#Windows message queue code

(And now you know what the window procedure is for.) The Message LoopĪn application will receive thousands of messages while it runs.

To pass a message to a window, the operating system calls the window procedure registered for that window. For example, the WM_LBUTTONDOWN message includes the x-coordinate and y-coordinate of the mouse cursor. Some messages have data associated with them. For example, if the user presses the left mouse button, the window receives a message that has the following message code.

#Windows message queue code

A message is simply a numeric code that designates a particular event. The operating system communicates with your application window by passing messages to it. To solve this problem, Windows uses a message-passing model. How do you structure a program whose flow of execution cannot be predicted in advance? These events can occur at any time while the program is running, in almost any order. For example, the user might plug in a new hardware device, or Windows might enter a lower-power state (sleep or hibernate). Events from the operating system include anything 'outside' of the program that can affect how the program behaves.Events from the user include all the ways that someone can interact with your program: mouse clicks, key strokes, touch-screen gestures, and so on.A GUI application must respond to events from the user and from the operating system.