Path: csiph.com!news.swapon.de!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Keith Thompson Newsgroups: comp.lang.c Subject: Re: "undefined behavior"? Date: Wed, 12 Jun 2024 15:30:52 -0700 Organization: None to speak of Lines: 56 Message-ID: <87y1796bfn.fsf@nosuchdomain.example.com> References: <666a095a$0$952$882e4bbb@reader.netnews.com> <8t3k6j5ikf5mvimvksv2t91gbt11ljdfgb@4ax.com> <666a18de$0$958$882e4bbb@reader.netnews.com> MIME-Version: 1.0 Content-Type: text/plain Injection-Date: Thu, 13 Jun 2024 00:30:53 +0200 (CEST) Injection-Info: dont-email.me; posting-host="32c0f168ad8ff54df06981ba253a92e6"; logging-data="1935800"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/jMtGZKigGaNBGP/UVjCnt" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) Cancel-Lock: sha1:nw9fkPLIJRX1ipIKVXuvgLRyrwU= sha1:YErO+7MdFET652FxrUGnTAynvDk= Xref: csiph.com comp.lang.c:385885 DFS writes: > On 6/12/2024 5:30 PM, Barry Schwarz wrote: >> On Wed, 12 Jun 2024 16:47:23 -0400, DFS wrote: >> >>> Wrote a C program to mimic the stats shown on: >>> >>> https://www.calculatorsoup.com/calculators/statistics/descriptivestatistics.php >>> >>> My code compiles and works fine - every stat matches - except for one >>> anomaly: when using a dataset of consecutive numbers 1 to N, all values >>>> 40 are flagged as outliers. Up to 40, no problem. Random numbers >>> dataset of any size: no problem. >>> >>> And values 41+ definitely don't meet the conditions for outliers (using >>> the IQR * 1.5 rule). >>> >>> Very strange. >>> >>> Edit: I just noticed I didn't initialize a char: >>> before: char outliers[100]; >>> after : char outliers[100] = ""; >>> >>> And the problem went away. Reset it to before and problem came back. >>> >>> Makes no sense. What could cause the program to go FUBAR at data point >>> 41+ only when the dataset is consecutive numbers? >>> Also, why doesn't gcc just do you a solid and initialize to "" for you? >> Makes perfect sense. The first rule of undefined behavior is >> "Whatever happens is exactly correct." You are not entitled to any >> expectations and none of the behavior (or perhaps all of the behavior) >> can be called unexpected. > > I HATE bogus answers like this. > > Aren't you embarrassed to say things like that? He has nothing to be embarrassed about. What he wrote is correct. The C standard's definition of "undefined behavior" is "behavior, upon use of a nonportable or erroneous program construct or of erroneous data, for which this International Standard imposes no requirements". If you don't like the way C deals with undefined behavior, that's perfectly valid, and a lot of people are likely to agree with you. But I advise against lashing out at people who are correctly explaining what the C standard says. DFS, since you've been posting in comp.lang.c for at least ten years, I'm surprised you're having difficulties with this. [...] -- Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com void Void(void) { Void(); } /* The recursive call of the void */