結構體要註意位補齊（有4位補齊和8位補齊，默認8位）

 1 #include<stdio.h>
 2 #pragma pack(push)
 3 #pragma pack(4)
 4 struct test
 5 {    
 6     
 7     char a; //補3位
 8     long c;
 9     char d;
10     char h;//補2位
11     int b;
12     char e;  //補3位或補7位  
13     double f;
14     char g;   //補3位或補7位
15 }s1;
16 #pragma pack(pop)
17
 
 
18 typedef struct{
19     double a;
20     char b;
21 }s2;
22 
23 union test2
24 {    
25     char a;
26     short b;
27 }s3;
28 
29 enum week{sun=7,mon=1,tue,wed,thu,fri,sta};
30 enum week weekday;
31 
32 void main(void)
33 {
34     printf("s1:%d \n",sizeof(s1));
35     printf("s2:%d \n",sizeof(s2));
 
36     printf("s3:%d \n",sizeof(s3));
37     printf("week:%d \n",sizeof(weekday));
38 } 

以下是運行結果

結構體，共用體，枚舉所占內存大小