dynamic_bitset<Block, Allocator>
Contents
 Description
 Synopsis
 Definitions
 Examples
 Rationale
 Header Files
 Template Parameters
 Concepts modeled
 Type requirements
 Public base classes
 Nested type names
 Public data members
 Constructors
 Destructor
 Member functions
 Nonmember functions
 Exception guarantees
 Changes from previous version(s)
 See also
 Acknowledgements
Description
The dynamic_bitset class represents a set of bits. It provides accesses to the value of individual bits via an operator[] and provides all of the bitwise operators that one can apply to builtin integers, such as operator& and operator<<. The number of bits in the set is specified at runtime via a parameter to the constructor of the dynamic_bitset.
The dynamic_bitset class is nearly identical to the std::bitset class. The difference is that the size of the dynamic_bitset (the number of bits) is specified at runtime during the construction of a dynamic_bitset object, whereas the size of a std::bitset is specified at compiletime through an integer template parameter.
The main problem that dynamic_bitset is designed to solve is that of representing a subset of a finite set. Each bit represents whether an element of the finite set is in the subset or not. As such the bitwise operations of dynamic_bitset, such as operator& and operator, correspond to set operations, such as intersection and union.
Synopsis
namespace boost { template <typename Block, typename Allocator> class dynamic_bitset { public: typedef Block block_type; typedef Allocator allocator_type; typedef implementationdefined size_type; static const int bits_per_block = implementationdefined; static const size_type npos = implementationdefined; class reference { void operator&(); // not defined public: // An automatically generated copy constructor. reference& operator=(bool value); reference& operator=(const reference& rhs); reference& operator=(bool value); reference& operator&=(bool value); reference& operator^=(bool value); reference& operator=(bool value); bool operator~() const; operator bool() const; reference& flip(); }; typedef bool const_reference; dynamic_bitset(); explicit dynamic_bitset(const Allocator& alloc); explicit dynamic_bitset(size_type num_bits, unsigned long value = 0, const Allocator& alloc = Allocator()); template <typename CharT, typename Traits, typename Alloc> explicit dynamic_bitset(const std::basic_string<CharT, Traits, Alloc>& s, 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, const Allocator& alloc = Allocator()); template <typename BlockInputIterator> dynamic_bitset(BlockInputIterator first, BlockInputIterator last, const Allocator& alloc = Allocator()); dynamic_bitset(const dynamic_bitset& b); dynamic_bitset(dynamic_bitset&& b); void swap(dynamic_bitset& b); dynamic_bitset& operator=(const dynamic_bitset& b); dynamic_bitset& operator=(dynamic_bitset&& b); allocator_type get_allocator() const; void resize(size_type num_bits, bool value = false); void clear(); void pop_back(); void push_back(bool bit); void append(Block block); template <typename BlockInputIterator> void append(BlockInputIterator first, BlockInputIterator last); dynamic_bitset& operator&=(const dynamic_bitset& b); dynamic_bitset& operator=(const dynamic_bitset& b); dynamic_bitset& operator^=(const dynamic_bitset& b); dynamic_bitset& operator=(const dynamic_bitset& b); dynamic_bitset& operator<<=(size_type n); dynamic_bitset& operator>>=(size_type n); dynamic_bitset operator<<(size_type n) const; dynamic_bitset operator>>(size_type n) const; dynamic_bitset& set(size_type n, size_type len, bool val); dynamic_bitset& set(size_type n, bool val = true); dynamic_bitset& set(); dynamic_bitset& reset(size_type n, size_type len); dynamic_bitset& reset(size_type n); dynamic_bitset& reset(); dynamic_bitset& flip(size_type n, size_type len); dynamic_bitset& flip(size_type n); dynamic_bitset& flip(); bool test(size_type n) const; bool test_set(size_type n, bool val = true); bool all() const; bool any() const; bool none() const; dynamic_bitset operator~() const; size_type count() const noexcept; reference operator[](size_type pos); bool operator[](size_type pos) const; unsigned long to_ulong() const; size_type size() const noexcept; size_type num_blocks() const noexcept; size_type max_size() const noexcept; bool empty() const noexcept; size_type capacity() const noexcept; void reserve(size_type num_bits); void shrink_to_fit(); bool is_subset_of(const dynamic_bitset& a) const; bool is_proper_subset_of(const dynamic_bitset& a) const; bool intersects(const dynamic_bitset& a) const; size_type find_first() const; size_type find_next(size_type pos) const; }; template <typename B, typename A> bool operator==(const dynamic_bitset<B, A>& a, const dynamic_bitset<B, A>& b); template <typename Block, typename Allocator> bool operator!=(const dynamic_bitset<Block, Allocator>& a, const dynamic_bitset<Block, Allocator>& b); template <typename B, typename A> bool operator<(const dynamic_bitset<B, A>& a, const dynamic_bitset<B, A>& b); template <typename Block, typename Allocator> bool operator<=(const dynamic_bitset<Block, Allocator>& a, const dynamic_bitset<Block, Allocator>& b); template <typename Block, typename Allocator> bool operator>(const dynamic_bitset<Block, Allocator>& a, const dynamic_bitset<Block, Allocator>& b); template <typename Block, typename Allocator> bool operator>=(const dynamic_bitset<Block, Allocator>& a, const dynamic_bitset<Block, Allocator>& b); template <typename Block, typename Allocator> dynamic_bitset<Block, Allocator> operator&(const dynamic_bitset<Block, Allocator>& b1, const dynamic_bitset<Block, Allocator>& b2); template <typename Block, typename Allocator> dynamic_bitset<Block, Allocator> operator(const dynamic_bitset<Block, Allocator>& b1, const dynamic_bitset<Block, Allocator>& b2); template <typename Block, typename Allocator> dynamic_bitset<Block, Allocator> operator^(const dynamic_bitset<Block, Allocator>& b1, const dynamic_bitset<Block, Allocator>& b2); template <typename Block, typename Allocator> dynamic_bitset<Block, Allocator> operator(const dynamic_bitset<Block, Allocator>& b1, const dynamic_bitset<Block, Allocator>& b2); template <typename Block, typename Allocator, typename CharT, typename Alloc> void to_string(const dynamic_bitset<Block, Allocator>& b, std::basic_string<CharT, Alloc>& s); template <typename Block, typename Allocator, typename BlockOutputIterator> void to_block_range(const dynamic_bitset<Block, Allocator>& b, BlockOutputIterator result); template <typename CharT, typename Traits, typename Block, typename Allocator> std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const dynamic_bitset<Block, Allocator>& b); template <typename CharT, typename Traits, typename Block, typename Allocator> std::basic_istream<CharT, Traits>& operator>>(std::basic_istream<CharT, Traits>& is, dynamic_bitset<Block, Allocator>& b); } // namespace boost
Definitions
Each bit represents either the Boolean value true or false (1 or 0). To set a bit is to assign it 1. To clear or reset a bit is to assign it 0. To flip a bit is to change the value to 1 if it was 0 and to 0 if it was 1. Each bit has a nonnegative position. A bitset x contains x.size() bits, with each bit assigned a unique position in the range [0,x.size()). The bit at position 0 is called the least significant bit and the bit at position size()  1 is the most significant bit. When converting an instance of dynamic_bitset to or from an unsigned long n, the bit at position i of the bitset has the same value as (n >> i) & 1.
Examples
Example 1 (setting and reading some bits)
Example 2 (creating some bitsets from integers)
Example 3 (performing input/output and some bitwise operations).
Rationale
dynamic_bitset is not a Container and does not provide iterators for the following reason:
 A container with a proxy reference type can not fulfill the container requirements as specified in the C++ standard (unless one resorts to strange iterator semantics). std::vector<bool> has a proxy reference type and does not fulfill the container requirements and as a result has caused many problems. One common problem is when people try to use iterators from std::vector<bool> with a Standard algorithm such as std::search. The std::search requirements say that the iterator must be a Forward Iterator, but the std::vector<bool>::iterator does not meet this requirement because of the proxy reference. Depending on the implementation, they may or not be a compile error or even a runtime error due to this misuse. For further discussion of the problem see Effective STL by Scott Meyers). So dynamic_bitset tries to avoid these problems by not pretending to be a container.
Some people prefer the name "toggle" to "flip". The name "flip" was chosen because that is the name used in std::bitset. In fact, most of the function names for dynamic_bitset were chosen for this reason.
dynamic_bitset does not throw exceptions when a precondition is violated (as is done in std::bitset). Instead assert is used. See the guidelines for Error and Exception Handling for the explanation.
Header Files
The class dynamic_bitset is defined in the header boost/dynamic_bitset.hpp. Also, there is a forward declaration for dynamic_bitset in the header boost/dynamic_bitset_fwd.hpp.
Template parameters
Parameter  Description  Default 

Block  The integer type in which the bits are stored.  unsigned long 
Allocator  The allocator type used for all internal memory management.  std::allocator<Block> 
Concepts Modeled
Assignable, Default Constructible, Equality Comparable, LessThan Comparable.Type requirements
Block is an unsigned integer type. Allocator satisfies the Standard requirements for an allocator.Public base classes
None.Nested type names
dynamic_bitset::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 dynamic_bitset's operator[]. The following table describes the valid operations on the reference type. Assume that b is an instance of dynamic_bitset, i, j are of size_type and in the range [0,b.size()). Also, note that when we write b[i] we mean an object of type reference that was initialized from b[i]. The variable x is a bool.
Expression  Semantics 

x = b[i]  Assign the ith bit of b to x. 
(bool)b[i]  Return the ith bit of b. 
b[i] = x  Set the ith bit of b to the value of x and return b[i]. 
b[i] = x  Or the ith bit of b with the value of x and return b[i]. 
b[i] &= x  And the ith bit of b with the value of x and return b[i]. 
b[i] ^= x  ExclusiveOr the ith bit of b with the value of x and return b[i]. 
b[i] = x  If x==true, clear the ith bit of b. Returns b[i]. 
b[i] = b[j]  Set the ith bit of b to the value of the jth bit of b and return b[i]. 
b[i] = b[j]  Or the ith bit of b with the jth bit of b and return b[i]. 
b[i] &= b[j]  And the ith bit of b with the jth bit of b and return b[i]. 
b[i] ^= b[j]  ExclusiveOr the ith bit of b with the jth bit of b and return b[i]. 
b[i] = b[j]  If the jth bit of b is set, clear the ith bit of b. Returns b[i]. 
x = ~b[i]  Assign the opposite of the ith bit of b to x. 
(bool)~b[i]  Return the opposite of the ith bit of b. 
b[i].flip()  Flip the ith bit of b and return b[i]. 
dynamic_bitset::const_referenceThe type bool.
dynamic_bitset::size_typeThe unsigned integer type for representing the size of the bit set.
dynamic_bitset::block_typeThe same type as Block.
dynamic_bitset::allocator_type;The same type as Allocator.
Public data members
dynamic_bitset::bits_per_blockThe number of bits the type Block uses to represent values, excluding any padding bits. Numerically equal to std::numeric_limits<Block>::digits.
dynamic_bitset::nposThe maximum value of size_type.
Constructors
dynamic_bitset()Effects: Constructs a bitset of size zero. The allocator for this bitset is a defaultconstructed object of type Allocator.
Postconditions: this>size() == 0.
Throws: Nothing unless the default constructor of Allocator throws an exception.
(Required by Default Constructible.)
dynamic_bitset(const Allocator& alloc)Effects: Constructs a bitset of size zero. A copy of the alloc object will be used in subsequent bitset operations such as resize to allocate memory.
Postconditions: this>size() == 0.
Throws: nothing.
dynamic_bitset(size_type num_bits, unsigned long value = 0, const Allocator& alloc = Allocator())Effects: Constructs a bitset from an integer. The first M bits are initialized to the corresponding bits in value and all other bits, if any, to zero (where M = min(num_bits, std::numeric_limits<unsigned long>::digits)). A copy of the alloc object will be used in subsequent bitset operations such as resize to allocate memory. Note that, e.g., the following
dynamic_bitset b<>( 16, 7 );
will match the constructor from an iterator range (not this one), but the underlying implementation will still "do the right thing" and construct a bitset of 16 bits, from the value 7.
Postconditions:
 this>size() == num_bits
 For all i in the range [0,M), (*this)[i] == (value >> i) & 1.
 For all i in the range [M,num_bits), (*this)[i] == false.
dynamic_bitset(const dynamic_bitset& x)Effects: Constructs a bitset that is a copy of the bitset x. The allocator for this bitset is a copy of the allocator in x.
Postconditions: For all i in the range [0,x.size()), (*this)[i] == x[i].
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
(Required by Assignable.)
dynamic_bitset(dynamic_bitset&& x)Effects: Constructs a bitset that is the same as the bitset x, while using the resources from x. The allocator for this bitset is moved from the allocator in x.
Postconditions: For all i in the range [0,x.size()), (*this)[i] == x[i].
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
template <typename BlockInputIterator> explicit dynamic_bitset(BlockInputIterator first, BlockInputIterator last, const Allocator& alloc = Allocator());Effects:

If this constructor is called with a type BlockInputIterator which
is actually an integral type, the library behaves as if the constructor
from unsigned long were called, with arguments
static_cast<size_type>(first), last and alloc, in that order.
Example:// b is constructed as if by calling the constructor // // dynamic_bitset(size_type num_bits, // unsigned long value = 0, // const Allocator& alloc = Allocator()) // // with arguments // // static_cast<dynamic_bitset<unsigned short>::size_type>(8), // 7, // Allocator() // dynamic_bitset<unsigned short> b(8, 7);
Note:
At the time of writing (October 2008) this is aligned with the proposed resolution for library issue 438. That is a post C++03 change, and is currently in the working paper for C++0x. Informally speaking, the critical changes with respect to C++03 are the drop of a static_cast on the second argument, and more leeway as to when the templated constructor should have the same effect as the (size, value) one: only when InputIterator is an integral type, in C++03; when it is either an integral type or any other type that the implementation might detect as impossible to be an input iterator, with the proposed resolution. For the purposes of dynamic_bitset we limit ourselves to the first of these two changes.
 Otherwise (i.e. if the template argument is not an integral type), constructs—under the condition in the requires clause—a bitset based on a range of blocks. Let *first be block number 0, *++first block number 1, etc. Block number b is used to initialize the bits of the dynamic_bitset in the position range [b*bits_per_block, (b+1)*bits_per_block). For each block number b with value bval, the bit (bval >> i) & 1 corresponds to the bit at position (b * bits_per_block + i) in the bitset (where i goes through the range [0, bits_per_block)).
Requires: BlockInputIterator must be either an integral type or a model of Input Iterator whose value_type is the same type as Block.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
template<typename Char, typename Traits, typename Alloc> explicit dynamic_bitset(const std::basic_string<Char,Traits,Alloc>& s, typename std::basic_string<CharT, Traits, Alloc>::size_type pos = 0, typename std::basic_string<CharT, Traits, Alloc>::size_type n = std::basic_string<Char,Traits,Alloc>::npos, const Allocator& alloc = Allocator())Precondition: pos <= s.size() and the characters used to initialize the bits must be 0 or 1.
Effects: Constructs a bitset from a string of 0's and 1's. The first M bits are initialized to the corresponding characters in s, where M = 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, dynamic_bitset(string("1101")) is the same as dynamic_bitset(13ul).
Throws: an allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
Destructor
~dynamic_bitset()Effects: Releases the memory associated with this bitset and destroys the bitset object itself.
Throws: nothing.
Member Functions
void swap(dynamic_bitset& b);Effects: The contents of this bitset and bitset b are exchanged.
Postconditions: This bitset is equal to the original b, and b is equal to the previous version of this bitset.
Throws: nothing.
dynamic_bitset& operator=(const dynamic_bitset& x)Effects: This bitset becomes a copy of the bitset x.
Postconditions: For all i in the range [0,x.size()), (*this)[i] == x[i].
Returns: *this.
Throws: nothing.
(Required by Assignable.)
dynamic_bitset& operator=(dynamic_bitset&& x)Effects: This bitset becomes the same as the bitset x, while using the resources from x.
Postconditions: For all i in the range [0,x.size()), (*this)[i] == x[i].
Returns: *this.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
allocator_type get_allocator() const;Returns: A copy of the allocator object used to construct *this.
void resize(size_type num_bits, bool value = false);Effects: Changes the number of bits of the bitset to num_bits. If num_bits > size() then the bits in the range [0,size()) remain the same, and the bits in [size(),num_bits) are all set to value. If num_bits < size() then the bits in the range [0,num_bits) stay the same (and the remaining bits are discarded).
Postconditions: this>size() == num_bits.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
void clear()Effects: The size of the bitset becomes zero.
Throws: nothing.
void pop_back();Precondition: !this>empty().
Effects: Decreases the size of the bitset by one.
Throws: nothing.
void push_back(bool value);Effects: Increases the size of the bitset by one, and sets the value of the new mostsignificant bit to value.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
void append(Block value);Effects: Appends the bits in value to the bitset (appends to the mostsignificant end). This increases the size of the bitset by bits_per_block. Let s be the old size of the bitset, then for i in the range [0,bits_per_block), the bit at position (s + i) is set to ((value >> i) & 1).
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
template <typename BlockInputIterator> void append(BlockInputIterator first, BlockInputIterator last);Effects: This function provides the same end result as the following code, but is typically more efficient.
for (; first != last; ++first) append(*first);Requires: The BlockInputIterator type must be a model of Input Iterator and the value_type must be the same type as Block.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
dynamic_bitset& operator&=(const dynamic_bitset& rhs)Requires: this>size() == rhs.size().
Effects: BitwiseAND all the bits in rhs with the bits in this bitset. This is equivalent to:
for (size_type i = 0; i != this>size(); ++i) (*this)[i] = (*this)[i] & rhs[i];Returns: *this.
Throws: nothing.
dynamic_bitset& operator=(const dynamic_bitset& rhs)Requires: this>size() == rhs.size().
Effects: BitwiseOR's all the bits in rhs with the bits in this bitset. This is equivalent to:
for (size_type i = 0; i != this>size(); ++i) (*this)[i] = (*this)[i]  rhs[i];Returns: *this.
Throws: nothing.
dynamic_bitset& operator^=(const dynamic_bitset& rhs)Requires: this>size() == rhs.size().
Effects: BitwiseXOR's all the bits in rhs with the bits in this bitset. This is equivalent to:
for (size_type i = 0; i != this>size(); ++i) (*this)[i] = (*this)[i] ^ rhs[i];Returns: *this.
Throws: nothing.
dynamic_bitset& operator=(const dynamic_bitset& rhs)Requires: this>size() == rhs.size().
Effects: Computes the set difference of this bitset and the rhs bitset. This is equivalent to:
for (size_type i = 0; i != this>size(); ++i) (*this)[i] = (*this)[i] && !rhs[i];Returns: *this.
Throws: nothing.
dynamic_bitset& operator<<=(size_type n)Effects: Shifts the bits in this bitset to the left by n bits. For each bit in the bitset, the bit at position pos takes on the previous value of the bit at position pos  n, or zero if no such bit exists.
Returns: *this.
Throws: nothing.
dynamic_bitset& operator>>=(size_type n)Effects: Shifts the bits in this bitset to the right by n bits. For each bit in the bitset, the bit at position pos takes on the previous value of bit pos + n, or zero if no such bit exists.
Returns: *this.
Throws: nothing.
dynamic_bitset operator<<(size_type n) constReturns: a copy of *this shifted to the left by n bits. For each bit in the returned bitset, the bit at position pos takes on the value of the bit at position pos  n of this bitset, or zero if no such bit exists.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
dynamic_bitset operator>>(size_type n) constReturns: a copy of *this shifted to the right by n bits. For each bit in the returned bitset, the bit at position pos takes on the value of the bit at position pos + n of this bitset, or zero if no such bit exists.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
dynamic_bitset& set()Effects: Sets every bit in this bitset to 1.
Returns: *this
Throws: nothing.
dynamic_bitset& flip()Effects: Flips the value of every bit in this bitset.
Returns: *this
Throws: nothing.
dynamic_bitset operator~() constReturns: a copy of *this with all of its bits flipped.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
dynamic_bitset& reset()Effects: Clears every bit in this bitset.
Returns: *this
Throws: nothing.
dynamic_bitset& set(size_type n, size_type len, bool val);Precondition: n + len < this>size().
Effects: Sets every bit indexed from n to n + len  1 inclusively if val is true, and clears them if val is false.
Returns: *this
dynamic_bitset& set(size_type n, bool val = true)Precondition: n < this>size().
Effects: Sets bit n if val is true, and clears bit n if val is false.
Returns: *this
dynamic_bitset& reset(size_type n, size_type len);Precondition: n + len < this>size().
Effects: Clears every bit indexed from n to n + len  1 inclusively.
Returns: *this
dynamic_bitset& reset(size_type n)Precondition: n < this>size().
Effects: Clears bit n.
Returns: *this
dynamic_bitset& flip(size_type n, size_type len)Precondition: n + len < this>size().
Effects: Flips every bit indexed from n to n + len  1 inclusively.
Returns: *this
dynamic_bitset& flip(size_type n)Precondition: n < this>size().
Effects: Flips bit n.
Returns: *this
size_type size() constReturns: the number of bits in this bitset.
Throws: nothing.
size_type num_blocks() constReturns: the number of blocks in this bitset.
Throws: nothing.
size_type max_size() const;Returns: the maximum size of a dynamic_bitset object having the same type as *this. Note that if any dynamic_bitset operation causes size() to exceed max_size() then the behavior is undefined.
[The semantics of this function could change slightly when lib issue 197 will be closed]
bool empty() const;Returns: true if this>size() == 0, false otherwise. Note: not to be confused with none(), that has different semantics.
size_type capacity() const;Returns: The total number of elements that *this can hold without requiring reallocation.
Throws: nothing.
void reserve(size_type num_bits);Effects: A directive that informs the bitset of a planned change in size, so that it can manage the storage allocation accordingly. After reserve(), capacity() is greater or equal to the argument of reserve() if reallocation happens; and equal to the previous value of capacity() otherwise. Reallocation happens at this point if and only if the current capacity is less than the argument of reserve().
Note: It does not change the size() of the bitset.
Postcondtitions: this>capacity() >= num_bits.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
void shrink_to_fit();Effects: shrink_to_fit() is a request to reduce memory use by removing unused capacity.
Note: It does not change the size() of the bitset.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
size_type count() constReturns: the number of bits in this bitset that are set.
Throws: nothing.
bool all() constReturns: true if all bits in this bitset are set or if size() == 0, and otherwise returns false.
Throws: nothing.
bool any() constReturns: true if any bits in this bitset are set, and otherwise returns false.
Throws: nothing.
bool none() constReturns: true if no bits are set, and otherwise returns false.
Throws: nothing.
bool test(size_type n) constPrecondition: n < this>size().
Returns: true if bit n is set and false is bit n is 0.
bool test_set(size_type n, bool val = true)Precondition: n < this>size().
Effects: Sets bit n if val is true, and clears bit n if val is false.
Returns: true if the previous state of bit n was set and false is bit n is 0.
reference operator[](size_type n)Precondition: n < this>size().
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. However, in many other respects the proxy is not the same as the true reference type bool&.
bool operator[](size_type n) constPrecondition: n < this>size().
Returns: The same as test(n).
unsigned long to_ulong() constReturns: The numeric value corresponding to the bits in *this.
Throws: std::overflow_error if that value is too large to be represented in an unsigned long, i.e. if *this has any nonzero bit at a position >= std::numeric_limits<unsigned long>::digits.
bool is_subset_of(const dynamic_bitset& a) constRequires: this>size() == a.size()
Returns: true if this bitset is a subset of bitset a. That is, it returns true if, for every bit that is set in this bitset, the corresponding bit in bitset a is also set. Otherwise this function returns false.
Throws: nothing.
bool is_proper_subset_of(const dynamic_bitset& a) constRequires: this>size() == a.size()
Returns: true if this bitset is a proper subset of bitset a. That is, it returns true if, for every bit that is set in this bitset, the corresponding bit in bitset a is also set and if this>count() < a.count(). Otherwise this function returns false.
Throws: nothing.
bool intersects(const dynamic_bitset& a) constRequires: this>size() == a.size()
Returns: true if this bitset and a intersect. That is, it returns true if, there is a bit which is set in this bitset, such that the corresponding bit in bitset a is also set. Otherwise this function returns false.
Throws: nothing.
size_type find_first() const;Returns: the lowest index i such as bit i is set, or npos if *this has no on bits.
size_type find_next(size_type pos) const;Returns: the lowest index i greater than pos such as bit i is set, or npos if no such index exists.
bool operator==(const dynamic_bitset& rhs) constReturns: true if this>size() == rhs.size() and if for all i in the range [0,rhs.size()), (*this)[i] == rhs[i]. Otherwise returns false.
Throws: nothing.
(Required by Equality Comparable.)
bool operator!=(const dynamic_bitset& rhs) constReturns: !((*this) == rhs)
Throws: nothing.
(Required by Equality Comparable.)
bool operator<(const dynamic_bitset& rhs) constReturns: true if this bitset is lexicographically less than rhs, and returns false otherwise. (See the description of lexicographical_compare for a definition of lexicographic ordering).
Throws: nothing.
(Required by Less Than Comparable.)
bool operator>(const dynamic_bitset& rhs) constReturns: !((*this) < rhs  (*this) == rhs)
Throws: nothing.
(Required by Less Than Comparable.)
bool operator<=(const dynamic_bitset& rhs) constReturns: (*this) < rhs  (*this) == rhs
Throws: nothing.
(Required by Less Than Comparable.)
bool operator>=(const dynamic_bitset& rhs) constReturns: (*this) > rhs  (*this) == rhs
Throws: nothing.
(Required by Less Than Comparable.)
NonMember Functions
dynamic_bitset operator&(const dynamic_bitset& a, const dynamic_bitset& b)Requires: a.size() == b.size()
Returns: A new bitset that is the bitwiseAND of the bitsets a and b.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
dynamic_bitset operator(const dynamic_bitset& a, const dynamic_bitset& b)Requires: a.size() == b.size()
Returns: A new bitset that is the bitwiseOR of the bitsets a and b.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
dynamic_bitset operator^(const dynamic_bitset& a, const dynamic_bitset& b)Requires: a.size() == b.size()
Returns: A new bitset that is the bitwiseXOR of the bitsets a and b.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
dynamic_bitset operator(const dynamic_bitset& a, const dynamic_bitset& b)Requires: a.size() == b.size()
Returns: A new bitset that is the set difference of the bitsets a and b.
Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator).
template <typename CharT, typename Alloc> void to_string(const dynamic_bitset<Block, Allocator>& b, std::basic_string<Char,Traits,Alloc>& s)Effects: Copies a representation of b into the string s. A character in the string is '1' if the corresponding bit is set, and '0' if it is not. Character position i in the string corresponds to bit position b.size()  1  i.
Throws: If memory is exhausted, the string will throw an allocation error.
Rationale: This function is not a member function taking zero arguments and returning a string for a couple reasons. First, this version can be slighly more efficient because the string is not copied (due to being passed by value). Second, as a member function, to allow for flexibility with regards to the template parameters of basic_string, the member function would require explicit template parameters. Few C++ programmers are familiar with explicit template parameters, and some C++ compilers do not handle them properly.
template <typename Block, typename Alloc, typename BlockOutputIterator> void to_block_range(const dynamic_bitset<Block, Alloc>& b, BlockOutputIterator result)Effects: Writes the bits of the bitset into the iterator result a block at a time. The first block written represents the bits in the position range [0,bits_per_block) in the bitset, the second block written the bits in the range [bits_pre_block,2*bits_per_block), and so on. For each block bval written, the bit (bval >> i) & 1 corresponds to the bit at position (b * bits_per_block + i) in the bitset.
Requires: The type BlockOutputIterator must be a model of Output Iterator and its value_type must be the same type as Block. Further, the size of the output range must be greater or equal b.num_blocks().
template <typename BlockIterator, typename Block, typename Alloc> void from_block_range(BlockIterator first, BlockIterator last, const dynamic_bitset<Block, Alloc>& b)Effects: Reads blocks from the iterator range into the bitset.
Requires: The type BlockIterator must be a model of Input Iterator and its value_type must be the same type as Block. The size of the iterator range must be less or equal to b.num_blocks().
template <typename Char, typename Traits, typename Block, typename Alloc> basic_ostream<Char, Traits>& operator<<(basic_ostream<Char, Traits>& os, const dynamic_bitset<Block, Alloc>& b)Effects: Inserts a textual representation of b into the stream os (highest bit first). Informally, the output is the same as doing
std::basic_string<Char, Traits> s; boost::to_string(x, s): os << s;except that the stream inserter takes into accout the locale imbued into os, which boost::to_string() can't do. Here is a more precise specification, given in terms of "as if" rule: first, for each valid position i into the bitset b let's put: character_of(b[i)]) = b[i]? os.widen('1') : os.widen('0'); Let also s be a std::basic_string<Char, Traits> object, having length b.size() and such as, for each i in [0, b.size()), s[i] is character_of(b[i]) Then, the output, the effects on os and the exception behavior is the same as outputting the object s to os (same width, same exception mask, same padding, same setstate() logic)
Returns: os
Throws: std::ios_base::failure if there is a problem writing to the stream.
template <typename Char, typename Traits, typename Block, typename Alloc> std::basic_istream<Char,Traits>& operator>>(std::basic_istream<Char,Traits>& is, dynamic_bitset<Block, Alloc>& b)Effects: Extracts a dynamic_bitset from an input stream.
Definitions:
Let Tr be the traits_type of is. Then:
 A (noneof) character c extracted from is is a bitset digit if and only if either Tr::eq(c, is.widen('0')) or Tr::eq(c, is.widen('1')) return true.
 If c is a bitset digit, it's corresponding bit value is 0 if Tr::eq(c, is.widen('0')) is true, 1 otherwise.
 n bits are stored into the bitset;
 endoffile, or an error, occurs on the input sequence;
 the next available input character isn't a bitset digit
If no exception caused the function to exit then is.width(0) is called, regardless of how many characters were actually extracted. The sentry object k is destroyed.
If the function extracts no characters[???], it calls is.setstate(std::ios::failbit), which may throw std::ios_base::failure.

Throws: An allocation error if memory is exhausted (std::bad_alloc if Allocator=std::allocator). A std::ios_base::failure if there is a problem reading from the stream.
Exception guarantees
All of dynamic_bitset functions offer at least the basic exception guarantee.Changes from previous version(s)
Changes in Boost 1.56.0
 Support for C++11 move constructors.
 Warning fixes on MSVC 2013.
 Support for C++11 minimal allocators.
 Add noexcept specifications.
Changes in Boost 1.37.0
 The constructor from a block range implements a "do the right thing" behavior, a la standard sequences.
Changes from Boost 1.31.0

The stream extractor has completely different semantics: as natural
for a dynamic structure, it now expands the bitset as needed during
extraction. The new behaviour mimics that of the basic_string
extractor but there are some differences the user should be aware of;
so, please, check the documentation. (One
difference concerns the case where
stream.width() > bitset.max_size() > 0
. In that circumstance the extractor of dynamic_bitset never attempts to extract more than max_size() characters, whereas the extractor of basic_string goes on and, on conforming implementations, eventually throws a length_error exception. Note: That's what the standard mandates see especially library issue 83 but not all implementations conform)
The stream extractor is now also "exceptionaware" in the sense that it works correctly when setting exception masks on the stream.
 Several member functions (empty(), find_first() , find_next(), get_allocator(), intersects() , max_size() ) have been added.
 The constructor from basic_string has a new parameter that was totally forgotten before.
 The class reference has been reimplemented so that dynamic_bitset's references behave more like references to standard container elements. In particular it is now guaranteed that they cannot be invalidated from a standard library swap() function applied to their corresponding dynamic_bitsets.
 Several optimizations to member and nonmember functions and to the nested class reference.
See also
std::bitset, std::vector,Acknowledgements
We would like to thank the Boost community for putting in the time to review and accept this library. This library is much better than it ever would have been due to all the suggestions from Boost members. We especially thank Matt Marcus for taking on the task of review manager. Also, a special thanks goes to James Kanze for his invaluable help with the internationalization issues.
Copyright © 2001  Jeremy
Siek, Indiana University (jsiek@osl.iu.edu) Chuck Allison, Senior Editor, C/C++ Users Journal (cda@freshsources.com) 
Copyright © 20032004, 2008  Gennaro Prota (name.surname yahoo.com) 
Copyright © 2014  Ahmed Charles (acharles@outlook.com) 
Copyright © 2014  Glen Fernandes (glenjofe@gmail.com) 
Copyright © 2014  Riccardo Marcangelo (ricky.65@outlook.com) 