struct，enum和uion

 1 #include <stdio.h>
 2
 3 struct struct_a
 4 {
 5     int a;
 6     int b;
 7 };
 8
 9 enum Weekday
10 {
11     Mon,
12     Tue,
13     sat,
14     sun
15 };
16
17 union bigend
18 {
19     int a;
20     char c;
21 };
22
23 int main()
24 {
25     struct_a sa;
26     sa.b = 2;
27     sa.a = 1;
28
29     printf("struct %d\n",sa.b);
30
31     Weekday wd;
32     wd = sun;
33
34     printf("enum %d\n", wd);
35
36     bigend be;
37     be.a = 97;
38
39     printf("union %c\n",be.c);
40     return 0;
41 }

三者用法相似，enum限定了取值范围，union更多作用应该是在以void*类型拷贝数据后，按内部类型做具体解析。