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Well. It didn't take long to prototype the MQTT client as I was expecting - once I figured out it wasn't my code and it was just properties weren't supported by the public Mosquito server. The Hive MQTT public server doesn't seem to support V5 either. Anyone know of a public V5 server?

It took a while to code it, but here it is finally. 😉 I have found a way to retrieve the object's pointer soon after the last post in this thread, but had to debug and test everything. Refnum_to_Pointer.rar How it works: As we don't have any public or private API to obtain Base Cookie Jar (BCJ) pointer (that is a LabVIEW global variable), the only way is to examine some function, which uses it, find the place with this global and save the pointer. Actually, this is how we're getting our BCJ. To clarify, it's for Object References only, not for any other references out there. After we've got BCJ, we call MCGetCookieInfo and get the information, associated with that refnum. As far as I understand, CookieInfo appears to be a C++ class with a few methods and properties (not just an ordinary struct). One of the methods is able to extract the object's pointer from VI DS. Further we call that unnamed method, using the hard-coded offset of 0xC (for 32 bit) / 0x18 (for 64 bit) and it returns the necessary pointer. The method should be called using __thiscall convention, that is why I'm using the technique described here. I decided not to write a wrapper library, so that everyone everywhere could easily browse the code and alter it, when needed. Currently tested on all LabVIEW versions from 2009 to 2020 (both 32- and 64-bit, both IDE and RTE). It won't work on anything earlier than LV 2009, because ExtFuncCBWrapper is absent there. Also no Linux or macOS at the moment, sorry. Oh, and it may become broken in the future LV releases. Or may not, nobody knows yet. 🙂