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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - compare function with equal semantics cause std::sort function core dump"
href="http://llvm.org/bugs/show_bug.cgi?id=16819">16819</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>compare function with equal semantics cause std::sort function core dump
</td>
</tr>
<tr>
<th>Product</th>
<td>libc++
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Windows NT
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>All Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>hhinnant@apple.com
</td>
</tr>
<tr>
<th>Reporter</th>
<td>xtaotao@qq.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>If a compare function implement by “>=” will cause std::sort function core
dump,
and the sort range [begin, end) will be overflow, the end element will be
compared.
// libc++ version 3.3
// clang version 3.3
// $ clang++ a.cpp -std=c++11
// $ ./a.out
// 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6,
5, 4, 3, 2, 1, 0,
// $ clang++ a.cpp -std=c++11 -stdlib=libc++
// $ ./a.out
// why x == y?
// why x == y?
// why x == y?
// why x == y?
// why x == y?
// why vector::cend() is here? ? ? ?
// segment fault(core dump)
#include <algorithm>
#include <vector>
#include <iostream>
// a struct with constructor and assignment operator.
struct SomeData
{
SomeData(int value) : data(value) {}
SomeData& operator = (const SomeData& rhs)
{
data = rhs.data;
return *this;
}
int data;
};
struct CompareFunction
{
CompareFunction(const SomeData* begin, const SomeData* end) :
_begin(begin), _end(end)
{
}
bool operator()(const SomeData& x, const SomeData& y) const
{
if (&x == &y)
std::cout << "why x == y?" << std::endl;
else if (&x == _end)
std::cout << "why vector::cend() is here? ? ? ?" << std::endl;
return x.data >= y.data;
}
const SomeData* _begin;
const SomeData* _end;
};
int main(int argc, char* argv[])
{
std::srand(time(0));
const int array[] =
{
0, 3, 6, 8, 7, 9, 4, 14, 13, 12,
11, 10, 2, 23, 22, 21, 20, 19, 18, 17,
16, 15, 1, 25, 24, 5
};
const int count = sizeof(array) / sizeof(array[0]);
std::vector<SomeData> vec;
for (int i = 0; i < count; ++ i)
vec.push_back(SomeData(array[i]));
CompareFunction compare(&(*vec.begin()), &(*vec.end()));
std::sort(vec.begin(), vec.end(), compare);
for (auto it = vec.cbegin(); it != vec.cend(); ++ it)
std::cout << it->data << ", ";
std::cout << std::endl;
return 0;
}</pre>
</div>
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