> Each such allocation shall yield a pointer to an object disjoint from any other object.
Phrasing could be slightly more clear to prevent someone from making the argument that -1 is disjoint from all objects as it does not point to an object
Phrasing could be slightly more clear to prevent someone from making the argument that -1 is disjoint from all objects as it does not point to an object
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).
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While it's rare to find a platform nowadays that uses something other than a zero bit pattern for NULL as normal pointer type; it's extremely common in C++ for pointer-to-member types: 0 is the first field at the start of a struct (offset 0); and NULL is instead represented with -1.
Well, yes and no. A 4-byte int can not reside at -4, but a char could be; but no object can reside at -1. So implementations need to take care that one-past-the-end addresses never equal to whatever happens to serve as nullptr but this requirement only makes address -1 completely unavailable for the C-native objects.