The WinMain function performs the same tasks as a regular Windows function:

  • It calls the initialization functions to register window classes and create windows.

  • It enters a message loop to process messages from the application queue.

  • The message loop ends when the user chooses Exit from the menu, generating a WM_DESTROY message, which in turn posts a WM_QUIT message to WinMain. When the GetMessage function detects the WM_QUIT message, it returns NULL to end the loop.

The WinMain function calls GetSystemMetrics to check whether pen services are installed. If they are not found, the application should either exit with an explanatory message or alter its behavior to run without pen input.

Note that Microsoft pen services must be installed when Windows starts. Simply linking PENWIN.DLL and loading it at runtime is not sufficient to initialize pen services. For this reason, unless it is known that the application being developed will always be run on a system with pen services installed, pen API should be called through function pointers. This mechanism insures that a pen-aware application can run only on a system on which pen services has been properly installed and will not run on any system that merely has PENWIN.DLL on the path. See the HFORM sample application for an example of this technique.

For the sake of simplicity and readability, the PENAPP application described in this chapter links directly to PENWIN.DLL and does not use function pointers.

int PASCAL WinMain(

HANDLE hInstance, // Instance handle

HANDLE hPrevInstance, // Previous instance handle

LPSTR lpszCommandLine, // Command line string

int cmdShow ) // ShowWindow flag


MSG msg;

// Mention to prevent compiler warnings ....


if (!hPrevInstance) // If first instance,

if (!InitApp( hInstance )) // register window class

return FALSE; // Exit if can't register

if (!InitInstance( hInstance, nCmdShow ))

// Create this instance's window

return FALSE; // Exit if error

if (!GetSystemMetrics( SM_PENWINDOWS )) // If no pen services

return FALSE; // exit

while (GetMessage( (LPMSG) &msg, NULL, 0, 0) )


TranslateMessage( (LPMSG) &msg );

DispatchMessage( (LPMSG) &msg );


return 0; // Success


The InitApp function initializes data and registers the window classes. Following standard programming practice for Windows, the function returns FALSE if it cannot register the window classes.

For the Input window, InitApp specifies a cursor type of IDC_PEN. This is the default cursor type supplied by the pen-aware display driver. For more information on pen types, see the reference section for the IDC_ constants in Chapter 13, "Pen Application Programming Interface Constants."

The following fragment shows how InitApp creates the Input window:

BOOL InitApp( HANDLE hInstance ) // Instance handle







// Register PenApp child window classes


wc.hCursor = LoadCursor( NULL, IDC_PEN );

wc.hIcon = NULL;

wc.lpszMenuName = NULL;

wc.lpszClassName = (LPSTR) szPenAppInputClass;


wc.lpfnWndProc = InputWndProc;

if (!RegisterClass( (LPWNDCLASS) &wc) )

return FALSE;





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