From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 40530 invoked by alias); 14 Jun 2018 07:25:30 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Received: (qmail 40371 invoked by uid 89); 14 Jun 2018 07:25:28 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-26.9 required=5.0 tests=BAYES_00,GIT_PATCH_0,GIT_PATCH_1,GIT_PATCH_2,GIT_PATCH_3,SPF_PASS autolearn=ham version=3.3.2 spammy=schwab X-HELO: mx2.suse.de From: Andreas Schwab To: Martin Sebor Cc: GNU C Library Subject: Re: [PATCH] mention disabling GCC built-ins for customization References: <2f2f96d3-5487-f791-8554-310beae0721b@gmail.com> X-Yow: Laundry is the fifth dimension!! ...um...um... th' washing machine is a black hole and the pink socks are bus drivers who just fell in!! Date: Thu, 14 Jun 2018 07:25:00 -0000 In-Reply-To: <2f2f96d3-5487-f791-8554-310beae0721b@gmail.com> (Martin Sebor's message of "Wed, 13 Jun 2018 12:19:00 -0600") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-SW-Source: 2018-06/txt/msg00389.txt.bz2 On Jun 13 2018, Martin Sebor wrote: > diff --git a/manual/stdio.texi b/manual/stdio.texi > index 38be236..d945955 100644 > --- a/manual/stdio.texi > +++ b/manual/stdio.texi > @@ -2963,7 +2963,11 @@ The facilities of this section are declared in the header file > > @strong{Portability Note:} The ability to extend the syntax of > @code{printf} template strings is a GNU extension. ISO standard C has > -nothing similar. > +nothing similar. When using the GNU C compiler or any other compiler > +that interprets calls to standard I/O functions according to the rules > +of the language standard it is necessary to disable such handling by > +the appropriate compiler option. Otherwise the behavior of a program > +that relies on the extension is undefined. The manual already says that redefining existing conversions causes problems: You can redefine the standard output conversions, but this is probably not a good idea because of the potential for confusion. Library routines written by other people could break if you do this. We should extend that with a stronger language, independent of any compiler behaviour. Andreas. -- Andreas Schwab, SUSE Labs, schwab@suse.de GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7 "And now for something completely different."