Page 126 - DCAP408_WEB_PROGRAMMING

Windows Programming

Notes
Figure 7.3

The system also sustains accelerator tables for each application. An application can define any
number of accelerator tables for utilization with its own windows. A unique 32-bit handle
(HACCEL) identifies each table. Though, only one accelerator table can be active at a time for a
particular thread. The handle to the accelerator table passed to the TranslateAccelerator function
identifies which accelerator table is active for a thread. The active accelerator table can be altered
at any time by passing a dissimilar accelerator-table handle to TranslateAccelerator.

7.11.2 Accelerator Table Creation

Several steps are required to create an accelerator table for an application. First, a resource
compiler is used to create accelerator-table resources and to add them to the application's
executable file. At run time, the LoadAccelerators function is used to load the accelerator table
into memory and retrieve the handle to the accelerator table. This handle is passed to the
TranslateAccelerator function to activate the accelerator table.
An accelerator table can also be created for an application at run time by passing an array of
ACCEL structures to the CreateAcceleratorTable function. This method supports user-defined
accelerators in the application. Like the LoadAccelerators function, CreateAcceleratorTable returns
an accelerator-table handle that can be passed to TranslateAccelerator to activate the accelerator
table.

The system automatically destroys accelerator tables loaded by LoadAccelerators or created by
CreateAcceleratorTable. However, an application can free resources while it is running by
destroying accelerator tables no longer needed by calling the DestroyAcceleratorTable function.
An existing accelerator table can be copied and modified. The existing accelerator table is copied
by using the CopyAcceleratorTable function. After the copy is modified, a handle to the new
accelerator table is retrieved by calling CreateAcceleratorTable. Finally, the handle is passed to
TranslateAccelerator to activate the new table.

7.11.3 Accelerator Keystroke Assignments

An ASCII character code or a virtual-key code can be used to define the accelerator. An ASCII
character code makes the accelerator case sensitive. Thus, using the ASCII "C" character defines
the accelerator as ALT+C rather than ALT+c. However, case-sensitive accelerators can be confusing
to use. For example, the ALT+C accelerator will be generated if the CAPS LOCK key is down or
if the SHIFT key is down, but not if both are down.
Typically, accelerators don't need to be case sensitive, so most applications use virtual-key
codes for accelerators rather than ASCII character codes.

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