Looking For a GetWindowLongPtr() Type Function (or workaround) for Dialog Boxes

Hi,

I’m trying to find a couple functions along the lines of the GetWindowLong(), SetWindowLong() variety except for dialog boxes. It’s my understanding that there’s no HWND created for a dialog box until runtime so I don’t know how to SetWindowLong() without it. For whatever reason I believed that the dialog box’s HWND would inherit the GetWindowLong() that I have set for my main window… nope. I didn’t get any compiler errors (understandable) so when errors started cropping up I started thinking there was a memory leak, after a couple hours I figured out my use of GetWindowLong() was incorrect inside of the dialog box.

What I’m doing is creating a map maker. I have a class that stores all the information for the map as well as all the functions to manipulate it. The intent for dialog box I’m creating is to change the Width/Height of the map (64x64 pixel tiles). I’ve got the dialog box giving me the correct data upon entry but I can’t change the map without either making the “Info” data global or finding a GetWindowLong() workaround.

Here’s some code in case I’m doing something stupid, it’s just my callback function for my dialog box. I’m not sure if it’s necessary to show more… I’ve got a lot of code so far and a lot of it is a pretty jumbled mess. It’s my first try taking on something this size by myself.

Code:

// Message handler for Height/Width Option box.
LRESULT CALLBACK Options(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
	char height[4];
	char width[4];
	WORD sizeOfInput;

	DisplayInfo* Info = (DisplayInfo*)(DWORD_PTR)GetWindowLongPtr(hDlg, GWLP_USERDATA);
	
	switch (message)
	{
	case WM_INITDIALOG:
		return TRUE;

	case WM_COMMAND:
		switch( LOWORD(wParam) )
		{
		case IDCANCEL:
			{
			EndDialog(hDlg, LOWORD(wParam));
			return TRUE;
			}
		break;
		case IDOK:
			{
			// Getting Height Value
            // Get number of characters. 
            sizeOfInput = (WORD) SendDlgItemMessage(hDlg, 
                                                    IDC_HEIGHT, 
                                                    EM_LINELENGTH, 
                                                    (WPARAM) 0, 
                                                    (LPARAM) 0); 

            if (sizeOfInput == 0) 
            { 
                MessageBox(hDlg, 
                           "No characters entered for Height.", 
                           "Error", 
                           MB_OK); 

				break;
            }
			else if (sizeOfInput == 1)
			{
                MessageBox(hDlg, 
                           "Height must be greater than or equal to 10.", 
                           "Error", 
                           MB_OK); 

                break;
			}

            // Put the number of characters into first word of buffer. 
            *((LPWORD)height) = sizeOfInput; 

            // Get the characters. 
            SendDlgItemMessage(hDlg, 
                               IDC_HEIGHT, 
                               EM_GETLINE, 
                               (WPARAM) 0,       // line 0 
                               (LPARAM) height); 

            // Null-terminate the string. 
            height[sizeOfInput] = 0; 

			// Getting Width Value
			sizeOfInput = (WORD) SendDlgItemMessage(hDlg, 
                                                    IDC_WIDTH, 
                                                    EM_LINELENGTH, 
                                                    (WPARAM) 0, 
                                                    (LPARAM) 0); 

            if (sizeOfInput == 0) 
            { 
                MessageBox(hDlg, 
                           "No characters entered for Width.", 
                           "Error", 
                           MB_OK); 

                break;
            }
			else if (sizeOfInput == 1)
			{
                MessageBox(hDlg, 
                           "Width must be greater than or equal to 10.", 
                           "Error", 
                           MB_OK); 

                break;
			}

            // Put the number of characters into first word of buffer. 
            *((LPWORD)width) = sizeOfInput; 

            // Get the characters. 
            SendDlgItemMessage(hDlg, 
                               IDC_WIDTH, 
                               EM_GETLINE, 
                               (WPARAM) 0,       // line 0 
                               (LPARAM) width); 

            // Null-terminate the string. 
            width[sizeOfInput] = 0;

			Info->SetWidthHeight(atoi(height), atoi(width));

			EndDialog(hDlg, TRUE); 
            return TRUE;
			}
		}
	}
	return FALSE;
}

Thanks for any insight anyone can give. I’ve been searching the internet for a while but I have a feeling I’m probably looking for the wrong type of solution.

-Peter

PS sorry for the weird formatting of my code, not sure what's going on there. I'm using VS 2005

*******EDIT*******
As a side note I just tried my code with "Info" being a global and everything appears to work fine.

1. Use DWLP_USER rather than GWLP_USERDATA.
2. Call DialogBoxParam rather than DialogBox and pass the pointer in the lParam argument.
3. In WM_INITDIALOG, call SetWindowLongPtr with the lParam value.
4. Your use of EM_GETLINE will cause a buffer overrun. You need to pass the size of the buffer (minus one to leave room for a nul character), not the number of characters. In your case this would be 3 (sizeof(height) - 1).

Hello again,

I'm afraid I'm missing something in steps 1-3 (as for 4 my dialog box doesn't have room for more than 3 characters and cuts the user off if they try and enter more but thanks for the help).

Here's what I've got...

Code:

// Message handler for Height/Width Option box.
LRESULT CALLBACK Options(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
	char height[4];
	char width[4];
	WORD sizeOfInput;

	DisplayInfo* Info = (DisplayInfo*)(DWORD_PTR)GetWindowLongPtr(hDlg, DWLP_USER);
	
	switch (message)
	{
	case WM_INITDIALOG:
			SetWindowLongPtr(hDlg, DWLP_USER, (LONG)(DWORD_PTR)&Info); 
		return TRUE;

and where I'm creating the window in my WndProc...

Code:

DisplayInfo* Info = (DisplayInfo*)(DWORD_PTR)GetWindowLongPtr(hWnd, GWLP_USERDATA);
.
.
. // bunch of random code which would be out of context
.
.

		case ID_EDIT_OPTIONS:
			DialogBoxParam(hInst, (LPCSTR)IDD_SIZEOPTIONS, hWnd, (DLGPROC)Options, (LPARAM)Info); 
			//DialogBox(hInst, (LPCSTR)IDD_SIZEOPTIONS, hWnd, (DLGPROC)Options);
			break;

Unfortunately I'm still getting the same NULL pointer for Info which probably has to do with me using GetWindowLongPtr() too soon but then I run in to the problem of not knowing how to set it in WM_INITDIALOG. Should I be setting it outside somewhere? Currently it's set to the main window's GWLP_USERDATA.

Thanks for your help.

Nearly, try:

Code:

SetWindowLongPtr(hDlg, DWLP_USER, lParam);

Remember, that lParam at this point contains the value you passed as the last argument to DialogBoxParam.

Thank you, you were very helpful, that worked like a charm.