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.