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bitset<N>


Category: containers	Component type: type

Description

Bitset is very similar to vector<bool> (also known as bit_vector): it contains a collection of bits, and provides constant-time access to each bit. There are two main differences between bitset and vector<bool>. First, the size of a bitset cannot be changed: bitset's template parameter N, which specifies the number of bits in the bitset, must be an integer constant. Second, bitset is not a Sequence; in fact, it is not an STL Container at all. It does not have iterators, for example, or begin() and end() member functions. Instead, bitset's interface resembles that of unsigned integers. It defines bitwise arithmetic operators such as &=, |=, and ^=.

In general, bit 0 is the least significant bit and bit N-1 is the most significant bit.

Example

int main() {
  const bitset<12> mask(2730ul); 
  cout << "mask =      " << mask << endl;

  bitset<12> x;

  cout << "Enter a 12-bit bitset in binary: " << flush;
  if (cin >> x) {
    cout << "x =        " << x << endl;
    cout << "As ulong:  " << x.to_ulong() << endl;
    cout << "And with mask: " << (x & mask) << endl;
    cout << "Or with mask:  " << (x | mask) << endl;
  }
}

Definition

Defined in the standard header bitset.

Template parameters

Parameter	Description	Default
`N`	A nonzero constant of type `size_t`: the number of bits that the bitset contains.

Model of

Assignable, Default Constructible, Equality Comparable

Type requirements

N is a constant integer expression of a type convertible to size_t, and N is a positive number.

Public base classes

None.

Members

Member	Where defined	Description
`reference`	`bitset`	A proxy class that acts as a reference to a single bit.
`bitset()`	Default Constructible	The default constructor. All bits are initially zero.
`bitset(unsigned long val)`	`bitset`	Conversion from unsigned long.
`bitset(const bitset&)`	Assignable	Copy constructor.
`bitset& operator=(const bitset&)`	Assignable	Assignment operator.
template<class Char, class Traits, class Alloc> explicit bitset(const basic_string<Char,Traits,Alloc>& s, size_t pos = 0, size_t n = basic_string<Char,Traits,Alloc>::npos)	`bitset`	Conversion from string.
`bitset& operator&=(const bitset&)`	`bitset`	Bitwise and.
`bitset& operator\|=(const bitset&)`	`bitset`	Bitwise inclusive or.
`bitset& operator^=(const bitset&)`	`bitset`	Bitwise exclusive or.
`bitset& operator<<=(size_t)`	`bitset`	Left shift.
`bitset& operator>>=(size_t)`	`bitset`	Right shift.
`bitset operator<<(size_t n) const`	`bitset`	Returns a copy of `*this` shifted left by `n` bits.
`bitset operator>>(size_t n) const`	`bitset`	Returns a copy of `*this` shifted right by `n` bits.
`bitset& set()`	`bitset`	Sets every bit.
`bitset& flip()`	`bitset`	Flips the value of every bit.
`bitset operator~() const`	`bitset`	Returns a copy of `*this` with all of its bits flipped.
`bitset& reset()`	`bitset`	Clears every bit.
`bitset& set(size_t n, int val = 1)`	`bitset`	Sets bit `n` if `val` is nonzero, and clears bit `n` if `val` is zero.
`bitset& reset(size_t n)`	`bitset`	Clears bit `n`.
`bitset flip(size_t n)`	`bitset`	Flips bit `n`.
`size_t size() const`	`bitset`	Returns `N`.
`size_t count() const`	`bitset`	Returns the number of bits that are set.
`bool any() const`	`bitset`	Returns `true` if any bits are set.
`bool none() const`	`bitset`	Returns `true` if no bits are set.
`bool test(size_t n) const`	`bitset`	Returns `true` if bit `n` is set.
`reference operator[](size_t n)`	`bitset`	Returns a `reference` to bit `n`.
`bool operator[](size_t n) const`	`bitset`	Returns `true` if bit `n` is set.
`unsigned long to_ulong() const`	`bitset`	Returns an `unsigned long` corresponding to the bits in `*this`.
template<class Char, class Traits, class Alloc> basic_string<Char,Traits,Alloc> to_string() const	`bitset`	Returns a string representation of `*this`.
`bool operator==(const bitset&) const`	Equality Comparable	The equality operator.
`bool operator!=(const bitset&) const`	Equality Comparable	The inequality operator.
`bitset operator&(const bitset&, const bitset&)`	`bitset`	Bitwise and of two bitsets. This is a global function, not a member function.
`bitset operator\|(const bitset&, const bitset&)`	`bitset`	Bitwise or of two bitsets. This is a global function, not a member function.
`bitset operator^(const bitset&, const bitset&)`	`bitset`	Bitwise exclusive or of two bitsets. This is a global function, not a member function.
template <class Char, class Traits, size_t N> basic_istream<Char,Traits>& operator>>(basic_istream<Char,Traits>&, bitset<N>&)	`bitset`	Extract a `bitset` from an input stream.
template <class Char, class Traits, size_t N> basic_ostream<Char,Traits>& operator>>(basic_ostream<Char,Traits>&, const bitset<N>&)	`bitset`	Output a `bitset` to an output stream.

New members

These members are not defined in the Assignable, Default Constructible, or Equality Comparable requirements, but are specific to bitset.

Member	Description
`reference`	A proxy class that acts as a reference to a single bit. It contains an assignment operator, a conversion to `bool`, an `operator~`, and a member function `flip`. It exists only as a helper class for `bitset`'s `operator[]`. That is, it supports the expressions `x = b[i]`, `b[i] = x`, `b[i] = b[j]`, `x = ~b[i]`, and `b[i].flip()`. (Where `b` is a `bitset` and `x` is a `bool`.)
`bitset(unsigned long val)`	Conversion from unsigned long. Constructs a bitset, initializing the first `min(N, sizeof(unsigned long) * CHAR_BIT)` bits to the corresponding bits in `val` and all other bits, if any, to zero.
template<class Char, class Traits, class Alloc> explicit bitset(const basic_string<Char,Traits,Alloc>& s, size_t pos = 0, size_t n = basic_string<Char,Traits,Alloc>::npos)	Conversion from string. Constructs a bitset, initializing the first `M` bits to the corresponding characters in `s`, where `M` is defined as `min(N, min(s.size() - pos, n))`. Note that the highest character position in `s`, not the lowest, corresponds to the least significant bit. That is, character position `pos + M - 1 - i` corresponds to bit `i`. So, for example, `bitset(string("1101"))` is the same as `bitset(13ul)`. This function throws `out_of_range` if `pos > s.size()`, and `invalid_argument` if any of the characters used to initialize the bits are anything other than `0` or `1`.
`bitset& operator&=(const bitset&)`	Bitwise and.
`bitset& operator\|=(const bitset&)`	Bitwise inclusive or.
`bitset& operator^=(const bitset&)`	Bitwise exclusive or.
`bitset& operator<<=(size_t n)`	Left shift, where bit `0` is considered the least significant bit. Bit `i` takes on the previous value of bit `i - n`, or zero if no such bit exists.
`bitset& operator>>=(size_t n)`	Right shift, where bit `0` is considered the least significant bit. Bit `i` takes on the previous value of bit `i + n`, or zero if no such bit exists.
`bitset operator<<(size_t n) const`	Returns a copy of `*this` shifted left by `n` bits. Note that the expression `b << n` is equivalent to constructing a temporary copy of `b` and then using `operator<<=`.
`bitset operator>>(size_t n) const`	Returns a copy of `*this` shifted right by `n` bits. Note that the expression `b >> n` is equivalent to constructing a temporary copy of `b` and then using `operator>>=`.
`bitset& set()`	Sets every bit.
`bitset& flip()`	Flips the value of every bit.
`bitset operator~() const`	Returns a copy of `*this` with all of its bits flipped.
`bitset& reset()`	Clears every bit.
`bitset& set(size_t n, int val = 1)`	Sets bit `n` if `val` is nonzero, and clears bit `n` if `val` is zero. Throws `out_of_range` if `n >= N`.
`bitset& reset(size_t n)`	Clears bit `n`. Throws `out_of_range` if `n >= N`.
`bitset flip(size_t n)`	Flips bit `n`. Throws `out_of_range` if `n >= N`.
`size_t size() const`	Returns `N`.
`size_t count() const`	Returns the number of bits that are set.
`bool any() const`	Returns `true` if any bits are set.
`bool none() const`	Returns `true` if no bits are set.
`bool test(size_t n) const`	Returns `true` if bit `n` is set. Throws `out_of_range` if `n >= N`.
`reference operator[](size_t n)`	Returns a `reference` to bit `n`. Note that `reference` is a proxy class with an assignment operator and a conversion to `bool`, which allows you to use `operator[]` for assignment. That is, you can write both `x = b[n]` and `b[n] = x`.
`bool operator[](size_t n) const`	Returns `true` if bit `n` is set.
`unsigned long to_ulong() const`	Returns an `unsigned long` corresponding to the bits in `this`. Throws `overflow_error` if it is impossible to represent `this` as an `unsigned long`. (That is, if `N` is larger than the number of bits in an `unsigned long` and if any of the high-order bits are set.
template<class Char, class Traits, class Alloc> basic_string<Char,Traits,Alloc> to_string() const	Returns a string representation of `this`: each character is `1` if the corresponding bit is set, and `0` if it is not. In general, character position `i` corresponds to bit position `N - 1 - i`. Note that this member function relies on two language features, member templates* and explicit function template argument specification, that are not yet universally available; this member function is disabled for compilers that do not support those features. Note also that the syntax for calling this member function is somewhat cumbersome. To convert a bitset `b` to an ordinary string, you must write b.template to_string<char, char_traits<char>, allocator<char> >()
`bitset operator&(const bitset&, const bitset&)`	Bitwise and of two bitsets. This is a global function, not a member function. Note that the expression `b1 & b2` is equivalent to creating a temporary copy of `b1`, using `operator&=`, and returning the temporary copy.
`bitset operator\|(const bitset&, const bitset&)`	Bitwise or of two bitsets. This is a global function, not a member function. Note that the expression `b1 \| b2` is equivalent to creating a temporary copy of `b1`, using `operator\|=`, and returning the temporary copy.
`bitset operator^(const bitset&, const bitset&)`	Bitwise exclusive or of two bitsets. This is a global function, not a member function. Note that the expression `b1 ^ b2` is equivalent to creating a temporary copy of `b1`, using `operator^=`, and returning the temporary copy.
template <class Char, class Traits, size_t N> basic_istream<Char, Traits>& operator>>(basic_istream<Char,Traits>& is, bitset<N>& x)	Extract a `bitset` from an input stream. This function first skips whitespace, then extracts up to `N` characters from the input stream. It stops either when it has successfully extracted `N` character, or when extraction fails, or when it sees a character that is something other than `1` (in which case it does not extract that character). It then assigns a value to the `bitset` in the same way as if it were initializing the `bitset` from a string. So, for example, if the input stream contains the characters `"1100abc"`, it will assign the value `12ul` to the `bitset`, and the next character read from the input stream will be `a`.
template <class Char, class Traits, size_t N> basic_ostream<Char,Traits>& operator>>(basic_ostream<Char,Traits>& os, const bitset<N>& x)	Output a `bitset` to an output stream. This function behaves as if it converts the `bitset` to a string and then writes that string to the output stream. That is, it is equivalent to os << x.template to_string<Char,Traits,allocator<Char> >()