* Marek Polacek: > On Thu, Nov 10, 2022 at 07:25:21PM +0100, Florian Weimer via Gcc wrote: >> GCC accepts various conversions between pointers and ints and different >> types of pointers by default, issuing a warning. >> >> I've been reading the (hopefully) relevant partso f the C99 standard, >> and it seems to me that C implementations are actually required to >> diagnose errors in these cases because they are constraint violations: >> the types are not compatible. > > It doesn't need to be a hard error, a warning is a diagnostic message, > which is enough to diagnose a violation of any syntax rule or > constraint. > > IIRC, the only case where the compiler _must_ emit a hard error is for > #error.
Hmm, you could be right. The standard says that constraint violations are not undefiend behavior, but of course it does not define what happens in the presence of a constraint violation. So the behavior is undefined by omission. This seems to be a contradiction. I assumed that there was a rule similar to the the rule for #error for any kind of diagnostic, which would mean that GCC errors are diagnostic messages in the sense of the standard, but GCC warnings are not. I wonder how C++ handles this. Thanks, Florian
