Subclass Help

Can you tell why this code doesn't subclass the window?

Code:

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#include <windows.h>

#define WIN32_LEAN_AND_MEAN

static HINSTANCE hInstance = NULL;
char szClassName[] = "StartButton";

HWND hwndTask;
HWND hwndStart;
WNDPROC wpOldStBtnProc;

LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam,
                                                                LPARAM lParam);

LRESULT APIENTRY wpNewStBtnProc(HWND hwnd, UINT message, WPARAM wParam,
                                                                LPARAM lParam);

// main window procedure
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                                  LPSTR lpszArgument, int nCmdShow){
       
        HWND hwnd;        // main window handle
    MSG messages;
    WNDCLASSEX wincl;
    wincl.hInstance = hInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure;
    wincl.style = CS_DBLCLKS;
    wincl.cbSize = sizeof(WNDCLASSEX);
        wincl.hIcon = LoadIcon(NULL, IDI_WINLOGO);
    wincl.hIconSm = LoadIcon(NULL, IDI_WINLOGO);
    wincl.hCursor = LoadCursor(NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;
    wincl.cbClsExtra = 0;
    wincl.cbWndExtra = 0;
        wincl.hbrBackground = (HBRUSH)COLOR_BTNSHADOW;
       
    if(!RegisterClassEx(&wincl)) return 0;
       
    hwnd = CreateWindowEx(0, szClassName, "Start Button", WS_OVERLAPPEDWINDOW,
                CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
                HWND_DESKTOP, NULL,        hInstance, NULL);
       
    ShowWindow(hwnd, nCmdShow);
    while(GetMessage(&messages, NULL, 0, 0))
               
               
        {
        TranslateMessage(&messages);
        DispatchMessage(&messages);
    }
    return messages.wParam;
}

// callback procedure
LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam,
                                                                LPARAM lParam){
    switch(message){
        case WM_CREATE:
                hwndTask = FindWindowEx(0, 0, "Shell_TrayWnd", 0);
                hwndStart = FindWindowEx(hwndTask, 0, "Button", 0);
               
                if(hwndStart != NULL){
                        wpOldStBtnProc = (WNDPROC) SetWindowLong(hwndStart,
                                GWL_WNDPROC, (LONG) wpNewStBtnProc);
                }
                else{
                        MessageBox(NULL, "Failed to Subclass!", "Error", NULL);
                }
               
                break;
               
        case WM_COMMAND:
        break;
               
        case WM_DESTROY:
                SetWindowLong(hwndStart, GWL_WNDPROC,
                        (LONG) wpOldStBtnProc);
               
                DestroyWindow(hwnd);
        PostQuitMessage(0);
        break;
       
        default:
        return DefWindowProc(hwnd, message, wParam, lParam);
    }
    return 0;
}


// Subclass procedure
// IS NOT WORKING
LRESULT APIENTRY wpNewStBtnProc(HWND hwnd, UINT message, WPARAM wParam,
                                                                LPARAM lParam)
{
        MessageBox(NULL, "New procedure", "Success", NULL);
       
       
        return CallWindowProc(wpOldStBtnProc, hwnd, message, wParam, lParam);
}

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It needs to be in a DLL, because the protected memory space of your program is separate to the shell.

Here is an example