this pointer to access

in my window creation class, i have a static WndProc which will be used for adding events. i read here http://www.mvps.org/windev/cpp/class.html that by passing the this pointer to the lParam of CreateWindow, i can then retrieve that pointer when i handle WM_CREATE in my WndProc, and store it.. after i can cast it back to the class, and use the pointer to access and modify members...the problem is that everytime i try to actually modify a member, the program crashes..could anybody help me?
thanks

Amon Ra

ok so here is my wndproc, which is a static member of the WINDOW class

PHP Code:

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//WindowProc: this is the real one...the one that does all the work
LRESULT CALLBACK WINDOW::WindowProc (HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
{
    PAINTSTRUCT ps;
    WINDOW *const ptThis = (WINDOW*) lParam;    //store "this" in variable;
    
    switch (Msg)
    {
    case WM_CREATE:
        SetWindowLong (hWnd, GWL_USERDATA, (LONG) lParam);    //stores "this" on window data just in case
            return 0;
    case WM_LBUTTONDOWN:
        MessageBox (hWnd, ptThis->m_pcText , "BLAH", MB_OK | MB_ICONINFORMATION);
            return 0;
    case WM_PAINT:            // this must be handled
        BeginPaint(hWnd, &ps);
        EndPaint(hWnd, &ps);
            return 0;
    case WM_DESTROY:            // must also be handled in the main window
        PostQuitMessage(0);
            return 0;
    }
        return    DefWindowProc (hWnd, Msg, wParam, lParam);
}    //WindowProc 


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to have the "this" pointer stored in the lParam, i used:

PHP Code:

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        hWnd = CreateWindowEx (    m_dwExStyle,
                                                m_pcClassName,
                                                m_pcText,
                                                m_dwStyle,
                                                m_XPos, m_YPos, m_Width, m_Height,
                                                m_hParent,
                                                NULL,
                                                m_hInstance,
                                                this    ); 


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The problem is that when i get to

PHP Code:

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MessageBox (hWnd, ptThis->m_pcText , "BLAH", MB_OK | MB_ICONINFORMATION); 


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it crashes the program. anyone have any idea? thanks in advance

Amon Ra

any body please? basically i want a class with a windowproc in it, so that the user has no acces to it

great! i got it..after adjusting a few things.. =)

Not sure if you already have the solution...
the lParam passed to the WM_CREATE message is not the lParam you passed to CreateWindow, but rather the address of a CREATESTRUCT.

yea exactly..i found that out in the msdn... i did this

PHP Code:

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pThis = (WINDOW*) ((LPCREATESTRUCT)lParam)->lpCreateParams; 


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and i passed the "this" to the lParam of CreateWindow

You didn't notice the code I posted ages ago about this then? :D

Everyone and his dog seems to be writing window-wrapper classes at the moment, strange really.

I want .NET *sigh* Was so much easier to use :D

lol..no i didn't see it..i ma writing this for the info tech class at our school (high school)... =)

The problem of passing the class as create parameter and saving it in a static variable of the WndProc is that every new class will replace the last! Keep that in mind! (someone here did it that way)

Use a method like the SetWindowLong(hWnd, GWL_USERDATA, this) one.

I've posted about that one a LOT now...so I won't repeat it ;)

ok apparently, as you said CornedBee, when everything is created , and i use the pointer to this, i get an error..
i am gonna see how i can fix, and try to find yours Parksie..
thanks =

Amon Ra

i fixed it and it works beautifully now :)

Amon Ra