title: Objective-C : #define vs extern const
body: <p>I know this question has been asked before, but I can't seem to find information about it in Apple's documentation; maybe some of you guys did.</p>
  
  <p>A lot of Objective-C code has cross-file constants in a <code>.h</code> file, using <code>#define</code>.
  Others use the approach of a <code>.m</code> with constants and <code>extern</code> them in the <code>.h</code> file.</p>
  
  <p>I understand the difference, both pros and cons, but does Apple state which one to use in iOS development?</p>