Chapter 12.特殊容器bitset

bitset簡介

bitset是一個特殊的容器用來存儲位的狀態，元素只可能是0、1或者true、false

bitset這個類非常類似一般的數組，但是被優化爲一個元素只用1個位來存儲，但是因爲C++環境中不存在這麼小的類型，所以用最小的bool類型來模擬

bitset可以隨機訪問，即支持下標訪問

Constructor

1.bitset ( );

2.bitset ( unsigned long val );

3.template<class charT, class traits, class Allocator>

explicit bitset ( const basic_string<charT,traits,Allocator>& str,

   typename basic_string<charT,traits,Allocator>::size_type pos = 0,

   typename basic_string<charT,traits,Allocator>::size_type n =

      basic_string<charT,traits,Allocator>::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<N>& operator&= (const bitset<N>& rhs);

bitset<N>& operator|= (const bitset<N>& rhs);

bitset<N>& operator^= (const bitset<N>& rhs);

bitset<N>& operator<<= (size_t pos);

bitset<N>& operator>>= (size_t pos);

bitset<N> operator~() const;

bitset<N> operator<<(size_t pos) const;

bitset<N> operator>>(size_t pos) const;

bool operator== (const bitset<N>& rhs) const;

bool operator!= (const bitset<N>& rhs) const;

*** global functions: ***

template<size_t N>

  bitset<N> operator& (const bitset<N>& lhs, const bitset<N>& rhs);

template<size_t N>

  bitset<N> operator| (const bitset<N>& lhs, const bitset<N>& rhs);

template<size_t N>

  bitset<N> operator^ (const bitset<N>& lhs, const bitset<N>& rhs);

//

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

template<class charT, class traits, size_t N>

  basic_istream<charT, traits>&

    operator>> (basic_istream<charT,traits>& is, bitset<N>& rhs);

template<class charT, class traits, size_t N>

  basic_ostream<charT, traits>&

    operator<< (basic_ostream<charT,traits>& os, bitset<N>& 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<N>& set ( );//全部設置爲1

2.bitset<N>& set ( size_t pos, bool val = true );//對應位置設置爲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<N>& reset ( );//全部設置爲0

2.bitset<N>& reset ( size_t pos );//對應位置設置爲0

//flip

1.bitset<N>& flip ( );//翻轉bitset，所有的元素，0→1，1→0

2.bitset<N>& flip ( size_t pos );//對應位置翻轉

Bitset operations:

to_ulong	Convert to unsigned long integer//如果bitset轉爲unsigned long太長，則拋出異常
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裏有無元素值爲1，有則返回true，否則返回false
none	Test if no bit is set//看bitset裏有無元素值爲0，有則返回true，否則返回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 <class charT, class traits, class Allocator>

  basic_string<charT,traits,Allocator> to_string() const;

eg:
  string mystring;
  bitset<4> mybits;     // mybits: 0000
  mybits.set();         // mybits: 1111
  mystring=mybits.to_string<char,char_traits<char>,allocator<char> >();
  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<mybits.size(); ++i)
    cout << mybits.test(i) << endl;

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.