How can pointers be totally ordered?

Question

Pointers in C++ may in general only be compared for equality. By contrast, less-than comparison is only allowed for two pointers that point to subobjects of the same complet

Answer 1

Is it possible to implement the standard library on targets where pointers do not form a global, total order?

Yes. Given any finite set you can always define an arbitrary total order over it.

Consider a simple example where you have only five possible distinct pointer values. Let's call these O (for nullptr), γ, ζ, χ, ψ¹.

Let's say that no pair of two distinct pointers from the four non-null pointers can be compared with <. We can simply arbitrarily say that std::less gives us this order: O ζ γ ψ χ, even if < doesn't.

Of course, implementing this arbitrary ordering in an efficient manner is a matter of quality of implementation.

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¹ I am using Greek letters to remove subconscious notion of order that would arise due to familiarity with the latin alphabet; my apologies to readers that know the Greek alphabet order