220 29467 <634b6222-d3e2-828b-75ec-f9da31b0493a@honermann.net> article Path: news.gmane.org!.POSTED!not-for-mail From: Tom Honermann Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allowing string literals to match `char...` packs in templates Date: Fri, 18 Nov 2016 11:19:01 -0500 Lines: 84 Approved: news@gmane.org Message-ID: <634b6222-d3e2-828b-75ec-f9da31b0493a@honermann.net> References: <9de07b5f-f870-4a02-882f-54f9fdd12ffd@isocpp.org> <7366336.xLjCtBizz3@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1479485960 24021 195.159.176.226 (18 Nov 2016 16:19:20 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 18 Nov 2016 16:19:20 +0000 (UTC) User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDBNXSHG6UDBBBGUXTAQKGQEEHQ3TYY@isocpp.org Fri Nov 18 17:19:15 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f197.google.com ([209.85.161.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1c7lsg-0005bl-Js for gclcip-std-proposals@m.gmane.org; Fri, 18 Nov 2016 17:19:14 +0100 Original-Received: by mail-yw0-f197.google.com with SMTP id d187sf497039951ywe.1 for ; Fri, 18 Nov 2016 08:19:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-transfer-encoding:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=EERofbta4eZPj+FIlrq8jiUlLJ8fgw3tZGI1BcH07QU=; b=lcgodYk7SizC+FaahaKEm1HsMQN7qYRqPskQLAztrWG5lRIAd0EpbIda/6Xzh4tLwY QRiznoch+loFc4VJQGlv0fjVcAab14yWepMwjlbeS46uXKJvPc4g2FMAo25ynSAnSkGf QgkjAabRj0IhJH3jLnIZER59Fx1ZIiGQPzF4P5W2ISgYRPCJZawUx2TXBPweLIiGGTY/ tN9alQ191bPAum2SjWbiqTYU8niwd7iELXQ5MBrYtCwdh5dO8PZNELTd2NpggbIv9zE3 mseYs3KgkNg96/UP3enskDCkNqvp9Ir2UET5SzOJGUEE1SlZwgMMdWRyxhIpSh9HeetA X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=EERofbta4eZPj+FIlrq8jiUlLJ8fgw3tZGI1BcH07QU=; b=ioF1zbU3UXVU3Y2iiYVhi0cQFgoKhHXRWW6tuVk7c/bxn/rqUOawJSpYLhConCEjQJ YVHOWsDHhUCeKmdesnTigRIgQEorxXQTEjo86peErmlOuTeC+J8L+SuEPppoSJ8XnrUJ lAOhEKNnrY2JSNkKzqtBuwhFCkKall0te0AvfgVuu6DWyKshU9kvaL7PJqRAhFO/oRqn BaEghewIYkGxrfu6tO37+1G1GP3V7FjpqdT/nZU/YBXpGeAfdJaxyGU+v85paC4JOJVf AfrWy5XGRF/+kY9ISVXmv/wedfFr7at1UcmKmPgFl8oy8G1YHgpwjE732b/7R5EB2LWn X-Gm-Message-State: AKaTC01QFy2IxGmFXeqIFlaELd8n833ZihxbacROFw1zzAWo0Xkie6+tdonss85uj0pS1A== X-Received: by 10.129.87.140 with SMTP id l134mr125546ywb.22.1479485957591; Fri, 18 Nov 2016 08:19:17 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.11.120 with SMTP id p53ls428178otd.13.gmail; Fri, 18 Nov 2016 08:19:16 -0800 (PST) X-Received: by 10.55.6.13 with SMTP id 13mr593379qkg.272.1479485956721; Fri, 18 Nov 2016 08:19:16 -0800 (PST) Original-Received: from smtp123.iad3a.emailsrvr.com (smtp123.iad3a.emailsrvr.com. [173.203.187.123]) by mx.google.com with ESMTPS id f67si5583892qkj.69.2016.11.18.08.19.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 18 Nov 2016 08:19:15 -0800 (PST) Received-SPF: neutral (google.com: 173.203.187.123 is neither permitted nor denied by best guess record for domain of tom@honermann.net) client-ip=173.203.187.123; Original-Received: from smtp16.relay.iad3a.emailsrvr.com (localhost [127.0.0.1]) by smtp16.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 6D6665B16 for ; Fri, 18 Nov 2016 11:19:15 -0500 (EST) X-Auth-ID: tom@honermann.net Original-Received: by smtp16.relay.iad3a.emailsrvr.com (Authenticated sender: tom-AT-honermann.net) with ESMTPSA id 588075BA5 for ; Fri, 18 Nov 2016 11:19:15 -0500 (EST) X-Sender-Id: tom@honermann.net Original-Received: from [10.12.196.91] (pool-71-176-249-9.rcmdva.fios.verizon.net [71.176.249.9]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA) by 0.0.0.0:587 (trex/5.7.12); Fri, 18 Nov 2016 11:19:15 -0500 In-Reply-To: <7366336.xLjCtBizz3@tjmaciei-mobl1> X-Original-Sender: tom@honermann.net X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 173.203.187.123 is neither permitted nor denied by best guess record for domain of tom@honermann.net) smtp.mailfrom=tom@honermann.net 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:29467 Archived-At: On 11/17/2016 5:58 PM, Thiago Macieira wrote: > On quinta-feira, 17 de novembro de 2016 10:18:22 PST Tom Honermann wrote: >> On 11/17/2016 03:13 AM, Jonathan M=C3=BCller wrote: >>> Sorry if I'm asking the obvious question here: Why not guarantee that >>> different string literals have different addresses and the same string >>> literal has the same address and use const char* as non-type template >>> parameters? >> I believe one of the complications here is systems that support shared >> libraries. The opportunity to assign common addresses for equal string >> literals doesn't arise until run-time. > But everything that depended on those literals would also be resolved at > runtime only (vague linkage). Vague linkage is not supported by all compilers/linkers, at least not=20 when shared libraries are involved. Consider the following example compiled with MSVC 2013: $ cat t.h extern inline const char* f() { return "text"; } $ cat dll1.cpp #include "t.h" __declspec(dllexport) const char* dll1() { return f(); } $ cat dll2.cpp #include "t.h" __declspec(dllexport) const char* dll2() { return f(); } $ cat main.cpp #include __declspec(dllimport) const char* dll1(); __declspec(dllimport) const char* dll2(); int main() { assert(dll1() =3D=3D dll2()); } $ cl /LD dll1.cpp /Fedll1.dll .... $ cl /LD dll2.cpp /Fedll2.dll .... $ cl main.cpp /Femain.exe dll1.lib dll2.lib .... $ ./main Assertion failed: dll1() =3D=3D dll2(), file main.cpp, line 5 Since f() is an inline function, the returned string literal is required=20 to have the same address in all TUs: C++14 [dcl.fct.spec] Function specifiers p4: .... A string literal in the body of an extern inline function is the same=20 object in different translation units. .... However, Microsoft's compiler/linker does not implement this requirement=20 across shared library boundaries. Since shared libraries are not=20 described by the standard, it is arguable whether this is a=20 non-conformance issue or not. If the above code is compiled into a single executable on Windows, the=20 assert does not fail. Tom. --=20 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 e= mail 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/634b6222-d3e2-828b-75ec-f9da31b0493a%40honermann= ..net. .