struct ThingType * tt = world.thing_types;
for (; NULL != tt && id != tt->id; tt = tt->next);
char * err_intro = "Requested thing type of unused ID ";
struct ThingType * tt = world.thing_types;
for (; NULL != tt && id != tt->id; tt = tt->next);
char * err_intro = "Requested thing type of unused ID ";
sprintf(err, "%s%d.", err_intro, id);
exit_err(NULL == tt, err);
sprintf(err, "%s%d.", err_intro, id);
exit_err(NULL == tt, err);