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std::bitset<N>::bitset

From cppreference.com
< cpp‎ | utility‎ | bitset
 
 
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(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)

Contents

[edit] 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

[edit] 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.

[edit] 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)

[edit] Example

#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

[edit] 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

[edit] See also

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