c 位域

#include<stdio.h>struct Date1{  unsigned int year;//4个字节  unsigned int month;  unsigned int day;  unsigned int hour;  unsigned int minute;  unsigned int second;};struct Date2{  unsigned int year ;  unsigned int month: 4;//4bit  unsigned int day: 5;  unsigned int : 0;//空域，下面的从下一单元开始存放  unsigned int hour: 5;  unsigned int minute: 6;  unsigned int second: 6;};struct Date3{  unsigned int year ;  unsigned int month: 4;  unsigned int day: 5;  unsigned int : 0;//空域，下面的从下一单元开始存放  unsigned int hour: 5;  unsigned int minute: 6;  unsigned int second: 30;//注意，此处不能超过一个int的位数大小（本机为32bit）};int main(){    printf("%d\n",sizeof(struct Date1));    printf("%d\n",sizeof(struct Date2));    printf("%d\n",sizeof(struct Date3));    return 0;}

The result is ：

241216Process returned 0 (0x0)   execution time : 0.196 sPress any key to continue.

位域的讲解可以参考

http://hi.baidu.com/xiao1dian/item/7cfa8e0e9d0e51cc905718ed

http://tonybai.com/2013/05/21/talk-about-bitfield-in-c-again/

例2：

#include <stdio.h>//#pragma pack(push,1)//#pragma pack(push,2)#pragma pack(push,4)struct A{char t:4;char k:4;unsigned short i:8;unsigned long m;};#pragma pop()int main(){printf("%d",sizeof(A));return 0;}

the result is

6、6、8

参考http://bbs.csdn.net/topics/330138880