Lynn Johnson

Lynn Johnson

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FindFirstDevice wince error 18

Jan 15 2013 4:55 PM
I have a c# application running on winCE 6.0 version.  I need to unload/reload the SD card driver at run time.  I am attempting to do this via calling FindFirstDevice, then DeactivateDevice/ActivateDeviceEX calls.  My problem is the FindFirstDevice() call always fails.  I believe it to be a problem with the way I am marshalling the second parameter to it.  Can anyone tell me what I am doing wrong?  Here is the code:


      [DllImport("coredll.dll", SetLastError = true)]
      public static extern int FindFirstDevice(DeviceSearchType
      searchType, IntPtr searchParam, ref DEVMGR_DEVICE_INFORMATION pdi);

      public bool MountSDCardDrive(string mRegPath)
      {
         const int INVALID_HANDLE_VALUE = -1;
         
         int handle = INVALID_HANDLE_VALUE;
         DeviceSearchType searchType = DeviceSearchType.DeviceSearchByDeviceName;

         DEVMGR_DEVICE_INFORMATION di = new DEVMGR_DEVICE_INFORMATION();
         di.dwSize = (uint)Marshal.SizeOf(typeof(DEVMGR_DEVICE_INFORMATION));

         string searchParamString = "*";
         IntPtr searchParam = Marshal.AllocHGlobal(searchParamString.Length);
         Marshal.StructureToPtr(searchParamString, searchParam, false);

         handle = FindFirstDevice(searchType, searchParam, ref di);
         if (handle == INVALID_HANDLE_VALUE)
         {
            // Failure - print error
            int hFindFirstDeviceError = Marshal.GetLastWin32Error();

            using (StreamWriter bw = new StreamWriter(File.Open(App.chipDebugFile, FileMode.Append)))
            {
               String iua = "DevDriverInterface: error from FindFirstDevice: " + hFindFirstDeviceError.ToString();
               bw.WriteLine(iua);
            }
            return false;
         }

... (rest of code)

If I change the line "Marshal.StructureToPtr(searchParamString, searchParam, false);" to "searchParam = Marshal.StringToBSTR(searchParamString);" I end up with error 1168 (ERROR_NOT_FOUND) instead of 18 (no more files).  

Note my intent is to use a searchParamString of "SDH1" when I get this working.  I am currently using searchParamString of "*" as examples I see on the web indicate that should always return something.  

Thanks for any help you can give  - Lynn