Path: ...!weretis.net!feeder9.news.weretis.net!news.quux.org!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Keith Thompson Newsgroups: comp.lang.c Subject: Re: do { quit; } else { } Date: Mon, 12 May 2025 13:25:30 -0700 Organization: None to speak of Lines: 41 Message-ID: <87ecwt37b9.fsf@nosuchdomain.example.com> References: <868qoaeezc.fsf@linuxsc.com> <86mscqcpy1.fsf@linuxsc.com> <86iknecjz8.fsf@linuxsc.com> <86o6x5at05.fsf@linuxsc.com> <20250409170901.947@kylheku.com> <87wmbs45oa.fsf@nosuchdomain.example.com> <87semf4pw5.fsf@nosuchdomain.example.com> <87zfgn344c.fsf@nosuchdomain.example.com> <20250411142636.00006c00@yahoo.com> <20250411102119.431@kylheku.com> <20250413204521.0000238e@yahoo.com> <861psuziq2.fsf@linuxsc.com> MIME-Version: 1.0 Content-Type: text/plain Injection-Date: Mon, 12 May 2025 22:25:31 +0200 (CEST) Injection-Info: dont-email.me; posting-host="ec3410180c1ee7cec196ae011e16bd7a"; logging-data="1352697"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/eDqhzKHjIVmqf9VOKX0R0" User-Agent: Gnus/5.13 (Gnus v5.13) Cancel-Lock: sha1:qwGLj74KcAgPq5XW+7MHDRzuVzk= sha1:009sGhkCUlIukU1+vhpFH82VmC8= Bytes: 3772 David Brown writes: [...] > For plain integer types, however, I think the argument for making > equal-sized types compatible is a lot stronger. Some compilers > specifically say that they allow aliasing between such types (MSVC, > according to what I have read, have said they never intend to support > "strict aliasing" optimisations). Many software projects (such as > Linux) use "-fno-strict-aliasing". And countless C programmers > mistakenly believe that identically sized integer types are compatible > (though I am not advocating for a weaker language simply because some > users misunderstand the rules). I think that a lot of C programmers misunderstand what "compatible types" means. Many seem to think that two types are compatible if they have the same representation and can be assigned without a cast. In fact type compatibility is a much stricter concept than that. Two types are compatible if they are *the same type*, and in a few other circumstances. For example, char, signed char, and unsigned char are all incompatible with each other, even though two of them are guaranteed to have the same representation. A good way to think about it is that pointers to two types can be assigned without a cast if and only if the two types are compatible. For example, int and long objects can be assigned to each other without a cast, but int* and long* objects cannot. And changing the language to make int and long conditionally compatible would (a) make it too easy to write code that's valid in one implementation but violates a constraint in another, and (b) would break existing code. For example, a generic selection cannot have two associations with compatible types. _Generic with "int:" and "long:" would become invalid for implementations that make int and long compatible. (I wouldn't mind seeing a new form of generic association that selects the *first* matching type, but that's another can of worms.) -- Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com void Void(void) { Void(); } /* The recursive call of the void */