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In particular, how can LabVIEW interface with the DefineVar function:


I see that the function expects a pointer to a variable from LabVIEW. MuParser stores this pointer internally and dereferences it in the Eval function. I doubt that the value that I passed along the wire into the DefineVar function will (reliably) remain at the same memory address by the time Eval is called. 

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Use DSNewPtr, which you can call through a Call Library Function Node with the library name set to "LabVIEW". See the LabVIEW help or posts on the NI forum about this function and the other memory manager functions. You then use MoveBlock (same idea) to copy data between LabVIEW and that pointer.

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  • 8 months later...

Thanks again ned! DSNewPtr and MoveBlock did the trick. There is also a nice GetValueByPointer.xnode that really helps getting string values from pointers.

muParser seems to be about 3x faster than the expression parser provided with labview and it supports logical operators.


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