Manual Pages for UNIX Operating System command usage for man XIfEvent

XLIB FUNCTIONS                                     XIfEvent(3x11)



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

SYNTAX
     cc [ flag... ] file... -lX11 [ library... ]

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

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

     int XPeekIfEvent(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.

     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
     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



X Version 11        Last change: libX11 1.3.5                   1






XLIB FUNCTIONS                                     XIfEvent(3x11)



     flushes the output buffer if it blocks waiting for addi-
     tional events.

     Each of these functions requires you to pass a predicate
     procedure that determines if an event matches what you want.
     Your predicate procedure must decide if the event is useful
     without calling any Xlib functions.  If the predicate
     directly or indirectly causes the state of the event queue
     to change, the result is not defined.  If Xlib has been ini-
     tialized for threads, the predicate is called with the
     display locked and the result of a call by the predicate to
     any Xlib function that locks the display is not defined
     unless the caller has first called XLockDisplay.

     The predicate procedure and its associated arguments are:

     Bool (*predicate)(Display *display, XEvent *event, XPointer
          arg)

     display   Specifies the connection to the X server.

     event     Specifies the XEvent structure.

     arg       Specifies the argument passed in from the
               XIfEvent, XCheckIfEvent, or XPeekIfEvent function.

     The predicate procedure is called once for each event in the
     queue until it finds a match. After finding a match, the
     predicate procedure must return True.  If it did not find a
     match, it must return False.

SEE ALSO
     XAnyEvent(3x11), XNextEvent(3x11), XPutBackEvent(3x11)
     XSendEvent(3x11)
     Xlib - C Language X Interface


ATTRIBUTES
     See attributes(5) for descriptions of the following attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Availability                | x11/library/libx11          |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | MT-Level                    | See XInitThreads(3X11)      |
    |_____________________________|_____________________________|





X Version 11        Last change: libX11 1.3.5                   2