C++ : Reference : STL Containers : bitset

bitset

class template

<bitset>

Bitset

A bitset is a special container class that is designed to store bits (elements with only two possible values: 0 or 1, true or false, ...).

The class is very similar to a regular array, but optimizing for space allocation: each element occupies only one bit (which is eight times less than the smallest elemental type in C++: char).

Each element (each bit) can be accessed individually: for example, for a given bitset named mybitset, the expression mybitset[3] accesses its fourth bit, just like a regular array accesses its elements.

Because no such small elemental type exists in most C++ environments, the individual elements are accessed as special references which mimic bool elements:

1 2 3 4 5 6 7 8 9 10 11

class bitset::reference { friend class bitset; reference(); // no public constructor public: ~reference(); operator bool () const; // convert to bool reference& operator= ( bool x ); // assign from bool reference& operator= ( const reference& x ); // assign from bit reference& flip(); // flip bit value bool operator~() const; // return inverse value }

Apart from overriding several operators and to provide direct access to the bits, bitsets have the feature of being able to be constructed from and converted to both integer values and binary strings (see constructor, bitset::to_ulong and bitset::to_string). They can also be directly inserted and extracted from streams in binary format.

Bitsets have a fixed size. For a similar container class that also optimizes for space allocation and allows for dynamic resizing, see the bool specialization of vector (vector<bool>).

In their implementation in the C++ Standard Template Library, bitsets take a single template parameter:

template < size_t N > class bitset;

Where the template parameter has the following meaning:

• N: Number of bits to contain (size_t is an integral type).

Member functions

(constructor)

Construct bitset (public member function)

applicable operators

Bitset operators (functions)

Bit access:

operator[]

Access bit (public member function)

Bit operations:

set	Set bits (public member function)

reset

Reset bits (public member function)

flip	Flip bits (public member function)

Bitset operations:

to_ulong

Convert to unsigned long integer (public member function)

to_string

Convert to string (public member function)

count

Count bits set (public member function)

size	Return size (public member function)

test	Return bit value (public member function)

any	Test if any bit is set (public member function)

none	Test if no bit is set (public member function)