Applications That Run with or Without Pen Extensions

• Microsoft Windows for Pen Computing version 1.0

SUMMARY

Typically, applications that are developed for Microsoft Windows for Pen Computing do not run unless the pen extensions are installed in memory. The reason for this is that these applications are implicitly linked to PENWIN.DLL. When a user runs an application that is implicitly linked to PENWIN.DLL on a system where the pen extensions are not installed, the application fails to load with the following error message:

   File Error
   Cannot find PENWIN.DLL

Applications can be designed to run in either environment, under Windows with or without the pen extensions. The HFORM sample application, also provided with the Windows for Pen Computing in the Windows SDK, is an example of this type of application.

This article lists the steps required to create an application that runs in either environment; this article also lists other sample applications that do not implicitly link with PENWIN.DLL.

MORE INFORMATION

An application that does not implicitly link with PENWIN.DLL can use the pen API functions when they are available and can run in the Windows environment when the pen extensions are not available. The application must not reference any of the pen functions directly. At run time, the application must retrieve the handle to PENWIN.DLL and explicitly load any functions that the application will use. The following four steps detail how an application that is not implicitly linked to PENWIN.DLL would load and use the Recognize function:

1. Prototype the Recognize function in the application's header file as follows:

         REC (FAR PASCAL *lpfnRecognize)(LPRC);
   

2. In the application's initialization, use GetSystemMetrics() to see if the pen extensions are installed. If the value returned from this function is zero, the pen extensions are not installed. Otherwise, the return value is the handle to PENWIN.DLL.

3. If the extensions are installed, use GetProcAddress() to retrieve the address of the Recognize function. A NULL return value indicates an error. The following fragment demonstrates this step:

         if (lpfnRecognize = GetProcAddress(hPenWinDLL, "Recognize"))
   

4. Finally, call the function using the procedure address, as follows:

         lpfnRecognize(&rc);