# std::bitset

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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 integers. For the purpose of the string representation and of naming directions for shift operations, the sequence is thought of as having its lowest indexed elements at the right, as in the binary representation of integers.

`bitset` meets the requirements of CopyConstructible and CopyAssignable.

All member functions of `std::bitset` are constexpr: it is possible to create and use `std::bitset` objects in the evaluation of a constant expression. | (since C++23)

### Template parameters

N | - | the number of bits to allocate storage for

### Member types

reference | proxy class representing a reference to a bit (class)

### Member functions

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

##### Element access

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

##### Capacity

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

##### Modifiers

operator&=operator|=operator^=operator~ | performs binary AND, OR, XOR and NOT (public member function)
operator<<=operator>>=operator<<operator>> | performs binary shift left and shift right (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)

##### Conversions

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 (C++11) | returns an unsigned long long integer representation of the data (public member function)

### Non-member functions

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

### Helper classes

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

### Notes

If the size of a bit-set is not known at compile time, or it is necessary to change its size at run-time, the dynamic types such as `std::vector<bool>` or `boost::dynamic_bitset<>` may be used instead.

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_constexpr_bitset` | `202207L` | (C++23) | A more constexpr `std::bitset`
`__cpp_lib_bitset` | `202306L` | (C++26) | Interfacing `std::bitset` with std::string_view

### Example

Run this code

    #include <bitset>
    #include <cassert>
    #include <cstddef>
    #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 also be constexpr since C++23
        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");
    }

Output:

    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

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