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Date: Wed, 28 Nov 2007 12:31:43 -0800 (PST)
From: "Travis Vitek (JIRA)" <jira@apache.org>
To: stdcxx-dev@incubator.apache.org
Subject: [jira] Commented: (STDCXX-645) stream iterators into different
 streams compare equal
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    [ https://issues.apache.org/jira/browse/STDCXX-645?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12546374 ] 

Travis Vitek commented on STDCXX-645:
-------------------------------------

In most cases the iterator is going to be used in a loop which calls op!= and op++ repeatedly. In this case op== would get called one time more than op++. Of course there are some scenerios where op++ is called more frequently than op== [std::distance or std::advance], but I don't believe that those are the most common use cases for an istream_iterator.

If we fix op++, then op== becomes a pointer comparison and op++ gets an additional assignment. I think fixing op++ would be the preferred solution if we are just counting instructions.

> stream iterators into different streams compare equal
> -----------------------------------------------------
>
>                 Key: STDCXX-645
>                 URL: https://issues.apache.org/jira/browse/STDCXX-645
>             Project: C++ Standard Library
>          Issue Type: Bug
>          Components: 24. Iterators
>    Affects Versions: 4.1.3, 4.2.0
>            Reporter: Mark Brown
>
> As Travis says in his reply to my post here:
> http://www.nabble.com/stream-iterators-into-different-streams-compare-equal--tf4721505.html#a13498487:
>     Given 24.5.1.1 p1 and p2, it is pretty clear to me that the two iterators are both non-end-of-stream type, and they are both created on different streams. The streams are different, so the iterators should not compare equal. I guess one could claim that 24.5.1.2 p6 conflicts with 24.5 p3 because 'end-of-stream' isn't clearly defined, but in this particular case that doesn't matter.
> This program aborts with stdcxx but not with gcc:
> #include <assert.h>
> #include <iterator>
> #include <sstream>
> int main ()
> {
>     std::istringstream a ("1");
>     std::istream_iterator<int> i (a);
>     std::istringstream b ("2");
>     std::istream_iterator<int> j (b);
>     assert (!(i == j));
> } 

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