std::bitset<N>:: bitset

From cppreference.com

	(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)

bit positions to the corresponding bit values of val , where

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)

is less than

, 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 .

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	`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

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