2. 举例来说明container_of的使用
1>正确示例:
#include
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
struct test_struct {
int num;
char ch;
float f1;
};
int main(void)
{
struct test_struct *test_struct;
struct test_struct init_struct ={12,'a',12.3};
char *ptr_ch = &init_struct.ch;
test_struct = container_of(ptr_ch,struct test_struct,ch);
printf("test_struct->num =%d\n",test_struct->num);
printf("test_struct->ch =%c\n",test_struct->ch);
printf("test_struct->ch =%f\n",test_struct->f1);
return 0;
}
执行结果：
jibo@jibo-VirtualBox:~/cv_work/work/list/container_of $ ./main
test_struct->num =12
test_struct->ch =a
test_struct->ch =12.300000

2>错误示例：
#include
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
struct test_struct {
int num;
char ch;
float f1;
};
int main(void)
{
struct test_struct *test_struct;
char real_ch = 'A';
char *ptr_ch = &real_ch;
test_struct = container_of(ptr_ch,struct test_struct,ch);
printf("test_struct->num =%d\n",test_struct->num);
printf("test_struct->ch =%c\n",test_struct->ch);
printf("test_struct->ch =%f\n",test_struct->f1);
return 0;
}
执行结果为:
jibo@jibo-VirtualBox:~/cv_work/work/list/container_of1 $ ./main
test_struct->num =0
test_struct->ch =A
test_struct->ch =0.000000
注意，由于这里并没有使用一个具体的结构体变量，所以成员num和f1的值是不确定的。