is false, the behavior is undefined.

(until C++26)

If pos < size() is false:

If the implementation is hardened, a contract violation occurs.
If the implementation is not hardened, the behavior is undefined.

(since C++26)

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

Throws nothing.

Example

#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.