title: Why is this struct not standard-layout?
body: <p>A piece of code is worth a thousands words.</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;type_traits&gt;
  
  using namespace std;
  
  struct A
  {
      int a;
  };
  
  struct B : A
  {
      int b;
  };
  
  int main()
  {
      cout &lt;&lt; is_standard_layout&lt;B&gt;::value &lt;&lt; endl; // output false! WHY?
      return 0; 
  }
  </code></pre>