LabVIEW has its own memory management. You cannot tell LabVIEW where to explicitly store something. Is the C++ program a DLL? If so you can allocate an array of sufficient size and then pass it to the DLL as a pointer so the DLL can write to that memory location. Please do a search on the NI site for calling DLLs from LabVIEW. There is also an entire chapter in the LabVIEW Help, as well as an example that ships with LabVIEW on how to call DLLs. Open the Example Finder (Help -> Find Examples) and search for "DLL".
