On Sep 16, 2025, at 04:33, Andrey Semashev via Std-Discussion <std-discussion@lists.isocpp.org> wrote:

On 15 Sep 2025 16:48, David Brown via Std-Discussion wrote:

First ask yourself, is there any reason why you would want to compare
unrelated pointers for ordering?

One common use case is testing whether the pointers point to a subobject
of the same object. For example, if a pointer points within a string or
an array. This check is often needed to properly implement operations on
the string/array, such as selecting the direction of element iteration.

I don't actually think you can do this even with std::less. It's defined to use the implementation-defined strict total order over pointers (https://eel.is/c++draft/defns.order.ptr); that has to be consistent with the < operator, but no other promises are made. So for instance, given `char foo[100];`, if we have `std::greater_equal<char *>{}(foo, p) && std::less<char *>{}(p, foo+3)`, I don't think the standard allows us to conclude that `p == foo || p == foo+1 || p == foo+2`. The converse holds, of course.

Really, the language already defines the logic under the name of
std::less. Why the same logic cannot be invoked as the built-in
operrator< for pointers?

That's what I and others have answered: operator< can be more efficient because it is not required to handle the case of pointers to unrelated objects, and there are implementations where handling this case carries substantial extra cost.