220 14133 article Path: news.gmane.org!not-for-mail From: Bo Persson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: #pragma once Date: Wed, 22 Oct 2014 20:29:06 +0200 Lines: 44 Approved: news@gmane.org Message-ID: References: <3d0ab5b0-73d9-434a-9ae4-cd47d8275590@isocpp.org> <202c5550-8669-4b45-aa39-9a8d26c37015@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed X-Trace: ger.gmane.org 1414002572 23036 80.91.229.3 (22 Oct 2014 18:29:32 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 22 Oct 2014 18:29:32 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCZ6RLW3UIKBBBPPT6RAKGQEUZMUZ3Y@isocpp.org Wed Oct 22 20:29:27 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lb0-f199.google.com ([209.85.217.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Xh0f0-0006mc-DK for gclcip-std-proposals@m.gmane.org; Wed, 22 Oct 2014 20:29:26 +0200 Original-Received: by mail-lb0-f199.google.com with SMTP id w7sf2334444lbi.2 for ; Wed, 22 Oct 2014 11:29:26 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:to:from:subject:date:lines:message-id:references :mime-version:user-agent:in-reply-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=pZr8KZ1ZjX0OclvVf9kD5QQd19WZ/Gh/gRpHrnzEU44=; b=h8CVA05oC+MtOMALl5THBznsUD/Ij8Nj2RE3F9NN1DHSZzJd8U7SFHz7GoJiBjNpI9 wjOn3yk3yAI7tzC6A8bhEF7qadpmmUFjc/qFyiGCkTQjGNPN7IzmNJgIK32mk94NGYnJ yyG2LlCtve3dQ9NnqkEGkLVLa1dWeQzKpEeIqZxH4r23Z8du3BxBY+VBdy5RzN+kVuc9 x7CnTlm1ZxPT+f/yq0gRAcVgBMEKqJ/3R9hPKyjP3UUNgvn79hqSsPLmdr6ORZ7C3Gwf NWXAfcqjRLGXtZRjuR0nJoEsGEAyzjeBcO+LREZSjAD4nyXOK5h/Kbm6F3WPLbBZnmUI uavg== X-Gm-Message-State: ALoCoQmNkutjDZZ7F76JJwXmFPgMLZrrX7A0YbWTsKrmrwsiw5lDcbdICKzaf7BvcUbcaOhktIgv X-Received: by 10.112.225.135 with SMTP id rk7mr6821641lbc.6.1414002566121; Wed, 22 Oct 2014 11:29:26 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.204.44 with SMTP id kv12ls219923lac.44.gmail; Wed, 22 Oct 2014 11:29:24 -0700 (PDT) X-Received: by 10.152.88.70 with SMTP id be6mr43682089lab.72.1414002564470; Wed, 22 Oct 2014 11:29:24 -0700 (PDT) Original-Received: from plane.gmane.org (plane.gmane.org. [80.91.229.3]) by mx.google.com with ESMTPS id q9si24377235lag.92.2014.10.22.11.29.24 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 22 Oct 2014 11:29:24 -0700 (PDT) Received-SPF: pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) client-ip=80.91.229.3; Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1Xh0eu-0006jm-Qy for std-proposals@isocpp.org; Wed, 22 Oct 2014 20:29:20 +0200 Original-Received: from c193-14-6-157.cust.tele2.se ([193.14.6.157]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 22 Oct 2014 20:29:20 +0200 Original-Received: from bop by c193-14-6-157.cust.tele2.se with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 22 Oct 2014 20:29:20 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 35 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: c193-14-6-157.cust.tele2.se User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 In-Reply-To: X-Original-Sender: gclcip-std-proposals@m.gmane.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) smtp.mail=gclcip-std-proposals@m.gmane.org 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:14133 Archived-At: On 2014-10-22 09:04, Olaf van der Spek wrote: > On Tuesday, October 21, 2014 10:32:00 PM UTC+2, Chet wrote: > > It has been determined that it is more difficult to implement than > you would think: > http://stackoverflow.com/questions/23696115/is-pragma-once-part-of-the-c11-standard > > http://stackoverflow.com/questions/1695807/why-isnt-c-cs-pragma-once-an-iso-standard > > > The Modules proposal aims to solve the problems of include files in > a better way: > http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4047.pdf > > > > Is it really that difficult? > If the name doesn't match an already seen file but the size does one > could hash the contents and check the hash. > It really IS that difficult. On my work computer I have mounts to several departmental servers (located in different cities), some NAS devices that I don't even know where they are, a ClearCase system on a Unix machine, and the file system on a z/OS mainframe. Add a local hard disk, a DVD and some USB-devices, and you get a real world system. How is the standard supposed to specify what a unique file means? And how useful is it for every existing compiler to support this? Bo Persson -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. .