A window receives this message when the user chooses a command from the Window menu (formerly known as the system or control menu) or when the user chooses the maximize button, minimize button, restore button, or close button.

Syntax

WM_SYSCOMMAND

    WPARAM wParam
    LPARAM lParam;
    

Parameters

wParam

Specifies the type of system command requested. This parameter can be one of the following values.

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 lParam parameter identifies the window to activate.

SC_HSCROLL

Scrolls horizontally.

SC_KEYMENU

Retrieves the window menu as a result of a keystroke. For more information, see the Remarks section.

SC_MAXIMIZE

Maximizes the window.

SC_MINIMIZE

Minimizes the window.

SC_MONITORPOWER

Sets the state of the display. This command supports devices that have power-saving features, such as a battery-powered personal computer.

The lParam parameter can have the following values:

1 - the display is going to low power

2 - the display is being shut off

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

Activates the Start menu.

SC_VSCROLL

Scrolls vertically.

lParam（东西被点中时的鼠标位置，低位是光标的X轴坐标，高位是光标的Y轴坐标）

The low-order word specifies the horizontal position of the cursor, in screen coordinates, if a window menu command is chosen with the mouse. Otherwise, this parameter is not used.

The high-order word 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 mnemonic.