title: Calling callback function from c++ to objective c
body: <ol>
  <li>I am using c++ library in my objective c project.</li>
  <li>I integrated c++ library and implemented .mm file to bridge c++ and objective c.</li>
  <li><p>I can successfully call c++ function from my objective c using this .mm bridge.</p></li>
  <li><p>The issue is that methods in given c++ library return's nothing i.e Void.
  For example void login( const char* email,  const char* password);</p></li>
  <li><p>This c++ library have call back function implemented to know the result of this login method.</p></li>
  </ol>
  
  <p>Example: </p>
  
  <pre><code>class DemoApp : public XClass
  {
  
  int urandomfd;
  
  public:
  uint32_t dstime(void);
  
  FileAccess* newfile();
  
  void request_error(MegaClient*, error);
  
  void login_result(MegaClient*, error);
  
  void users_updated(MegaClient*, User**, int);
  void nodes_updated(MegaClient*, Node**, int);
  
  int prepare_download(MegaClient*, Node*);
  
  void share_result(MegaClient*, int, error);
  
  void account_details(MegaClient*, AccountDetails*, int, int, int, int, int, int);
  
  void topen_result(MegaClient*, int, error);
  void topen_result(MegaClient*, int, string*, const char*, int);
  
  void transfer_update(MegaClient*, int, off_t, off_t, uint32_t);
  void transfer_error(MegaClient*, int, int, int);
  void transfer_failed(MegaClient*, int, error);
  void transfer_failed(MegaClient*, int, string&amp;, error);
  void transfer_limit(MegaClient*, int);
  void transfer_complete(MegaClient*, int, chunkmac_map*, const char*);
  void transfer_complete(MegaClient*, int, const byte*, const byte*, SymmCipher*);
  void changepw_result(MegaClient*, error);
  
  void reload(MegaClient*, const char*);
  
  void notify_retry(MegaClient*, int);
  void debug_log(MegaClient*, const char*);
  
  DemoApp();
  };
  </code></pre>
  
  <ol>
  <li><p>So now my concern is how and when should i call these CALLBACK function's in my objective C library, which look's to me that they are called internally in c++ library.</p></li>
  <li><p>This is my wrapper.mm file, wrapping c++ methods, need to call in objective c.</p>
  
  <p>-(void) WrapLogin:(NSString*) email :(NSString*) pwd{</p>
  
  <p>self.wrappedModelAccessMega->Login([email UTF8String], [pwd UTF8String]);
    //No return as Login mfunction from c++ library returns nothing i.e void</p>
  
  <p>}</p></li>
  <li><p>I am working on it from a while and already pushed hard to integrate this library to my objective C library now i got stuck to it due to these callback function's. 
  Please small example showing how should i use callback function of c++, wrap it and call in my objective c to get/know result/return of my login function will do the great job for me.</p></li>
  </ol>