Using an accelerator is the same as choosing a menu item: Both actions cause Windows to send a WM_COMMAND or WM_SYSCOMMAND message to the corresponding window procedure. The WM_COMMAND message includes an identifier that the window procedure examines to determine the source of the message. If an accelerator generated the WM_COMMAND message, the identifier is that of the accelerator. Similarly, if a menu item generated the WM_COMMAND message, the identifier is that of the menu item. Because an accelerator provides a shortcut for choosing a command from a menu, an application usually assigns the same identifier to the accelerator and the corresponding menu item.
An application processes an accelerator WM_COMMAND message in exactly the same way as the corresponding menu item WM_COMMAND message. However, the WM_COMMAND message contains a flag that specifies whether the message originated from an accelerator or a menu item, in case accelerators must be processed differently from their corresponding menu items. The WM_SYSCOMMAND message does not contain this flag.
The identifier determines whether an accelerator generates a WM_COMMAND or WM_SYSCOMMAND message. If the identifier has the same value as a menu item in the System menu, the accelerator generates a WM_SYSCOMMAND message. Otherwise, the accelerator generates a WM_COMMAND message.
If an accelerator has the same identifier as a menu item and the menu item is grayed or disabled, the accelerator is disabled and does not generate a WM_COMMAND or WM_SYSCOMMAND message. Also, an accelerator does not generate a command message if the corresponding window is minimized.
When the user uses an accelerator that corresponds to a menu item, the window procedure receives the WM_INITMENU and WM_INITMENUPOPUP messages as though the user had selected the menu item. For information about how to process these messages, see Menus.
An accelerator that corresponds to a menu item should be included in the text of the menu item.