XIfEvent(3X11)      RISC/os Reference Manual       XIfEvent(3X11)



NAME
     XIfEvent, XCheckIfEvent, XPeekIfEvent - check the event
     queue with a predicate procedure

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

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

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

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

     display   Specifies the connection to the X server.

     event_return
               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 procedure returns True for an event, which indi-
     cates 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 struc-
     ture.

     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, XCheckI-
     fEvent returns False, and the output buffer will have been
     flushed.  All earlier events stored in the queue are not



                         Printed 1/24/91         Release 4 Page 1

XIfEvent(3X11)      RISC/os Reference Manual       XIfEvent(3X11)



     discarded.

     The XPeekIfEvent function returns only when the specified
     predicate procedure 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 addi-
     tional events.

SEE ALSO
     XAnyEvent(3X11), XNextEvent(3X11), XPutBackEvent(3X11)
     XSendEvent(3X11)
     Xlib - C Language X Interface









































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