bit 運算

bit的運算其實沒啥了不起,但除非是作跟硬體相關的程式設計,用到的機會還真是不多.
但很不巧的是,有時就是偏偏會碰上,更不巧的是.因為很少碰.所以也就不知道該怎麼寫處理bit的程式.
其實在C++是使用bitset這個class
bitset的操作行為:

any	true if any bits are set
count	returns the number of set bits
flip	reverses the bitset
none	true if no bits are set
reset	sets bits to zero
set	sets bits
size	number of bits that the bitset can hold
test	returns the value of a given bit
to_string	string representation of the bitset
to_ulong	returns an integer representation of the bitset

範例1 (開啟某個bit):

#include 
#include 
using namespace std;

int main ()
{
bitset<4> mybits;

cout << class="comm">// 1111
cout << class="comm">// 1011
cout << class="comm">// 1111

return 0;
}

範例2:
#include 
#include 
#include 
using namespace std;

int main (關閉某個bit)
{
bitset<4> mybits (string("1011"));

cout << class="comm">// 1001
cout << class="comm">// 0000

return 0;
}