220 30400 article Path: news.gmane.org!.POSTED!not-for-mail From: Chris Hallock Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: P0298: A byte type definition: with undefined pointer arithmetic? Date: Sat, 7 Jan 2017 11:52:21 -0800 (PST) Lines: 71 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1912_1678509821.1483818741705" X-Trace: blaine.gmane.org 1483818751 20877 195.159.176.226 (7 Jan 2017 19:52:31 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 7 Jan 2017 19:52:31 +0000 (UTC) Cc: neilmac@microsoft.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCHINCHEQEFBB5UNYXBQKGQEE5JAOEQ@isocpp.org Sat Jan 07 20:52:26 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pg0-f72.google.com ([74.125.83.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cPx2J-0004Hb-1Z for gclcip-std-proposals@m.gmane.org; Sat, 07 Jan 2017 20:52:19 +0100 Original-Received: by mail-pg0-f72.google.com with SMTP id 5sf1651099872pgi.2 for ; Sat, 07 Jan 2017 11:52:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=wpSOVh4p/PMwG3G8VyROrEM+LJ//fXykbf/UdVtXnFo=; b=KlKh1h7f2S4WE94vCD2eyapLQnjudGYUE5lxEmW39bpW+k3BWJjHL50OFkOE/LkmyU e8n8+KzVkH8dhu2tmIpuStgr8YvSCQ6jVYK6RW6RNFj+//6NuXfdUYyIW2ZYHJdFTpM+ 9spMqGc9rm4vnjFyHSOT+A1HOedBvDmu8Wh1tKa070XEMHfE81kLvXCm7dMCz1ZxDAM0 chaxKPaVRZU1Cp11z5u5JPOBufCpSzLy7IS0t2dLFiazS2v6eElOgRYBnZn4KkcAGrxb Nnn0ZubD9mG7IQvjk+Omn9t7FDlpBsOD8PQTthfnW265K+Draljw/7nwf0zoFgKBp/I6 NljA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=wpSOVh4p/PMwG3G8VyROrEM+LJ//fXykbf/UdVtXnFo=; b=DuwRjQkyMv9bHk2rzMuNlTt0VVjSiyfoFM24O87PKijVBrgoD0Sw1JVwcu+XWszWBk Vp0xCckqp/qmBjZcDruV4nHF8y2DRl1anviRGOpMn+shIRiCBgW7w+ehyQQMRtY1El2j /gVwtiZJ03/F/UOJeWoyZxNmvQa16xZb8J1Xp690WJsvBHvrfzXGTIIvHda+KlPN0p1S 2uMoypmqMFiMHhVYWVWIZbJuz36eyiTJANgaYFmvBpuFZXpSmaXFweHdzChjtZ5ViI6a zC/t1iGoapIS1QMoqS3CqyiCSo5xFBaJY8JUPYS9pKpcdsuVQvA4DgS4K3uYepMHslCB kNFA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:message-id:in-reply-to :references:subject:mime-version:x-original-sender:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=wpSOVh4p/PMwG3G8VyROrEM+LJ//fXykbf/UdVtXnFo=; b=LBKmitcCiekJ36EsusO4C9Z9VCX28H1pwxWUFYWPUH8D/q4yM4kGGRUHKVo6nYyWup yeqsOGJpSUmEU78A19uX/elTikDo37rFIrnjETISrZr3HFETn0iiRjHI3XObIVWCeS3C 3+mKEXxvSrg/2ZLJRv1HXd6QpGGckOqcUzZcVXVQZC4KrIWqoz/Vz5ui9qVXYIZMOf6R i9g7R+csCoTDGMd3JtoxHPlJCxVMhWFmo24p2TfUC1ePYEyhA93xl2dGr+t/uE2Io2vL I7hgk3HiW2b4Fhtp9mM4r7MnGdo/ZGn1sidsOTLDZZT77UxWZpXO2moOGV/RWeEMW9sJ FPrA== X-Gm-Message-State: AIkVDXLMSb1jVf6N3HGlsU31c7w6P1IYSDiDBSKlEC/miiWn2gdCEtJdLa18OXrePK0Htg== X-Received: by 10.99.115.21 with SMTP id o21mr40495300pgc.149.1483818742936; Sat, 07 Jan 2017 11:52:22 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.27.137 with SMTP id z9ls4188937otd.28.gmail; Sat, 07 Jan 2017 11:52:22 -0800 (PST) X-Received: by 10.157.35.89 with SMTP id k25mr607382otd.11.1483818742182; Sat, 07 Jan 2017 11:52:22 -0800 (PST) In-Reply-To: X-Original-Sender: christopherhallock@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:30400 Archived-At: ------=_Part_1912_1678509821.1483818741705 Content-Type: multipart/alternative; boundary="----=_Part_1913_1414418781.1483818741705" ------=_Part_1913_1414418781.1483818741705 Content-Type: text/plain; charset=UTF-8 On Wednesday, January 4, 2017 at 2:43:24 AM UTC-8, Kazutoshi SATODA wrote: > [...] AFAIK, the current standard doesn't (or fails to) give > well-defined behavior to such byte-oriented access on objects of > arbitrary types. [...] > I, for one, would be shocked if the Committee (or anyone, really) actually wants byte-oriented pointer arithmetic within objects to be undefined. I strongly anticipate that CWG will accept issue 1701 as a defect and make it well-defined. Remember, we're not really talking about the byte accesses themselves; such aliasing is already well-defined for char and unsigned char. It is only the charPtr + i (or charPtr[i]) expression that is currently undefined, and that expression can be awkwardly worked around anyway on some platforms (e.g., cast to integer, add, cast back to pointer). -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/b7eda119-bc5d-4940-b359-45088e6f4d3e%40isocpp.org. ------=_Part_1913_1414418781.1483818741705 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Wednesday, January 4, 2017 at 2:43:24 AM UTC-8, Kazutos= hi SATODA wrote:
[...] AFAI= K, the current standard doesn't (or fails to) give
well-defined behavior to such byte-oriented access on objects of
arbitrary types. [...]

I, for one, would be sh= ocked if the Committee (or anyone, really) actually wants byte-oriented poi= nter arithmetic within objects to be undefined. I strongly anticipate that = CWG will accept issue 1701 as a defect and make it well-defined. Remember, = we're not really talking about the byte accesses themselves; such alias= ing is already well-defined for char and charPtr + i (or charPtr[i]) expression that is currently undefined, = and that expression can be awkwardly worked around anyway on some platforms= (e.g., cast to integer, add, cast back to pointer).

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