typedef struct data_t{
  int x;
  int y;
}data_t;

int main(){
  data_t data;
  int *k=&(data.x);
  data_t *dptr;

  data.x=0;
  data.x=1;
  dptr=(data_t *)((char *)k- (unsigned long)(&((data_t *)0)->x));
  dptr->x=100;
  dptr->y=100;
  $assert(data.x==100 && data.y==100);
}