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Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Tim Rentsch <tr.17687@z991.linuxsc.com> Newsgroups: comp.lang.c Subject: Re: No warning at implicit removal of const. Was: relearning C: why does an in-place change to a char* segfault? Date: Mon, 12 Aug 2024 16:05:29 -0700 Organization: A noiseless patient Spider Lines: 56 Message-ID: <86jzgl1gw6.fsf@linuxsc.com> References: <IoGcndcJ1Zm83zb7nZ2dnZfqnPWdnZ2d@brightview.co.uk> <20240801174026.00002cda@yahoo.com> <v8gi7i$29iu1$1@dont-email.me> <slrnvaorkl.34j6.candycanearter07@candydeb.host.invalid> <87zfpvfdk4.fsf@nosuchdomain.example.com> <86ttfp2zpf.fsf@linuxsc.com> <871q2tiffa.fsf@nosuchdomain.example.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Date: Tue, 13 Aug 2024 01:05:30 +0200 (CEST) Injection-Info: dont-email.me; posting-host="7741d78d7fa92162b25738c81b1a0845"; logging-data="3686921"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX188CBPSvdtoi015VbUW5g07rRt648OGt+0=" User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.4 (gnu/linux) Cancel-Lock: sha1:6vTbZw6m7SDBX9bqSbxHzVpHqEI= sha1:FVU1aSWTsTR7gNzo8O6v5NTCAdk= Bytes: 3196 Keith Thompson <Keith.S.Thompson+u@gmail.com> writes: > Tim Rentsch <tr.17687@z991.linuxsc.com> writes: > >> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes: >> >>> candycanearter07 <candycanearter07@candycanearter07.nomail.afraid> >>> writes: >>> >>>> David Brown <david.brown@hesbynett.no> wrote at 17:56 this Thursday (GMT): >>> >>> [...] >>> >>>>> gcc has the option "-Wwrite-strings" that makes string literals in >>>>> C have "const char" array type, and thus give errors when you try >>>>> to assign to a non-const char * pointer. But the option has to be >>>>> specified explicitly (it is not in -Wall) because it changes the >>>>> meaning of the code and can cause compatibility issues with >>>>> existing correct code. >>>> >>>> -Wwrite-strings is included in -Wpedantic. >>> >>> No it isn't, nor is it included in -Wall -- and it wouldn't make >>> sense to do so. >>> >>> The -Wpedantic option is intended to produce all required >>> diagnostics for the specified C standard. -Wwrite-strings >>> gives string literals the type `const char[LENGTH]`, which >>> enables useful diagnostics but is *non-conforming*. >> >> As long as the -Wwrite-strings diagnostics are only warnings the >> result is still conforming. > > It's not just about diagnostics. This program: > > #include <stdio.h> > int main(void) { > puts(_Generic("hello", > char*: "char*", > const char*: "const char*", > default: "?")); > } > > must print "char*" in a conforming implementation. With > (gcc|clang) -Wwrite-strings, it prints "const char*". Good point. I hadn't considered such cases. > And something as simple as: > > char *p = "hello"; > > is rejected with a fatal error with "-Wwrite-strings -pedantic-errors". That violates the "As long as the -Wwrite-strings diagnostics are only warnings" condition.