> I'm not anything other than a C tourist, and I see that the man page says it returns either NULL or a "unique pointer value that can later be successfully passed to free()."

>

> I'm kind of at a loss about why it can return either of those two things, somebody want to take a shot at explaining it?

Any return from malloc, whether it succeeds or not, is a valid argument to `free()`. Hence, it can return NULL because `free(NULL)` is legal, and anything other than NULL has to be a unique pointer, because if it returns a duplicate then calling `free()` no the duplicate will crash.

Both NULL and a unique pointer value can be safely passed to free() :-).

Answers to this question taught me about the candidates taste and understanding of good API design :-).

Both NULL and "unique pointer" are correct answers, but all modern implementations only chose to return one of these. My follow-up question is "why ?" :-).