title: Portable alternative to #pragma once
body: <p>Can somebody tell me a workaround for <code>#pragma once</code> directive support for various compilers?</p>
  
  <p>I want to use in my header something like:</p>
  
  <pre><code>#if _MSC_VER &gt; ... || __GNUC__ &gt; ... || ...
  
  #pragma once
  
  #endif
  </code></pre>
  
  <p>Maybe it already exists in boost sources or in your code?</p>