<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>

I always use
```
INCLUDED_FOO_HPP
```
I wouldn't use the double underscore one, because starting things with double underscores is reserved.