title: Vector going out of bounds without giving error
body: <p>I have a <code>std::vector</code>. I check its size which is 6 but when I try to access <code>vec[6]</code> to check whether it will give error, I get no error but some number instead. Should not it give an error?</p>
  
  <p>edit: something like:</p>
  
  <pre><code>struct Element
  {
      std::vector&lt;double&gt; face;
  };
  
  int main()
  {
      Element elm;
  
      .... // insert 6 elements into elm.face
  
      std::cout &lt;&lt; elm.face.size() &lt;&lt; std::endl; // answer is 6
      std::cout &lt;&lt; elm.face[6] &lt;&lt; std::endl; // answer is some number
  }
  </code></pre>