title: #include header guard format?
body: <p>I know it makes little difference to a project but, assuming you use #defined header guards for your C++ code, what format do you use?  e.g. assuming a header called <code>foo.hpp</code>:</p>
  
  <pre><code>#ifndef __FOO_HPP__
  ...
  
  #ifndef INCLUDED_FOO_HPP
  ...
  
  #ifndef SOME_OTHER_FORMAT
  </code></pre>
  
  <p>I'm sold on the idea of upper-case #defines but cannot settle on a format for these guards.</p>