220 40200 <1730cf0b-2236-49d5-a2e2-0df97b1aa24e@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Bengt Gustafsson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Should istream::read() be allowed to clobber the buffer beyond the file's size. Date: Thu, 20 Sep 2018 00:50:06 -0700 (PDT) Lines: 164 Approved: news@gmane.org Message-ID: <1730cf0b-2236-49d5-a2e2-0df97b1aa24e@isocpp.org> References: <21a506dd-40ae-4cae-986d-4f014de8d859@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_276_1601830266.1537429806370" X-Trace: blaine.gmane.org 1537429684 3987 195.159.176.226 (20 Sep 2018 07:48:04 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 20 Sep 2018 07:48:04 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCRIRSPDTQIRBL5CRXOQKGQEYBQKMZY@isocpp.org Thu Sep 20 09:48:00 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw1-f71.google.com ([209.85.161.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1g2tgr-0000pp-O2 for gclcip-std-proposals@m.gmane.org; Thu, 20 Sep 2018 09:47:57 +0200 Original-Received: by mail-yw1-f71.google.com with SMTP id j71-v6sf3807433ywb.22 for ; Thu, 20 Sep 2018 00:50:08 -0700 (PDT) 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 :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=fmliOj9Tq6AttGSvuIRP90a4IbglRqYFdo3X07GKEzI=; b=qMA9XSVDyqJM3Aqn1kPfL/NNrQ+GcGCUR2mMQIk04ryKFSHTE4JQnAfZy1fFxScPZw ojt5DxDSDQGAF3HO+rNWgOxyTXFPdliEVZfwNLZMjUGtmEwmiT7iCUDBL51EN7ygaXEe kw49iQdX92yUSEX+abIEH1zW84NtPS9ZOiczMSGQogYu5vDriqAs5hw/bI1oT2Wy+60z 1N4XG6so8THW5YGtp8/FZ6D2BDVStkfNsBdi3xp5cTvTmAJxp2JKLd6Z8OpIg5QYzRga C+AmLa7GfKs6LbJnSZ72hq4fU8THrjkaTyYej0T+Oy5SOwe5lyWVxouWRxql1mQGrZ4/ aqqA== 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=fmliOj9Tq6AttGSvuIRP90a4IbglRqYFdo3X07GKEzI=; b=VcFhNX6SV//2ZjOWlERIK+FERZufQSTdjUkVgn5LHSB3ZATs5Ja3sgHnRpFvCwoFkJ 3a0+LdLacFm+wfTJqhtM0UY8F4QUu/radZxF3uwl0AfTfotPfbcWGrj5gSfrx87dbVJ8 lx/rLfnNTvscyd5NjO82E1g/3ZkaojH0Aq0HfIWmxi4x9T0/gC2t521dH4Rw37bG1xLR vjDAYon1GuZd1t8wBhvPx+cOi6ifyLJyqhtEygOlYrQzhk52ioKW4F2mM3mVgVTe/6DE VktIkho0BYr+kQ8sOQ41unv9yS7hesEjCtKXqxakPnLuS7nh5nv0i4Yx+CB5AkRbUZNX tj6Q== X-Gm-Message-State: APzg51B34WbpqQbr5qmjZ/8d4fJKhmOd3k6S7ZctSj/yS+svppxIMd8A UUbYqXPDGjL3ROvxWkDx5ryhqg== X-Google-Smtp-Source: ANB0VdaIrpOh6lkQ5GKL++BRzmO5JIToVabYWW791QlKQF/SFFeqRHgZR8nY0Yr/KnC1/yBZQA695Q== X-Received: by 2002:a0d:e3c4:: with SMTP id m187-v6mr4906392ywe.50.1537429808160; Thu, 20 Sep 2018 00:50:08 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a81:48d2:: with SMTP id v201-v6ls3265657ywa.35.gmail; Thu, 20 Sep 2018 00:50:07 -0700 (PDT) X-Received: by 2002:a81:308e:: with SMTP id w136-v6mr365975yww.0.1537429806917; Thu, 20 Sep 2018 00:50:06 -0700 (PDT) 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-Spam-Checked-In-Group: std-proposals@isocpp.org 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:40200 Archived-At: ------=_Part_276_1601830266.1537429806370 Content-Type: multipart/alternative; boundary="----=_Part_277_266712490.1537429806371" ------=_Part_277_266712490.1537429806371 Content-Type: text/plain; charset="UTF-8" Here is the issue I posted to Microsoft: https://developercommunity.visualstudio.com/content/problem/326138/istreamread-clobbers-up-buffer-after-last-byte-rea.html Den torsdag 20 september 2018 kl. 03:19:54 UTC+2 skrev Brian Bi: > > Can you provide an example of the code and the file that produce this > behaviour? The C standard seems to allow some garbage to be written for the > last object's value if the size of the file isn't a multiple of the object > size, but I'm not sure if that's what you're talking about. > > (C11 7.21.8.1/2) > > ... If a partial element is read, its value is indeterminate. >> > Well, that doesn't seem to be the same thing. Well, if they decided to call with size == buffer size and count == 1 it could be interpreted like that, I guess. It seems that both C and C++ standards need to be clarified on this point. > On Wed, Sep 19, 2018 at 6:06 PM Bengt Gustafsson > wrote: > >> When you do a read on an istream with a buffer larger than the file (in >> text mode) the MSVC was recently changed so that it may change bytes in the >> buffer after the file length. The same goes for the C function fread(). >> >> I'm unsure if the standard actually allows this behaviour. Microsoft >> recently changed the behaviour and it broke our test programs. >> >> Microsoft claims this is allowed, I think it is not logical to allow it. >> >> Is this behaviour allowed? If it is allowed, should it be? >> >> >> -- >> 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-proposal...@isocpp.org . >> To post to this group, send email to std-pr...@isocpp.org . >> To view this discussion on the web visit >> https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/21a506dd-40ae-4cae-986d-4f014de8d859%40isocpp.org >> >> . >> > > > -- > *Brian Bi* > -- 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/1730cf0b-2236-49d5-a2e2-0df97b1aa24e%40isocpp.org. ------=_Part_277_266712490.1537429806371 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Here is the issue I posted to Microsoft:=C2=A0https://deve= lopercommunity.visualstudio.com/content/problem/326138/istreamread-clobbers= -up-buffer-after-last-byte-rea.html



Den torsdag = 20 september 2018 kl. 03:19:54 UTC+2 skrev Brian Bi:
Can you provid= e an example of the code and the file that produce this behaviour? The C st= andard seems to allow some garbage to be written for the last object's = value if the size of the file isn't a multiple of the object size, but = I'm not sure if that's what you're talking about.

(C11 7.21.8.1/2= )

... If a partial element is read, its value is indeterminate.
Well, that doesn't seem to= be the same thing. Well, if they decided to call with size =3D=3D buffer s= ize and count =3D=3D 1 it could be interpreted like that, I guess. It seems= that both C and C++ standards need to be clarified on this point.

<= div dir=3D"ltr">

= On Wed, Sep 19, 2018 at 6:06 PM Bengt Gustafsson <bengt.gu...@beamways.com> wrote:
= When you do a read on an istream with a buffer larger than the file (in tex= t mode) the MSVC was recently changed so that it may change bytes in the bu= ffer after the file length. The same goes for the C function fread().
<= br>
I'm unsure if the standard actually allows this behaviour= .. Microsoft recently changed the behaviour and it broke our test programs.<= /div>

Microsoft claims this is allowed, I think it is no= t logical to allow it.

Is this behaviour allowed? = If it is allowed, should it be?


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--
Brian Bi

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
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