220 11491 <5c9d83ad-b2ba-4b4f-8344-f2a1755ef98d@isocpp.org> article Path: news.gmane.org!not-for-mail From: Matthew Fioravante Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Controversy and debate: Uninitialized variables by default is a bug Date: Tue, 17 Jun 2014 09:24:29 -0700 (PDT) Lines: 134 Approved: news@gmane.org Message-ID: <5c9d83ad-b2ba-4b4f-8344-f2a1755ef98d@isocpp.org> References: <60caa4ef-b32d-40fe-97b6-8918fbb2bd51@isocpp.org> <0c70b26d-9af9-498d-b27f-37cf7afe9655@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_419_15585578.1403022269665" X-Trace: ger.gmane.org 1403022280 27713 80.91.229.3 (17 Jun 2014 16:24:40 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 17 Jun 2014 16:24:40 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDELF54RTIGRBPWXQGOQKGQEWIM2YXY@isocpp.org Tue Jun 17 18:24:34 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ie0-f199.google.com ([209.85.223.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1WwwBU-0007TI-8H for gclcip-std-proposals@m.gmane.org; Tue, 17 Jun 2014 18:24:32 +0200 Original-Received: by mail-ie0-f199.google.com with SMTP id rd18sf43132721iec.10 for ; Tue, 17 Jun 2014 09:24:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe :content-type; bh=+Xdxg57h/F2Cx9rqRdnf1EMXJhLzGe7Dp0jPjCFn860=; b=mAqsgAXIQCuD1SVMSFN84/GSnumeRuqvtmIxB2eaco/0WKpUM+ZXZSa8wqWZMSaZgS AatfFkSgAHYA4biuJHwEDluyT3NEXGGmVsTgVHrqxqvhzVKnTubaYYfNTfhfZ850O0ax ESj44aNcyFGzgcn1+RH7o5nrKpNmq2QyXFOCl3oRv5s344gr3IhbP9eomwzWVcJySIBs Dyf39lEowPuk+BwB0643LO02NIcr4tzI3gfO5Mr6c0So3HfijfeaBNxRl0e9iwoyb2IH 0pw2+OlgABvQ6TrEv/XLq4ZMJ3FUHMV5TXBxLxjr3lnOC62wxVuCDR4UgM/Dq7HjYER8 r0iw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; 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:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=+Xdxg57h/F2Cx9rqRdnf1EMXJhLzGe7Dp0jPjCFn860=; b=Jn5p4QkcLmM80/DhmUUHlDL3NBO+3gg0Uir+iK73D345VPjwljFnvL+8LLw4Rrp6tq swE05LnVIW4a4uQyuw18bY59cgYklBn9WwkVbDdk/jp9Idzvc5LKVX55TRLmWYvoFNPa voheA9hA48RQIYnR/hEBlUM/Ld2gXX2WanKy/xBdR6Ov0GdrPkxURoBVaA0wcsH3p6+I 8HhyEVTcUMoCiFagUwRsB66aE/1rg1qnJDt4i0UuTgsTXmhqLqIEHDhLGmcuAVKWWq9/ XX6TTcaXbcYdyAivZ4q8Azge1jbQZPzA6nehqRt67c9m2SBqkxrdXUH34YD50xoLPkWB Qb1Q== X-Gm-Message-State: ALoCoQmhV4a3nujYzM7dYvuUOOdmtckHGCU2efkqNHV+nVxw/oIsZpQebkMGOg+sZzGdZuiMsgwL X-Received: by 10.42.36.10 with SMTP id s10mr685217icd.5.1403022271102; Tue, 17 Jun 2014 09:24:31 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.26.40 with SMTP id 37ls230167qgu.23.gmail; Tue, 17 Jun 2014 09:24:30 -0700 (PDT) X-Received: by 10.140.108.162 with SMTP id j31mr53961qgf.18.1403022270513; Tue, 17 Jun 2014 09:24:30 -0700 (PDT) In-Reply-To: X-Original-Sender: fmatthew5876@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:11491 Archived-At: ------=_Part_419_15585578.1403022269665 Content-Type: text/plain; charset=UTF-8 On Tuesday, June 17, 2014 12:09:18 PM UTC-4, Ville Voutilainen wrote: > > On 17 June 2014 19:07, Matthew Fioravante > wrote: > >> char buf[MEGABYTE]; > > Arrays are not an exception. > > If buf[MEGABYTE] is a global, its already initialized to 0. > > If its a class member or on the stack, you can say > > char buf[MEGABYTE] = void; > > to skip initialization. Otherwise it gets filled with 0s. > > Yeah. And this sort of a difference to existing code has killed this idea > EVERY TIME. > Why not write a conversion tool to check for instances of this? On Tuesday, June 17, 2014 12:13:33 PM UTC-4, Nevin ":-)" Liber wrote: > > On 17 June 2014 18:09, Matthew Fioravante wrote: > >> After this idea it will still do the same thing. Not sure how a >> benchmark is needed for that. >> > > You've made a bold, unsubstantiated claim this has no performance > implications, and hand wave away anyone who disagrees. This is a question > that data quite easily answer, and anyone making performance claims ought > to have it. > The 2 things we are discussing (initializing aggregates by default vs standard library container initialization behavior) are orthogonal. Do you test the performance of std::map every time you write a file parsing routine? Ville's point about buf[MEGABYTE] is valid. There are real performance implications there because the behavior changes with arrays. Standard library containers do not behave any differently, they always initialize their contents by default as they were designed to do in the beginning. > -- > Nevin ":-)" Liber (847) 691-1404 > -- --- 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/. ------=_Part_419_15585578.1403022269665 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Tuesday, June 17, 2014 12:09:18 PM UTC-4, Ville= Voutilainen wrote:
On 17 June = 2014 19:07, Matthew Fioravante <fma= tth...@gmail.com> wrote:
>> char buf[MEGABYTE];
> Arrays are not an exception.
> If buf[MEGABYTE] is a global, its already initialized to 0.
> If its a class member or on the stack, you can say
> char buf[MEGABYTE] =3D void;
> to skip initialization. Otherwise it gets filled with 0s.

Yeah. And this sort of a difference to existing code has killed this id= ea
EVERY TIME.

Why not write a conversion tool to check for inst= ances of this?

On Tuesday, June 17, 2014 12:13:33 PM UTC-4, Nevin ":= -)" Liber wrote:
On 17 June 2014 18:09, Matthew Fioravante <fmatth...@gmail.com> wrote:
 After this idea it wi= ll still do the same thing. Not sure how a benchmark is needed for that.

You've made a bold, unsubstantiated claim this has=20 no performance implications, and hand wave away anyone who disagrees.=20  This is a question that data quite easily answer, and anyone making= =20 performance claims ought to have it.

The 2 things we are discussing (initializing aggregates by default v= s standard library container initialization behavior) are orthogonal. Do yo= u test the performance of std::map every time you write a file parsing rout= ine?

Ville's point about buf[MEGABYTE] is valid. There are real per= formance implications there because the behavior changes with arrays.
Standard library containers do not behave any differently, they always in= itialize their contents by default as they were designed to do in the begin= ning.
 
--
 Nevin ":-)" Liber  <mailto:= ne...@eviloverlord.com>  (847) 691-1404

--

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