Question

i have this abstract code : i want to use lParam (last parameter) in CreateWindowEx() to save a pointer to a class thats declared in the begining of main - SaveArr. then, i want to use it in the function WndProc. in the begining i did a global array, and then i could use it anywhere, but its not so "clever" as far as c++ concern, so im trying to upgrade it a bit.

class Samples
{
        int arr[ITERATIONS+1];
        int index;
        ...
}

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                   LPSTR lpCmdLine, int nCmdShow)
{
        Samples * SaveArr;
        ...
    hWnd = CreateWindowEx(WS_EX_OVERLAPPEDWINDOW,
                          ClsName,
                          WindowCaption,
                          WS_OVERLAPPEDWINDOW,
                          INITIAL_WIN_LOCAT_X,
                          INITIAL_WIN_LOCAT_Y,
                          WIN_WIDTH,
                          WIN_HIGHT,
                          NULL,
                          NULL,
                          hInstance,
                          NULL);    //here i want to pass SaveArr, so that i can use it in the WndProc(...) function

...
return 0;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
{
   ...      //here i would like to use lParam as the class pointer, meaning using the 
              SaveArr declared in the main function.

}

}

Answer 1

www.un.org/Depts/DGACM/index_spanish.htm 向窗口添加打电话信息:

m_window = CreateWindow(..., this);

延伸<代码>CreateWindowEx类似。

www.un.org/Depts/DGACM/index_spanish.htm • 找到电线人:

template< typename CallerT >
[[nodiscard]]
CallerT* WindowCaller(HWND window, UINT message, LPARAM lParam) noexcept
{
    if (message == WM_NCCREATE) [[unlikely]]
    {
        const auto caller = reinterpret_cast< CallerT* >(
                            reinterpret_cast< CREATESTRUCT* >(lParam)->lpCreateParams);

        // Change the user data of the window for subsequent messages.
        ::SetWindowLongPtr(window, GWLP_USERDATA,
                           reinterpret_cast< LONG_PTR >(caller));

        return caller;
    }
    else
    {
        // Retrieve the user data of the window.
        return reinterpret_cast< CallerT* >(
                    ::GetWindowLongPtr(window, GWLP_USERDATA));
    }
}

这一方法需要用在你的信息反馈中。

Answer 2

最好的方式

    LRESULT CALLBACK WndProc(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
    {
           Samples *savearr = (Samples*)GetWindowLong(hWnd,GWL_USERDATA)
           switch(Msg)
           {
                case WM_CREATE:
                    SetWindowLong(hWnd, GWL_USERDATA, (LONG)lParam);
                    break;
           }
    }

下次WndProc被称作价值时,会节省费用,并且可以使用。

Answer 3

http://msdn.microsoft.com/en-us/library/ms632680%28v=vs.85%29.aspx”rel=“nofollow”参引:

lpParam [in, optional]
Type: LPVOID

Pointer to a value to be passed to the window through the
CREATESTRUCT structure (lpCreateParams member) pointed to by the lParam param of the WM_CREATE message. This message is sent to the created window by this function before it returns.
If an application calls CreateWindow to create a MDI client
window, lpParam should point to a CLIENTCREATESTRUCT structure. If an MDI client window calls CreateWindow to create an MDI child window, lpParam should point to a MDICREATESTRUCT structure. lpParam may be NULL if no additional data is needed.

你回过来,希望能够永远传给WndProc,但只有WM_通过。公布。

请注意,即便如此,也并非直接通过,而是通过一个实际为WM_提供的帕拉姆结构。公布。

Answer 4

在WM_CREATE期间,你唯一的读过“灯塔”的机会。如果你想在晚些时候继续使用这一价值,那么你必须将其存放在其他地方。或许作为《京都议定书》的静态,或者将《任择议定书》转让给其他有待扩大的范围。

Answer 5

为什么所有坚持使用这最后一点,即把pParam数值推到X,然后将其赶上WM_CREATE(通过所有这种间接的障碍,至少!) 并且随后建立GWL_ USERDATA?

Why not cut to the chase and do this: HWND H=CreateWindow(.....) SetWindowLong(H,GWL_USERDATA,X) In other words, just put X there directly, yourself, right after the window creation statement.

In my tests it works, and so long as you test the window handle against some list of known handles, you can prevent some errant message picked up by your program, and prevent inappropriate use of something else s userdata.

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