title: Eclipse CDT Builtin Include Directories
body: <p>Under</p>
  
  <pre><code>Eclipse CDT &gt;
      Project Settings &gt; 
          C/C++ General &gt;
              Paths and Symbols &gt;
                   Includes &gt;
                       GNU C++
  </code></pre>
  
  <p>There is a list of include paths.</p>
  
  <p>Some are in bold and are project specific.</p>
  
  <p>Others are <strong>builtin</strong>:</p>
  
  <p>For example:</p>
  
  <pre><code> /usr/include/C++/4.6/
   /usr/include/x86_64-linux-gnu
   etc
  </code></pre>
  
  <p>If I delete:</p>
  
  <pre><code>work/.metadata/.plugins/org.eclipse.cdt.make.core/*.sc
  </code></pre>
  
  <p>The paths are automatically rescanned when Eclipse launches.</p>
  
  <p>I have gcc 4.6 and gcc 4.7 installed side-by-side.</p>
  
  <p><strong>When Eclipse rescans it only finds the 4.6 headers and not the 4.7 ones.</strong></p>
  
  <p>My question is this:  By what mechanism does Eclipse determine the list of builtin include paths?  (and hence why is it only finding the 4.6 headers and not the 4.7 headers?)</p>