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From: Ben Bacarisse <ben@bsb.me.uk>
Newsgroups: comp.lang.c
Subject: Re: The difference between strtol() and strtoul() ?
Date: Mon, 24 Jun 2024 00:49:13 +0100
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>> Ben Bacarisse <ben@bsb.me.uk> writes:
>> [range questions for strtol(), etc]
>>
>>> I think there /is/ something problematic with the wording about the
>>> negation.  It happens "in the return type" but how can
>>> 9223372036854775808 be negated in the type long long int?  OK, the
>>> negated value can be /represented/ in the type long long int but that's
>>> not quite the same thing.  On the othee hand, for the unsigned return
>>> types, the negation "in the return type" is what produces ULONG_MAX for
>>> "-1" when the negated value, -1, can't be /represented/ in the return
>>> type.  It's a case where, over the years, I've just got used to what's
>>> happening.
>>
>> I understand what these functions do, but their specification in the
>> C standard is a little off.  To my way of thinking the impact is
>> minimal, but the specified behavior is either unequivocally wrong or
>> there are some cases that give rise to undefined behavior.
>
> Can you give an example where the specified behavior causes undefined
> behavior?

I don't want to pre-empt Tim's answer, but the wording that bothers me
is

  "If the subject sequence begins with a minus sign, the value resulting
  from the conversion is negated (in the return type)."

For strtoll("-9223372036854775808", 0, 0) the value resulting from the
conversion is 9223372036854775808 which can not even be represented in
the return type, so how can it be negated "in the return type"?

-- 
Ben.