IteratorToExpiredContainer.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>
<overview>
<p>
Using an iterator owned by a container after the lifetime of the container has expired can lead to undefined behavior.
This is because the iterator may be invalidated when the container is destroyed, and dereferencing an invalidated iterator is undefined behavior.
These problems can be hard to spot due to C++'s complex rules for temporary object lifetimes and their extensions.
</p>

</overview>
<recommendation>

<p>
Never create an iterator to a temporary container when the iterator is expected to be used after the container's lifetime has expired.
</p>

</recommendation>
<example>
<p>

</p>

<p>
The rules for lifetime extension ensures that the code in <code>lifetime_of_temp_extended</code> is well-defined. This is because the
lifetime of the temporary container returned by <code>get_vector</code> is extended to the end of the loop. However, prior to C++23,
the lifetime extension rules do not ensure that the container returned by <code>get_vector</code> is extended in <code>lifetime_of_temp_not_extended</code>.
This is because the temporary container is not bound to a rvalue reference.
</p>
<sample src="IteratorToExpiredContainerExtendedLifetime.cpp" />

<p>
To fix <code>lifetime_of_temp_not_extended</code>, consider rewriting the code so that the lifetime of the temporary object is extended.
In <code>fixed_lifetime_of_temp_not_extended</code>, the lifetime of the temporary object has been extended by storing it in an rvalue reference.
</p>
<sample src="IteratorToExpiredContainerExtendedLifetime-fixed.cpp" />

</example>
<references>

<li>CERT C Coding Standard:
<a href="https://wiki.sei.cmu.edu/confluence/display/c/MEM30-C.+Do+not+access+freed+memory">MEM30-C. Do not access freed memory</a>.</li>
<li>
OWASP:
<a href="https://owasp.org/www-community/vulnerabilities/Using_freed_memory">Using freed memory</a>.
</li>
<li>
<a href="https://github.com/isocpp/CppCoreGuidelines/blob/master/docs/Lifetime.pdf">Lifetime safety: Preventing common dangling</a>
</li>
<li>
<a href="https://en.cppreference.com/w/cpp/container">Containers library</a>
</li>
<li>
<a href="https://en.cppreference.com/w/cpp/language/range-for">Range-based for loop (since C++11)</a>
</li>

</references>
</qhelp>