
 

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 constanttime 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 N1 is the most significant bit.
Example
int main() {
const bitset<12> mask(2730ul);
cout << "mask = " << mask << endl;
bitset<12> x;
cout << "Enter a 12bit 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, DefaultConstructible, EqualityComparable
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()  DefaultConstructible  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  EqualityComparable  The equality operator. 
bool operator!=(const bitset&) const  EqualityComparable  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, DefaultConstructible, or EqualityComparable 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 highorder 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> >()

Notes
See also
Vector , bit_vector , basic_string
