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Hello I hope someone can help me, I have been trying to get this to work for days but no success yet. What I want to do I got a dll with a wrapper, this dll and wrapper can be used for a special datalogger. The wrapper contains multiple functions, I have got some of them working using a CLFN, for instance I can read a jumper setting from the datalogger in LabView. So far everything is fine. Of course I am not that interested in the jumper setting, I would rather use the datalogger to log data. I need to run one function to start logging. When there is enough data in the databuffer of the driver dll it will call a callback function I need to write in Labview, here is the function which starts the logging as described in the header file: Int LOGEXPORT __sdcall LOG_StartLogging{const char ** logFilename, ptLogCallbackfunction ptFunction, ptObject ptObject} logFilename needs to be a NULL pointer, from my understanding I do not need to do anything with it. Only provide it. If I do not do anything with it some data is saved at a default location. ptLogCallbackfunction, as far as I know I need to provide a pointer to the callback function ptObject ptObject, this must be a void pointer The header also provided how the callback function could look like in 😄 Void __stdcall callbackLog(ptObject object, const int ArraySize, const StructLogdata *const logDataArray) { // copy data from logDataArray for use in my code } StructLogdata is a struct with different datatypes. What I did try I did a search on internet there are some examples about callback functions, most of them point to NET and active X. They use a reg Event Callback. I did read the helpfile at the end of the helpfile there is the text: “Use the Event structure or the Register For Events function to register and handle non-.NET or non-ActiveX events dynamically” I am having a hard time to find a proper example. I did find this site with some information: https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000P8XJSA0&l=nl-NL and this one about the refnum: https://forums.ni.com/t5/LabVIEW/Passing-Event-Refnum-to-Call-Library-Function/td-p/4107748 So I did make a user event, I wired a static Vi ref containing a callback vi to the input of this user event. I did wire the user event to a Reg event and wired the event registration refnum to the start logging dll call library function node function pointer input and also to an event structure. I did place a counter in the event structure. But nothing happens besides for an exception which makes Labview crash. The parameters I did use in the call library function are: logFilename: type numeric, datatype: Signed Pointer-sized int Pass: pointer to value ptLogCallbackfunction: type: adapt to type, Data format handles by value (tried all options) ptObject: same as logFilename I did try a lot of different things. Writing them in this post will result in chaos and I don’t want that. I hope someone can help me with a simple example how to make this work, or point me into the correct direction. Thank you all for the help!

Hello, I am trying to figure out, if it is possible to create a native LabVIEW I/O interface to C/C++ code, that is using the I/O functions through callbacks. The scenario is as follows: I made a toolkit to process multimedia formats and (so far only) video codecs, it is using internally FFmpeg shared objects (DLLs or SOs, further just "DLLs"). They way the FFmpeg DLLs access I/O is through callback mechanism. Following all happens in the wrapper. If I want the toolkit to read data from some I/O like network or disk, I have to create a session, and part of the session are function pointers to callbacks doing various tasks, one of them is reading data. Anytime a user tries to read more data (1 data packet), he forces a call to the session demuxer, that further uses the I/O callback so long, until it parses one packet/hits EOF/corrupt data/etc..., now this works nicely if you want to provide data through standard means like video file or stream URL. Since the capabilities of FFmpeg allow for example (de)muxers and codecs for images, I thought it would be cool to give the user possibility to supply his own data, that he reads via LabVIEW from database or whatever. Not just limit the usage of I/Os implemented inside the DLLs. All I know, is that I cannot use VIs as callbacks inside C/C++ code, so the only way is to somehow "decallback" the implemented I/O mechanism.