Code translation from pascal to c#

Question

I have a c++ dll which is used in a delphy pascal project and I want to create ac# project to use it. The dll returns an interface object and I am stuck right now on how to implement the C# interface to be recognized by dllImport. I have the code in pascal, that works. Also, I do not have access to the c++ source of the dll.

here is the delphy part:

interface
uses
  IdGlobal;
type
//  TIdBytes = array of Byte;
  TBUF2 = array[0..1] of Byte;
  TBUF3 = array[0..2] of Byte;
  TBUF4 = array[0..3] of Byte;
  PBUF4 = ^TBUF4;
  TBUF6 = array[0..5] of Byte;
  TBUF8 = array[0..7] of Byte;
  TBUF16 = array[0..15] of Byte;

  TUDPRcvRcd = record
    Head: TBUF3;
    DevType: Byte;
    DevID: Byte;
    DevIP: TBUF4;
    DevMAC: TBUF6;
    SoftVer: TBUF2;
    HardVer: TBUF2;
    DevName: TBUF16;
    CHK: Byte;
  end;

  ReceiveDataEvent = procedure(aData: TIdBytes) of object;
  ListRecive = procedure(aData: TIdBytes; aMac: PChar) of object;

  ILhm = interface
    function SearchDev: Integer; stdcall;
    function SetRcvSearchResultProc(aReceiveDataEvent: ReceiveDataEvent ): Boolean; stdcall;
    function ConnectDev(aMac, aIp, aPort, aPsd: PChar): Boolean; stdcall;
    function RemoveDev(aMac: PChar): Boolean; stdcall;
    function SendDataByMac(aData: TIdBytes; aMac: PChar): Boolean; stdcall;
    function SetRcvDevDataProc(aListRecive: ListRecive ): Boolean; stdcall;
  end;


function ControllerInit: ILhm; stdcall; external 'controller.dll' name 'ControllerInit';

implementation
end.

I wrote this in my c# project until now

 [DllImport("controller.dll",
 //EntryPoint = "ControllerInt", SetLastError = true, 
 CallingConvention = CallingConvention.Cdecl)]
 public static extern ILhm ControllerInit();

 public delegate object ReceiveDataEvent (byte[] aData);
 public delegate object ListRecive(byte[] aData, string aMac);


    public interface ILhm
    {
        int SearchDev();

        bool SetRcvSearchResultProc(ReceiveDataEvent aReceiveDataEvent);

        bool ConnectDev(string aMac, string aIp, string aPort, string aPsd);
        bool RemoveDev(string aMac);
        bool SendDataByMac(byte[] aData, string aMac);
        bool SetRcvDevDataProc(ListRecive aListRecive);
    }

I receive various errors regarding wrong definition of PInvoke or :

Additional information: The runtime has encountered a fatal error. The address of the error was at 0x7221dd74, on thread 0x305c. The error code is 0xc0000005. This error may be a bug in the CLR or in the unsafe or non-verifiable portions of user code. Common sources of this bug include user marshaling errors for COM-interop or PInvoke, which may corrupt the stack.

Thanks!

Answer 1

Long story short - your DLL is not compatible as-is with C#.

Delphi interfaces cannot be used in C# unless:

• they derive from IInterface (known as IUnknown in COM) and you use COM interop on the C# side.

• you fake the interface on the C# side by declaring a C-style struct that contains a pointer to a vtable (an array of C-style function pointers) for the interface methods. And then you can use a pointer to that outer struct wherever the Delphi interface is expected.

Also, your two event types, ReceiveDataEvent and ListRecive , are using a Delphi-specific feature ( procedure of object ) that is not compatible with C# at all, so your use of delegates will not work for them. Either use C-style function pointers or a COM-style event interface.

Delphi-style dynamic arrays, like TIdBytes , are also not compatible with C# at all, or even COM for that matter. You need to use static arrays, C-style dynamic arrays, or COM SafeArrays instead.

Also, a mistake in your code is that the DLL is using the stdcall calling convention but your C# import is using cdecl instead.

In short, you should really redesign the DLL before you can use it directly in C#. If that is not an option, then at least write a COM wrapper around it and then import that into C# instead.