Chapter 12.特殊容器bitset

bitset简介

bitset是一个特殊的容器用来存储位的状态，元素只可能是0、1或者true、false

bitset这个类非常类似一般的数组，但是被优化为一个元素只用1个位来存储，但是因为C++环境中不存在这么小的类型，所以用最小的bool类型来模拟

bitset可以随机访问，即支持下标访问

Constructor

1.bitset ( );

2.bitset ( unsigned long val );

3.template

explicit bitset ( const basic_string& str,

   typename basic_string::size_type pos = 0,

   typename basic_string::size_type n =

      basic_string::npos);

eg:
  bitset<10> first;                   // empty bitset
  bitset<10> second (120ul);          // initialize from unsigned long to binary is:0001111000
  bitset<10> third (string("01011")); // initialize from string

applicable operators

***

bitset& operator&= (const bitset& rhs);

bitset& operator|= (const bitset& rhs);

bitset& operator^= (const bitset& rhs);

bitset& operator<<= (size_t pos);

bitset& operator>>= (size_t pos);

bitset operator~() const;

bitset operator<<(size_t pos) const;

bitset operator>>(size_t pos) const;

bool operator== (const bitset& rhs) const;

bool operator!= (const bitset& rhs) const;

*** global functions: ***

template

  bitset operator& (const bitset& lhs, const bitset& rhs);

template

  bitset operator| (const bitset& lhs, const bitset& rhs);

template

  bitset operator^ (const bitset& lhs, const bitset& rhs);

//

*** iostream global functions (extraction/insertion): ***

template

  basic_istream&

    operator>> (basic_istream& is, bitset& rhs);

template

  basic_ostream&

    operator<< (basic_ostream& os, bitset& rhs);

eg:
  bitset<4> first (string("1001"));
  bitset<4> second (string("0011"));
  cout << (first^=second) << endl;          // 1010 (XOR,assign)
  cout << (first&=second) << endl;          // 0010 (AND,assign)
  cout << (first|=second) << endl;          // 0011 (OR,assign)
  cout << (first<<=2) << endl;              // 1100 (SHL,assign)
  cout << (first>>=1) << endl;              // 0110 (SHR,assign)
  cout << (~second) << endl;                // 1100 (NOT)
  cout << (second<<1) << endl;              // 0110 (SHL)
  cout << (second>>1) << endl;              // 0001 (SHR)
  cout << (first==second) << endl;          // false (0110==0011)
  cout << (first!=second) << endl;          // true  (0110!=0011)
  cout << (first&second) << endl;           // 0010
  cout << (first|second) << endl;           // 0111
  cout << (first^second) << endl;           // 0101

Bit access:

operator[]

Access bit

eg:
	bitset<10> bs(120UL);
	for (size_t i = 0; i != 10; ++i)
	{
		cout << bs[i];
	}
	bs[1] = bs[2];
	bs[3] = true;

Bit operations:

set	Set bits
reset	Reset bits
flip	Flip bits

//set

1.bitset& set ( );//全部设置为1

2.bitset& set ( size_t pos, bool val = true );//对应位置设置为1

eg:
  bitset<4> mybits;
  cout << mybits.set() << endl;       // 1111
  cout << mybits.set(2,0) << endl;    // 1011
  cout << mybits.set(2) << endl;      // 1111

//reset

1.bitset& reset ( );//全部设置为0

2.bitset& reset ( size_t pos );//对应位置设置为0

//flip

1.bitset& flip ( );//翻转bitset，所有的元素，0→1，1→0

2.bitset& flip ( size_t pos );//对应位置翻转

Bitset operations:

to_ulong	Convert to unsigned long integer//如果bitset转为unsigned long太长，则抛出异常
to_string	Convert to string
count	Count bits set//i.e.,value is 1
size	Return size
test	Return bit value//0 or 1
any	Test if any bit is set//看bitset里有无元素值为1，有则返回true，否则返回false
none	Test if no bit is set//看bitset里有无元素值为0，有则返回true，否则返回false

//to_ulong

eg:
  bitset<4> mybits;     // mybits: 0000
  mybits.set();         // mybits: 1111
  cout << mybits << " as an integer is: " << mybits.to_ulong() << endl;

//to_string

template

  basic_string to_string() const;

eg:
  string mystring;
  bitset<4> mybits;     // mybits: 0000
  mybits.set();         // mybits: 1111
  mystring=mybits.to_string,allocator >();
  cout << "mystring: " << mystring << endl;

Output:

1111

//test

eg:
 bitset<5> mybits (string("01011"));
  cout << "mybits contains:\n";
  cout << boolalpha;
  for (size_t i=0; i

Output:

mybits contains:

true

true

false

true

false

//any

eg:
	bitset<16> mybits;
	cout << "enter a binary number: ";
	cin >> mybits;//1011
	if (mybits.any())
		cout << "mybits has " << (int)mybits.count() << " bits set.\n";
	else cout << "mybits has no bits set.\n";

Output:

mybits has 3 bits set.

//none

eg:
	bitset<16> mybits;
	cout << "enter a binary number: ";
	cin >> mybits;//1011
	if (mybits.none())
		cout << "mybits has no bits unset.\n";
	else
		cout << "mybits has " << (int)mybits.count() << " bits unset.\n";

Output:

mybits has 1 bits unset.