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

 

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std::bitset

Member types
bitset::reference
Member functions
bitset::bitset
bitset::operator==bitset::operator!= (until C++20)
Element access
bitset::operator[]
bitset::test
bitset::allbitset::anybitset::none (C++11)
bitset::count
Capacity
bitset::size
Modifiers
bitset::operator&=bitset::operator|=bitset::operator^=bitset::operator~
bitset::operator<<=bitset::operator>>=bitset::operator<<bitset::operator>>
bitset::set
bitset::reset
bitset::flip
Conversions
bitset::to_string
bitset::to_ulong
bitset::to_ullong (C++11)
Non-member functions
operator&operator|operator^	operator<<operator>>
Helper classes
std::hash (C++11)

 

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

See also

test	accesses specific bit (public member function)