Question

I have an windows application that performs a simple routine to determine whether a USB token is present. The method has always worked correctly on 32-bit machines however during testing on a 64-bit machine we started to see unexpected results.

I am calling the following method

[StructLayout(LayoutKind.Sequential)]
internal struct SP_DEVINFO_DATA
{
    public Int32 cbSize;
    public Guid ClassGuid;
    public Int32 DevInst;
    public UIntPtr Reserved;
};

[DllImport("setupapi.dll")] 
internal static extern Int32 SetupDiEnumDeviceInfo(IntPtr DeviceInfoSet, Int32 MemberIndex, ref  SP_DEVINFO_DATA DeviceInterfaceData);

The documentation for the SP_DEVINFO_DATA structure tells us that the cbSize is
the size, in bytes, of the SP_DEVINFO_DATA structure.

If we calculate cbSize for a 32-bit machine it will be 28 and 32 for a 64-bit machine.

I have tested this on both machines by recompiling with different cbSize values, what i want to know is how can i calculate this as runtime? My application need to run on both architectures.

internal static Int32 GetDeviceInfoData(Int32 iMemberIndex)
{
    _deviceInfoData = new Win32DeviceMgmt.SP_DEVINFO_DATA
    {
        cbSize = ?? // 28 When 32-Bit, 32 When 64-Bit,
        ClassGuid = Guid.Empty,
        DevInst = 0,
        Reserved = UIntPtr.Zero
    };

    return Win32DeviceMgmt.SetupDiEnumDeviceInfo(_deviceInfoSet, iMemberIndex, ref _deviceInfoData);
}

Thanks

Rohan

Answer 1

Use Marshal.SizeOf:

_deviceInfoData = new Win32DeviceMgmt.SP_DEVINFO_DATA
    {
        cbSize = System.Runtime.InteropServices.Marshal.SizeOf(typeof(Win32DeviceMgmt.SP_DEVINFO_DATA);
        // etc..
    }