// DLL imports
__declspec (dllimport) LONG GetInstanceCount (void);
__declspec (dllimport) LONG IncrementInstanceCount (void);
__declspec (dllimport) LONG DecrementInstanceCount (void);
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.
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int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpszCmdLine, int nCmdShow)
{
    static char szAppName[] = "MyApp";
    static char szWndClass[] = "MyWindowClass";

    WNDCLASS wc;
    HWND hwnd;
    MSG msg;

    // Check the instance count and terminate if it's
    // nonzero.
    if (GetInstanceCount ())
    {
        MessageBox (NULL, "Another instance of this application is running", "Error", MB_OK |
                    MB_ICONSTOP);
        return -1;
    }
    
    // Increment the instance count.
    IncrementInstanceCount ();
    
    wc.style = 0;
    wc.lpfnWndProc = (WNDPROC) WndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInstance;
    wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor (NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH) (COLOR_WINDOW + 1);
    wc.lpszMenuName = NULL;
    wc.lpszClassName = szWndClass;
    
    RegisterClass (&wc);
    hwnd = CreateWindow (szWndClass, szAppName,
                        WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, 
                        CW_USEDEFAULT, HWND_DESKTOP, NULL, hInstance, NULL);
    ShowWindow (hwnd, nCmdShow);
    
    UpdateWindow (hwnd);
    
    while (GetMessage (&msg, NULL, 0, 0))
    {
        TranslateMessage (&msg);
        DispatchMessage (&msg);
    }
    
    // Decrement the instance count.
    DecrementInstanceCount ();
    
    return msg.wParam;
}