How to get string thru lParam in window message

[TusharV]

Hi All,

I have two dialog based applications in which first dialog has implemented a user message, with wParam and lParam as parameter.
Now from other dialog based application I want to send the above user message to get a string value. (It is somewhat similar to WM_GETTEXT message)
I have implemented code like this

Application 2:-

void SomeFunction()
{
CWnd* pWnd = FindWindow();	// Find the Application 1's Window (i.e. CUsrSNDlg)
TCHAR pname[100];
memset(pname, '\0', sizeof(TCHAR)*100);
pWnd->SendMessage(WM_USR_GETNAME, 0, (LPARAM)(LPCTSTR)pname);
}

Application 1:-

LRESULT CUsrSNDlg::OnUsrGetName(WPARAM wParam, LPARAM lParam) 
{
::CopyMemory((LPVOID)lParam, m_UsrName, 100);	// Here copy fails as this is a address of other appln's address space
return TRUE;
}

Here I want to use lParam as an out parameter to send a string value back.
Can anyone please tell me that how can I get string value in lParam?

Regards,
Tushar

[ovidiucucu]

Use WM_COPYDATA instead of user message.
Search this forum and you'll find examples.

[wayside]

Use WM_COPYDATA and the COPYDATASTRUCT structure to do this.

Here's sample code form MSDN:

// ************ Globals ************
//
#define MYDISPLAY 1
typedef struct tagMYREC
{
   char  s1[80];
   char  s2[80];
   DWORD n;
} MYREC;
COPYDATASTRUCT MyCDS;
MYREC MyRec;
HRESULT hResult;
BOOL CALLBACK InfoDlgProc( HWND, UINT, WPARAM, LPARAM );

// ************ Code fragment ****************
// Get data from user. InfoDlgProc stores the information in MyRec.
//
   DialogBox( ghInstance, "InfoDlg", hWnd, (DLGPROC) InfoDlgProc );
//
// Copy data into structure to be passed via WM_COPYDATA.
// Also, we assume that truncation of the data is acceptable.
//
   hResult = StringCbCopy( MyRec.s1, sizeof(MyRec.s1), szFirstName );
   if (hResult != S_OK)
   		return False;
   hResult = StringCbCopy( MyRec.s2, sizeof(MyRec.s2), szLastName );
   if (hResult != S_OK)
   		return False;
   MyRec.n = nAge;
//
// Fill the COPYDATA structure
// 
   MyCDS.dwData = MYPRINT;          // function identifier
   MyCDS.cbData = sizeof( MyRec );  // size of data
   MyCDS.lpData = &MyRec;           // data structure
//
// Call function, passing data in &MyCDS
//
   hwDispatch = FindWindow( "Disp32Class", "Hidden Window" );
   if( hwDispatch != NULL )
      SendMessage( hwDispatch,
                   WM_COPYDATA,
                   (WPARAM)(HWND) hWnd,
                   (LPARAM) (LPVOID) &MyCDS );
   else
      MessageBox( hWnd, "Can't send WM_COPYDATA", "MyApp", MB_OK );


The receiving application has a hidden window which receives the information from WM_COPYDATA and displays it to the user.



// ************ Globals ************
//
#define MYDISPLAY 1
typedef struct tagMYREC
{
   char  s1[80];
   char  s2[80];
   DWORD n;
} MYREC;
PCOPYDATASTRUCT pMyCDS;
void WINAPI MyDisplay( LPSTR, LPSTR, DWORD );
//
// ************ Code fragment ****************
//
case WM_COPYDATA:
   pMyCDS = (PCOPYDATASTRUCT) lParam;
   switch( pMyCDS->dwData )
   {
      case MYDISPLAY:
         MyDisplay( (LPSTR) ((MYREC *)(pMyCDS->lpData))->s1,
                    (LPSTR) ((MYREC *)(pMyCDS->lpData))->s2,
                    (DWORD) ((MYREC *)(pMyCDS->lpData))->n );
   }
   break;

[ovidiucucu]

Wow, such a nice example from MSDN!!!
Anyhow, we can observe that OP already uses MFC.
So...

BOOL CDlgSender::Send(HWND hWndReceiver, LPCTSTR pszText)
{
   COPYDATASTRUCT cds;
   cds.lpData = (LPVOID)pszText;
   cds.cbData = (_tcslen( pszText ) + 1) * sizeof(TCHAR);
   cds.dwData = (DWORD)m_hWnd; //you may put anything else here
   BOOL bRet = ::SendMessage( hWndReceiver, 
                              WM_COPYDATA, 
                              (WPARAM)m_hWnd, 
                              (LPARAM)&cds );
   return bRet;
}

BOOL CDlgReceiver::OnCopyData(CWnd* pWnd, COPYDATASTRUCT* pCDS)
{
   CString strText = (LPCTSTR)pCDS->lpData;
// ...enjoy...
   return TRUE; // handled
}

...it's a little bit easier, isn't it?

[TusharV]

Thanks for the answer,
I implemented like that, but I need the data on the sender's side, which I am not getting.
As I mentioned you guys earlier that I want to get data and not to send.

Application 2:-

void SomeFunction()	// This can be any function under any window class in my appln 2
{
CWnd* pWnd = FindWindow();	// Find the Application 1's Window (i.e. CUsrSNDlg)
TCHAR pname[100];
memset(pname, '\0', sizeof(TCHAR)*100);
COPYDATASTRUCT cds;
cds.lpData = (LPVOID)pname;
cds.cbData = 100 * sizeof(TCHAR);
cds.dwData = (DWORD)pWnd->m_hWnd; //you may put anything else here
BOOL bRet = ::SendMessage(pWnd->m_hWnd , WM_COPYDATA, (WPARAM)NULL, (LPARAM)&cds );
// Here I want "pname" to have a valid user name copied in applicn 1
// But pname will be still blank here
}

Application 1:-

LRESULT CUsrSNDlg::OnCopyData(CWnd* pWnd, COPYDATASTRUCT* pCopyDataStruct)
{
lstrcpy((LPTSTR)pCopyDataStruct->lpData, m_UsrName); // everything goes fine here (lpData will have m_UsrName copied correctly)
						// But this will not reflect on the appln 2's side
return TRUE;
}

Please suggest me the correct way. Am I missing something in my implementation?

Regards,
Tushar

[ovidiucucu]

Aha...
Just reverse: send m_UsrName using WM_COPYDATA from Application 1 to Application 2.
Is there any problem to do like that?

[TusharV]

Ya.. It will be a problem, as I mentioned earliar the sender can be any window or may be a windowless object (a command line interface). So the reverse way is not possible.

One thing I want to know how WM_GETTEXT message works?
how he returns the window text thru lParam?

Thanks n Regards,
Tushar

[ovidiucucu]

Well, in this case use, for example, a pipe.
Read Interprocess Communications chapter in MSDN.

How WM_GETTEXT works? I don't know. Ask MS-team or deeply Google search

Keep ahead!