C# USB driver from C++: SetupDiGetDeviceInterfaceDetail

Question

I\'ve a problem trying to call SetupDiGetDeviceInterfaceDetail from C#. It always returns 1784 error code (\"The supplied user buffer is not valid for the requested operation\")

Answer 1

The struct is a variable sized structure which cannot be marshalled automatically. You'll need to do so yourself.

You'll need to remove the SP_DEVICE_INTERFACE_DETAIL_DATA type. It's no use to you. Change the declaration of SetupDiGetDeviceInterfaceDetail to:

[DllImport(@"setupapi.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern Boolean SetupDiGetDeviceInterfaceDetail(
    IntPtr hDevInfo, 
    SP_DEVICE_INTERFACE_DATA deviceInterfaceData, 
    IntPtr deviceInterfaceDetailData, 
    uint deviceInterfaceDetailDataSize, 
    out uint requiredSize, 
    SP_DEVINFO_DATA deviceInfoData
);

Pass IntPtr.Zero in the first call to SetupDiGetDeviceInterfaceDetail. Then allocate a buffer of the required size by calling Marshal.AllocHGlobal. Then write the size into the first 4 bytes of that buffer. Then call SetupDiGetDeviceInterfaceDetail again.

Something along these lines:

bool result3 = Win32.SetupDiGetDeviceInterfaceDetail(hDevInfo, ifData, IntPtr.Zero, 0, 
    out needed, null);
if(!result3)
{
    int error = Marshal.GetLastWin32Error();
}
// expect that result3 is false and that error is ERROR_INSUFFICIENT_BUFFER = 122, 
// and needed is the required size

IntPtr DeviceInterfaceDetailData = Marshal.AllocHGlobal((int)needed);
try
{
    uint size = needed;
    Marshal.WriteInt32(DeviceInterfaceDetailData, (int)size);
    bool result4 = Win32.SetupDiGetDeviceInterfaceDetail(hDevInfo, ifData, 
        DeviceInterfaceDetailData, size, out needed, null);
    if(!result4)
    {
        int error = Marshal.GetLastWin32Error();
    }
    // do whatever you need with DeviceInterfaceDetailData
}
finally
{
    Marshal.FreeHGlobal(DeviceInterfaceDetailData);
}