Question

I have a structure

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct SERVER_USB_DEVICE
{
    USB_HWID usbHWID;
    byte status;
    bool bExcludeDevice;
    bool bSharedManually;
    ulong ulDeviceId;
    ulong ulClientAddr;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 256)]
    string usbDeviceDescr;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 256)]
    string locationInfo;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 256)]
    string nickName;
}

When I pass it in a win32 DLL function as below:

[DllImport ("abc.dll", EntryPoint="EnumDevices", CharSet=CharSet.Ansi)]
public static extern bool EnumDevices(IntPtr lpUsbDevices,
                                      ref  ulong pulBufferSize, 
                                      IntPtr lpES);

I get some missing text in the string members of the structure.

Suppose SERVER_USB_DEVICE.usbDeviceDescr contains value “Mass Storage Device” which is wrong it should contain value “USB Mass Storage Device”

What is wrong in the code?

Answer 1

Actually i was making a small mistake here ulong is 8 bytes in c# where as it is 4 bytes in c++ (as we all know). converting ulong to uint solved the problem.