XIfEvent(XS)

Syntax

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

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

   XPeekIfEvent(display, event_return, predicate, arg)
         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

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.

See also