Full duplex operation, functions C++ C#

Noah Aas 605

I have a C# application and a C++ application. Between the two, data should now be exchanged.

In C# 
   ReceiveDataFromCPP(String data)    
   SendDatatoCPP(string data)       
   
In C++ 
   ReceiveDataFromCSharp(String data)
   SendDatatoCSharp(string data)      

  How can I achieve this?    I think I need CLI.       
Can you give me an example?

I don't know when who sends what, it's event-oriented.

Picture, overview

Full_Duplex_C#C++

Viorel 119.7K Reputation points

2025-01-30T19:56:14.9233333+00:00

In short, because your programs have windows (or can create special hidden windows), you can use the WM_COPYDATA message to send the strings. But first you need to determine the target windows (HWND).

This is probably one of the simplest solutions.
RLWA32 46,861 Reputation points

2025-01-30T20:24:06.95+00:00

Windows supports a variety of methods for processes to communicate with each other as summarized here -- Interprocess Communications.
Noah Aas 605 Reputation points

2025-01-31T14:44:36.1366667+00:00

this is probably one of the simplest solutions.

Ups.

https://learn.microsoft.com/en-us/windows/win32/dataxchg/using-data-copy?redirectedfrom=MSDN

Is there sample code for C++ and C#?

AppCSharp.EXE ---- AppCPP.EXE

??? Callback
Noah Aas 605 Reputation points

2025-01-31T14:45:31.34+00:00

@RLWA32
Ups.

https://learn.microsoft.com/en-us/windows/win32/ipc/interprocess-communications

Using Windows Sockets for IPC

https://learn.microsoft.com/en-us/windows/win32/winsock/windows-sockets-start-page-2

That looks really difficult.

I just want to send and receive data. The time is event-oriented.

Is there sample code for C++ and C#?
Castorix31 86,971 Reputation points

2025-01-31T15:05:28.4666667+00:00

As @Viorel said, WM_COPYDATA is simple.

I had also posted a test sample in VB (or with MMF in page 2), easy to convert into C# with ChatGPT, in this thread https://learn.microsoft.com/en-us/answers/questions/594919/how-do-i-share-specific-pieces-of-information-betw
Noah Aas 605 Reputation points

2025-02-02T07:43:45.1266667+00:00

@Castorix31 right.

My problem is, I have C# and a C++/MFC application. Is there perhaps an example?
RLWA32 46,861 Reputation points

2025-02-05T08:53:03.49+00:00

@Noah Aas Have you had a chance to try the sample C# and MFC applications that I shared on Onedrive?

Accepted answer

RLWA32 46,861 Reputation points

2025-02-02T16:16:36.61+00:00

@Noah Aas I put together a sample that demonstrates using WM_COPYDATA to transfer strings between two different processes. The sample was created with VS2022 and includes an MFC C++ application and two C# Winforms applications (.Net Framework 4.8 and .Net 8). The sample applications transfer unicode strings (UTF-16LE) so do not change character encodings without making the appropriate changes to the sample code. The samples use a registered windows message to broadcast their process id and main window handle when they start up. So they can be started in any order. These samples were written so that only two processes can communicate with each other.

You can get the samples from https://1drv.ms/u/c/c389bf4121acea69/EfJ-SJJqXI9Fk2LruNlkr4oBjXrHT1q9skW_Y1dUe92_cg?e=NXaucj Don't forget to unblock the zip file before extracting the contents.
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1 person found this answer helpful.
Noah Aas 605 Reputation points

2025-02-05T15:42:47.9933333+00:00

Simply great. How did you come up with this code? I would never have found it. It works perfectly.

Who should receive the messages, can I define the address and ID myself?

There are sometimes a lot of open applications. How do I know that the right one will get it?

private void Form1_Load(object sender, EventArgs e) { WM_READY_COPYDATA = RegisterWindowMessage("ReadyForCopyData"); m_pid = (IntPtr) Process.GetCurrentProcess().Id; SendNotifyMessage(HWND_BROADCAST, WM_READY_COPYDATA, m_pid, Handle); }

BOOL CMFCCopyDataDlg::OnInitDialog() { CDialogEx::OnInitDialog(); m_pid = GetCurrentProcessId(); // WPARAM - process id // LPARAM - HWND WM_READY_COPYDATA = RegisterWindowMessage(_T("ReadyForCopyData")); ::SendNotifyMessage(HWND_BROADCAST, WM_READY_COPYDATA, m_pid, reinterpret_cast<LPARAM>(m_hWnd)); return TRUE; // return TRUE unless you set the focus to a control

RLWA32 46,861 Reputation points

2025-02-05T16:06:28.15+00:00

Who should receive the messages, can I define the address and ID myself?

The sample was written to use a registered message (WM_READY_COPYDATA) to identify the sender and receiver to each other. So only applications that know about the registered message can participate in data exchange.

In this particular sample, only one sender/receiver combination is allowed. So a third instance of either a C# application or MFC application will not connect. Of course, you could adjust the code so that limitation doesn't exist or even use another method to implement the "handshake" between senders/receivers. But the purpose of the sample was to show how WM_COPYDATA can be used to send data between a C# and C++ MFC application.

Noah Aas 605 Reputation points

2025-02-05T19:19:38.04+00:00

OK.

Process.GetCurrentProcess().Id;

Where or who defines the ID, sets it?

There are two applications. How do they know that they can communicate? I was thinking of a configuration value.

RLWA32 46,861 Reputation points

2025-02-05T19:41:06.2233333+00:00

Process identifiers are assigned by the system when a process is created. The applications know that communication is possible because of the registered message. For example, process1 broadcasts the registered message to all top-level windows on the desktop when it is started. If no other process knows about the message process1 is ready for communication but there's nobody to talk to. When process2 starts it also broadcasts the registered message. Process1 gets the message and knows that process2 is available so it then sends the registered message with it's own information back to process2 to complete the handshake and the two can then communicate. I suggest you read the documentation for the RegisterWindowMessageA function

Noah Aas 605 Reputation points

2025-02-06T09:23:22.8333333+00:00

RegisterWindowMessage("ReadyForCopyData")

Both Apps must have the same registering message. That is it.

RLWA32 46,861 Reputation points

2025-02-06T09:56:32.3866667+00:00

Both Apps must have the same registering message.

Yes, that is the technique used.Has your question been answered by the provided sample?

Noah Aas 605 Reputation points

2025-02-06T10:26:48.46+00:00

Sure, thanks a lot!
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1 additional answer

Minxin Yu 12,596 Reputation points Microsoft Vendor

2025-01-31T07:13:38.9966667+00:00

Hi,

Windows Message, you can refer to the sample:
https://learn.microsoft.com/en-us/windows/win32/dataxchg/using-data-copy

The following example demonstrates how to send information between two applications using the WM_COPYDATA message.

For named pipes, check sample: How to: Use Named Pipes for Network Interprocess Communication

Using Pipes

Best regards,

Minxin Yu

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Noah Aas 605 Reputation points

2025-02-02T15:56:51.5633333+00:00

Thanks for your help.
Do you have a complete example for C# Desktop and C++/MFC? It looks so difficult.
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