C

callback

A function that the programmer does not call directly; rather, the system calls the function in response to an event. You must define and register a callback with the system. A C callback function must strictly conform to a predefined prototype so that the arguments and types match, but usually, there is a customizable argument called a ( user ) data pointer.

canvas

A widget that displays structured graphics. Canvas widgets play a large role in the interfaces for several applications; the background for word processors, spreadsheets, and vector graphics programs usually consist of canvas widgets. The GNOME canvas widget is quite powerful (with architecture borrowed from the Tk toolkit). A canvas widget has its own coordinate and object management systems. An application often displays only a piece of the whole canvas, which you can scroll and zoom.

child

(widget) A widget packed into a container is called the container's child. A widget tree represents the relationships between many connected containers and children.

child class

(or subclass) A class derived from a parent class that inherits methods , signals, and properties from the parent.

class

The type of an object : that is, the definition of an object's methods and attributes.

See also object-oriented programming.

class hierarchy

The tree-structured hierarchy of classes formed by their inheritance relationships.

class structure

In GObject, a data structure that holds various class- related items, primarily function pointers for working with properties and signals.

closure

An anonymous "frozen" function with some parameters and variables already initialized . You can invoke something inside a closure later to reuse these parameters (similar to the way you can use a static variable in C). GLib uses the GClosure implementation for signals.

component

In general, a reusable piece of code that implements a certain interface that you can load into a program at run time.

constructor

A method called during instantiation of a class.

container

(widget) Any widget that can hold another widget. A system of several nested containers and the widgets inside is a widget tree. To make a widget visible, you must place the widget inside at least one special container such as a program window or dialog window.

control

In Bonobo , a compound widget that you can activate and operate as a single widget (for example, in one line of code).

See also component.

controller

The C in MVC. A controller is a (normally user-accessible) element that manipulates a model. The controller often also picks up the job of a view.

CORBA

Common Object Request Broker Architecture. A system for communication between software modules. Unlike earlier remote procedure call methods, CORBA is object oriented, where programs define interfaces to their objects with the IDL. The so-called broker handles the requests and parameters between these interfaces. The idea is that the entire process is abstract, so that you can exchange data between programs in different programming languages and over a network with the IIOP protocol, if necessary. Unlike its competitors such as COM, CORBA is an open standard.

CVS

Concurrent Versioning System. This package manages source code tree access to distributed developers. CVS helps prevent conflicts, supports source code rollbacks , can concurrently manage different versions of the code, and more. Nearly all large open-source software projects use CVS.