one trick in C pointer.

#include <stdio.h>#include <stdlib.h>struct common_protocol{    int b;    int c;    int d;};struct Object{    int a;    struct common_protocol *b;};/*really wonderful trickstruct Object *a = malloc(sizeof(struct Object) + sizeof(struct common_protocol));a->b = (struct common_protocol*) (a+1);*/int main(){   struct Object *a = malloc(sizeof(struct Object) + sizeof(struct common_protocol));   //a->b->d = 1;    //error here due to b point to a unknown address or NULL.    a->b = (struct common_protocol*) (a+1);    printf("a: %x\n", a);    printf("b: %x\n", a->b);    printf("a: %x\n", &a->a);    printf("b: %x\n", &a->b);    printf("hello: %x\n", ((struct common_protocol *)a + 1));    a->b->d = 1;    printf("%d\n", a->b->d);    printf("%d\n", a->b->c);   sleep(100);    return 0;}

a: df0200
b: df0208
a: df0200
b: df0204
hello: df020c
1
0