title: C errors - Cannot combine with previous 'struct' declaration specifier && Redefinition of 'MyMIDINotifyProc' as different kind of symbol
body: <p>I'm still new to C but trying to understand it better by working my way through a small MIDI audio unit (in Xcode 4.3.3).  I've been searching for an answer to this all day and still don't even understand exactly what the problem is.  Here's the code in question:</p>
  
  <pre><code>//MyMIDINotifyProc.h
  
  #ifndef MIDIInstrumentUnit_CallbackProcs_h
  #define MIDIInstrumentUnit_CallbackProcs_h
  
  void MyMIDINotifyProc (const MIDINotification *message, void *refCon);
  
  #endif
  
  
  //MyMIDINotifyProc.c
  
  #include &lt;CoreMIDI/CoreMIDI.h&gt;
  #include "MyMIDINotifyProc.h"
  
  void MyMIDINotifyProc (const MIDINotification *message, void *refCon) {
  //manage notification
  }
  </code></pre>
  
  <p>In the header definition I get this:</p>
  
  <pre><code>! Cannot combine with previous 'struct' declaration specifier
  </code></pre>
  
  <p>I've made sure the definitions match and tried renaming them and I still get this in my .c file:</p>
  
  <pre><code>! Redefinition of 'MyMIDINotifyProc' as different kind of symbol
  </code></pre>
  
  <p>Which points to the .h definition as the 'Previous definition'.</p>
  
  <p>I know that MIDIServices.h in the CoreMIDI framework defines:</p>
  
  <pre><code>typedef void
  (*MIDINotifyProc)(const MIDINotification *message, void *refCon);
  </code></pre>
  
  <p>But I don't understand if/why that would cause an error. I would be grateful if anyone could offer some help.</p>