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: unassig...@gcc.gnu.org
ReportedBy: cu...@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
