That's not the point, though. In the case of undefined behavior, a compiler doesn't have to define the behavior or even act consistently (most evident by the be

That's not the point, though. In the case of undefined behavior, a compiler doesn't have to define the behavior or even act consistently (most evident by the behavior of the compiler's optimizer). This is entirely different than implementation defined in that a conforming compiler has to document the behavior they implement and do it consistently.