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std::bitset(3) C++ Standard Libary std::bitset(3)


std::bitset - std::bitset


Defined in header <bitset>
template< std::size_t N >
class bitset;

The class template bitset represents a fixed-size sequence of N bits. Bitsets can be
manipulated by standard logic operators and converted to and from strings and

bitset meets the requirements of CopyConstructible and CopyAssignable.

Template parameters

N - the number of bits to allocate storage for

Member types

reference proxy class representing a reference to a bit

Member functions

constructor constructs the bitset
(public member function)
operator== compares the contents
operator!= (public member function)
(removed in C++20)

Element access

operator[] accesses specific bit
(public member function)
test accesses specific bit
(public member function)
any checks if all, any or none of the bits are set to true
none (public member function)
count returns the number of bits set to true
(public member function)


size returns the number of bits that the bitset holds
(public member function)


operator|= performs binary AND, OR, XOR and NOT
operator^= (public member function)
operator>>= performs binary shift left and shift right
operator<< (public member function)
set sets bits to true or given value
(public member function)
reset sets bits to false
(public member function)
flip toggles the values of bits
(public member function)


to_string returns a string representation of the data
(public member function)
to_ulong returns an unsigned long integer representation of the data
(public member function)
to_ullong returns an unsigned long long integer representation of the data
(C++11) (public member function)

Non-member functions

operator& performs binary logic operations on bitsets
operator| (function template)
operator<< performs stream input and output of bitsets
operator>> (function template)

Helper classes

std::hash<std::bitset> hash support for std::bitset
(C++11) (class template specialization)


If the size of the bitset is not known at compile time, std::vector<bool> or
boost::dynamic_bitset<> may be used.

Feature-test macro: __cpp_lib_constexpr_bitset


// Run this code

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

int main()
typedef std::size_t length_t, position_t; // the hints

// constructors:
constexpr std::bitset<4> b1;
constexpr std::bitset<4> b2{0xA}; // == 0B1010
std::bitset<4> b3{"0011"}; // can't be constexpr yet
std::bitset<8> b4{"ABBA", length_t(4), /*0:*/'A', /*1:*/'B'}; // == 0B0000'0110

// bitsets can be printed out to a stream:
std::cout << "b1:" << b1 << "; b2:" << b2 << "; b3:" << b3 << "; b4:" << b4 << '\n';

// bitset supports bitwise operations:
b3 |= 0b0100; assert(b3 == 0b0111);
b3 &= 0b0011; assert(b3 == 0b0011);
b3 ^= std::bitset<4>{0b1100}; assert(b3 == 0b1111);

// operations on the whole set:
b3.reset(); assert(b3 == 0);
b3.set(); assert(b3 == 0b1111);
assert(b3.all() && b3.any() && !b3.none());
b3.flip(); assert(b3 == 0);

// operations on individual bits:
b3.set(position_t(1), true); assert(b3 == 0b0010);
b3.set(position_t(1), false); assert(b3 == 0);
b3.flip(position_t(2)); assert(b3 == 0b0100);
b3.reset(position_t(2)); assert(b3 == 0);

// subscript operator[] is supported:
b3[2] = true; assert(true == b3[2]);

// other operations:
assert(b3.count() == 1);
assert(b3.size() == 4);
assert(b3.to_ullong() == 0b0100ULL);
assert(b3.to_string() == "0100");


b1:0000; b2:1010; b3:0011; b4:00000110

See also

vector<bool> space-efficient dynamic bitset
(class template specialization)
Bit manipulation (C++20) utilities to access, manipulate, and process individual
bits and bit sequences