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POAutomatically adding and removing an object from a list
 

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  1. POAutomatically adding and removing an object from a list
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    <p>I have a class. When this class is instantiated, I want the instance added to a list. When the object is deleted, I want it removed from the list.</p> <p>So I give the object a shared pointer to itself. I then have a list of weak pointers to those shared pointers. When an object is created, it creates a shared pointer to itself, makes a weak pointer to that, and puts the weak pointer in a list.</p> <p>When the object is destroyed, the shared pointer is as well. Whenever I try to access a member in the list, I ensure that it hasn't expired and that its use count isn't 0. Despite this, I still crash when the list member is destroyed. Why? Can I get around it? Here's my SSCCE:</p> <pre class="lang-cpp prettyprint-override"><code>#include &lt;iostream&gt; #include &lt;memory&gt; #include &lt;vector&gt; class test { private: std::shared_ptr&lt;test&gt; self; public: int val; test(int set); test(test &amp;copy) = delete; // making sure there weren't issues // with a wrong instance being deleted }; std::vector&lt;std::weak_ptr&lt;test&gt;&gt; tests; test::test(int set): val(set) { this-&gt;self = std::shared_ptr&lt;test&gt;(this); tests.push_back(std::weak_ptr&lt;test&gt;(this-&gt;self)); } void printTests() { for (auto i = tests.begin(); i != tests.end(); i++) { if (i-&gt;use_count() == 0 || i-&gt;expired()) { tests.erase(i); continue; } std::cout &lt;&lt; i-&gt;lock()-&gt;val &lt;&lt; std::endl; } std::cout &lt;&lt; std::endl; } int main(int argc, char **argv) { { test t(3); std::cout &lt;&lt; "First tests printing: " &lt;&lt; std::endl; printTests(); } // SEGFAULTS HERE std::cout &lt;&lt; "Second tests printing: " &lt;&lt; std::endl; printTests(); return 0; } </code></pre> <p>The output of this program is as follows: </p> <pre><code>First tests printing: 3 Segmentation fault (core dumped) </code></pre>
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    1. COI will virtually *guarantee* you that `this->self = std::shared_ptr<test>(this);` is not doing what you think it is, especially since the actual object, `test t(3)`, is on the *stack*.
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    2. COThat it's on the stack just means that test is destroyed at the end of its scope, which is what I want. How else am I going to do what I want to do?
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    3. COWhat do you think `std::shared_ptr<>` does with the object pointer contained within when the shared ptr obj is destroyed?
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