4 ms·

But adding 1 to a pointer will add sizeof(T) to the underlying value, so you actually need to reserve more than two addresses if you want to distinguish the "pa

by ynik 1y ago

But adding 1 to a pointer will add sizeof(T) to the underlying value, so you actually need to reserve more than two addresses if you want to distinguish the "past-the-end" pointer for every object from NULL. -- 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.

Joker_vD 1y ago
> so you actually need to reserve more than two addresses if you want to distinguish the "past-the-end" pointer for every object from NULL. 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.