Legacy DLLs and Callbacks

[Woogoo]

Hi,

I assume this has been asked before but I can't find an answer that works for me. My application is written in C++/CLI and I'm using a legacy C DLL via a Type Lib. I need to pass the address of a C++/CLI Callback Function to the Legacy DLL but nothing I've read works.

I assume this can be done but I can't work it out for the life of me. Can anyone help me here please?

--
Woogoo

[darwen]

Can you post the interface definition from the type library ?

You can get this by opening the COM dll in OLEView.exe (found in C:\Program Files\Microsoft Visual Studio 8\Common7\Tools\Bin\OLEView.exe).

I need to see

(a) The callback function declaration.
(b) The declaration of the method you're trying to pass the callback into.
(c) The type of the interface.

Darwen.

[Woogoo]

Hi, first things first I got it wrong I'm NOT using a typelib that was my mistake I am simply including a DLL within my search path.

But to answer two of the questions:

(a) int LSsetCallbackSolverLng(pLSenvLINGO pL, lngCBFuncError_t pcbf, void* pUserData) ;
(b) int __clrcall FormMain::SolverCallback(void* pModel, int nReserved, void* pUserData) {...}

When b is declared as :

int __stdcall FormMain::SolverCallback(void* pModel, int nReserved, void* pUserData)

I get the following complier warning:

C4441: calling convention of '__cdecl ' ignored; '__clrcall ' used instead Matrix.cpp 114

and when either __stdcall or __clrcall I get

error C2664: 'LSsetCallbackSolverLng' : cannot convert parameter 2 from 'Matrix::FormMain::CallBackDelegate ^' to 'lngCBFunc_t' Matrix.cpp 79

This is line 79
ProcessErrorCode(LSsetCallbackSolverLng(pLingo, MyDelegate, &dBestObjective)) ;

And MyDelegate is defined:
CallBackDelegate^ MyDelegate = gcnew CallBackDelegate(this, &FormMain::SolverCallback) ;

I have tried all manner of incantations to get this to work but for the life of me I just can't do it.

Does this make any sense to you?

[darwen]

Try not passing a delegate : try passing the function pointer directly. e.g.


// not in any class : just an ordinary 'C' style method
int __stdcall MyCallback(void* pModel, int nReserved, void* pUserData)
{
return 0;
}

// ...
LSsetCallbackSolverLng(pLingo, &MyCallback, &dBestObjective);


You can do this using delegates, but you'd have to define the necessary method first in managed code using p/invoke i.e. with DllImport attribute.

Darwen.

[Woogoo]

I had already tried a variation of that but since the Solver is on a thread there are callbacks in there to update the interface as the solution progresses, so the compiler *****es.

When you said "You can do this using delegates, but you'd have to define the necessary method first in managed code using p/invoke i.e. with DllImport attribute."

Do you have an example or a point of reference I can look at?

Thanks.

[Alex F]

Use Marshal.GetFunctionPointerForDelegate Method. Apply it to managed callback function. It returns IntPtr, which can be converter to void* using ToPointer method. Pass this value to the Set Callback function.

[Alex F]

#include "stdafx.h"
#include <windows.h>

using namespace System;
using namespace System::Runtime::InteropServices;

delegate int HandleWindowDelegate(IntPtr handle, IntPtr lParam);

ref class TestClass
{
public:
TestClass()
{
}

void EnumWindows()
{
HandleWindowDelegate^ d = gcnew HandleWindowDelegate(this, &TestClass::HandleWindow);

::EnumWindows(
(WNDENUMPROC)Marshal::GetFunctionPointerForDelegate(d).ToPointer(),
0);
}

int HandleWindow(IntPtr handle, IntPtr lParam)
{
Console::WriteLine(handle.ToInt32().ToString(L"X"));
return 1;
}
};



int main(array<System::String ^> ^args)
{
TestClass^ t = gcnew TestClass();

t->EnumWindows();

return 0;
}

[Woogoo]

Hi, with the addition of Marshal::... I now have:
CallBackDelegate^ MyDelegate = gcnew CallBackDelegate(this, &FormMain::SolverCallback) ;
if (pLingo != 0)
{
ProcessErrorCode(LSsetCallbackSolverLng(pLingo, Marshal::GetFunctionPointerForDelegate(MyDelegate).ToPointer(), &dBestObjective)) ;
...
}

But I still get the C2664 Compiler Error! With the declaration of the Callback being:

int __clrcall FormMain::SolverCallback(void* pModel, int nReserved, void* pUserData);

It's evident by now that I'm no expert on this which makes me think there may be a touch of WoMBat in this application. This application contains NO DllImport statements and the reference to the typelib has been remove. So how does the IntelliSense still work!

So I guess it must be working by accident as I can't see what I'm doing wrong, and my head's starting to hurt!

[darwen]

Intellisense will be picking up the function types from the .h file for the dll.

Try this :


ProcessErrorCode(
LSsetCallbackSolverLng(
pLingo,
(lngCBFuncError_t)Marshal::GetFunctionPointerForDelegate(MyDelegate).ToPointer(),
&dBestObjective)) ;


And PLEASE USE CODE TAGS as we all have done when responding. It makes code much easier to read.

Also, what is CallBackDelegate defined as ? It should be


delegate void CallbackDelegate(IntPtr pModel, int nReserved, IntPtr pUserData);


Darwen.

[buddhikasgj]

Im having s similar kind of senario. I want to write a C++ DLL and consume it from C#. what i want to do is pass a call back function with one string parameter to the dll and call it from the DLL, For the purposes of providing a status during long operation done at the DLL. I googled mybest to find the way but i couldnt find a simple guid to do that. So please anyone can help me with simple code sample of how to implement the C++ function with a function pointer argument, how to call the function pointed by the funtion pointer from the DLL and how to call the DLL function from the C# code. Any sort of help would be appriciated. thanks