title: How to use cppclean to find unused headers
body: <p>I'm looking for a tool to help detect unnecessary header includes in a large c++ code base. The other stackoverflow questions on this topic all suggest cppclean. So I've installed cppclean and I'm trying to use it but even on trivially wrong examples it doesn't give any results.</p>
  
  <p>For example, here's what I'm trying to clean. The source file:</p>
  
  <pre><code>// foo.cpp
  #include "bar.h"
  
  void main() { };
  </code></pre>
  
  <p>And the header file:</p>
  
  <pre><code>// bar.h
  class bar {
  };
  </code></pre>
  
  <p>And I run:</p>
  
  <pre><code>cppclean foo.cpp
  </code></pre>
  
  <p>But it prints nothing and returns 0.</p>
  
  <p>Am I doing something wrong? Are there any tutorials anywhere on how to use this tool? </p>