【位图】STL中bitset的使用

在C++STL中提供了位图的库bitset类，下面记录一下bitset的使用

template <size_t N> class bitset;
//N: Number of bits to contain

构造函数

(1)bitset ( );//空的，默认设置为0

(2)bitset ( unsigned long val );

(3)参数可以使字符串，

使用：

// constructing bitsets
#include <iostream>
#include <string>
#include <bitset>
using namespace std;

int main ()
{
bitset<10> first;                   // empty bitset

bitset<10> second (120ul);          // initialize from unsigned long

bitset<10> third (string("01011")); // initialize from string
cout << first << endl;   // 00000 00000
cout << second << endl;  // 00011 11000（120的二进制表示）
cout << third << endl;  //  00000 01011
return 0;
}

Bit access：operator[]

bool operator[] ( size_t pos ) const;
reference operator[] ( size_t pos );

使用

bitset<4> mybits;

mybits[1]=1;             // 0010
mybits[2]=mybits[1];     // 0110

cout << "mybits: " << mybits << endl

Bit operations:

bit::set

bitset<N>& set ( ); //全部设置为1
bitset<N>& set ( size_t pos, bool val = true );

bit::reset

bitset<N>& reset ( ); //全部设置为0，复位
bitset<N>& reset ( size_t pos ); //指定位置设为0

bitset::flip 取反

changes all 0s for 1s and all 1s for 0s.

改变所有的0位1，改变所有的1位0。

bitset<N>& flip ( ); //全部取反
bitset<N>& flip ( size_t pos );//指定位置取反

Bitset operations:

(1) bitset::to_ulong

将位图转换为unsigned long

unsigned long to_ulong ( ) const;
//Convert to unsigned long integer

bitset<4> mybits;     // mybits: 0000

mybits.set();         // mybits: 1111

mybits.to_ulong();    //  15

(2)bitset::to_string

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

//Convert to string

使用

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; //1111

(3) bitset::count

统计位图中1的个数

size_t count ( );
//Count bits set

使用

bitset<8> myset (string("10110011"));

cout << "myset has " << int(myset.count()) << " ones ";
cout << "and " << int(myset.size()-myset.count()) << " zeros.\n";

// myset has 5 ones and 3 zeros

(4)bitset::size

size_t size() const;
//Return size
//Returns the number of bits in the bitset.

(5)bitset::test

判断某个位置是否被设置为true，

注：位图是从右边起始位置为0的位置，

bool test ( size_t pos ) const;
//Return bit value
//Returns whether bit at position pos in the bitset is set

使用

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;

输出

mybits contains:
true
true
false
true
false

(5)bitset::any

测试所有的bit位是否被设置

bool any ( ) const;
//Test if any bit is set
//Returns whether any of the bits in the bitset is set.

(6)bitset::none

测试是否所有bit位没有被设置

bool none ( ) const;
//Test if no bit is set
//Returns whether none of the bits in the bitset are set.

位图的实现可以参考上篇博客

http://blog.csdn.net/wenqiang1208/article/details/76724338