title: How to clear "warning: declaration does not declare anything [-fpermissive]"
body: <p>When I compile a program with GCC, it will show that <em>"warning: declaration does not declare anything [-fpermissive]"</em>.</p>
  
  <p>The code in question is the following:</p>
  
  <pre class="lang-c prettyprint-override"><code>typedef int BOOL;
  </code></pre>
  
  <p>How can I clear the warning?</p>