Asynchronous communication between C++ and C#

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I have a console application in C++ that when loaded load a library in C#, which, in turn, when loaded shows a modal form with several buttons.

I need to implement a call back function from C# to C++ to indicate, in the C++ console output, every time an action is made in the modal form.

When the C ++ application is executed, the form is not displayed and the application ends without an answer after a few seconds (15 mm).

If the section indicated as //Return call function statement is commented (on C# side), the application is executed and the form is displayed. This indicates that something is not declared as it should be on the C# side.

For me it is totally new to make C++ converge with C# during a modal function like that of the form.

I need to know how to correct the statement so that the callback function is recognized.

What I have tried:

I have corrected the code but when I run the callback function it gives me an ECall security error

I have treated the following code C++:

int wmain(int argc, _TCHAR* argv[]) {

if (hResult == S_OK) {
std::wcout << returned_thing << std::endl;
return 0;
}
return 1;
}

The previous application communicates with the library in C # with the following code C #:

C#

namespace CSharpClass
{
    public class The33Class
    {
        CPPCallBack _CPPCallBack = null;

        public void SetCallBacks(IntPtr cppCallBack)
        {
        }


        public String Getng(String arg) // Make sure this is public
        {
        }

    }
}

Posted 16-Nov-18 3:23am

fisadmaster

Updated 20-Nov-18 0:21am

v6

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Comments

Richard MacCutchan 16-Nov-18 9:33am

You could have solved this problem some time ago if you had used a proper C# main class to interface with the library.

fisadmaster 16-Nov-18 9:37am

That is the reason that I am asking how to adjust the code, the original code is not mine, but it has been useful for me before making bridges. If you are so kind could you show me how to correct the statements?

Richard MacCutchan 16-Nov-18 11:12am

Unmanaged C++ code does not fit well with .NET so I do not know how you could solve this. I can only suggest that you use Google to try and find a sample that someone has actually made to work.

Rick York 16-Nov-18 12:33pm

If I were you I would need to have a VERY compelling reason to fight with this issue so much. So far, I have not read one from you but that's OK. You don't have to justify this to me. I would rewrite one of those two modules in the same language as the other and all of this complexity would be eliminated. You could probably have done a rewrite in the time you have spent fighting this and from all indications will likely continue to spend.

fisadmaster 17-Nov-18 11:07am

I have corrected the code but when I run the callback function it gives me an ECall security error

2 solutions

Solution 1

Is there a reason the console has to be in C++? Is this a dumbed-down example so you can get this working in another, more complicated context, like a legacy C++ app or COM object?

If not, then ...

1) Why not use C++/CLI which is also managed code?

or

2) You can write a console app in C#. So that may resolve the issue for you.

Posted 16-Nov-18 8:23am

TheGreatAndPowerfulOz

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User 11060979 · Accepted Answer · 2018-11-17T07:07:00

Solution 2

I did similar things before some years. A very pragmatic Approach (and maybe also a very dirty one).
Keep in mind I noted here what I remember...

The c# part

public class CSharpCom
{
   // c++ Callback stuff
   private delegate void CPPCallBack([MarshalAs(UnmanagedType.BStr)] string text);

   CPPCallBack _CPPCallBack= null;

   // To set callback from c++ 
   public void SetCallBacks(IntPtr cppCallBack)
   {
      _CPPCallBack= (CPPCallBack)Marshal.GetDelegateForFunctionPointer(
                     cppCallBack,
                     typeof(CPPCallBack));
   }

   // Using of the callback
   public void LogMsg(string msg)
   {
      try
      {
          _CPPCallBack?.Invoke(msg);
      }
      catch
      {
         // Error handling
      }
   }


   // You other COM stuff
}

The c++ part

static void __stdcall CPPCallBack(BSTR msg)
{
  // Implement callback stuff here
}

int wmain(int argc, char* argv[])
{
	CoInitialize(0); // Init COM

	BSTR thing_to_send = ::SysAllocString(L"10 20");
	BSTR returned_thing;
	CSharpDll::_TheClassPtr obj(__uuidof(CSharpDll::TheClass));

        // Register the callback
        obj->SetCallBacks((INT64)CPPCallBack);

	HRESULT hResult = obj->GetTheThing(thing_to_send, &returned_thing);

	if (hResult == S_OK) {
		std::wcout << returned_thing << std::endl;
		return 0;
	}
	return 1;
}

I hope it helps

[Edit]
code adjusted according to OP's feedback

Posted 17-Nov-18 7:07am

User 11060979

Updated 18-Nov-18 4:47am

v5

Comments

fisadmaster 17-Nov-18 13:37pm

Thanks for the code but the part,
_CPPCallBack = (CPPCallBack) .Marshal.GetDelegateForFunctionPointer (
cppCallBack,
typeof (CPPCallBack));

shows me the error: CSharpCom.CPPCallBack is a type which is not valid in the given context and CSharpCom.CPPCallBack does not contain a definition for 'Marshal'

I have included your code in the question so you can see the side of C # implemented
Any idea?

[no name] 17-Nov-18 13:46pm

Ok, not sure but maybe the delegate Definition Needs to be public. Try this public delegate void CPPCallBack([MarshalAs(UnmanagedType.BStr)] string text);

fisadmaster 17-Nov-18 13:48pm

I try that too, same problem

[no name] 17-Nov-18 13:51pm

Ok, give me "un rato", I will try to Setup a small test Project.

[no name] 17-Nov-18 14:21pm

It was simply a small typo. I corrected my answer.
a.) void SetCallback // void instead of bool (was not the Problem)
b.) _CPPCallBack= (CPPCallBack)Marshal.GetDelegateForFunctionPointer(
cppCallBack,
typeof(CPPCallBack));
instead
_CPPCallBack= (CPPCallBack).Marshal.

fisadmaster 17-Nov-18 14:52pm

Check the changes but nothing happens, not return to C++

[no name] 17-Nov-18 14:58pm

But it compiles?
What tells you the Debugger on both sides?

For me it runs now very ok.

fisadmaster 17-Nov-18 15:08pm

with the debug the C # form is not shown, the form is show on released but the callback function is not executed. My configuration is for 64 bits

[no name] 17-Nov-18 15:17pm

Understand, but this is a different thing I think. In GetThings you Show the form with "ShowForm" which I do not know in Details. Make sure that the form is shown as dialogue.

fisadmaster 17-Nov-18 15:22pm

Now you can see the complete code I have published for C++ and C#, the code of the button that should send the message of the release is:
TheClass myClass = new TheClass ();
myClass.LogMsg ("Work !!!");

fisadmaster 17-Nov-18 15:26pm

I have done a test without showing the form and the function works, the return call sends the message, but what I need is to send several messages while the form is displayed

[no name] 17-Nov-18 15:51pm

That it is some good News I think. Now you have to Show how your instance of Form1 does use the callback.

BTW: Use the reply widget of the comment to reply. It makes it more structured

fisadmaster 17-Nov-18 15:58pm

the form has a button which in the click event has this code:

[no name] 17-Nov-18 16:08pm

This like it will never work. Keep in mind only BimObjectCSharpClass does know the call back. Either you pass BimObjectCSharpClass to your Form1, save it in a private variable e.g. _BimObjectCSharpClass and call then _BimObjectCSharpClass.LogMsg from your form or you establish a delegate for Form1

fisadmaster 17-Nov-18 16:18pm

I'm sorry but I'm lost, BimObjectCSharpClass is the namespace and the class is TheClass. which I have referenced in the button code to access LogMsg, the form have the same namespace:

[no name] 17-Nov-18 16:23pm

Sorry, my mistake.
I mean you Need to pass TheClass to your Form1. Keep in mind this is not a nice way, but to test it it will be ok so far. Cosmetics can be done later ;)

fisadmaster 17-Nov-18 16:50pm

But if I pass TheClass to the form I can not see it and declare it from C ++?

[no name] 17-Nov-18 16:59pm

TheClass and Form1 are both on the c# side. I don't see the Problem...
Form1 needs to have access to TheClass.LogMsg

fisadmaster 17-Nov-18 17:05pm

I'm sorry, I was thinking that I had to pass all the code of the class to the code of the form, but I do not know how to pass the class as a reference to the form?

[no name] 17-Nov-18 17:23pm

You bring me to the Limit :). I do not know .net that exactly. Please forgive me all my mistakes in advance ;)

public Form1(TheClass theClass)
{
_TheClass= theClass;
}

After this you can use _TheClass.LogMsg....

As mentioned, this is not the clean way, but very ok for a first trial

fisadmaster 18-Nov-18 3:21am

I have made a clean compilation, I have rewritten all the code, I thought something was strange and now the C # library does not load, if I disable the line: obj-> SetCallBacks ((long) CPPCallBack); the form is displayed, if enabled, it enters a loop without an answer and ends after a few seconds. I believe that there is a problem in the statement, Any idea of the problem?

fisadmaster 18-Nov-18 4:48am

I make a simple change from long to INT64 and pass the class as reference and is working now, thanks man!!!!.
obj->SetCallBacks((INT64)CPPCallBack);

[no name] 18-Nov-18 9:18am

Thank you for accepting and voting.