Linux Manual Pages

Free Software * Books

Source Code

Free Media

Linux

XIfEvent

NAME
SYNTAX
ARGUMENTS
DESCRIPTION
SEE ALSO

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 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.

Opportunity

Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.

Education

Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.