C 语言位域使用及其注意事项
#include "stdio.h"void main(int argn ,char *argv){ struct test { unsigned a:10; unsigned b:10; unsigned c:6; unsigned :2;//this two bytes can't use unsigned d:4; }data,*pData; data.a=0x177; data.b=0x111; data.c=0x7; data.d=0x8; pData=&data; printf("data.a=%x data.b= %x data.c=%x data.d=%xn",pData->a,pData->b,pData->c,pData->d);//位域可以使用指针 printf("sizeof(data)=%dn",sizeof(data)); //4 bytes ,最常用的情况 struct testLen{ char a:5; char b:5; char c:5; char d:5; char e:5; }len; printf("sizeof(len)=%dn",sizeof(len)); //5bytes 规则2 struct testLen1{ char a:5; char b:2; char d:3; char c:2; char e:7; }len1; printf("sizeof(len1) =%dn",sizeof(len1)); //3bytes 规则1 struct testLen2{ char a:2; char :3; char b:7; long d:20; //4bytes char e:4; }len2; printf("sizeof(len2)=%dn",sizeof(len2)); //12 规则3,4,5,总长为4的整数倍,2+3 占1byte,b占1bye 由于与long对其,2+3+7 占4字节,后面 d 与 e进行了优化 占一个4字节 struct testLen3{ char a:2; char :3; char b:7; long d:30; char e:4; }len3; printf("sizeof(len3)=%dn",sizeof(len3));//12 规则3,4,5,总长为4的整数倍,2+3 占1byte,b占1bye 由于与long对其,2+3+7 占4字节,后面 d占一个4字节,为了保证与long对其e独占一个4字节}
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