读了codeproject上的这篇《An introduction to bitwise operators》,前面两个运算符说得不错,但第三个异或运算符感觉不够准确,作者给出的示例不知道有什么用处,不就是把数做了两次异或又回来了么?
&运算符用来判定某些位是0还是1:
#include <iostream>
using namespace std;
int main(void)
{
int num = 17;
if(num&0x10)
{
cout<<"第四位是"<<endl;
}
else
{
cout<<"第四位是"<<endl;
}
return 0;
}
|运算符用来对某些位置1:
#include <iostream>
using namespace std;
int main(void)
{
int num = 50;
num = num|0x04;
cout<<hex<<num<<endl;
return 0;
}
异或运算符最常用的应该是用其实现两个数的交换:
#include <iostream>
using namespace std;
int main(void)
{
int n1 = 17,n2 = 20;
n1 = n1^n2;
n2 = n2^n1;
n1 = n1^n2;
cout<<n1<<" "<<n2<<endl;
return 0;
}
将取反运算符和与运算符结合起来,可以对某些位置零:
#include <iostream>
using namespace std;
int main(void)
{
int b = 50;
cout << "b = " << b << endl;
int c = b & ~0x10;
cout <<hex<< "c = " << c << endl;
return 0;
}
最后的位域有一个问题没搞懂:
#include <iostream>
using namespace std;
struct date_struct
{
int day:4, // 1 to 31
month : 4, // 1 to 12
year:12;
};
int main(void)
{
date_struct d1;
d1.day = 8;
d1.month = 8;
d1.year = 1844;
cout<<d1.year<<" "<<d1.month<<" "<<d1.day<<endl;
return 0;
}
我已经设置day和month各自占据4位,应该是可以满足的,可结果却都是-8,why?
本文转自Phinecos(洞庭散人)博客园博客,原文链接:http://www.cnblogs.com/phinecos/archive/2007/12/15/996211.html,如需转载请自行联系原作者