That is OK, at least in the sense that there's no undefined behaviour. I'm not sure it's also OK, because the memcmp suggestion you are replying to seems a bit

That is OK, at least in the sense that there's no undefined behaviour. I'm not sure it's also OK, because the memcmp suggestion you are replying to seems a bit suspect. There's still the problem that comparing the uintptr_t's is not guaranteed to yield the same result as the pointers they were cast from. But that's merely implementation-specific behaviour, not undefined.