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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - False-positive when pop_front from std::list<unique_ptr<T>> in C++11"
href="http://llvm.org/bugs/show_bug.cgi?id=19637">19637</a>
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<th>Summary</th>
<td>False-positive when pop_front from std::list<unique_ptr<T>> in C++11
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.4
</td>
</tr>
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<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Static Analyzer
</td>
</tr>
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<th>Assignee</th>
<td>kremenek@apple.com
</td>
</tr>
<tr>
<th>Reporter</th>
<td>renauxthierry+llvmBugzilla@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The following C++11 code is a minimal example of what I believe triggers a
false positive in the clang static analyzer:
*** begin code ***
#include <iostream>
#include <list>
#include <memory>
class ElementType {};
int main(int argc, const char * argv[]) {
std::list<std::unique_ptr<ElementType>> theList(5);
theList.pop_front();
for (const auto &element: theList) { // (*)
std::cout << "This should be fine." << std::endl;
}
return 0;
}
*** end code ***
On the line marked by an asterisk (*), the clang analyzer claims
".../main.cpp:21:29: Use of memory after it is freed (within a call to
'begin')"
As far as I see, this code is harmless. My guess is that the analyzer misses
the point that std::list<T>::pop_front() not only calls its elements'
destructor, but that it also moves the location of std::list<T>::begin().
Replacing the call to pop_front by pop_back makes the analyzer warning
disappear, and even replacing it by erase(theList.begin()) makes it come out
warning-free.
For reference: These results come from XCode 5.1.1 (5B1008) on Mac OS X 10.9.2,
clang --version "Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM
3.4svn)", "Target: x86_64-apple-darwin13.1.0", "Thread model: posix"</pre>
</div>
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