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Table of Contents
XIfEvent, XCheckIfEvent,
XPeekIfEvent - check the event queue with a predicate procedure
- 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);
- arg
- Specifies
the user-supplied argument that will be passed to the predicate procedure.
- display
- Specifies the connection to the X server.
- event_return
- Returnsv 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.
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 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 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 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.
XAnyEvent(3X11)
, XNextEvent(3X11)
,
XPutBackEvent(3X11)
XSendEvent(3X11)
Xlib - C Language X Interface
Table of Contents
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