This manual page is for Mac OS X version 10.6.3

Reading manual pages

XIfEvent(3)                                    XLIB FUNCTIONS                                    XIfEvent(3)



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

SYNTAX
       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 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 clientsupplied
       supplied XEvent structure and returns True.  (This event is removed from the queue.)  If the predi-cate predicate
       cate 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 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 additional 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 initialized 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 func-tion. function.
                 tion.

       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



X Version 11                                    libX11 1.2.1                                     XIfEvent(3)