title: Why do SGI stl source code use #if 0?
body: <p>In the <code>iterator.h</code> file of the SGI source code file, line 67:</p>
  
  <pre><code>#if 0
  using __STD::iterator;
  #endif
  </code></pre>
  
  <p>Why do the standard template library coders write this way? Isn't it a better to declare another macro, and use it as a test condition like:</p>
  
  <pre><code>#define STD_ITERATOR
  #ifndef STD_ITERATOR
  using __STD::iterator;
  #endif
  </code></pre>
  
  <p>Why write it hard-coded with a <em>rude</em> <code>#if 0</code>?</p>