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std::bitset<N>:: bitset

From cppreference.net
C++
Utilities library
std::bitset
bitset ( ) ;
(1) (noexcept since C++11)
(constexpr 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 from an unsigned integer val .
Given the number of bits in the value representation of unsigned long (until C++11) unsigned long long (since C++11) as S :
  • The first (rightmost, least significant) std:: min ( S, N ) bit positions are initialized with the corresponding bit values of val .
  • If S is less than N , the remaining bit positions are initialized to zeroes.
3) Constructs a bitset using the characters in 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 ) .
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:: basic_string < CharT > :: npos
? std:: basic_string < CharT > ( str )
: std:: basic_string < CharT > ( str, n ) , 0 , n, zero, one ) .

(until C++26)

Equivalent to bitset ( n == std:: basic_string_view < CharT > :: npos
? std:: basic_string_view < CharT > ( str )
: std:: basic_string_view < CharT > ( str, n ) , 0 , n, zero, one ) .

(since C++26)

Contents

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
zero - alternate character for unset bits in str
one - alternate character for set 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 .

Notes

Feature-test macro Value Std Feature
__cpp_lib_constexpr_bitset 202207L (C++23) A more constexpr std::bitset , overloads ( 3,5 )
__cpp_lib_bitset 202306L (C++26) Interfacing std::bitset with std::string_view , ( 4 )

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 S was 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
LWG 2250 C++98 the behavior was undefined if pos > str. size ( ) is true always throws an
exception in this case

See also

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