And if you use 0 as the value of NULL pointer, then -1 can't ever point to an object (because adding 1 to it should generate a non-NULL pointer, so that pointer comparisons are not UB).
So yeah, C implementations have to reserve at least two addresses, not just one. By the way, the standard to this day allows NULL, when cast to a pointer type, to be something else than all-bits-zero pattern (and some implementations indeed took this opportunity).
So yeah, C implementations have to reserve at least two addresses, not just one. By the way, the standard to this day allows NULL, when cast to a pointer type, to be something else than all-bits-zero pattern (and some implementations indeed took this opportunity).