StackAddressEscapes.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>
<overview>
<p>
This rule finds assignments that might store the address of a local
variable in non-local memory. The address of the local variable is
only valid until the function returns, after which it becomes a
dangling pointer. Such code is safe if the dangling pointer is never
used after the function returns, but it is not a recommended coding
practice. There is also a risk that the code is not thread-safe,
unless the non-local memory is protected by a mutex.
</p>

</overview>
<recommendation>

<ol>

<li>
If it is necessary to take the address of a local variable, then make
sure that the address is only stored in memory that does not outlive
the local variable. For example, it is safe to store the address in
another local variable. Similarly, it is also safe to pass the address
of a local variable to another function provided that the other
function only uses it locally and does not store it in non-local
memory.
</li>
<li>
If it is necessary to store an address which will outlive the
current function scope, then it should be allocated on the heap.  Care
should be taken to make sure that the memory is deallocated when it is
no longer needed, particularly when using low-level memory management
routines such as <tt>malloc</tt>/<tt>free</tt> or
<tt>new</tt>/<tt>delete</tt>. Modern C++ applications often use smart
pointers, such as <tt>std::shared_ptr</tt>, to reduce the chance of
a memory leak.
</li>
</ol>

</recommendation>
<example>

<sample src="StackAddressEscapes.cpp" />

</example>
<references>

<li>Wikipedia: <a href="https://en.wikipedia.org/wiki/Dangling_pointer">Dangling pointer</a>.</li>

</references>
</qhelp>