220 8659 article Path: news.gmane.org!not-for-mail From: =?ISO-8859-1?Q?Daniel_Kr=FCgler?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: string_view::is_null() Date: Fri, 17 Jan 2014 23:04:51 +0100 Lines: 33 Approved: news@gmane.org Message-ID: References: <8045a4d2-721d-4725-8bb7-7a91b6f53ec8@isocpp.org> <186E0927-C962-4E34-AED0-E7509DD1F0A0@gmail.com> <7aad44d8-6b4e-438a-b309-bd898b994b34@isocpp.org> <9C2C439F-7983-4224-B272-53CAD0E2E456@gmail.com> <8E74B747-7450-41E0-8D1E-48C2D6F81535@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 X-Trace: ger.gmane.org 1389996287 16392 80.91.229.3 (17 Jan 2014 22:04:47 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 17 Jan 2014 22:04:47 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCT7RVFA4QORBBGS42LAKGQE4A37JOQ@isocpp.org Fri Jan 17 23:04:54 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-la0-f72.google.com ([209.85.215.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1W4HX3-0002Go-EC for gclcip-std-proposals@m.gmane.org; Fri, 17 Jan 2014 23:04:53 +0100 Original-Received: by mail-la0-f72.google.com with SMTP id er20sf7627516lab.11 for ; Fri, 17 Jan 2014 14:04:53 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=EHPEUHAnkA7hyI52UXFPmYxr+GqeAEz+Z5hvz1nJ4TM=; b=bgZf80WchSt7YrKWrvNrkgCxYuq48zP4LEK0nzXrnBECgpK89dLnyuXmojl/VMZ1LW W8WP5BH7Kvk6YYRHTqUyYzI5xVTte1a1p4WnyyzKPkGpTgH+XPE29+esA1j+rwE6Mwd5 GpcrtvWnaUDrYJNXx3qW53Dy+5/+rjaFaiay3BBjnVJGTNRlNMKJ2h7QPlvtPMn1cZr6 1UiHnsUIVxj5SR27Gf1yJn0GaVlQHNOrmQzshPYkZRsL7F5buSQcIFsYKTKrX6jiYC0p vIiQ4jZ4TeT3KeWw1jefISzZuY942QqjSzX9Z1yn7wjRIUyPR3XqOzwdW9GIlkgIyg2c 3lrg== X-Gm-Message-State: ALoCoQnAfh9j3bkMke4xo/qGoE1qwoVSj9AborcAWtbtV+eGDhNPh2E1Yfag1+mgwQMOzPFqmwlo X-Received: by 10.204.69.203 with SMTP id a11mr1115073bkj.0.1389996292932; Fri, 17 Jan 2014 14:04:52 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.77.194 with SMTP id u2ls192261wiw.52.gmail; Fri, 17 Jan 2014 14:04:51 -0800 (PST) X-Received: by 10.194.2.228 with SMTP id 4mr35702wjx.95.1389996291872; Fri, 17 Jan 2014 14:04:51 -0800 (PST) Original-Received: from mail-wi0-x230.google.com (mail-wi0-x230.google.com [2a00:1450:400c:c05::230]) by mx.google.com with ESMTPS id v8si2358067wiz.76.2014.01.17.14.04.51 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 17 Jan 2014 14:04:51 -0800 (PST) Received-SPF: pass (google.com: domain of daniel.kruegler@gmail.com designates 2a00:1450:400c:c05::230 as permitted sender) client-ip=2a00:1450:400c:c05::230; Original-Received: by mail-wi0-f176.google.com with SMTP id hi8so1313858wib.9 for ; Fri, 17 Jan 2014 14:04:51 -0800 (PST) X-Received: by 10.180.206.104 with SMTP id ln8mr386769wic.13.1389996291781; Fri, 17 Jan 2014 14:04:51 -0800 (PST) Original-Received: by 10.216.5.197 with HTTP; Fri, 17 Jan 2014 14:04:51 -0800 (PST) In-Reply-To: <8E74B747-7450-41E0-8D1E-48C2D6F81535@gmail.com> X-Original-Sender: daniel.kruegler@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of daniel.kruegler@gmail.com designates 2a00:1450:400c:c05::230 as permitted sender) smtp.mail=daniel.kruegler@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:8659 Archived-At: 2014/1/17 Marshall Clow : > > Maybe I missed something earlier in the discussion, but I believe that > std::string foo { nullptr, 0 }; > > is a perfectly legal way of creating an empty string. No, it is not, it undefined behaviour. > Section 21.4.2 says only: > basic_string(const charT* s, size_type n, > const Allocator& a = Allocator()); > Requires: s points to an array of at least n elements of charT. Exactly this requirement makes above code undefined. There exists an explicit rule in [res.on.arguments] p1 b2 for this kind of wording: "If a function argument is described as being an array, the pointer actually passed to the function shall have a value such that all address computations and accesses to objects (that would be valid if the pointer did point to the first element of such an array) are in fact valid." - Daniel -- --- 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. 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