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Path: ...!feeds.phibee-telecom.net!2.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Ben Bacarisse <ben@bsb.me.uk> Newsgroups: comp.lang.c Subject: Re: The difference between strtol() and strtoul() ? Date: Sun, 23 Jun 2024 16:30:13 +0100 Organization: A noiseless patient Spider Lines: 91 Message-ID: <87jzifpth6.fsf@bsb.me.uk> References: <v51d1l$2fklr$1@news.xmission.com> <v540t9$2gsdu$1@news.xmission.com> <20240621182839.00000dc4@yahoo.com> <20240621185314.00004fda@yahoo.com> <87o77uqktg.fsf@bsb.me.uk> <20240623121952.00005fa9@yahoo.com> <87r0cnq46s.fsf@bsb.me.uk> <20240623153219.000009b0@yahoo.com> MIME-Version: 1.0 Content-Type: text/plain Injection-Date: Sun, 23 Jun 2024 17:30:16 +0200 (CEST) Injection-Info: dont-email.me; posting-host="8e298ef9233142ad2625f347aab31424"; logging-data="436210"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19KwI0LbGBfuPE+3ZiPGnDEdAe4iIiw9bE=" User-Agent: Gnus/5.13 (Gnus v5.13) Cancel-Lock: sha1:ujEOe8CPqA/GCkwqjSkOB0vJ0xI= sha1:BkZVJm93hftXSeKRyxxEOrDQEeM= X-BSB-Auth: 1.764f99bba00de620e70d.20240623163013BST.87jzifpth6.fsf@bsb.me.uk Bytes: 5146 Michael S <already5chosen@yahoo.com> writes: > On Sun, 23 Jun 2024 12:38:51 +0100 > Ben Bacarisse <ben@bsb.me.uk> wrote: > >> Michael S <already5chosen@yahoo.com> writes: >> >> > On Fri, 21 Jun 2024 18:15:07 +0100 >> > Ben Bacarisse <ben@bsb.me.uk> wrote: >> > >> >> Michael S <already5chosen@yahoo.com> writes: >> >> >> >> > On Fri, 21 Jun 2024 18:28:39 +0300 >> >> > Michael S <already5chosen@yahoo.com> wrote: >> >> > >> >> >> On Fri, 21 Jun 2024 13:58:01 -0000 (UTC) >> >> >> gazelle@shell.xmission.com (Kenny McCormack) wrote: >> >> >> > >> >> >> > Yeah, now I get it. You really only need strtoimax() and >> >> >> > strtoumax(). >> >> >> >> >> >> Which are? uunfortunately, not part of C standard. >> >> >> >> >> >> > A result of any smaller type can be obtained by calling one of >> >> >> > these functions and storing the result in an object of the >> >> >> > smaller type. >> >> >> >> >> >> Or check for range and handle out of range values as >> >> >> appropriate by situation. >> >> > >> >> > BTW, I don't know what The Standard says about out-of-range >> >> > inputs, but at least >> >> > https://en.cppreference.com/w/c/string/byte/strtol does not say >> >> > anything certain. especially about what stored in *str_end. >> >> >> >> It says what value should be returned. That's something certain! >> >> >> > >> > In case of strtol, yes. >> > In case of strtoul it also says what value should be returned, but >> > plain reading of cppreference.com text (at least *my* plain reading) >> > does not match observed behaviour. The text on cppreference.com >> > resembles Standard text, but does not match it. >> >> Ah. What's the discrepancy you see? > > IMHO, the Standard texts allows for more interpretations (and > misinterpretations) than cppreference.com text I was hoping for an example. As I've used these functions for decades, I find it hard to see where the alternative interpretations might lie. >> > Also, at least to me, Standard text itself appear very far from >> > clear and way too open to interpretations. >> > My own interpretation would be that for any negative input strtoul() >> > should return ULONG_MAX and set errno to ERANGE. None of the actual >> > implementation that I tested behaves in this manner. >> >> I don't get that from the text. There is, after all, no "negative >> input". There is a "subject sequence" which, if it starts with a >> minus sign, causes the "value resulting from the conversion is >> negated (in the return type)" which seems clear enough. > > I find it less than clear. > The most non-clear part is that for strtouxx() as long as "subject > sequence" is in range, I think it helps to be precise here: the subject sequence has to be of the right form, not in the right range. > it is first converted and then negated. However > when "subject sequence" is out of range it is converted, then clipped > and then *not* negated. If the conversion (before negation) is out of range the result will be ULONG_MAX and errno will be set to ERANGE. Calling this "clipping" is possibly confusing. For what it's worth, I'm just describing what happens. I am not saying it is crystal clear. 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. -- Ben.