WM_SYSCOMMAND

WM_SYSCOMMAND

A window receives this message when the user chooses a command from the window menu (also known as the System menu or Control menu) or when the user chooses the Maximize button or Minimize button.

WM_SYSCOMMAND

uCmdType = wParam; // type of system command requested

xPos = LOWORD(lParam); // horizontal postion, in screen coordinates

yPos = HIWORD(lParam); // vertical postion, in screen coordinates

Parameters

uCmdType

Specifies the type of system command requested. This can be one of these values:

Value	Meaning
SC_CLOSE	Closes the window.
SC_CONTEXTHELP	Changes the cursor to a question mark with a pointer. If the user then clicks a control in the dialog box, the control receives a WM_HELP message.
SC_DEFAULT	Selects the default item; the user double-clicked the window menu.
SC_HOTKEY	Activates the window associated with the application-specified hot key. The low-order word of lParam identifies the window to activate.
SC_HSCROLL	Scrolls horizontally.
SC_KEYMENU	Retrieves the window menu as a result of a keystroke.
SC_MAXIMIZE (or SC_ZOOM)	Maximizes the window.
SC_MINIMIZE (or SC_ICON)	Minimizes the window.
SC_MONITORPOWER	Windows 95 only: Sets the state of the display. This command supports devices that have power-saving features, such as a battery-powered personal computer.
SC_MOUSEMENU	Retrieves the window menu as a result of a mouse click.
SC_MOVE	Moves the window.
SC_NEXTWINDOW	Moves to the next window.
SC_PREVWINDOW	Moves to the previous window.
SC_RESTORE	Restores the window to its normal position and size.
SC_SCREENSAVE	Executes the screen saver application specified in the [boot] section of the SYSTEM.INI file.
SC_SIZE	Sizes the window.
SC_TASKLIST	Executes or activates Windows Task Manager.
SC_VSCROLL	Scrolls vertically.

xPos

Specifies the horizontal position of the cursor, in screen coordinates, if a window menu command is chosen with the mouse. Otherwise, the xPos parameter is not used.

yPos

Specifies the vertical position of the cursor, in screen coordinates, if a window menu command is chosen with the mouse. This parameter is -1 if the command is chosen using a system accelerator, or zero if using a mnenomic.

Return Values

An application should return zero if it processes this message.

Remarks

The DefWindowProc function carries out the window menu request for the predefined actions specified in the previous table.

In WM_SYSCOMMAND messages, the four low-order bits of the uCmdType parameter are used internally by Windows. To obtain the correct result when testing the value of uCmdType, an application must combine the value 0xFFF0 with the uCmdType value by using the bitwise AND operator.

The menu items in a window menu can be modified by using the GetSystemMenu, AppendMenu, InsertMenu, ModifyMenu, InsertMenuItem, and SetMenuItem functions. Applications that modify the window menu must process WM_SYSCOMMAND messages.

An application can carry out any system command at any time by passing a WM_SYSCOMMAND message to DefWindowProc. Any WM_SYSCOMMAND messages not handled by the application must be passed to DefWindowProc. Any command values added by an application must be processed by the application and cannot be passed to DefWindowProc.

Accelerator keys that are defined to choose items from the window menu are translated into WM_SYSCOMMAND messages; all other accelerator keystrokes are translated into WM_COMMAND messages.