title: What are the GCC default include directories?
body: <p>When I compile a very simple source file with gcc I don't have to specify the path to standard include files such as stdio or stdlib.</p>
  
  <p>How does GCC know how to find these files?</p>
  
  <p>Does it have the <code>/usr/include</code> path hardwired inside, or it will get the paths from other OS components?</p>