Editing X Toolkit Intrinsics (section)

{{About|X toolkit|compiler intrinsics|Intrinsic function|Telecom's XT Mobile Network|XT Mobile Network}}

'''X Toolkit Intrinsics''' (also known as '''Xt''', for '''X toolkit''') is a [[library (computing)|library]] that implements an [[Application programming interface|API]] to facilitate the development of programs with a [[graphical user interface]] (GUI) for the [[X Window System]]. It can be used in the [[C (programming language)|C]] language (or any language that can use the C [[API]], such as [[C++]]). Design took place late 1980s to early 1990s.{{cn|date=March 2024}}

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[[File:Xlib and XCB in the X Window System graphics stack.svg|center|500px|'''Xt''' (mint-green) in the X Window System graphics stack]]

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The low-level library [[Xlib]] is the client-side implementation of the [[X Window System core protocol|X11 protocol]]. It communicates with an [[display server#X11|X server]], but does not provide any function for implementing [[Graphical control element (software)|graphical control elements]] ("widgets"), such as [[Button (computing)|buttons]] or [[Menu (computing)|menus]]. The Xt library provides support for creating widget types, but does not provide any itself. A programmer could use the Xt library to create and use a new type of widget. Xt implemented some object oriented concepts, such as inheritance (the user could make their own button by reusing code written for another type of button), events, and callbacks.

Since the graphical user interface of applications typically requires a number of widget types, most developers were reluctant to write their own, and instead prefer to use libraries such as [[Xaw]], [[Motif (software)|Motif]] and [[OLIT]] that provide a set of widgets.

Xt programs had a notorious problem of being unusable if the "app-defaults Xrm database", a text file describing all the widgets, could not be found.{{cn|date=March 2024}} Most modern, widely-used toolkits such as [[GTK]] and [[Qt (software)|Qt]] do not use the Xt library. Rather, they use [[Xlib]] or [[XCB]] directly.