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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - std::copy_n requires non-overlapping inputs"
href="https://bugs.llvm.org/show_bug.cgi?id=36850">36850</a>
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<th>Summary</th>
<td>std::copy_n requires non-overlapping inputs
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>All
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>t.p.northover@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=20096" name="attach_20096" title="Example of unexpected behaviour">attachment 20096</a> <a href="attachment.cgi?id=20096&action=edit" title="Example of unexpected behaviour">[details]</a></span>
Example of unexpected behaviour
Most of the "std::copy*" functions explicitly require their input and output
iterators not to overlap, but std::copy_n doesn't seem to.
However, the implementation of std::copy_n in libc++ forwards to a version of
std::copy which behaves differently than expected from a straightforward
reading of copy_n's effects clause and calls memmove.
This came up on IRC, where Eelis came up with the attached C++ file
demonstrating the difference from a naive copy_n.</pre>
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