GCC 中允许使用零长数组(__GNUC__ >= 3)。
零长数组在有固定头部的可变对象上非常适用，我们可以根据对象的大小动态地去分配结构体的大小。
gui ftk里经常用的。在分配内存时，零长数组指向变长的PrivInfo。
FTK_ZALLOC(sizeof(FtkSource) + sizeof(PrivInfo))
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50 |
#if __GNUC__ >= 3#define ZERO_LEN_ARRAY 0#else#define ZERO_LEN_ARRAY 1#endif struct
_FtkSource{ FtkSourceGetFd get_fd; FtkSourceCheck check; FtkSourceDispatch dispatch; FtkSourceDestroy destroy; int
ref; int
disable; char
priv[ZERO_LEN_ARRAY];}; typedef
struct _PrivInfo{ FtkTimer action; void* user_data; size_t
interval; size_t
next_time;}PrivInfo; FtkSource* ftk_source_timer_create(int
interval, FtkTimer action, void* user_data){ FtkSource* thiz = NULL; return_val_if_fail(interval > 0 && action != NULL, NULL); thiz = (FtkSource*)FTK_ZALLOC(sizeof(FtkSource) + sizeof(PrivInfo)); if(thiz != NULL) { DECL_PRIV(thiz, priv); //PrivInfo* priv = PrivInfo*(thiz->priv); //zlz comment thiz->get_fd = ftk_source_timer_get_fd; thiz->check = ftk_source_timer_check; thiz->dispatch = ftk_source_timer_dispatch; thiz->destroy = ftk_source_timer_destroy; thiz->ref = 1; priv->interval = interval; priv->user_data = user_data; priv->action = action; ftk_source_timer_calc_timer(priv); } return
thiz;} |
demo
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78 |
#ifdef __cplusplusextern
"C"{#endif #include <stdio.h>#include <string.h>#if __GNUC__ >= 3#define ZERO_LEN_ARRAY 0#else#define ZERO_LEN_ARRAY 1#endiftypedef
struct taglcgi_msg_head{ //MessageHead mh; int
is_return; int
result; int
reason; char
user[32]; char
ipaddr[16]; //char priv[0];}LCGI_MSG_HEAD, *PLCGI_MSG_HEAD; typedef
struct taglcgi_msg_head0{ //MessageHead mh; int
is_return; int
result; int
reason; char
user[32]; char
ipaddr[16]; char
priv[0]; //不占空间，用的时候才占}LCGI_MSG_HEAD0, *PLCGI_MSG_HEAD0; typedef
struct taglcgi_msg_head1{ //MessageHead mh; int
is_return; int
result; int
reason; char
user[32]; char
ipaddr[16]; char
priv[1]; //大小/功能都等同于void* priv}LCGI_MSG_HEAD1, *PLCGI_MSG_HEAD1; typedef
struct taglcgi_msg_head2{ //MessageHead mh; int
is_return; int
result; int
reason; char
user[32]; char
ipaddr[16]; void* priv; //大小/功能都等同于void* priv}LCGI_MSG_HEAD2, *PLCGI_MSG_HEAD2; int
main(int
argc,char* argv[]){ printf("sizeof(LCGI_MSG_HEAD) len %d\n", sizeof(LCGI_MSG_HEAD)); printf("sizeof(LCGI_MSG_HEAD0) len %d\n", sizeof(LCGI_MSG_HEAD0)); printf("sizeof(LCGI_MSG_HEAD1) len %d\n", sizeof(LCGI_MSG_HEAD1)); printf("sizeof(LCGI_MSG_HEAD2) len %d\n", sizeof(LCGI_MSG_HEAD2)); char
*p ="123"; //char const *p ="123"; p = "3214545"; //p[1] = ‘d‘; printf("p %s\n", p); return
0;} #ifdef __cplusplus}#endif |
原文：http://www.cnblogs.com/freezlz/p/3590148.html