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 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
function completes only when the specified predicate
procedure returns
for an event,
which indicates an event in the queue matches.
flushes the output buffer if it blocks waiting for additional events.
removes the matching event from the queue
and copies the structure into the client-supplied
structure.
When the predicate procedure finds a match,
copies the matched event into the client-supplied
structure and returns
(This event is removed from the queue.)
If the predicate procedure finds no match,
returns
and the output buffer will have been flushed.
All earlier events stored in the queue are not discarded.
The
function returns only when the specified predicate
procedure returns
for an event.
After the predicate procedure finds a match,
copies the matched event into the client-supplied
structure without removing the event from the queue.
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
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
structure.
arg
Specifies the argument passed in from the
or
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
If it did not find a match, it must return
SEE ALSO
XAnyEvent(3X11),
XNextEvent(3X11),
XPutBackEvent(3X11)
XSendEvent(3X11)
