[Bug libstdc++/50119] New: copy_n advances InputIterator one more time than necessary

[Bug libstdc++/50119] New: copy_n advances InputIterator one more time than necessary

[cubbi at cubbi dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50119

             Bug #: 50119
           Summary: copy_n advances InputIterator one more time than
                    necessary
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: cubbi@cubbi.org


The naive implementation of std::copy_n() incorrectly increments InputIterator
one more time than needed, which fails with single-pass input iterators such as
istream_iterator

Test program:

#include <algorithm>
#include <vector>
#include <sstream>
#include <iterator>
#include <iostream>
int main()
{
    std::istringstream s("1 2 3 4 5");
    std::vector<int> v;
    copy_n(std::istream_iterator<int>(s), 2, back_inserter(v));
    copy_n(std::istream_iterator<int>(s), 2, back_inserter(v));

    copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << '\n';
}

Output with GCC 4.5.3 and 4.7.0-alpha20110716
1 2 4 5
expected output:
1 2 3 4

Similar bug was fixed in LLVM's libc++ in february 2011, the fix is
straightforward:
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20110221/039404.html

[Bug libstdc++/50119] copy_n advances InputIterator one more time than necessary

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50119

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-08-18
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
   Target Milestone|---                         |4.7.0
     Ever Confirmed|0                           |1

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-08-18 15:03:26 UTC ---
Ok.

[Bug libstdc++/50119] [C++0x] copy_n advances InputIterator one more time than necessary

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50119

--- Comment #2 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2011-08-18 16:32:31 UTC ---
Author: paolo
Date: Thu Aug 18 16:32:23 2011
New Revision: 177871

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=177871
Log:
2011-08-18  Paolo Carlini  <paolo.carlini@oracle.com>

    PR libstdc++/50119
    * include/bits/stl_algo.h (__copy_n(_InputIterator, _Size,
    _OutputIterator, input_iterator_tag)): Fix.
    * testsuite/25_algorithms/copy_n/50119.cc: New.

Added:
    trunk/libstdc++-v3/testsuite/25_algorithms/copy_n/50119.cc
Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/bits/stl_algo.h

[Bug libstdc++/50119] [C++0x] copy_n advances InputIterator one more time than necessary

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50119

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-08-18 16:36:16 UTC ---
Done, thanks!