REFERENCE GUIDE

WM_SYSCOMMANDDefault actionCommentsThe DefWindowProc function carries out the System-menu request for thepredefined actions specified above.In WM_SYSCOMMAND messages, the four low-order bits of the wParamparameter are used internally by Windows. When an application tests thevalue of wParam, it must combine the value OxFFFO with the wParam valueby using the bitwise AND operator to obtain the correct result.The menu items in a System menu can be modified by using theGetSystemMenu, AppendMenu, InsertMenu, and ModifyMenu functions.Applications that modify the System menu must processWM_SYSCOMMAND messages. Any WM_SYSCOMMAND messagesnot handled by the application must be passed to the DefWindowProcfunction. Any command values added by an application must beprocessed by the application and cannot be passed to DefWindowProc.An application can carry out any system command at any time by passinga WM_SYSCOMMAND message to the DefWindowProc function.Accelerator key strokes that are defined to select items from the Systemmenu are translated into WM_SYSCOMMAND messages; all otheraccelerator key strokes are translated into WM_COMMAND messages.WM_SYSDEADCHARThis message results when a WM_SYSKEYUP and WM_SYSKEYDOWNmessage are translated. It specifies the character value of a dead key.Parameters wParam Contains the dead-key character value.IParamWM_SYSKEYDOWNContains a repeat count and an auto-repeat count. The loworderword contains the repeat count; the high-order wordcontains the auto-repeat count.This message is sent when the user holds down the ALT key and thenpresses another key. It also occurs when no window currently has theinput focus; in this case, the WM_SYSKEYDOWN message is sent to theactive window. The window that receives the message can distinguishbetween these two contexts by checking the context code in the IParamparameter.Parameters wParam Contains the virtual-key code of the key being pressed.Chapter 6, Messages directory 691