XIfEvent(XS)      X Version 11 (Release 5) 6 January 1993       XIfEvent(XS)


 Name

    XIfEvent - check the event queue with a predicate procedure

 Syntax


    XIfEvent(display, event_return, predicate, arg)
          Display *display;
          XEvent *event_return;
          Bool (*predicate)();
          XPointer arg;

    Bool XCheckIfEvent(display, event_return, predicate, arg)
          Display *display;
          XEvent *event_return;
          Bool (*predicate)();
          XPointer arg;

    XPeekIfEvent(display, event_return, predicate, arg)
          Display *display;
          XEvent *event_return;
          Bool (*predicate)();
          XPointer arg;


 Arguments


    arg            Specifies the user-supplied argument that will be passed
                   to the predicate procedure.

    display        Specifies the connection to the X server.

    eventreturn   Returns either a copy of or the matched event's associated
                   structure.

    predicate      Specifies the procedure that is to be called to determine
                   if the next event in the queue matches what you want.

 Description

    The XIfEvent function completes only when the specified predicate pro-
    cedure returns True for an event, which indicates an event in the queue
    matches.  XIfEvent flushes the output buffer if it blocks waiting for
    additional events.  XIfEvent removes the matching event from the queue
    and copies the structure into the client-supplied XEvent structure.

    When the predicate procedure finds a match, XCheckIfEvent copies the
    matched event into the client-supplied XEvent structure and returns True.
    (This event is removed from the queue.)  If the predicate procedure finds
    no match, XCheckIfEvent returns False, and the output buffer will have
    been flushed.  All earlier events stored in the queue are not discarded.

    The XPeekIfEvent function returns only when the specified predicate pro-
    cedure returns True for an event.  After the predicate procedure finds a
    match, XPeekIfEvent copies the matched event into the client-supplied
    XEvent structure without removing the event from the queue.  XPeekIfEvent
    flushes the output buffer if it blocks waiting for additional events.

 See also

    XAnyEvent(XS), XNextEvent(XS), XPutBackEvent(XS) XSendEvent(XS)
    Xlib - C Language X Interface