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.
See Also
AppendMenu, DefWindowProc, GetSystemMenu, InsertMenu, ModifyMenu, WM_COMMAND
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