std::bitset::bitset - cppreference.com (original) (raw)
| 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:
Default constructor. Constructs a bitset with all bits set to zero.
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.
- 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).
- 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) |
[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 |
| zero | - | alternate character for unset bits in str |
| one | - | alternate character for set bits in str |
[edit] Exceptions
[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 #include #include #include 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 providevalues for these characters |
| LWG 457 | C++98 | S was CHAR_BIT * sizeof(unsigned long)for overload (2), but unsigned long is notguaranteed to use all its bits to represent its value | consider the numberof bits of the valuerepresentation instead |
| LWG 2250 | C++98 | the behavior was undefined if pos > str.size() is true | always throws anexception in this case |
[edit] See also
| | sets bits to true or given value (public member function) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | sets bits to false (public member function) [edit] |