title: C Language: what does the .mm extension stand for?
body: <p>A project with some Objective-C has a few C classes with the implementation files having a <strong>.mm</strong> extension.</p>
  
  <pre><code>file.h
  file.mm
  </code></pre>
  
  <p>What does the <strong>.mm</strong> mean? Shouldn't it just be <strong>.m</strong>?</p>