WM_SYSCOMMAND message

Article
08/19/2021

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.

#define WM_SYSCOMMAND                   0x0112

Example

 case WM_SYSCOMMAND:
        if ((wParam & 0xFFF0) == SC_CLOSE)
        {
            EndDialog (hDlg, TRUE);
            return(TRUE);
        }
        break;

Example from Windows Classic Samples on GitHub.

Parameters

wParam

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

Value	Meaning
SC_CLOSE 0xF060	Closes the window.
SC_CONTEXTHELP 0xF180	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 0xF160	Selects the default item; the user double-clicked the window menu.
SC_HOTKEY 0xF150	Activates the window associated with the application-specified hot key. The lParam parameter identifies the window to activate.
SC_HSCROLL 0xF080	Scrolls horizontally.
SCF_ISSECURE 0x00000001	Indicates whether the screen saver is secure.
SC_KEYMENU 0xF100	Retrieves the window menu as a result of a keystroke. For more information, see the Remarks section.
SC_MAXIMIZE 0xF030	Maximizes the window.
SC_MINIMIZE 0xF020	Minimizes the window.
SC_MONITORPOWER 0xF170	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 powering on) 1 (the display is going to low power) 2 (the display is being shut off)
SC_MOUSEMENU 0xF090	Retrieves the window menu as a result of a mouse click.
SC_MOVE 0xF010	Moves the window.
SC_NEXTWINDOW 0xF040	Moves to the next window.
SC_PREVWINDOW 0xF050	Moves to the previous window.
SC_RESTORE 0xF120	Restores the window to its normal position and size.
SC_SCREENSAVE 0xF140	Executes the screen saver application specified in the [boot] section of the System.ini file.
SC_SIZE 0xF000	Sizes the window.
SC_TASKLIST 0xF130	Activates the Start menu.
SC_VSCROLL 0xF070	Scrolls vertically.

lParam

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.

Return value

An application should return zero if it processes this message.

Remarks

To obtain the position coordinates in screen coordinates, use the following code:

xPos = GET_X_LPARAM(lParam);    // horizontal position 
yPos = GET_Y_LPARAM(lParam);    // vertical position

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 wParam parameter are used internally by the system. To obtain the correct result when testing the value of wParam, an application must combine the value 0xFFF0 with the wParam 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 SetMenuItemInfo 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.

If password protection is enabled by policy, the screen saver is started regardless of what an application does with the SC_SCREENSAVE notification even if fails to pass it 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.

If the wParam is SC_KEYMENU, lParam contains the character code of the key that is used with the ALT key to display the popup menu. For example, pressing ALT+F to display the File popup will cause a WM_SYSCOMMAND with wParam equal to SC_KEYMENU and lParam equal to 'f'.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Header	Winuser.h (include Windows.h)

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