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https://issues.apache.org/jira/browse/STDCXX-645?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12546374
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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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