Trying out container_of macro

container_of.c

#include <stdio.h>

struct inner {  };

struct outer {
    int a;
    char b;
    float c;
    struct inner obj;
    char asdf[];
};

#define member_type(type, member) (((type *)0)->member)
#define offsetof(type, member)	((size_t) &member_type(type, member))

#define container_of(ptr, type, member) \
    ({ const typeof(member_type(type, member)) *m = (ptr); \
    (type *) ((char *) m - offsetof(type, member)); })

int main() {
    struct outer o = { .a = 3, .b = 5, .c = 3.14 };
    struct inner *inner = &o.obj;

    struct outer *oo = container_of(inner, struct outer, obj);
    printf("%d %d %f\n", oo->a, oo->b, oo->c);

    int x = ({1; 2;}) + 3;
    printf("%d\n", x);

    printf("%d\n", offsetof(struct outer, c));

    return 0;
}