Inter-Process Communication using WM_COPYDATA

Download demo project - 83 Kb

Download 32-bit source - 20 Kb

Download 16-bit source - 13 Kb

This demo shows how to send and receive message between apps (32-bit and 16-bit) using WM_COPYDATA.

There are two samples. One is 32-bit and one is 16-bit. The 32-bit sample will check and see whether it is already running and if so, will start another instance with a different window header.

• The 'Send' button will send the text from the editbox to the other 32-bit app.
  
• The 'Send16' button will send the text to the 16-bit app.

The received data will show up in the static box.Only 2 instances of the 32-bit apps are supported in this demo. The 16-bit app will only send and receive data to/from the 32-bit apps.

The exchange of data is performed by finding the other application (using FindWindow) and sending a WM_COPYDATA message to that window:

    CString strWindowTitle = _T("Window Name");
    CString strDataToSend  = _T("This is a message to send");
    
	LRESULT copyDataResult;
	CWnd *pOtherWnd = CWnd::FindWindow(NULL, strWindowTitle);

	if (pOtherWnd)
	{
		COPYDATASTRUCT cpd;
		cpd.dwData = 0;
		cpd.cbData = strDataToSend.GetLength();
		cpd.lpData = (void*)strDataToSend.GetBuffer(cpd.cbData);
		copyDataResult = pOtherWnd->SendMessage(WM_COPYDATA,
                                                (WPARAM)AfxGetApp()->m_pMainWnd->GetSafeHwnd(),
                                                (LPARAM)&cpd);
		strDataToSend.ReleaseBuffer();
		// copyDataResult has value returned by other app
		
	} 
	else 
	{
		AfxMessageBox("Unable to find other app.");
	}	
}

The other app should handle the WM_COPYDATA message in the following manner

BEGIN_MESSAGE_MAP(CMyWnd, CWnd)
	//{{AFX_MSG_MAP(CMyWnd)
	...
	ON_WM_COPYDATA()
	...
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

...

BOOL CMyWnd::OnCopyData(CWnd* pWnd, COPYDATASTRUCT* pCopyDataStruct) 
{
	CString strRecievedText = (LPCSTR) (pCopyDataStruct->lpData);
	
	return CMyWnd::OnCopyData(pWnd, pCopyDataStruct);
}