Help with WM_COPYDATA

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Hello all, I am tring to communicate between 2 applications using wm_copydata.

I am not sure how to pass HWND using COPYDTASTRUCT.

C++

HWND hWnd = FindWindow(NULL, "Advisor");
	if (hWnd)
	{
/////Sending Application.
		COPYDATASTRUCT cds;
		ZeroMemory(&cds, sizeof(COPYDATASTRUCT));
		cds.dwData = WM_CREATE;
		cds.lpData = (HWND)ResulthWnd;
		cds.cbData = sizeof(ResulthWnd);
		SendMessage(hWnd,WM_COPYDATA,(WPARAM)ResulthWnd,(LPARAM)&cds);
         }

////////Receiving Application
switch (pCopyDataStruct->dwData)
	{
	case WM_CREATE:
         HWND SenderWnd = (HWND)pCopyDataStruct->lpData;
break;
         }

Can someone please help.

Thanks in advance.

Posted 4-May-12 11:32am

FISH786

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Sergey Alexandrovich Kryukov · Answer 1 · 2012-05-04T11:53:00

The member cds.lpData should be a pointer, (LPARAM)&ResultWnd (please fix the typo in the world "Result"), not HWND.

I would like to note, that exchanging data between two different processes is the artifact of the legacy Windows API created even before NT technology and is not a mainstream OS feature. The processes in real multi-process systems are supposed to be isolated and communicating only via IPC, such as sockets. So, WM_COPYDATA is neither safe not robust. You need to make a careful decision about it and consider alternative. The apparent simplicity of the approach could be very deceiving.

See also:
http://www.flounder.com/wm_copydata.htm[^],
Interprocess Communication Between .NET and MFC Using WM_COPYDATA[^].

—SA