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Chapter 8

The Timer

The Microsoft Windows timer is an input device that periodically notifies an application when a specified interval of time has elapsed. Your program tells Windows the interval, in effect saying, for example, "Give me a nudge every 10 seconds." Windows then sends your program recurrent WM_TIMER messages to signal the intervals.

At first, the Windows timer might seem a less important input device than the keyboard and mouse, and certainly it is for many applications. But the timer is more useful than you may think, and not only for programs that display time, such as the Windows clock that appears in the taskbar and the two clock programs in this chapter. Here are some other uses for the Windows timer, some perhaps not so obvious:

Another way to think of the timer is as a guarantee that a program can regain control sometime in the future after exiting the window procedure. Usually a program can't know when the next message is coming.