From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 18201 invoked by alias); 5 Sep 2011 12:39:03 -0000 Received: (qmail 18192 invoked by uid 22791); 5 Sep 2011 12:39:03 -0000 X-SWARE-Spam-Status: No, hits=-2.9 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from localhost (HELO gcc.gnu.org) (127.0.0.1) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 05 Sep 2011 12:38:49 +0000 From: "marc.glisse at normalesup dot org" To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/46906] istreambuf_iterator is late? Date: Mon, 05 Sep 2011 12:39:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: libstdc++ X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: marc.glisse at normalesup dot org X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2011-09/txt/msg00314.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46906 --- Comment #7 from Marc Glisse 2011-09-05 12:38:13 UTC --- (In reply to comment #6) > 1) The fact that repeated calls of operator* without intervening operator++ > calls produce the same result for a given iterator object is required by > expression *a: > > "The expression (void)*a, *a is equivalent to *a." There are operations between the 2 calls to operator*. > This explains the repeated values '1' and '1' from it1 and '2' and '2' from > it2. Oh, are you saying that this rule has priority over the one that says that operator* just forwards to sgetc? That would actually require istreambuf_iterator to keep the last value in cache the way libstdc++ does. If that's the case, I believe it would be worth mentioning in the standard (it's not just me, when I filed the bug report I had found at least one implementation that did not cache, Roguewave (haven't checked more recent Apache versions)). For a vector, touching the vector between 2 dereferencing of the same iterator invalidates the iterator. Here, my guess was that it didn't invalidate the iterator and we should blindly call sgetc. But your explanation makes sense.