title: What are the Issues with a vector-of-vectors?
body: <p>I've read that a <code>vector</code>-of-<code>vector</code>s is bad given a fixed 2<sup>nd</sup> dimension, but I cannot find a clear explanation of the problems on <a href="http://www.stackoverflow.com">http://www.stackoverflow.com</a>.</p>
  
  <p>Could someone give an explanation of why using 2D indexing on a single <code>vector</code> is preferable to using a <code>vector</code>-of-<code>vector</code>s for a fixed 2<sup>nd</sup> dimension?</p>
  
  <p>Also, I'm assuming that a <code>vector</code>-of-<code>vector</code>s is the preferable data structure for a 2D array with a variable 2<sup>nd</sup> dimension? If there is any proof to the contrary I'd love to see that.</p>