Question

I’m really struggling with using the CallNtPowerInformation function in C#. I need to get the Windows SystemExecutionState. (Possible values listed here).

I’ve found the appropriate C# signature:

    [DllImport("powrprof.dll", SetLastError = true)]

    private static extern UInt32 CallNtPowerInformation(
         Int32 InformationLevel,
         IntPtr lpInputBuffer,
         UInt32 nInputBufferSize,
         IntPtr lpOutputBuffer,
         UInt32 nOutputBufferSize
         );

Now I need to use information level 16 to read the “SystemExecutionState”. Here’s the code I have so far:

IntPtr status = Marshal.AllocCoTaskMem(Marshal.SizeOf(typeof(ulong)));
UInt32 returnValue = CallNtPowerInformation(
    16, 
    (IntPtr)null, 
    0, 
    status, (
    UInt32)Marshal.SizeOf(typeof(ulong)));
Marshal.FreeCoTaskMem(status);

According to the Microsoft documentation:

The lpOutputBuffer buffer receives a ULONG value containing the system
execution state buffer.

How do I get the ULONG value from the IntPtr?

Answer 1

Call Marshal.ReadInt32(status) to get the value.

uint statusValue = (uint)Marshal.ReadInt32(status);

The Marshal class has a whole family of ReadXXX methods that allow you to read from unmanaged memory.