c#/c++ how get voltage nvidia card?

Please help me. I don't think, how get voltage. Write general program on c#, testing use NvAPIWrapper, OpenHardwareMonitor, Cudafy library. Tried write mini-program on c++ with cuda, with nvApi. Use this links: OVERCLOCKING TOOLS FOR NVIDIA, Getting NVIDIA GPU Usage in C++, NVIDIA NVAPI. Use marshaling - adress in shield, use library - missing methods or incorrect value. I do not know what to do (