System-Defined Messages

The system sends or posts a system-defined message when it communicates with an application. It uses these messages to control the operations of applications and to provide input and other information for applications to process. An application can also send or post system-defined messages. Applications generally use these messages to control the operation of control windows created by using preregistered window classes.

Each system message has a unique message identifier and a corresponding symbolic constant (defined in the SDK header files) that states the purpose of the message. For example, the WM_PAINT constant requests that a window paint its contents.

Symbolic constants specify the category to which system-defined messages belong. The prefix of the constant identifies the type of window that can interpret and process the message. Following are the prefixes and their related message categories.

Prefix	Message category
ABM	Application desktop toolbar
BM	Button control
CB	Combo box control
CDM	Common dialog box
DBT	Device
DL	Drag list box
DM	Default push button control
EM	Edit control
HDM	Header control
LB	List box control
LVM	List view control
PBM	Progress bar
PSM	Property sheet
SB	Status bar window
SBM	Scroll bar control
STM	Static control
TB	Toolbar
TBM	Trackbar
TCM	Tab control
TTM	Tooltip control
TVM	Tree-view control
UDM	Up-down control
WM	General window

General window messages cover a wide range of information and requests, including messages for mouse and keyboard input, menu and dialog box input, window creation and management, and dynamic data exchange (DDE).

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