title: C++ shared+ptr use_count for nullptr
body: <p>I have 2 <code>shared_ptr</code>s defined and assigned <code>nullptr</code>. In case 1, I'm using default constructor and in case 2, I used constructor with delete method.</p>
  
  <pre><code>shared_ptr&lt;int&gt; sptr2(nullptr);
  
  cout &lt;&lt; "sptr2 use_count: " &lt;&lt; sptr2.use_count() &lt;&lt; endl;
  
  shared_ptr&lt;int&gt; sptr6(nullptr, default_delete&lt;int&gt;());
  
  cout &lt;&lt; "sptr6 use_count: " &lt;&lt; sptr6.use_count() &lt;&lt; endl;
  </code></pre>
  
  <p>The output is:</p>
  
  <pre><code>sptr2 use_count: 0
  sptr6 use_count: 1
  </code></pre>
  
  <p>I cannot understand why sptr6 has use count of 1 when it does not have any valid pointer.</p>
  
  <p>g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16)</p>