Communication by WM_COPY (first chance exception)

[Wolvorine]

Hi,
I have two applications , one is written in MFC and other is written in managed and unmanaged mix code of C++/CLI . MFC application send the data to CLI application. But after one or two times communication it crashed with first chance exception. Maybe i am missing something which you guys can point me for its correction...

MFC Application's Code which communicate

#define _WM_HEADER_SIZE	(2*sizeof(DWORD)+sizeof(HWND)+sizeof(ULONGLONG))

typedef struct _WM_DATASTRUCTURE{
	DWORD cbSize;
	DWORD iMessage;
	HWND hClient;
	ULONGLONG address;
	_TCHAR Data[_WM_MAXMESSAGE_SIZE - _WM_HEADER_SIZE];	
}WM_DATASTRUCTURE,*LPWM_DATASTRUCTURE;




void SendDataToCLIApp()
{
HWND hd = ::FindWindow(L"CLIAPP",L"CLIAPPS");

		if(!hd)
		{
			
			ShellExecute(NULL,L"open",L"CLIAPP.exe",L"-tRun", NULL, SW_SHOWNORMAL);
			Sleep(4000);
		}
		
		
		if(hd)
		{
			strBuff+="\0";
			TransferData(hd,MSG_SENDFILE,strBuff.GetBuffer(),(STRLEN(strBuff.GetBuffer())*2));
		}
}

BOOL TransferData(HWND hd,DWORD dwMsg, const _TCHAR *Buffer, DWORD dwBytes) 
{
  BOOL bSend;
  COPYDATASTRUCT cpStructData;
  
  dwBytes+=4;
  cpStructData.cbData = dwBytes + _WM_HEADER_SIZE;
  HLOCAL hcl = LocalAlloc(LMEM_FIXED | LMEM_ZEROINIT,cpStructData.cbData);
  lpMsg = (LPWM_DATASTRUCTURE)hcl;
  lpMsg->iMessage = dwMsg;
  lpMsg->hClient = NULL;
  lpMsg->cbSize = dwBytes;
  lpMsg->address = m_devices[m_iSelectedDeviceIndex].Address.ullLong;
  cpStructData.lpData = lpMsg; 
  if(Buffer!=NULL){
	  MEMCPY(lpMsg->Data,Buffer,dwBytes);
	  lpMsg->Data[dwBytes-1]='\0';
  }


  bSend = SendMessage(hd,WM_COPYDATA, (WPARAM)hd,(LPARAM)&cpStructData);

  
  return(bSend);
}

And here is CLI application which response

LPWM_DATASTRUCTURE lpMsg;

	switch (message)
	{
	
	case WM_PAINT:
		hdc = BeginPaint(hWnd, &ps);
		// TODO: Add any drawing code here...
		EndPaint(hWnd, &ps);
		break;
	case WM_DESTROY:
		{
			g_Log->WRITE(L"WM_DESTROY",L"Close Message Came");
			PostQuitMessage(0);
		}
		break;

		
	case WM_COPYDATA:
		{
	
		 g_Log->WRITE(L"WndProc",L"CopyData Called");
		 lpMsg = (LPWM_DATASTRUCTURE)((COPYDATASTRUCT*)lParam)->lpData;
		 g_Log->WRITE(L"GOT DATA",lpMsg->Data);

                wstring strData = lpMsg->Data;

		g_CurrentAddress = lpMsg->address;

    ..............process data .......................

if((lpMsg->Data==NULL)||(lpMsg->Data==INVALID_HANDLE_VALUE))
							LocalFree((HLOCAL)lpMsg);
                 }
break;

Thanks in advance

[marceln]

You should not free the message buffer in the C++/CLI application. From MSDN:

The receiving application should consider the data read-only. The lParam parameter is valid only during the processing of the message. The receiving application should not free the memory referenced by lParam. If the receiving application must access the data after SendMessage returns, it must copy the data into a local buffer.

[Wolvorine]

Thanks for pointing me that , but still it gives me error...do you think i should free this memory in the MFC app. But when i use LocalFree in MFC right after SendMessage to CLI , it get crashed with exception. what you think???

[Wolvorine]

I am using LocalFree right after SendMessage


bSend = SendMessage(hd,WM_COPYDATA, (WPARAM)hd,(LPARAM)&cpStructData);

LocalFree((HLOCAL)lpMsg);

but its getting crash , any idea how can solve this???