On Thu, Mar 21, 2013 at 12:45:37PM +0100, Johannes Sixt wrote: > Am 3/21/2013 12:03, schrieb Jeff King: > > I was fooling around with clang and noticed that it complains about the > > "int x = x" construct under -Wall. That is IMHO a deficiency in clang, > > since the idiom has a well-defined use in silencing -Wuninitialized > > warnings. > > IMO, that's a myth. The construct invokes undefined behavior at least > since C99, and the compilers are right to complain about it. While undefined behavior does leave the compiler free to do anything, including nasal demons, it would be a very poor implementation that did anything except leave random bytes in the value. And it also means that gcc is free to take it as a hint to silence the warning; given that clang tries to be compatible with gcc, I'd think it would want to do the same. But I may be wrong that the behavior from gcc is intentional or common (see below). > But you might just say that standards are not worth the paper they are > printed on, and you may possibly be right for practical reasons. But I > still consider it a myth that "int x = x" is an idiom. I'm in the C > business since more than 25 years, and the first time I saw the "idiom" > was in git code. Is there any evidence that the construct is used > elsewhere? Have I been in the wrong corner of the C world for such a long > time? Git code was my introduction to it, too, and I was led to believe it was idiomatic, so I can't speak further on that. I think it was Junio who introduced me to it, so maybe he can shed more light on the history. -Peff -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html