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Asked: 2026-05-11T06:14:19+00:00

In an application I wrote a few years back I use function SystemParametersInfo with

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In an application I wrote a few years back I use function SystemParametersInfo with SPI_GETPOWEROFFTIMEOUT to get the timeout for monitor off. On Vista this doesn’t work anymore.

So I decided to make this work on Vista, but after a few hours I feel like I’m no closer to a solution.

Most of the functions I am going to mention are described on http://msdn.microsoft.com/en-us/library/aa373163(VS.85).aspx

To my understanding I should: 1. use function PowerGetActiveScheme, to get current scheme 2. use PowerEnumerate with GUID_VIDEO_SUBGROUP 3. use PowerReadACValue (or DC value) to get the value.

Is this right? Seems like a lot of work to get to one setting. If this is the correct way, there is one thing I don’t understand. On my system PowerEnumerate returns 3 keys. How do I know which one is for Monitor timeout?

Here is my code so far. I’m having trouble with PowerReadACValue, I probably didn’t define or use it properly.

class Program {     [DllImport('powrprof.dll')]     static extern UInt32 PowerGetActiveScheme(IntPtr UserRootPowerKey, ref IntPtr ActivePolicyGuid);      [DllImport('powrprof.dll')]     static extern uint PowerEnumerate(                 IntPtr RootPowerKey,                 IntPtr SchemeGuid,                 Guid SubGroupOfPowerSettingGuid,                 UInt32 AcessFlags,                 UInt32 Index,                 ref Guid Buffer,                 ref UInt32 BufferSize);      [DllImport('powrprof.dll')]     static extern uint PowerReadACValue(                 IntPtr RootPowerKey,                 IntPtr SchemeGuid,                 IntPtr SubGroupOfPowerSettingGuid,                 Guid PowerSettingGuid,                 ref IntPtr Type,                 ref IntPtr Buffer,                 ref UInt32 BufferSize);      static void Main(string[] args)     {         IntPtr activeGuidPtr = IntPtr.Zero;         uint res = PowerGetActiveScheme(IntPtr.Zero, ref activeGuidPtr);         if (res == 0)         {             Guid VideoSettingGuid = new Guid();             UInt32 index = 0;             UInt32 BufferSize = (UInt32)Marshal.SizeOf(typeof(Guid));             while (0 == PowerEnumerate(                 IntPtr.Zero, activeGuidPtr, new Guid('7516b95f-f776-4464-8c53-06167f40cc99'), 18, index, ref VideoSettingGuid, ref BufferSize))             {                 Console.Write(VideoSettingGuid.ToString() + ': ');                  UInt32 size = 1024;                 IntPtr temp = Marshal.AllocHGlobal(1024);                 IntPtr type = IntPtr.Zero;                  PowerReadACValue(IntPtr.Zero, activeGuidPtr, IntPtr.Zero, VideoSettingGuid, ref type, ref temp, ref size);                  Console.Write(Marshal.PtrToStringUni(temp));                 Marshal.FreeHGlobal(temp);                 index++;             }         }     } }

I also tried using GetActivePwrScheme and then ReadPwrScheme, but it doesn’t seem to work either. GetActivePwrScheme always returns 0, even if I switch power schemes. I also tried running ReadPwrScheme with incremental values (1,2,3). I got to 5 or 6 but it never returned the correct number for the value I set for monitor timeout in control panel.

I hope I have this totally wrong and there is a much easier way of doing this.

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1 Answer

  1. I finally did have some luck and found a function which works on both XP and Vista – GetCurrentPowerPolicies. It is very simple to call and returns a lot of the current settings including the setting I wanted VideoTimeoutAc and VideoTimeoutDc.

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