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Dialog boxes are most often used for obtaining additional input from the user beyond what can be easily managed through a menu. The programmer indicates that a menu item invokes a dialog box by adding an ellipsis (...) to the menu item.
A dialog box generally takes the form of a popup window containing various child window controls. The size and placement of these controls are specified in a "dialog box template" in the program's resource script file. Although a programmer can define a dialog box template "manually," these days dialog boxes are usually interactively designed in the Visual C++ Developer Studio. Developer Studio then generates the dialog template.
When a program invokes a dialog box based on a template, Microsoft Windows 98 is responsible for creating the dialog box popup window and the child window controls, and for providing a window procedure to process dialog box messages, including all keyboard and mouse input. The code within Windows that does all this is sometimes referred to as the "dialog box manager."
Many of the messages that are processed by that dialog box window procedure located within Windows are also passed to a function within your own program, called a "dialog box procedure" or "dialog procedure." The dialog procedure is similar to a normal window procedure, but with some important differences. Generally, you will not be doing much within the dialog procedure beyond initializing the child window controls when the dialog box is created, processing messages from the child window controls, and ending the dialog box. Dialog procedures generally do not process WM_PAINT messages, nor do they directly process keyboard and mouse input.
The subject of dialog boxes would normally be a big one because it involves the use of child window controls. However, we have already explored child window controls in Chapter 9. When you use child window controls in dialog boxes, the Windows dialog box manager picks up many of the responsibilities that we assumed in Chapter 9. In particular, the problems we encountered with passing the input focus among the scroll bars in the COLORS1 program disappear when working with dialog boxes. Windows handles all the logic necessary to shift input focus among controls in a dialog box.
However, adding a dialog box to a program is a bit more involved than adding an icon or a menu. We'll begin with a simple dialog box to give you a feel for the interconnections between these various pieces.