title: __USE_FILE_OFFSET64 vs. _FILE_OFFSET_BITS=64
body: <p>I am trying to maintain code that compiles on lots of different systems. I've seen a dozen different ways of asking for <code>lseek</code> that takes 64-bits. Some systems use <code>lseek64</code>, some use <code>lseeko</code>, some require that you define <code>_FILE_OFFSET_BITS=64</code>, and now I just found a new one that requires that you define <code>__USE_FILE_OFFSET64</code>.</p>
  
  <p>Is there any standard to all of this?</p>