22 General utilities library [utilities]

22.9 Bitsets [bitset]

22.9.1 Header <bitset> synopsis [bitset.syn]

The header defines a class template and several related functions for representing and manipulating fixed-size sequences of bits.

#include <string> // see [string.syn] #include <iosfwd> // for istream ([istream.syn]), ostream ([ostream.syn]), see [iosfwd.syn] namespace std { template<size_t N> class bitset; // [bitset.operators], bitset operators template<size_t N> constexpr bitset<N> operator&(const bitset<N>&, const bitset<N>&) noexcept; template<size_t N> constexpr bitset<N> operator|(const bitset<N>&, const bitset<N>&) noexcept; template<size_t N> constexpr bitset<N> operator^(const bitset<N>&, const bitset<N>&) noexcept; template<class charT, class traits, size_t N> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& is, bitset<N>& x); template<class charT, class traits, size_t N> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const bitset<N>& x); }

22.9.2 Class template bitset [template.bitset]

22.9.2.1 General [template.bitset.general]

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namespace std { template<size_t N> class bitset { public: // bit reference class reference { public: constexpr reference(const reference&) = default; constexpr ~reference(); constexpr reference& operator=(bool x) noexcept; // for b[i] = x; constexpr reference& operator=(const reference&) noexcept; // for b[i] = b[j]; constexpr bool operator~() const noexcept; // flips the bit constexpr operator bool() const noexcept; // for x = b[i]; constexpr reference& flip() noexcept; // for b[i].flip(); }; // [bitset.cons], constructors constexpr bitset() noexcept; constexpr bitset(unsigned long long val) noexcept; template<class charT, class traits, class Allocator> constexpr explicit bitset( const basic_string<charT, traits, Allocator>& str, typename basic_string<charT, traits, Allocator>::size_type pos = 0, typename basic_string<charT, traits, Allocator>::size_type n = basic_string<charT, traits, Allocator>::npos, charT zero = charT('0'), charT one = charT('1')); template<class charT, class traits> constexpr explicit bitset( basic_string_view<charT, traits> str, typename basic_string_view<charT, traits>::size_type pos = 0, typename basic_string_view<charT, traits>::size_type n = basic_string_view<charT, traits>::npos, charT zero = charT('0'), charT one = charT('1')); template<class charT> constexpr explicit bitset( const charT* str, typename basic_string_view<charT>::size_type n = basic_string_view<charT>::npos, charT zero = charT('0'), charT one = charT('1')); // [bitset.members], bitset operations constexpr bitset& operator&=(const bitset& rhs) noexcept; constexpr bitset& operator|=(const bitset& rhs) noexcept; constexpr bitset& operator^=(const bitset& rhs) noexcept; constexpr bitset& operator<<=(size_t pos) noexcept; constexpr bitset& operator>>=(size_t pos) noexcept; constexpr bitset operator<<(size_t pos) const noexcept; constexpr bitset operator>>(size_t pos) const noexcept; constexpr bitset& set() noexcept; constexpr bitset& set(size_t pos, bool val = true); constexpr bitset& reset() noexcept; constexpr bitset& reset(size_t pos); constexpr bitset operator~() const noexcept; constexpr bitset& flip() noexcept; constexpr bitset& flip(size_t pos); // element access constexpr bool operator[](size_t pos) const; constexpr reference operator[](size_t pos); constexpr unsigned long to_ulong() const; constexpr unsigned long long to_ullong() const; template<class charT = char, class traits = char_traits<charT>, class Allocator = allocator<charT>> constexpr basic_string<charT, traits, Allocator> to_string(charT zero = charT('0'), charT one = charT('1')) const; // observers constexpr size_t count() const noexcept; constexpr size_t size() const noexcept; constexpr bool operator==(const bitset& rhs) const noexcept; constexpr bool test(size_t pos) const; constexpr bool all() const noexcept; constexpr bool any() const noexcept; constexpr bool none() const noexcept; }; // [bitset.hash], hash support template<class T> struct hash; template<size_t N> struct hash<bitset<N>>; }

The class template bitset<N> describes an object that can store a sequence consisting of a fixed number of bits, N.

Each bit represents either the value zero (reset) or one (set).

To toggle a bit is to change the value zero to one, or the value one to zero.

Each bit has a non-negative position pos.

When converting between an object of class bitset<N> and a value of some integral type, bit position pos corresponds to the bit value 1 << pos.

The integral value corresponding to two or more bits is the sum of their bit values.

The functions described in [template.bitset] can report three kinds of errors, each associated with a distinct exception:

(3.1)
an invalid-argument error is associated with exceptions of type invalid_argument ([invalid.argument]);
(3.2)
an out-of-range error is associated with exceptions of type out_of_range ([out.of.range]);
(3.3)
an overflow error is associated with exceptions of type overflow_error ([overflow.error]).

22.9.2.2 Constructors [bitset.cons]

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constexpr bitset() noexcept;

Effects: Initializes all bits in *this to zero.

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constexpr bitset(unsigned long long val) noexcept;

Effects: Initializes the first M bit positions to the corresponding bit values in val.

M is the smaller of N and the number of bits in the value representation ([basic.types.general]) of unsigned long long.

If M < N, the remaining bit positions are initialized to zero.

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template<class charT, class traits, class Allocator>
  constexpr explicit bitset(
    const basic_string<charT, traits, Allocator>& str,
    typename basic_string<charT, traits, Allocator>::size_type pos = 0,
    typename basic_string<charT, traits, Allocator>::size_type n
      = basic_string<charT, traits, Allocator>::npos,
    charT zero = charT('0'),
    charT one = charT('1'));
template<class charT, class traits>
  constexpr explicit bitset(
    basic_string_view<charT, traits> str,
    typename basic_string_view<charT, traits>::size_type pos = 0,
    typename basic_string_view<charT, traits>::size_type n
      = basic_string_view<charT, traits>::npos,
    charT zero = charT('0'),
    charT one = charT('1'));

Effects: Determines the effective length rlen of the initializing string as the smaller of n and str.size() - pos.

Initializes the first M bit positions to values determined from the corresponding characters in the string str.

M is the smaller of N and rlen.

An element of the constructed object has value zero if the corresponding character in str, beginning at position pos, is zero.

Otherwise, the element has the value one.

Character position pos + M - 1 corresponds to bit position zero.

Subsequent decreasing character positions correspond to increasing bit positions.

If M < N, remaining bit positions are initialized to zero.

The function uses traits::eq to compare the character values.

Throws: out_of_range if pos > str.size() or invalid_argument if any of the rlen characters in str beginning at position pos is other than zero or one.

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template<class charT>
  constexpr explicit bitset(
    const charT* str,
    typename basic_string_view<charT>::size_type n = basic_string_view<charT>::npos,
    charT zero = charT('0'),
    charT one = charT('1'));

Effects: As if by: bitset(n == basic_string_view<charT>::npos ? basic_string_view<charT>(str) : basic_string_view<charT>(str, n), 0, n, zero, one)

22.9.2.3 Members [bitset.members]

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constexpr bitset& operator&=(const bitset& rhs) noexcept;

Effects: Clears each bit in *this for which the corresponding bit in rhs is clear, and leaves all other bits unchanged.

Returns: *this.

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constexpr bitset& operator|=(const bitset& rhs) noexcept;

Effects: Sets each bit in *this for which the corresponding bit in rhs is set, and leaves all other bits unchanged.

Returns: *this.

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constexpr bitset& operator^=(const bitset& rhs) noexcept;

Effects: Toggles each bit in *this for which the corresponding bit in rhs is set, and leaves all other bits unchanged.

Returns: *this.

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constexpr bitset& operator<<=(size_t pos) noexcept;

Effects: Replaces each bit at position I in *this with a value determined as follows:

(7.1)
If I < pos, the new value is zero;
(7.2)
If I >= pos, the new value is the previous value of the bit at position I - pos.

Returns: *this.

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constexpr bitset& operator>>=(size_t pos) noexcept;

Effects: Replaces each bit at position I in *this with a value determined as follows:

(9.1)
If pos >= N - I, the new value is zero;
(9.2)
If pos < N - I, the new value is the previous value of the bit at position I + pos.

Returns: *this.

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constexpr bitset operator<<(size_t pos) const noexcept;

Returns: bitset(*this) <<= pos.

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constexpr bitset operator>>(size_t pos) const noexcept;

Returns: bitset(*this) >>= pos.

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constexpr bitset& set() noexcept;

Effects: Sets all bits in *this.

Returns: *this.

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constexpr bitset& set(size_t pos, bool val = true);

Effects: Stores a new value in the bit at position pos in *this.

If val is true, the stored value is one, otherwise it is zero.

Returns: *this.

Throws: out_of_range if pos does not correspond to a valid bit position.

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constexpr bitset& reset() noexcept;

Effects: Resets all bits in *this.

Returns: *this.

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constexpr bitset& reset(size_t pos);

Effects: Resets the bit at position pos in *this.

Returns: *this.

Throws: out_of_range if pos does not correspond to a valid bit position.

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constexpr bitset operator~() const noexcept;

Effects: Constructs an object x of class bitset and initializes it with *this.

Returns: x.flip().

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constexpr bitset& flip() noexcept;

Effects: Toggles all bits in *this.

Returns: *this.

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constexpr bitset& flip(size_t pos);

Effects: Toggles the bit at position pos in *this.

Returns: *this.

Throws: out_of_range if pos does not correspond to a valid bit position.

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constexpr bool operator[](size_t pos) const;

Preconditions: pos is valid.

Returns: true if the bit at position pos in *this has the value one, otherwise false.

Throws: Nothing.

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constexpr bitset::reference operator[](size_t pos);

Preconditions: pos is valid.

Returns: An object of type bitset::reference such that (*this)[pos] == this->test(pos), and such that (*this)[pos] = val is equivalent to this->set(pos, val).

Throws: Nothing.

Remarks: For the purpose of determining the presence of a data race ([intro.multithread]), any access or update through the resulting reference potentially accesses or modifies, respectively, the entire underlying bitset.

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constexpr unsigned long to_ulong() const;

Returns: x.

Throws: overflow_error if the integral value x corresponding to the bits in *this cannot be represented as type unsigned long.

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constexpr unsigned long long to_ullong() const;

Returns: x.

Throws: overflow_error if the integral value x corresponding to the bits in *this cannot be represented as type unsigned long long.

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template<class charT = char,
         class traits = char_traits<charT>,
         class Allocator = allocator<charT>>
  constexpr basic_string<charT, traits, Allocator>
    to_string(charT zero = charT('0'), charT one = charT('1')) const;

Effects: Constructs a string object of the appropriate type and initializes it to a string of length N characters.

Each character is determined by the value of its corresponding bit position in *this.

Character position N - 1 corresponds to bit position zero.

Subsequent decreasing character positions correspond to increasing bit positions.

Bit value zero becomes the character zero, bit value one becomes the character one.

Returns: The created object.

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constexpr size_t count() const noexcept;

Returns: A count of the number of bits set in *this.

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constexpr size_t size() const noexcept;

Returns: N.

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constexpr bool operator==(const bitset& rhs) const noexcept;

Returns: true if the value of each bit in *this equals the value of the corresponding bit in rhs.

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constexpr bool test(size_t pos) const;

Returns: true if the bit at position pos in *this has the value one.

Throws: out_of_range if pos does not correspond to a valid bit position.

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constexpr bool all() const noexcept;

Returns: count() == size().

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constexpr bool any() const noexcept;

Returns: count() != 0.

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constexpr bool none() const noexcept;

Returns: count() == 0.

22.9.3 bitset hash support [bitset.hash]

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template<size_t N> struct hash<bitset<N>>;

The specialization is enabled ([unord.hash]).

22.9.4 bitset operators [bitset.operators]

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template<size_t N>
  constexpr bitset<N> operator&(const bitset<N>& lhs, const bitset<N>& rhs) noexcept;

Returns: bitset<N>(lhs) &= rhs.

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template<size_t N>
  constexpr bitset<N> operator|(const bitset<N>& lhs, const bitset<N>& rhs) noexcept;

Returns: bitset<N>(lhs) |= rhs.

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template<size_t N>
  constexpr bitset<N> operator^(const bitset<N>& lhs, const bitset<N>& rhs) noexcept;

Returns: bitset<N>(lhs) ^= rhs.

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template<class charT, class traits, size_t N>
  basic_istream<charT, traits>&
    operator>>(basic_istream<charT, traits>& is, bitset<N>& x);

A formatted input function ([istream.formatted]).

Effects: Extracts up to N characters from is.

Stores these characters in a temporary object str of type basic_string<charT, traits>, then evaluates the expression x = bitset<N>(str).

Characters are extracted and stored until any of the following occurs:

(5.1)
N characters have been extracted and stored;
(5.2)
end-of-file occurs on the input sequence;
(5.3)
the next input character is neither is.widen('0') nor is.widen('1') (in which case the input character is not extracted).

If N > 0 and no characters are stored in str, ios_base::failbit is set in the input function's local error state before setstate is called.

Returns: is.

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template<class charT, class traits, size_t N>
  basic_ostream<charT, traits>&
    operator<<(basic_ostream<charT, traits>& os, const bitset<N>& x);

Returns: os << x.template to_string<charT, traits, allocator<charT>>( use_facet<ctype<charT>>(os.getloc()).widen('0'), use_facet<ctype<charT>>(os.getloc()).widen('1')) (see [ostream.formatted]).