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1) You don't, since it is not code. It is the function prototype (actually the function pointer declaration) of a function that YOU have to implement. And then you pass the name of that function as parameter to the other function that wants this callback function. Whenever that other function thinks it wants to tell YOU something it calls that callback function with the documented parameters and YOUR callback function implementation does then something with that data. But your function is called in the context of the other function at SOME time after you called the original function that you passed your callback function too. Are you still with me? If not, don't worry, most people have big trouble with that. If yes then you might have a chance to actually get this eventually solved. But don't expect to have this working tomorrow or next week. You have a steep learning curve in front of you. 2) The iCube Camera in is simply a LabVIEW class that handles the whole camera management in LabVIEW, and in some of its internal methods accesses the DLL interface, and creates the event message queue, and starts up an event handler, and ..., and ..., and .... 3) The RegEventCallback function is a LabVIEW node that you can use to register events on CERTAIN LabVIEW refnums. One of them are .Net refnums, IF the object class behind that refnum implements events. .Net events are the .Net way of doing callbacks. It is similarly complex to understand and implement but avoids a few of the more nasty problems of C callback pointers such as datatype safety. But to use that node you will need a .Net assembly that exposes some object class which supports some events of some sort. Since .Net uses typesafe interface descriptions, LabVIEW can determine the parameters that such an event has and create automatically a callback VI and connect it behind the scenes with the .Net event. It works fairly good but has a few drawbacks that can be painful during development. Once the callback VI has been registered and activated, it is locked inside LabVIEW and there are only two ways to get this VI back into an editable state. Restart LabVIEW or after the object classes on which the event occured have been properly closed (Close Reference node) you need to explicitly call the .Net Garbage Collector in LabVIEW to make .Net release the proxy caller that LabVIEW created and instantiated to translate between the .Net event and the LabVIEW callback VI. If you have a .Net assembly that exposes events for some of its object classes, it is usually quite a bit easier to interface from LabVIEW than trying to do callback pointers in a C(++) DLL/shared library. Writing an assembly in C# that implements events is also not really rocket science but definitely neither a beginners exercise. 4) If you interface to C(++) in LabVIEW there is no safety net, sturdy floor, soft cushions and a few trampolines to safe your ass from being hurt when something doesn't 100% match between what you told LabVIEW that the external code expects and what it really does expect. It's in the best case a hard crash with error message, the next best case is a hard crash with no error message and after that you are in the lands of maybes, good luck and sh*t storm. A memory corruption does not have to immediately crash your process, it could also simply overwrite your multimillion dollar experiment results without you noticing until a few hours later when the whole factory starts to blow up because it is operating on wrong data. So be warned, thread safely and make sure to have your C(++) solution tested by someone who really understands what the potential problems are, or don't use your code ever in a production environment. This is the biting in your ass that dadreamer talked about, and it is not really LabVIEW that did it, but you yourself! 5) Which video screen output are you talking about? Once you managed to get the camera data into your LabVIEW program without blowing up your lab? Well you could buy IMAQ Vision or start another project where you will need to learn a lot of new things to do it yourself. 🙂