title: Qt Creator can't find headers (says: "No such file or directory")
body: <p>How can I tell Qt Creator 2.4.1 (based on Qt 4.7.4 32-bit) where to look <strong>by default</strong> for header files?</p>
  <p>When I open a C file in Qt Creator and say</p>
  <pre><code>#include &lt;stdio.h&gt;
  </code></pre>
  <p>it underlines the line and says</p>
  <pre><code>stdio.h: No such file or directory
  </code></pre>
  <p>I would like to tell it to look for headers in a directory of my choice; how do I do this?</p>
  <h3>Update</h3>
  <p>I guess I should also ask: Is this even <em>possible</em>? Or must I create an entire project every time I want to edit a standalone C++ file?</p>
  <p><img src="https://i.stack.imgur.com/RGtlW.png" alt="" /></p>