I use the structure to get the name of the system.
char sysname[64] = { 0 };
NvGetName = (NvAPI_GPU_GetFullName_t)(*NvQueryInterface)(0xCEEE8E9F);
NvGetName(hdlGPU[0], sysname);
printf("Name: %s\n", sysname);
Where can I get the QueryInterface codes for the GetPowerUsage method in my own project?