220 30282 article Path: news.gmane.org!.POSTED!not-for-mail From: Bengt Gustafsson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: P0298: A byte type definition: with undefined pointer arithmetic? Date: Thu, 5 Jan 2017 02:45:41 -0800 (PST) Lines: 78 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_2888_1589656938.1483613141860" X-Trace: blaine.gmane.org 1483613152 9747 195.159.176.226 (5 Jan 2017 10:45:52 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 5 Jan 2017 10:45:52 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCRIRSPDTQIRBVWHXDBQKGQED3X7IEA@isocpp.org Thu Jan 05 11:45:44 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f69.google.com ([209.85.214.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cP5YB-00016D-7p for gclcip-std-proposals@m.gmane.org; Thu, 05 Jan 2017 11:45:39 +0100 Original-Received: by mail-it0-f69.google.com with SMTP id b123sf485805570itb.3 for ; Thu, 05 Jan 2017 02:45:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to: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=G4fecXRFWkWC1jonGDSNqXKZnlShu23KZUzRNKKDp0k=; b=x0PmAlMJUE14unrm2LgajCOkEZ2xDpB+8drUruy0RnD/KNZ5j44Pl8K18NyzUP6PRa +wHLB/PYy7ytHSt6rlhJMhK8jeC/HrniX/jB+Jnw17zXxCRKxXbNigL4dLW/jSrhe8Ot 2uUql93hYpZaRn31OELuNlhZ54C7cM7ZDpSoTaKj1F5P1BHJag2XEhkyilpcK6s3/SMa bVvviB/5isBoxbDmteqNokb/KKHIvjeMhDDSpVnSWo/TTF6cXDILFlgmOGWsPvgkZnEn iDPRl/F7j9Z6bDZZyGtrGngYd0wbZtTFzcM5t76Q9gsbHOJg8SCfNrwTg9WboOjJTOc1 t/Mw== 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: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=G4fecXRFWkWC1jonGDSNqXKZnlShu23KZUzRNKKDp0k=; b=TT4c5eEeYxCE/KB3yWamrm5bOggGeiE+AqaLfc2W19ZkosXPtPvO6iGUICboZfxdoj 7Ot5d1r2t1wwLBNtEgwhiNMeihfUuepWqXhqHhgfDvxT96g4Kf2mWGo9u+Db4rJlsbod 1UlNLmLKonaQqsVDoCWI16tu6Xn72uFHaBspPlipnkYfhO3eK2Yc27PfsKNaszb7BFQD NTgnsvbUrvDNfJ3fdk4R2Pn3r3ESiNxLRqtb6zFHTeqFNO+ZTcKfiwOHXjSqWJdc84GO vS0h9BDHA8yRGo6u/D0G83Rj7Ag7jNDfO4GOT9yLyIGqT8RoAYyCNxKMbSra0EdR448k CdtA== X-Gm-Message-State: AIkVDXLdPHxUzYC2tjBYadEraUQBqD5nO5z/MHXjPz9o+PDPSFKPQzwvm1a8jJS5YJZb0A== X-Received: by 10.107.0.7 with SMTP id 7mr19643824ioa.100.1483613143357; Thu, 05 Jan 2017 02:45:43 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.18.246 with SMTP id g109ls3984181otg.7.gmail; Thu, 05 Jan 2017 02:45:42 -0800 (PST) X-Received: by 10.157.14.183 with SMTP id 52mr602102otj.20.1483613142354; Thu, 05 Jan 2017 02:45:42 -0800 (PST) In-Reply-To: X-Original-Sender: bengt.gustafsson@beamways.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:30282 Archived-At: ------=_Part_2888_1589656938.1483613141860 Content-Type: multipart/alternative; boundary="----=_Part_2889_1247348354.1483613141860" ------=_Part_2889_1247348354.1483613141860 Content-Type: text/plain; charset=UTF-8 I can't say that I have checked but isn't an array of enum values equivalent to its underlying type when it comes to size and alignment? As byte is defined as an enum with a unsigned char as underlying type pointer arithmetic should be defined as expected: to be bytewise. I don't think this requires specific mention in the standard text. Den onsdag 4 januari 2017 kl. 21:33:27 UTC+1 skrev D. B.: > > Indeed, that's pretty much what I would like... not for selfish reasons > anymore, since the design where I thought I needed that had *worse* UB > that I had to resolve ;-) but simply because it makes sense, makes the > "sequence" concept at all useful, and means that the so-called special > properties of char* pointers can actually exist. > > But when I (thought I) needed this before, it was a fairly simple > situation where an object would have a method invoked on it, taking a > pointer to one of its members, and was then supposed to calculate the > offset of that member within itself and do stuff with it. That hardly seems > unreasonable. > -- 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/f39b3dd8-538e-4b84-8548-a9dc7e3f592a%40isocpp.org. ------=_Part_2889_1247348354.1483613141860 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
I can't say that I have checked but isn't an array= of enum values equivalent to its underlying type when it comes to size and= alignment?

As byte is defined as an enum with a unsigne= d char as underlying type pointer arithmetic should be defined as expected:= to be bytewise. I don't think this requires specific mention in the st= andard text.

Den onsdag 4 januari 2017 kl. 21:33:27 UTC+1 skrev D. B= ..:
Indeed= , that's pretty much what I would like... not for selfish reasons anymo= re, since the design where I thought I needed that had worse UB that= I had to resolve ;-) but simply because it makes sense, makes the "se= quence" concept at all useful, and means that the so-called special pr= operties of char* pointers can actually exist.

But when I (tho= ught I) needed this before, it was a fairly simple situation where an objec= t would have a method invoked on it, taking a pointer to one of its members= , and was then supposed to calculate the offset of that member within itsel= f and do stuff with it. That hardly seems unreasonable.

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