C-union的使用

 1 #include <iostream>
 2 using namespace std;
 3 
 4 //作用1，如果只是存a，20000000 个s_tag节约20M空间
 5 union s_tag { int a[100];
 6 char aaa; };
 7 s_tag fa, sa, ua;
 8 s_tag multiple(s_tag s) {
 9     int j;
10     for(j = 0; j < 100; j++)
11         s.a[j] *= 2; 
12     return s;
13 }
14 
15 //作用2，将同样一块32位内存解释为int或者分为四块解释为char
16 union bit32_tag{
17     int whole;
18     struct {char c0, c1, c2, c3; } byte;
19 } v;
20 
21 int main() {
22     fa.aaa = ‘a‘;
23     //for(int j = 0; j < 100; j++)
24     //    fa.a[j] = j; 
25     for(int j = 0; j < 100; j++)
26         cout << fa.a[j] << endl; 
27     cout << "aaa:" << fa.aaa << endl;
28 
29     //‘A‘
30     v.whole = 65;
31     cout << "v.byte.c0: " << v.byte.c0 << endl;
32     cout << "v.byte.c1: " << v.byte.c1 << endl;
33     cout << "v.byte.c2: " << v.byte.c2 << endl;
34     cout << "v.byte.c3: " << v.byte.c3 << endl; 
35 
36     return 0;
37 }

97
..
...
....
0
0
aaa:a
v.byte.c0: a
v.byte.c1:
v.byte.c2:
v.byte.c3: