How to properly shut down a node

edit

Crlt+C will be handled by the ros node logic internal and causes ros::ok() to no longer return true but false . After ros:ok() is not true any more there is no need to call ros::shutdown()

I think your code may look like this

 int main()
  {
      bool  running(false);
      //running is set to true by a condition statement somewhere here

      // exit the main loop 
      //              if running flag is set false, 
      //          or if ros::ok() is not ok anymore (likely we received Crlt+C), 
      //          or if the view was stopped
     for(; running && ros::ok() && !viewer->wasStopped() ;)
      {
       // ...             ...                          ...                  ...
       //do something
      }

  if ( ros::ok() )
  {
      // we exited the main loop because of false running value or the viewer was stopped,
      // no Crlt+C received, i. e. we have to ros::shutdown() explizitly
      ros::shutdown();
  }
  else
  {
      // nothing to be done here, ros::ok() no longer true, ros::shutdown not needed anymore
  }
  return 0;

}