title: Some questions about Vector in STL
body: <p>I have some questions about vector in STL to clarify.....</p>
  
  <ol>
  <li><p>Where are the objects in vector allocated? heap?</p></li>
  <li><p>does vector have boundary check? If the index out of the boundary, what error will happen?</p></li>
  <li><p>Why array is faster than vector? </p></li>
  <li><p>Is there any case in which vector is not applicable but array is a must?</p></li>
  </ol>