std::bitset<N>::bitset

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison (C++20) three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)    is_eqis_neqis_ltis_lteqis_gtis_gteq (C++20)(C++20)(C++20)(C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20) bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator> rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)    cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17)

 

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)

 

	(1)
bitset();			(until C++11)
constexpr bitset() noexcept;			(since C++11)
		(2)
bitset( unsigned long val );				(until C++11)
constexpr bitset( unsigned long long val ) noexcept;				(since C++11)
template< class CharT, class Traits, class Alloc > explicit bitset( const std::basic_string<CharT, Traits, Alloc>& str,                  typename std::basic_string<CharT, Traits, Alloc>::size_type                      pos = 0,                  typename std::basic_string<CharT, Traits, Alloc>::size_type                      n = std::basic_string<CharT, Traits, Alloc>::npos,                  CharT zero = CharT('0'),                  CharT one = CharT('1') );			(3)	(constexpr since C++23)
template< class CharT, class Traits > constexpr explicit bitset( std::basic_string_view<CharT, Traits> str,                            std::size_t pos = 0,                            std::size_t n = std::size_t(-1),                            CharT zero = CharT('0'),                            CharT one = CharT('1') );			(4)	(since C++26)
template< class CharT > explicit bitset( const CharT* str,                  std::size_t n = std::size_t(-1),                  CharT zero = CharT('0'),                  CharT one = CharT('1') );			(5)	(since C++11) (constexpr since C++23)

Constructs a new bitset from one of several optional data sources:

1) Default constructor. Constructs a bitset with all bits set to zero.

2) Constructs a bitset, initializing the first (rightmost, least significant) M bit positions to the corresponding bit values of val, where M is the smaller of

• N, and

the number of bits in the value representation of unsigned long. For typical implementations, it is 32 or 64.	(until C++11)
the number of bits in the value representation of unsigned long long. For typical implementations, it is 64.	(since C++11)

If M is less than N, the remaining bit positions are initialized to zeroes.

3) Constructs a bitset using the characters in the std::basic_string str. An optional starting position pos and length n can be provided, as well as characters denoting alternate values for set (one) and unset (zero) bits. Traits::eq() is used to compare the character values.

The effective length of the initializing string is std::min(n, str.size() - pos).

If pos > str.size(), this constructor throws std::out_of_range. If any character examined in str is not zero or one, this constructor throws std::invalid_argument.

4) Similar to (3), but uses a std::basic_string_view instead of a std::basic_string.

5) Similar to (3), but uses a const CharT* instead of a std::basic_string. Equivalent to

bitset(n == std::size_t(-1)
          ? basic_string<CharT>(str)
          : basic_string<CharT>(str, n), 0, n, zero, one)

This constructor may dynamically allocate memory, although implementations generally avoid dynamic allocation.	(until C++26)
This constructor does not dynamically allocate memory, as if only std::basic_string_view is involved.	(since C++26)

Parameters

val	-	number used to initialize the bitset
str	-	string used to initialize the bitset
pos	-	a starting offset into str
n	-	number of characters to use from str
one	-	alternate character for set bits in str
zero	-	alternate character for unset bits in str

Exceptions

3,4) std::out_of_range if pos > str.size(), std::invalid_argument if any character is not one or zero.

5) std::invalid_argument if any character is not one or zero.

Example

Run this code

#include <bitset>
#include <climits>
#include <iostream>
#include <string>
 
int main()
{
    // empty constructor (1)
    std::bitset<8> b1; // [0,0,0,0,0,0,0,0]
 
    // unsigned long long constructor (2)
    std::bitset<8> b2(42);          // [0,0,1,0,1,0,1,0]
    std::bitset<70> bl(ULLONG_MAX); // [0,0,0,0,0,0,1,1,1,...,1,1,1] in C++11
    std::bitset<8> bs(0xfff0);      // [1,1,1,1,0,0,0,0]
 
    // string constructor (3)
    std::string bit_string = "110010";
    std::bitset<8> b3(bit_string);       // [0,0,1,1,0,0,1,0]
    std::bitset<8> b4(bit_string, 2);    // [0,0,0,0,0,0,1,0]
    std::bitset<8> b5(bit_string, 2, 3); // [0,0,0,0,0,0,0,1]
 
    // string constructor using custom zero/one digits (3)
    std::string alpha_bit_string = "aBaaBBaB";
    std::bitset<8> b6(alpha_bit_string, 0, alpha_bit_string.size(),
                      'a', 'B');         // [0,1,0,0,1,1,0,1]
 
    // char* constructor using custom digits (5)
    std::bitset<8> b7("XXXXYYYY", 8, 'X', 'Y'); // [0,0,0,0,1,1,1,1]
 
    std::cout <<   "b1: " << b1 << "\nb2: " << b2 << "\nbl: " << bl
              << "\nbs: " << bs << "\nb3: " << b3 << "\nb4: " << b4
              << "\nb5: " << b5 << "\nb6: " << b6 << "\nb7: " << b7 << '\n';
}

Possible output:

b1: 00000000
b2: 00101010
bl: 0000001111111111111111111111111111111111111111111111111111111111111111
bs: 11110000
b3: 00110010
b4: 00000010
b5: 00000001
b6: 01001101
b7: 00001111

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 396	C++98	the values of the zero and one characters for overload (3) were ​0​ and 1 (which do not correspond to '0' and '1')	added parameters to provide values for these characters
LWG 457	C++98	M is the smaller of N and the value CHAR_BIT * sizeof(unsigned long) for overload (2), but unsigned long is not guaranteed to use all its bits to represent its value	consider the number of bits of the value representation instead

See also

set	sets bits to true or given value (public member function)
reset	sets bits to false (public member function)