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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Modifying a deque from emplace_back produces incorrect results"
href="http://llvm.org/bugs/show_bug.cgi?id=16238">16238</a>
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<th>Summary</th>
<td>Modifying a deque from emplace_back produces incorrect results
</td>
</tr>
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<th>Product</th>
<td>libc++
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>All Bugs
</td>
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<th>Assignee</th>
<td>hhinnant@apple.com
</td>
</tr>
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<th>Reporter</th>
<td>felixcca@yahoo.ca
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>From my skimming into the standard, nothing specifically seems to prohibit
modifying a `std::deque` from inside `emplace_back`. Take this snippet for
example:
#include <iostream>
#include <deque>
#include <string>
using namespace std;
struct foo
{
string m_marker;
foo(deque<foo>& into, const string& marker, bool createInner = true)
: m_marker(marker)
{
if (createInner)
{
cout << "Marker is " << m_marker << endl;
into.emplace_back(into, "my other marker", false);
cout << "Marker is now " << m_marker << endl;
}
}
};
int main()
{
deque<foo> foos;
foos.emplace_back(foos, "my initial marker");
cout << "There are " << foos.size() << " items in the deque:" << endl;
for (foo& f : foos)
cout << f.m_marker << endl;
}
(listing also at <a href="http://stackoverflow.com/q/16955265/">http://stackoverflow.com/q/16955265/</a>)
I would expect this as the result:
<span class="quote">> Marker is my initial marker
> Marker is now my initial marker
> There are 2 items in the deque:
> my initial marker
> my other marker</span >
However, this is what I get:
<span class="quote">> Marker is my initial marker
> Marker is now my other marker
> There are 2 items in the deque:
> my other marker
> </span >
It looks like calling `emplace_back` from within a constructor itself called
with `emplace_back` causes the deque to overwrite the first item with the
second.
I couldn't find anything that specifically prohibits modifying the container
from `emplace` methods in N3337, although I can see why this could be a
problem.</pre>
</div>
</p>
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