c->vftbl->subtype_offset = OFFSET(vftbl_t, subtype_display[0]) + sizeof(void*) * depth;
for (i=depth+1; i<=DISPLAY_SIZE; i++)
c->vftbl->subtype_display[i] = NULL;
c->vftbl->subtype_offset = OFFSET(vftbl_t, subtype_display[0]) + sizeof(void*) * depth;
for (i=depth+1; i<=DISPLAY_SIZE; i++)
c->vftbl->subtype_display[i] = NULL;