From owner-freebsd-questions@FreeBSD.ORG Tue Jun 10 13:00:44 2003 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id DA5B837B401 for ; Tue, 10 Jun 2003 13:00:44 -0700 (PDT) Received: from perrin.int.nxad.com (internal.ext.nxad.com [69.1.70.251]) by mx1.FreeBSD.org (Postfix) with ESMTP id 6152543FB1 for ; Tue, 10 Jun 2003 13:00:42 -0700 (PDT) (envelope-from sean@nxad.com) Received: by perrin.int.nxad.com (Postfix, from userid 1001) id 9E5B920F01; Tue, 10 Jun 2003 13:00:41 -0700 (PDT) Date: Tue, 10 Jun 2003 13:00:41 -0700 From: Sean Chittenden To: Malcolm Kay Message-ID: <20030610200041.GR65470@perrin.int.nxad.com> References: <20030609230324.GL65470@perrin.int.nxad.com> <200306101825.33674.malcolm.kay@internode.on.net> <20030610092129.GP65470@perrin.int.nxad.com> <200306101928.30765.malcolm.kay@internode.on.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200306101928.30765.malcolm.kay@internode.on.net> X-PGP-Key: finger seanc@FreeBSD.org X-PGP-Fingerprint: 3849 3760 1AFE 7B17 11A0 83A6 DD99 E31F BC84 B341 X-Web-Homepage: http://sean.chittenden.org/ User-Agent: Mutt/1.5.4i cc: questions@freebsd.org Subject: Re: gcc me harder: -Wconversion bug? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 10 Jun 2003 20:00:45 -0000 > > > It seems to me that this is doing exactly what is claimed for > > > -Wconversion. To quote from the gcc man page: > > > -Wconversion > > > Warn if a prototype causes a type conversion that > > > is different from what would happen to the same ar- > > > gument in the absence of a prototype. ... > > > > > > Now in the absence of a prototype for f() the argument true would be > > > promoted from char/bool to int before being passed to the > > > function. With the prototype in scope it is not promoted. Different > > > argument widths so warning delivered. > > > > % cpp test.c > > # 1 "test7.c" > > # 1 "" > > # 1 "" > > # 1 "test7.c" > > # 1 "test7.h" 1 > > # 13 "test7.h" > > void f(char b); > > # 2 "test7.c" 2 > > > > int > > main(int argc, char *argv[]) { > > f((((char)1))); > > > > return(0); > > } > > > > void > > f(char b) { > > } > > > > Am I missing something that says that there isn't the prototype of > > the same width? Last time I checked my vision, f(char b) was the > > same as f(char b)... :-/ or am I missing something? I believe > > that gcc's promoting the char to an int or to some other non-1 > > byte width data type... but I'm not seeing how, where, or why. > > -sc > > According to the man page we are comaring what does happen with the > prototype in scope with what would have happened if the prototype > was not there. > > You are aware theat the rules of C require that in the absence of a > prototype actual integer calling arguments of less width than int > (usually char and short) must be promoted to int before the call? Wow, that's a really worthless warning. I had to re-read it in the AM to fully appreciate its non-usefulness for properly written software. Thanks... when reading the error message and skimming the man page, I thought it was promoting width of the argument to 4 bytes, not that "in the event that the prototype isn't here, things will get hard to debug." Thank you, for your incite. -sc -- Sean Chittenden