gnu cc扩展

 1 #include <stdio.h>
 2 #include <unistd.h>
 3 #define my_min(x, y)  ({const typeof(x) __x = x;  4     const typeof(y) __y = y;  5     (void) (&__x == &__y);  6     __x < __y ? __x : __y;})
 7 
 8 struct Str
 9 {
10     int a;
11     char b;
12     short c;
13 } __attribute__((packed));
14 
15 #define ERR_PRINTF(fmt, args...) {16     char msg[1024]; 17     snprintf(msg, sizeof(msg), "%s:%d "fmt"\n", __FUNCTION__, __LINE__, ##args);18     printf("%s", msg); 19 }
20 
21 #define likely(x)  __builtin_expect((x), 1)
22 #define unlikely(x)  __builtin_expect((x), 0)
23 
24 void f_unlikely()
25 {
26     printf("go unlikely\n"); 
27 }
28 
29 void f_likely()
30 {
31     printf("go likely\n"); 
32 }
33 
34 
35 void test_likely(int x)
36 {
37     if(unlikely(x))
38         f_unlikely();
39     else
40         f_likely();
41 }
42 
43 int main()
44 {
45     //typeof
46     int c = my_min(1, 2);
47     printf("%d\n", c);
48 
49     //packed
50     printf("sizeof(Str) = %lu\n", sizeof(Str));
51 
52     //##
53     ERR_PRINTF("%d test", 1);
54     ERR_PRINTF("test2");
55 
56     //__builtin_expect
57     test_likely(1);
58 
59     //__builtin_return_address
60     printf("return address %p\n", __builtin_return_address(0));
61     while(1)
62         sleep(10);
63     return 0;
64 }