Getting a structure from a pointer

This is a discussion on Getting a structure from a pointer within the Windows Programming forums, part of the Platform Specific Boards category; I use something like this to get the structure out of lParam (in the low-level keyboard hook). But it only ...

  1. #1
    Reverse Engineer maxorator's Avatar
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    Getting a structure from a pointer

    I use something like this to get the structure out of lParam (in the low-level keyboard hook).
    But it only returns a pointer.
    Code:
    KBDLLHOOKSTRUCT *meep = (KBDLLHOOKSTRUCT *) lParam;
    If I use something like this to get a variable from this structure, I get memory addresses:
    Code:
    KBDLLHOOKSTRUCT *meep = (KBDLLHOOKSTRUCT *) lParam;
    char buffer[256];
    MessageBox(HWND_DESKTOP,atoi(meep->vkCode,buffer,10),"Button is:",MB_OK);
    it will give the memory address to that specific variable inside the structure. How can I get the value of vkCode?

  2. #2
    Gawking at stupidity
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    Maybe *meep->vkCode
    If you understand what you're doing, you're not learning anything.

  3. #3
    Reverse Engineer maxorator's Avatar
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    Then I get:
    Code:
    error: invalid type argument of `unary *'

  4. #4
    erstwhile
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    The problem is in your call to the MessageBox api function - the second paramater should be a string, not a number which atoi returns.
    Code:
    char buffer[256]='\0';
    wsprintf(buffer,"%d",meep->vkCode);
    MessageBox(HWND_DESKTOP,buffer,"Button is:",MB_OK);
    I'm surprised you didn't get an incompatible type error from the MessageBox call. Also, atoi only takes one parameter so that, too, should have fired off an error.
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  5. #5
    Reverse Engineer maxorator's Avatar
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    I am actually using itoa, just accidentally wrote the wrong one here.
    atoi has only one parameter, so I would've got many different errors.
    And that meep->vkCode is passed through a function as an int and then used with itoa.

    I am not getting any error. I am getting the memory address of meep->vkCode
    Last edited by maxorator; 09-21-2006 at 07:17 AM.

  6. #6
    erstwhile
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    I see - easily done.

    Just as a test does the snippet I provide produce the same result? The reason I ask, is because the syntax you are using to access the struct member variable via its pointer is correct and you should therefore get the actual value of the 'vkCode' and not the garbage you're reporting (you may just be getting the rubbish that 'buffer' contains).

    edit:

    >>And that meep->vkCode is passed through a function as an int and then used with itoa<<

    It would probably be better to show exactly how you're doing this as the code you've posted - typos aside - doesn't appear to contain any errors.
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  7. #7
    Reverse Engineer maxorator's Avatar
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    Just as a test does the snippet I provide produce the same result? The reason I ask, is because the syntax you are using to access the struct member variable via its pointer is correct and you should therefore get the actual value of the 'vkCode' and not the garbage you're reporting (you may just be getting the rubbish that 'buffer' contains).
    I don't get garbage. If I use meep->vkCode, lets say I get 2200340, when I use meep->scanCode, I get 2200344 and when I use meep->flags, I get 2200348.

    I am not at my home computer at the moment, but my program looks something like this:
    DLL file, LowLevelKeyboardProc, case HC_ACTION:
    Code:
    PostMessage(guiapplication,WM_KEYBDHOOK,wParam,lParam);
    GUI application, WindowProcedure, case WM_KEYBDHOOK:
    Code:
    KBDLLHOOKSTRUCT *meep = (KBDLLHOOKSTRUCT *) lParam;
    NewItem(meep->vkCode,0,0,0);
    NewItem function (ints):
    Code:
    counter++;
    data[counter].a=paramone;
    data[counter].b=paramtwo;
    data[counter].c=paramthree;
    data[counter].d=paramfour;
    And then, an other function shows the whole data array in a list view control. Uses itoa() to convert the integer to a string.
    Last edited by maxorator; 09-21-2006 at 07:46 AM.

  8. #8
    erstwhile
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    >>I don't get garbage.<<

    It seems possible that you're passing the address and not the value of the DWORD, vkCode, struct member variable in one of these helper functions you're using.
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  9. #9
    Reverse Engineer maxorator's Avatar
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    Oh no... I am passing this:
    Code:
    PostMessage(guiapplication,WM_KEYBDHOOK,wParam,lParam);
    But shouldn't lParam be passed with "&" or "*"??
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