non static WndProc problem

This is a discussion on non static WndProc problem within the C++ Programming forums, part of the General Programming Boards category; I have a class called CWindowFrame which can create a window. My problem is that I cannot have the WndProc ...

  1. #1
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    non static WndProc problem

    I have a class called CWindowFrame which can create a window. My problem is that I cannot have the WndProc static as I want it virtual too. Anyway, when specifying the WNDCLASSEX lpfnWndProc = (WNDPROC)WinProc; I get the following error:

    Code:
    '=' : cannot convert from 'long (__thiscall CWindowFrame::*)(struct HWND__ *, unsigned int, unsigned int, long) ' to 'long (__stdcall*)(struct HWND__ *, unsigned int, unsigned int, long)'
    What might be the problem?
    Thanks
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  2. #2
    pronounced 'fib' FillYourBrain's Avatar
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    this is MFC? CWndFrame I think is the class name in mfc and your naming convention is similar. Well obviously you must have a __stdcall for a callback. __thiscall is a member function that hides a "this" pointer in the first parameter. therefore, it must be either static or global (and a friend would be nice).
    "You are stupid! You are stupid! Oh, and don't forget, you are STUPID!" - Dexter

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    No, this is not MFC, plain win32 code. Any ideas???
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    pronounced 'fib' FillYourBrain's Avatar
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    I already told you. only my first question was bout mfc
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  5. #5
    pronounced 'fib' FillYourBrain's Avatar
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    Originally posted by FillYourBrain
    Well obviously you must have a __stdcall for a callback. __thiscall is a member function that hides a "this" pointer in the first parameter. therefore, it must be either static or global (and a friend would be nice).
    "You are stupid! You are stupid! Oh, and don't forget, you are STUPID!" - Dexter

  6. #6
    pronounced 'fib' FillYourBrain's Avatar
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    if you're having problems post the source. But in order for a callback to be declared inside a class it has to be one of the following:

    friend //a global function made a friend of the class
    static //which means global in a sense anyway

    either one with "APIENTRY", "WINAPI" or just __stdcall
    "You are stupid! You are stupid! Oh, and don't forget, you are STUPID!" - Dexter

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    Ok, thanks everyone. I made it global. But what if I want it to be virtual too?
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  8. #8
    pronounced 'fib' FillYourBrain's Avatar
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    I know what you're trying to do. I just posted this in another thread too. You don't make the actual callback virtual. Make a member function called "Callback" which is not global. The global function will need to call it.

    here it is: callbacks within a class?
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    Thank you, that was the solution to my problem. I have made the MsgProc function in my class virtual and non-CALLBACK and I created a CALLBACK function WndProc handling the actual messages. So, in my WNDCLASSEX struct, i define the lpfnWndProc = WndProc (WndProc is returning the MsgProc)

    This is how my code looks:
    Code:
    static CWindowFrame *win;
    
    LRESULT CALLBACK WndProc(...)
    {
       return win->MsgProc(...);
    }
    
    LRESULT CWindowFrame::MsgProc(...)
    {
    checking messages here
    }
    
    bool CWindowFrame::MakeWindow(........)
    {
    ...
    ...
    WNCLASSEX ex;
    ...
    ex.lpfnWndProc = WndProc;
    ..
    register, blah blah, create, blah. return true
    }
    The code compiles great. I have this class in a DLL, so there is another problem. When I try to create a window, it causes an access violation and points to WndProc!
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  10. #10
    pronounced 'fib' FillYourBrain's Avatar
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    could be that your pointer is not filled in. zip and post your code and I might be able to tell you for sure what's wrong
    "You are stupid! You are stupid! Oh, and don't forget, you are STUPID!" - Dexter

  11. #11
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    Ok, here is the code.
    Don't forget to set your VC++6 directories include to the window parent directory as well. Also tghe library directories the debug dir of window project. the dll is automatically copied correctly. In the file it is included both the DLL and the client application.
    Attached Files Attached Files
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  12. #12
    pronounced 'fib' FillYourBrain's Avatar
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    pretty simple actually. You have this "window" pointer that you never set. so obviously it crashes when you try to dereference it
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    It is fixed! Thank you soooo much man, you really helped me out here. I changed the pointer to an instance. But if I had a pointer, \what should I do to fix it?

    However it works now, I ask of curiosity
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  14. #14
    pronounced 'fib' FillYourBrain's Avatar
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    Not exactly sure what you're asking there. personally I would prefer not to have a global pointer like that. You can set a pointer per window with SetWindowLong and GWL_USERDATA.
    "You are stupid! You are stupid! Oh, and don't forget, you are STUPID!" - Dexter

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    Ok, I will look this up.
    Cya
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