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c++标准为处理二进制数值提供了两个工具：vector<bool>和bitset。
vector<bool>是对元素类型为bool的vector特化，它的内部并不真正存储bool值，而是以bit来压缩保存、使用代理技术来操作bit，造成的后果就是它很像容器，大多数情况下和标准容器一致，但它不是容器，不满足容器的定义。
bitset与vector<bool>类似，同样存储二进制位，但它的大小固定，而且比vector<bool>支持更多的位运算。
vector<bool>和bitset各有优缺点：vector<bool>可以动态增长，但不能方便地进行位运算；bitset则正好相反，可以方便地容纳的二进制位做位运算，但不能动态增长。
boost.dynamic_bitset的出现恰好填补了这两者之间的空白，它类似于标准库的bitset，提供丰富的位运算，同时长度又是动态变化的。
dynamic_bitset位于名字空间boost，为了使用dynamic_bitset组件，需要包含头文件<boost.dynamic_bitset.hpp>，即：
#include<boost/dynamic_bitset_hpp>
using namespace boost;
下面我给出部分源码的解析（只是个人的理解）：
//=============================================================================
// dynamic_bitset implementation
//函数的实现
//-----------------------------------------------------------------------------
// constructors, etc.
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>::dynamic_bitset(const Allocator& alloc)
: m_bits(alloc), m_num_bits(0)
{
}
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>::
dynamic_bitset(size_type num_bits, unsigned long value, const Allocator& alloc)
: m_bits(alloc),
m_num_bits(0)
{
//使用无符号整型进行初始化
init_from_unsigned_long(num_bits, value);
}
// copy constructor
template <typename Block, typename Allocator>
inline dynamic_bitset<Block, Allocator>::
dynamic_bitset(const dynamic_bitset& b)
: m_bits(b.m_bits), m_num_bits(b.m_num_bits)
{
}
template <typename Block, typename Allocator>
inline dynamic_bitset<Block, Allocator>::
~dynamic_bitset()
{
assert(m_check_invariants());
}
template <typename Block, typename Allocator>
inline void dynamic_bitset<Block, Allocator>::
swap(dynamic_bitset<Block, Allocator>& b) // no throw
{
std::swap(m_bits, b.m_bits);
std::swap(m_num_bits, b.m_num_bits);
}
//赋值
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>& dynamic_bitset<Block, Allocator>::
operator=(const dynamic_bitset<Block, Allocator>& b)
{
m_bits = b.m_bits;
m_num_bits = b.m_num_bits;
return *this;
}
template <typename Block, typename Allocator>
inline typename dynamic_bitset<Block, Allocator>::allocator_type
dynamic_bitset<Block, Allocator>::get_allocator() const
{
return m_bits.get_allocator();
}
//-----------------------------------------------------------------------------
// size changing operations
//num_bits:代表扩展多少位二进制
//vlaue为true是代表将每一位的值为都设为1
template <typename Block, typename Allocator>
void dynamic_bitset<Block, Allocator>::
resize(size_type num_bits, bool value) // strong guarantee
{
//num_blocks()函数返回二进制为占用的Block数量
//size() / sizeof(Block)*8 + 1
//size()函数返回二进制的位数
const size_type old_num_blocks = num_blocks();
//required_blocks统计需要的Block数量
const size_type required_blocks = calc_num_blocks(num_bits);
//根据value的真假，如果value为真时，拿1填充所有的位，
//否则拿0填充
const block_type v = value? ~Block(0) : Block(0);
//当需要的Block数量与原来的Block数量不相等时，进行扩展
if (required_blocks != old_num_blocks) {
m_bits.resize(required_blocks, v); // s.g. (copy)
}
// At this point:
//
// - if the buffer was shrunk, we have nothing more to do,
// except a call to m_zero_unused_bits()
//
// - if it was enlarged, all the (used) bits in the new blocks have
// the correct value, but we have not yet touched those bits, if
// any, that were 'unused bits' before enlarging: if value == true,
// they must be set.
//当value为1并且所要扩展的位数大于原来的位数
if (value && (num_bits > m_num_bits)) {
//
const block_width_type extra_bits = count_extra_bits();
if (extra_bits) {
assert(old_num_blocks >= 1 && old_num_blocks <= m_bits.size());
// Set them.
m_bits[old_num_blocks - 1] |= (v << extra_bits);
}
}
//更新比特位的数目
m_num_bits = num_bits;
m_zero_unused_bits();
}
//清空
template <typename Block, typename Allocator>
void dynamic_bitset<Block, Allocator>::
clear() // no throw
{
m_bits.clear();
m_num_bits = 0;
}
template <typename Block, typename Allocator>
void dynamic_bitset<Block, Allocator>::
push_back(bool bit)
{
//获取比特位的个数
const size_type sz = size();
//扩展一位
resize(sz + 1);
//位设置
set(sz, bit);
}
//把整数转换为二进制位全部追加到dynamic_bitset末尾（最高位）
//它将把整数转换为一个Block再追加
template <typename Block, typename Allocator>
void dynamic_bitset<Block, Allocator>::
append(Block value) // strong guarantee
{
const block_width_type r = count_extra_bits();
if (r == 0) {
//没有空间时，调用push_back进行尾插
// the buffer is empty, or all blocks are filled
m_bits.push_back(value);
}
else {
//存在空间时
//调用push_back进行追加
m_bits.push_back(value >> (bits_per_block - r));
m_bits[m_bits.size() - 2] |= (value << r); // m_bits.size() >= 2
}
m_num_bits += bits_per_block;
assert(m_check_invariants());
}
//-----------------------------------------------------------------------------
// bitset operations
//运算符的实现
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::operator&=(const dynamic_bitset& rhs)
{
//确保两个对象的二进制位数相同
assert(size() == rhs.size());
//num_block()为Block的块数
for (size_type i = 0; i < num_blocks(); ++i)
m_bits[i] &= rhs.m_bits[i];
return *this;
}
//|=的实现
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::operator|=(const dynamic_bitset& rhs)
{
assert(size() == rhs.size());
for (size_type i = 0; i < num_blocks(); ++i)
m_bits[i] |= rhs.m_bits[i];
//m_zero_unused_bits();
return *this;
}
//异或等的实现
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::operator^=(const dynamic_bitset& rhs)
{
assert(size() == rhs.size());
for (size_type i = 0; i < this->num_blocks(); ++i)
m_bits[i] ^= rhs.m_bits[i];
//m_zero_unused_bits();
return *this;
}
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::operator-=(const dynamic_bitset& rhs)
{
assert(size() == rhs.size());
for (size_type i = 0; i < num_blocks(); ++i)
m_bits[i] &= ~rhs.m_bits[i];
//m_zero_unused_bits();
return *this;
}
//
// NOTE:
// Note that the 'if (r != 0)' is crucial to avoid undefined
// behavior when the left hand operand of >> isn't promoted to a
// wider type (because rs would be too large).
//
//左移等的实现
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::operator<<=(size_type n)
{
//m_num_bits：二进制的位数
//当左移的位数大于二进制本身的位数时，相当于将每一位都置为0
if (n >= m_num_bits)
return reset();
//else
//当n大于0并且小于二进制位数时
if (n > 0) {
//num_blocks():统计Block的块数
size_type const last = num_blocks() - 1; // num_blocks() is >= 1
//bits_per_block:每一块所占的比特数
//div：移动的位数中占几个Block
size_type const div = n / bits_per_block; // div is <= last
//根据移动位数计算出二进制位的下标
//r == 0 说明移动的位数正好是Block的倍数，这时我们可以移动数组的元素
block_width_type const r = bit_index(n);
block_type * const b = &m_bits[0];
if (r != 0) {
//r！=0时，r正是n/Block所得的余数
block_width_type const rs = bits_per_block - r;
for (size_type i = last-div; i>0; --i) {
b[i+div] = (b[i] << r) | (b[i-1] >> rs);
}
b[div] = b[0] << r;
}
else {
//r == 0时，直接移动数组的元素
for (size_type i = last-div; i>0; --i) {
b[i+div] = b[i];
}
b[div] = b[0];
}
// zero out div blocks at the less significant end
// 移出的用0填充
std::fill_n(b, div, static_cast<block_type>(0));
// zero out any 1 bit that flowed into the unused part
// 将未使用的比特位置0
m_zero_unused_bits(); // thanks to Lester Gong
}
return *this;
}
//
// NOTE:
// see the comments to operator <<=
//
//右移和左移的原理是一样的
template <typename B, typename A>
dynamic_bitset<B, A> & dynamic_bitset<B, A>::operator>>=(size_type n) {
if (n >= m_num_bits) {
return reset();
}
//else
if (n>0) {
size_type const last = num_blocks() - 1; // num_blocks() is >= 1
size_type const div = n / bits_per_block; // div is <= last
block_width_type const r = bit_index(n);
block_type * const b = &m_bits[0];
if (r != 0) {
block_width_type const ls = bits_per_block - r;
for (size_type i = div; i < last; ++i) {
b[i-div] = (b[i] >> r) | (b[i+1] << ls);
}
// r bits go to zero
b[last-div] = b[last] >> r;
}
else {
for (size_type i = div; i <= last; ++i) {
b[i-div] = b[i];
}
// note the '<=': the last iteration 'absorbs'
// b[last-div] = b[last] >> 0;
}
// div blocks are zero filled at the most significant end
std::fill_n(b + (num_blocks()-div), div, static_cast<block_type>(0));
}
return *this;
}
//左移和右移
//创建临时对象调用<<= 、>>=，并将对象返回
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>
dynamic_bitset<Block, Allocator>::operator<<(size_type n) const
{
dynamic_bitset r(*this);
return r <<= n;
}
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>
dynamic_bitset<Block, Allocator>::operator>>(size_type n) const
{
dynamic_bitset r(*this);
return r >>= n;
}
//-----------------------------------------------------------------------------
// basic bit operations
//将某一位设置为0或1操作
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::set(size_type pos, bool val)
{
assert(pos < m_num_bits);
if (val)
//val为真是进行置位操作
//根据pos获取Block的下标
m_bits[block_index(pos)] |= bit_mask(pos);
else
//否则进行清零操作
reset(pos);
return *this;
}
//set（）无参数时将二进制的所有位都置为1
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::set()
{
std::fill(m_bits.begin(), m_bits.end(), ~Block(0));
//将未使用的比特位清0
m_zero_unused_bits();
return *this;
}
//将某一位置清零操作
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::reset(size_type pos)
{
assert(pos < m_num_bits);
#if defined __MWERKS__ && BOOST_WORKAROUND(__MWERKS__, <= 0x3003) // 8.x
// CodeWarrior 8 generates incorrect code when the &=~ is compiled,
// use the |^ variation instead.. <grafik>
m_bits[block_index(pos)] |= bit_mask(pos);
m_bits[block_index(pos)] ^= bit_mask(pos);
#else
m_bits[block_index(pos)] &= ~bit_mask(pos);
#endif
return *this;
}
//将二进制的所有位都进行清零操作
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::reset()
{
std::fill(m_bits.begin(), m_bits.end(), Block(0));
return *this;
}
//将二进制进行翻转某一位操作
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::flip(size_type pos)
{
assert(pos < m_num_bits);
m_bits[block_index(pos)] ^= bit_mask(pos);
return *this;
}
//将二进制的所有位进行翻转操作
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>&
dynamic_bitset<Block, Allocator>::flip()
{
for (size_type i = 0; i < num_blocks(); ++i)
m_bits[i] = ~m_bits[i];
//将未使用的比特位置0
m_zero_unused_bits();
return *this;
}
template <typename Block, typename Allocator>
bool dynamic_bitset<Block, Allocator>::m_unchecked_test(size_type pos) const
{
//根据pos的值获得Block的下标，将该下标的元素与掩码相与
return (m_bits[block_index(pos)] & bit_mask(pos)) != 0;
}
//检测某一位为1或0
//为1返回真
template <typename Block, typename Allocator>
bool dynamic_bitset<Block, Allocator>::test(size_type pos) const
{
assert(pos < m_num_bits);
return m_unchecked_test(pos);
}
//如果二进制位中存在1时返回真
template <typename Block, typename Allocator>
bool dynamic_bitset<Block, Allocator>::any() const
{
for (size_type i = 0; i < num_blocks(); ++i)
if (m_bits[i])
return true;
return false;
}
//与any()函数相反
//当二进制中存在0时返回真
template <typename Block, typename Allocator>
inline bool dynamic_bitset<Block, Allocator>::none() const
{
return !any();
}
//取反
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>
dynamic_bitset<Block, Allocator>::operator~() const
{
//拷贝构造另一个对象
dynamic_bitset b(*this);
//调用翻转函数
b.flip();
return b;
}
//统计二进制中1的个数
template <typename Block, typename Allocator>
typename dynamic_bitset<Block, Allocator>::size_type
dynamic_bitset<Block, Allocator>::count() const
{
using detail::dynamic_bitset_impl::table_width;
using detail::dynamic_bitset_impl::access_by_bytes;
using detail::dynamic_bitset_impl::access_by_blocks;
using detail::dynamic_bitset_impl::value_to_type;
#if BOOST_WORKAROUND(__GNUC__, == 4) && (__GNUC_MINOR__ == 3) && (__GNUC_PATCHLEVEL__ == 3)
// NOTE: Explicit qualification of "bits_per_block"
// breaks compilation on gcc 4.3.3
enum { no_padding = bits_per_block == CHAR_BIT * sizeof(Block) };
#else
// NOTE: Explicitly qualifying "bits_per_block" to workaround
// regressions of gcc 3.4.x
enum { no_padding =
dynamic_bitset<Block, Allocator>::bits_per_block
== CHAR_BIT * sizeof(Block) };
#endif
enum { enough_table_width = table_width >= CHAR_BIT };
enum { mode = (no_padding && enough_table_width)
? access_by_bytes
: access_by_blocks };
return do_count(m_bits.begin(), num_blocks(), Block(0),
static_cast<value_to_type<(bool)mode> *>(0));
}
//-----------------------------------------------------------------------------
// conversions
//转换函数
template <typename B, typename A, typename stringT>
void to_string_helper(const dynamic_bitset<B, A> & b, stringT & s,
bool dump_all)
{
typedef typename stringT::traits_type Tr;
typedef typename stringT::value_type Ch;
BOOST_DYNAMIC_BITSET_CTYPE_FACET(Ch, fac, std::locale());
const Ch zero = BOOST_DYNAMIC_BITSET_WIDEN_CHAR(fac, '0');
const Ch one = BOOST_DYNAMIC_BITSET_WIDEN_CHAR(fac, '1');
// Note that this function may access (when
// dump_all == true) bits beyond position size() - 1
typedef typename dynamic_bitset<B, A>::size_type size_type;
const size_type len = dump_all?
dynamic_bitset<B, A>::bits_per_block * b.num_blocks():
b.size();
s.assign (len, zero);
for (size_type i = 0; i < len; ++i) {
if (b.m_unchecked_test(i))
Tr::assign(s[len - 1 - i], one);
}
}
// A comment similar to the one about the constructor from
// basic_string can be done here. Thanks to James Kanze for
// making me (Gennaro) realize this important separation of
// concerns issue, as well as many things about i18n.
//
//将二进制转换位子符串
template <typename Block, typename Allocator, typename stringT>
inline void
to_string(const dynamic_bitset<Block, Allocator>& b, stringT& s)
{
to_string_helper(b, s, false);
}
// Differently from to_string this function dumps out
// every bit of the internal representation (may be
// useful for debugging purposes)
//
template <typename B, typename A, typename stringT>
inline void
dump_to_string(const dynamic_bitset<B, A>& b, stringT& s)
{
to_string_helper(b, s, true /* =dump_all*/);
}
template <typename Block, typename Allocator, typename BlockOutputIterator>
inline void
to_block_range(const dynamic_bitset<Block, Allocator>& b,
BlockOutputIterator result)
{
// note how this copies *all* bits, including the
// unused ones in the last block (which are zero)
std::copy(b.m_bits.begin(), b.m_bits.end(), result);
}
template <typename Block, typename Allocator>
unsigned long dynamic_bitset<Block, Allocator>::
to_ulong() const
{
if (m_num_bits == 0)
return 0; // convention
// Check for overflows. This may be a performance burden on very
// large bitsets but is required by the specification, sorry
if (find_next(ulong_width - 1) != npos)
throw std::overflow_error("boost::dynamic_bitset::to_ulong overflow");
// Ok, from now on we can be sure there's no "on" bit
// beyond the "allowed" positions
typedef unsigned long result_type;
const size_type max_size =
(std::min)(m_num_bits, static_cast<size_type>(ulong_width));
const size_type last_block = block_index( max_size - 1 );
assert((last_block * bits_per_block) < static_cast<size_type>(ulong_width));
result_type result = 0;
for (size_type i = 0; i <= last_block; ++i) {
const size_type offset = i * bits_per_block;
result |= (static_cast<result_type>(m_bits[i]) << offset);
}
return result;
}
//返回二进制的位数
template <typename Block, typename Allocator>
inline typename dynamic_bitset<Block, Allocator>::size_type
dynamic_bitset<Block, Allocator>::size() const
{
return m_num_bits;
}
//返回二进制所占的块数
template <typename Block, typename Allocator>
inline typename dynamic_bitset<Block, Allocator>::size_type
dynamic_bitset<Block, Allocator>::num_blocks() const
{
return m_bits.size();
}
template <typename Block, typename Allocator>
inline typename dynamic_bitset<Block, Allocator>::size_type
dynamic_bitset<Block, Allocator>::max_size() const
{
// Semantics of vector<>::max_size() aren't very clear
// (see lib issue 197) and many library implementations
// simply return dummy values, _unrelated_ to the underlying
// allocator.
//
// Given these problems, I was tempted to not provide this
// function at all but the user could need it if he provides
// his own allocator.
//
const size_type m = detail::dynamic_bitset_impl::
vector_max_size_workaround(m_bits);
return m <= (size_type(-1)/bits_per_block) ?
m * bits_per_block :
size_type(-1);
}
//判断二进制是否为空
template <typename Block, typename Allocator>
inline bool dynamic_bitset<Block, Allocator>::empty() const
{
return size() == 0;
}
//检测一个对象是否为另一个对象的子集
//子集就是两个二进制对象一模一样
//例如 10010 和 10010
template <typename Block, typename Allocator>
bool dynamic_bitset<Block, Allocator>::
is_subset_of(const dynamic_bitset<Block, Allocator>& a) const
{
//确保两个对象的二进制位数相同
assert(size() == a.size());
for (size_type i = 0; i < num_blocks(); ++i)
//不为0说明两个对象不相同
if (m_bits[i] & ~a.m_bits[i])
return false;
return true;
}
//检测一个对象是否为另一个对象的真子集
//例如 10101和 00101
template <typename Block, typename Allocator>
bool dynamic_bitset<Block, Allocator>::
is_proper_subset_of(const dynamic_bitset<Block, Allocator>& a) const
{
//确保二进制的位数相同
assert(size() == a.size());
//确保两个对象的块数相同
assert(num_blocks() == a.num_blocks());
bool proper = false;
for (size_type i = 0; i < num_blocks(); ++i) {
const Block & bt = m_bits[i];
const Block & ba = a.m_bits[i];
if (bt & ~ba)
return false; // not a subset at all
if (ba & ~bt)
proper = true;
}
return proper;
}
//将个对象中以二进制位数较少的进行两个对象相与
template <typename Block, typename Allocator>
bool dynamic_bitset<Block, Allocator>::intersects(const dynamic_bitset & b) const
{
//common_block：取两个对象中块数较小的数
size_type common_blocks = num_blocks() < b.num_blocks()
? num_blocks() : b.num_blocks();
for(size_type i = 0; i < common_blocks; ++i) {
if(m_bits[i] & b.m_bits[i])
return true;
}
return false;
}
// --------------------------------
// lookup
// look for the first bit "on", starting
// from the block with index first_block
//
//从某一块开始寻找1的位置
template <typename Block, typename Allocator>
typename dynamic_bitset<Block, Allocator>::size_type
dynamic_bitset<Block, Allocator>::m_do_find_from(size_type first_block) const
{
size_type i = first_block;
// skip null blocks
// 跳过为0的块
while (i < num_blocks() && m_bits[i] == 0)
++i;
//当i大于块数时，说明没找到
if (i >= num_blocks())
return npos; // not found
//找到后返回位置
return i * bits_per_block + boost::lowest_bit(m_bits[i]);
}
//从最低位找二进制位1
template <typename Block, typename Allocator>
typename dynamic_bitset<Block, Allocator>::size_type
dynamic_bitset<Block, Allocator>::find_first() const
{
return m_do_find_from(0);
}
//从pos位置开始找下一个二进制位1
template <typename Block, typename Allocator>
typename dynamic_bitset<Block, Allocator>::size_type
dynamic_bitset<Block, Allocator>::find_next(size_type pos) const
{
//获取二进制位的个数
const size_type sz = size();
//当pos大于二进制位的个数或者二进制位的个数为0时
//返回 没找到
if (pos >= (sz-1) || sz == 0)
return npos;
++pos;
//根据pos的值获取块的下标
const size_type blk = block_index(pos);
//根据pos的值获取二进制位的下标
const block_width_type ind = bit_index(pos);
// mask out bits before pos
//将pos所在的块和pos在块中的下标，将该块pos之前的二进制位都清零
//如果fore为1，说明存在1
//不为1时，说明该块不存在二进制位为1，从下一块开始找
const Block fore = m_bits[blk] & ( ~Block(0) << ind );
return fore?
blk * bits_per_block + lowest_bit(fore)
:
m_do_find_from(blk + 1);
}
//-----------------------------------------------------------------------------
// comparison
//重载比较运算符（全局函数）
//== 运算符
template <typename Block, typename Allocator>
bool operator==(const dynamic_bitset<Block, Allocator>& a,
const dynamic_bitset<Block, Allocator>& b)
{
return (a.m_num_bits == b.m_num_bits)
&& (a.m_bits == b.m_bits);
}
//！= 运算符
template <typename Block, typename Allocator>
inline bool operator!=(const dynamic_bitset<Block, Allocator>& a,
const dynamic_bitset<Block, Allocator>& b)
{
return !(a == b);
}
//< 运算符
template <typename Block, typename Allocator>
bool operator<(const dynamic_bitset<Block, Allocator>& a,
const dynamic_bitset<Block, Allocator>& b)
{
//确保两个对象二进制的位数相同
assert(a.size() == b.size());
typedef typename dynamic_bitset<Block, Allocator>::size_type size_type;
//if (a.size() == 0)
// return false;
// Since we are storing the most significant bit
// at pos == size() - 1, we need to do the comparisons in reverse.
//
//从高位开始判断，首次比较小的对象就返回真
for (size_type ii = a.num_blocks(); ii > 0; --ii) {
size_type i = ii-1;
if (a.m_bits[i] < b.m_bits[i])
return true;
else if (a.m_bits[i] > b.m_bits[i])
return false;
}
//相等时返回false
return false;
}
//<= 运算符
template <typename Block, typename Allocator>
inline bool operator<=(const dynamic_bitset<Block, Allocator>& a,
const dynamic_bitset<Block, Allocator>& b)
{
return !(a > b);
}
//> 运算符
template <typename Block, typename Allocator>
inline bool operator>(const dynamic_bitset<Block, Allocator>& a,
const dynamic_bitset<Block, Allocator>& b)
{
return b < a;
}
//>= 运算符
template <typename Block, typename Allocator>
inline bool operator>=(const dynamic_bitset<Block, Allocator>& a,
const dynamic_bitset<Block, Allocator>& b)
{
return !(a < b);
}
//-----------------------------------------------------------------------------
// stream operations
//重载输出<< 运算符
#ifdef BOOST_OLD_IOSTREAMS
template < typename Block, typename Alloc>
std::ostream&
operator<<(std::ostream& os, const dynamic_bitset<Block, Alloc>& b)
{
// NOTE: since this is aimed at "classic" iostreams, exception
// masks on the stream are not supported. The library that
// ships with gcc 2.95 has an exceptions() member function but
// nothing is actually implemented; not even the class ios::failure.
using namespace std;
const ios::iostate ok = ios::goodbit;
ios::iostate err = ok;
if (os.opfx()) {
//try
typedef typename dynamic_bitset<Block, Alloc>::size_type bitsetsize_type;
const bitsetsize_type sz = b.size();
std::streambuf * buf = os.rdbuf();
size_t npad = os.width() <= 0 // careful: os.width() is signed (and can be < 0)
|| (bitsetsize_type) os.width() <= sz? 0 : os.width() - sz;
const char fill_char = os.fill();
const ios::fmtflags adjustfield = os.flags() & ios::adjustfield;
// if needed fill at left; pad is decresed along the way
if (adjustfield != ios::left) {
for (; 0 < npad; --npad)
if (fill_char != buf->sputc(fill_char)) {
err |= ios::failbit;
break;
}
}
if (err == ok) {
// output the bitset
for (bitsetsize_type i = b.size(); 0 < i; --i) {
const char dig = b.test(i-1)? '1' : '0';
if (EOF == buf->sputc(dig)) {
err |= ios::failbit;
break;
}
}
}
if (err == ok) {
// if needed fill at right
for (; 0 < npad; --npad) {
if (fill_char != buf->sputc(fill_char)) {
err |= ios::failbit;
break;
}
}
}
os.osfx();
os.width(0);
} // if opfx
if(err != ok)
os.setstate(err); // assume this does NOT throw
return os;
}
#else
template <typename Ch, typename Tr, typename Block, typename Alloc>
std::basic_ostream<Ch, Tr>&
operator<<(std::basic_ostream<Ch, Tr>& os,
const dynamic_bitset<Block, Alloc>& b)
{
using namespace std;
const ios_base::iostate ok = ios_base::goodbit;
ios_base::iostate err = ok;
typename basic_ostream<Ch, Tr>::sentry cerberos(os);
if (cerberos) {
BOOST_DYNAMIC_BITSET_CTYPE_FACET(Ch, fac, os.getloc());
const Ch zero = BOOST_DYNAMIC_BITSET_WIDEN_CHAR(fac, '0');
const Ch one = BOOST_DYNAMIC_BITSET_WIDEN_CHAR(fac, '1');
try {
typedef typename dynamic_bitset<Block, Alloc>::size_type bitsetsize_type;
typedef basic_streambuf<Ch, Tr> buffer_type;
buffer_type * buf = os.rdbuf();
size_t npad = os.width() <= 0 // careful: os.width() is signed (and can be < 0)
|| (bitsetsize_type) os.width() <= b.size()? 0 : os.width() - b.size();
const Ch fill_char = os.fill();
const ios_base::fmtflags adjustfield = os.flags() & ios_base::adjustfield;
// if needed fill at left; pad is decresed along the way
if (adjustfield != ios_base::left) {
for (; 0 < npad; --npad)
if (Tr::eq_int_type(Tr::eof(), buf->sputc(fill_char))) {
err |= ios_base::failbit;
break;
}
}
if (err == ok) {
// output the bitset
for (bitsetsize_type i = b.size(); 0 < i; --i) {
typename buffer_type::int_type
ret = buf->sputc(b.test(i-1)? one : zero);
if (Tr::eq_int_type(Tr::eof(), ret)) {
err |= ios_base::failbit;
break;
}
}
}
if (err == ok) {
// if needed fill at right
for (; 0 < npad; --npad) {
if (Tr::eq_int_type(Tr::eof(), buf->sputc(fill_char))) {
err |= ios_base::failbit;
break;
}
}
}
os.width(0);
} catch (...) { // see std 27.6.1.1/4
bool rethrow = false;
try { os.setstate(ios_base::failbit); } catch (...) { rethrow = true; }
if (rethrow)
throw;
}
}
if(err != ok)
os.setstate(err); // may throw exception
return os;
}
#endif
#ifdef BOOST_OLD_IOSTREAMS
// A sentry-like class that calls isfx in its destructor.
// "Necessary" because bit_appender::do_append may throw.
class pseudo_sentry {
std::istream & m_r;
const bool m_ok;
public:
explicit pseudo_sentry(std::istream & r) : m_r(r), m_ok(r.ipfx(0)) { }
~pseudo_sentry() { m_r.isfx(); }
operator bool() const { return m_ok; }
};
//重载输入>>运算符
template <typename Block, typename Alloc>
std::istream&
operator>>(std::istream& is, dynamic_bitset<Block, Alloc>& b)
{
// Extractor for classic IO streams (libstdc++ < 3.0)
// ----------------------------------------------------//
// It's assumed that the stream buffer functions, and
// the stream's setstate() _cannot_ throw.
typedef dynamic_bitset<Block, Alloc> bitset_type;
typedef typename bitset_type::size_type size_type;
std::ios::iostate err = std::ios::goodbit;
pseudo_sentry cerberos(is); // skips whitespaces
if(cerberos) {
b.clear();
const std::streamsize w = is.width();
const size_type limit = w > 0 && static_cast<size_type>(w) < b.max_size()
? w : b.max_size();
typename bitset_type::bit_appender appender(b);
std::streambuf * buf = is.rdbuf();
for(int c = buf->sgetc(); appender.get_count() < limit; c = buf->snextc() ) {
if (c == EOF) {
err |= std::ios::eofbit;
break;
}
else if (char(c) != '0' && char(c) != '1')
break; // non digit character
else {
try {
appender.do_append(char(c) == '1');
}
catch(...) {
is.setstate(std::ios::failbit); // assume this can't throw
throw;
}
}
} // for
}
is.width(0);
if (b.size() == 0)
err |= std::ios::failbit;
if (err != std::ios::goodbit)
is.setstate (err); // may throw
return is;
}
#else // BOOST_OLD_IOSTREAMS
template <typename Ch, typename Tr, typename Block, typename Alloc>
std::basic_istream<Ch, Tr>&
operator>>(std::basic_istream<Ch, Tr>& is, dynamic_bitset<Block, Alloc>& b)
{
using namespace std;
typedef dynamic_bitset<Block, Alloc> bitset_type;
typedef typename bitset_type::size_type size_type;
const streamsize w = is.width();
const size_type limit = 0 < w && static_cast<size_type>(w) < b.max_size()?
w : b.max_size();
ios_base::iostate err = ios_base::goodbit;
typename basic_istream<Ch, Tr>::sentry cerberos(is); // skips whitespaces
if(cerberos) {
// in accordance with prop. resol. of lib DR 303 [last checked 4 Feb 2004]
BOOST_DYNAMIC_BITSET_CTYPE_FACET(Ch, fac, is.getloc());
const Ch zero = BOOST_DYNAMIC_BITSET_WIDEN_CHAR(fac, '0');
const Ch one = BOOST_DYNAMIC_BITSET_WIDEN_CHAR(fac, '1');
b.clear();
try {
typename bitset_type::bit_appender appender(b);
basic_streambuf <Ch, Tr> * buf = is.rdbuf();
typename Tr::int_type c = buf->sgetc();
for( ; appender.get_count() < limit; c = buf->snextc() ) {
if (Tr::eq_int_type(Tr::eof(), c)) {
err |= ios_base::eofbit;
break;
}
else {
const Ch to_c = Tr::to_char_type(c);
const bool is_one = Tr::eq(to_c, one);
if (!is_one && !Tr::eq(to_c, zero))
break; // non digit character
appender.do_append(is_one);
}
} // for
}
catch (...) {
// catches from stream buf, or from vector:
//
// bits_stored bits have been extracted and stored, and
// either no further character is extractable or we can't
// append to the underlying vector (out of memory)
bool rethrow = false; // see std 27.6.1.1/4
try { is.setstate(ios_base::badbit); }
catch(...) { rethrow = true; }
if (rethrow)
throw;
}
}
is.width(0);
if (b.size() == 0 /*|| !cerberos*/)
err |= ios_base::failbit;
if (err != ios_base::goodbit)
is.setstate (err); // may throw
return is;
}
#endif
//-----------------------------------------------------------------------------
// bitset operations（全局函数）
//位比较函数
//按位与（求交集）
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>
operator&(const dynamic_bitset<Block, Allocator>& x,
const dynamic_bitset<Block, Allocator>& y)
{
//创建对象（拷贝构造）
dynamic_bitset<Block, Allocator> b(x);
//调用与等函数
return b &= y;
}
//按位或（求并集）
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>
operator|(const dynamic_bitset<Block, Allocator>& x,
const dynamic_bitset<Block, Allocator>& y)
{
dynamic_bitset<Block, Allocator> b(x);
return b |= y;
}
//按位异或
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>
operator^(const dynamic_bitset<Block, Allocator>& x,
const dynamic_bitset<Block, Allocator>& y)
{
dynamic_bitset<Block, Allocator> b(x);
return b ^= y;
}
//求差集
template <typename Block, typename Allocator>
dynamic_bitset<Block, Allocator>
operator-(const dynamic_bitset<Block, Allocator>& x,
const dynamic_bitset<Block, Allocator>& y)
{
dynamic_bitset<Block, Allocator> b(x);
return b -= y;
}
//-----------------------------------------------------------------------------
// namespace scope swap
//交换函数
template<typename Block, typename Allocator>
inline void
swap(dynamic_bitset<Block, Allocator>& left,
dynamic_bitset<Block, Allocator>& right) // no throw
{
left.swap(right);
}
//-----------------------------------------------------------------------------
// private (on conforming compilers) member functions
//返回需要的Block数量
template <typename Block, typename Allocator>
inline typename dynamic_bitset<Block, Allocator>::size_type
dynamic_bitset<Block, Allocator>::calc_num_blocks(size_type num_bits)
{
//num_bit代表要扩展的位数
//bits_per_block代表每一个Block有几个比特
//例如int 有32个比特
return num_bits / bits_per_block
+ static_cast<int>( num_bits % bits_per_block != 0 );
}
// gives a reference to the highest block
//引用返回
template <typename Block, typename Allocator>
inline Block& dynamic_bitset<Block, Allocator>::m_highest_block()
{
return const_cast<Block &>
(static_cast<const dynamic_bitset *>(this)->m_highest_block());
}
// gives a const-reference to the highest block
//返回vector的最后一个元素（常引用返回）
template <typename Block, typename Allocator>
inline const Block& dynamic_bitset<Block, Allocator>::m_highest_block() const
{
assert(size() > 0 && num_blocks() > 0);
return m_bits.back();
}
// If size() is not a multiple of bits_per_block
// then not all the bits in the last block are used.
// This function resets the unused bits (convenient
// for the implementation of many member functions)
//
template <typename Block, typename Allocator>
inline void dynamic_bitset<Block, Allocator>::m_zero_unused_bits()
{
//calc_num_block():返回Block的数量
assert (num_blocks() == calc_num_blocks(m_num_bits));
// if != 0 this is the number of bits used in the last block
//count_extra_bits:判断二进制位是否为Block的倍数 size() / 每个块所占的比特数
const block_width_type extra_bits = count_extra_bits();
//当extra_bits不为0时说明二进制位数不是Block的倍数，存在未使用的比特位
//将未使用的比特置0
if (extra_bits != 0)
m_highest_block() &= ~(~static_cast<Block>(0) << extra_bits);
}
// check class invariants
// 检查是否越界
template <typename Block, typename Allocator>
bool dynamic_bitset<Block, Allocator>::m_check_invariants() const
{
//count_extra_bits:判断二进制位是否为Block的倍数 size() / 每个块所占的比特数
const block_width_type extra_bits = count_extra_bits();
//当extra_bits不为0时说明二进制位数不是Block的倍数，存在未使用的比特位
if (extra_bits > 0) {
//获取掩码
block_type const mask = (~static_cast<Block>(0) << extra_bits);
//将高位与掩码相与，当不为0时返回false
if ((m_highest_block() & mask) != 0)
return false;
}
if (m_bits.size() > m_bits.capacity() || num_blocks() != calc_num_blocks(size()))
return false;
return true;
}
} // namespace boost
#undef BOOST_BITSET_CHAR
#endif // include guard
下面对于整个类的实现做一个简单的说明：
整个类的私有数据成员包括两个： （1）m_ bits （2）m_num_bits
(1)m_bits是一个vector<Block>的数组，其类型参数Block默认为unsigned long，代表m_bits其实就是一个数组，其每个元素的类型就是unsigned long
（2）m_num_bits:二进制的位数，
数组的每一个比特就是用来保存二进制位，所有的操作都是围绕这这个数组进行的。
下面对于该类的一些操作函数简单的说明：
（a）构造函数：
该类提供了多种构造方式：
构建空的对象。
使用二进制进行构造。
使用“01”字符串进行构造。
使用unsigned long 数进行构造
使用另一个对象进行拷贝构造。
注：dynamic_bitset内部按照由高到低的顺序存储二进制位，也就是说，第0个元素存储最低位。
（b）容器的操作：
resize（）：调整容器的大小，扩展或收缩都是允许的，如果是扩展，原有的二进制位保持不变，新增加的二进制位用指定值置位，如果是收缩，收缩后容器的二进制位保持不变，多余的位被抛弃。
push_back（）：向容器末尾追加一个值；
append（）：把整数转换位二进制位全部追加到末尾。
（c）比较操作与位运算
==、&= 、|=、-=；
&、|、^等
（d）访问元素：
test（）：检测第n位是否为1
any（）：二进制位中存在1返回true
none（）：二进制位中存在0返回true
count（）：统计二进制位为1的数量
set（）：将某一位或所有位置1或置0
reset（）：将某一位或所有位置0
flip（）：反转某一位或所有位
find_first（）：从第0位置开始查找，返回第一个为1的位置
find_next（）：从第pos位置开始查找，返回第一个为1的位置，找不到返回npos
（e）类型转换：
to_ulong（）：将二进制转换为unsigned long
to_string（）：将二进制转换为一个标准字符串
（f）集合操作：
is_subset_of（）：检测一个对象是否为另一个对象的子集
is_proper_subset_of（）：检测一个对象是否为另一个对象的真子集
并集、交集、差集
上述就是类的一些基本的操作，每个函数的实现也都进行了注释，希望对大家有帮助。。。。
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原文地址：http://blog.csdn.net/ooooo12345re/article/details/51619961
