title: GetLastError(), errno, FormatMessageA() and strerror_s()?
body: <p>I'm confused as to the exact relationship between <code>GetLastError()</code> and <code>errno</code>.  Are they the same numerical values, or something completely different?  How do I know which one I should check?</p>
  
  <p>And if I want to convert an error code to a string for debugging, can I use <code>FormatMessageA()</code> interchangeably with <code>strerror_s()</code>?</p>
  
  <p>Lastly, is it true that <code>WSAGetLastError()</code> always returns the same as <code>GetLastError()</code>, or could they both return different values?</p>