From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/7401 Path: news.gmane.org!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: Explicit casts in ctype.h suppress compiler warnings Date: Fri, 17 Apr 2015 12:52:38 -0400 Message-ID: <20150417165238.GA6817@brightrain.aerifal.cx> References: <1429289394.7038.3.camel@inria.fr> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1429289574 29874 80.91.229.3 (17 Apr 2015 16:52:54 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 17 Apr 2015 16:52:54 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-7414-gllmg-musl=m.gmane.org@lists.openwall.com Fri Apr 17 18:52:54 2015 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1Yj9Vc-00005d-D7 for gllmg-musl@m.gmane.org; Fri, 17 Apr 2015 18:52:52 +0200 Original-Received: (qmail 6030 invoked by uid 550); 17 Apr 2015 16:52:51 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 6012 invoked from network); 17 Apr 2015 16:52:50 -0000 Content-Disposition: inline In-Reply-To: <1429289394.7038.3.camel@inria.fr> User-Agent: Mutt/1.5.21 (2010-09-15) Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:7401 Archived-At: On Fri, Apr 17, 2015 at 06:49:54PM +0200, Jens Gustedt wrote: > Am Freitag, den 17.04.2015, 13:59 +0300 schrieb Alexander Monakov: > > For the following erroneous source code: > > > > #include > > int f(char *c) > > { > > return isdigit(c) || isspace(c); > > } > > > > GCC warns only for passing a pointer to isspace; isdigit is implemented as a > > macro that casts its argument to unsigned, and the warning is suppresed > > because the origin of the cast is in a system header. Since isspace is > > implemented with a static inline helper function, there is a warning. With > > glibc headers, no warning is issued in either case for a similar reason. > > I generally think that casts are a bad idea, anyhow, and should only > be used where it must be done, that is basically for pointer to > integer conversion (and back). Code like this > > #define isdigit(a) (((unsigned)(a)-'0') < 10) > > can easily be replaced by > > #define isdigit(a) (((unsigned const){a}-'0') < 10) > > to change the explicit conversion to an implicit one in the > initializer of the compound literal. Then, any compiler would have to > diagnose if "a" would be a pointer. In another place (math.h) I removed this type of compound literal usage because it was incompatible with C++, but the macros are suppressed in C++ anyway. Still they might break -pedantic with -std=c89. I do like this approach best in principle if it works though, because the rules for when an error occurs are basically the same as the rules for a real function. Rich