An application can send a message to multiple windows by using the WinBroadcastMsg function. Often this function is used to broadcast the WM_SYSVALUECHANGED message after an application changes a system value. The following code fragment shows how to broadcast this message to all frame windows in all applications:
HWND hwnd; WinBroadcastMsg( hwnd, /* Window handle */ WM_SYSVALUECHANGED, /* Message identifier */ NULL, /* No message parameters */ NULL, BMSG_FRAMEONLY | BMSG_POSTQUEUE); /* All frame windows */
An application can broadcast messages to all windows, just frame windows, or just the windows in the application.