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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Baby X is bor nagain
Date: Mon, 24 Jun 2024 07:40:46 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>
>> James Kuyper <jameskuyper@alumni.caltech.edu> writes:
>> [on the requirements for qsort]
>>
>>> I certainly would favor improved wording that made this clearer.
>>> In fact, simply explicitly mandating total ordering rather than
>>> making a vague comment about consistency would probably be the
>>> best approach.
>>
>> Clearly the C standard intends to impose a weaker requirement
>> than that the comparison function be a total ordering.
>
> "That is, for qsort they shall define a total ordering on the
> array".
>
> I presume you didn't intend to contradict that requirement, but
> I can't figure out what you meant -- unless, as Ben suggested,
> you're distinguishing between a total ordering of all possible
> arguments and a total ordering of objects present in the array.
> But even then, the standard explicitly imposes a total ordering.
> (The requirements for bsearch might be weaker, but we're discussing
> qsort.)
>
> Can you clarify what you meant?

For starters, saying that the comparison function defines a total
ordering of elements actually present in the array is already a
weaker requirement than saying that the comparison function defines
a total ordering of all values that might legally be present in the
array.

Now notice that the C standard isn't referring to the comparison
function in the statement quoted above.  The standard does not say
"the comparison function shall define".  What it does say is that
"/they/ shall define".  Those two aren't the same thing.