Qt (toolkit)

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The Qt designer used for GUI designing
Developed by Qt Software (formerly known as Trolltech)
Latest release 4.5 / 2009-3-3; 35 days ago
Written in C++
Operating system Cross-platform
Type Widget toolkit
License GNU LGPL
GNU GPL with Qt special exception
Q Public License
Website http://qtsoftware.com/

Qt (pronounced as the English word "cute"[1]) is a cross-platform application development framework, widely used for the development of GUI programs (in which case it is known as a widget toolkit), and also used for developing non-GUI programs such as console tools and servers. Qt is most notably used in KDE, Opera, Google Earth, Skype, Qt Extended, Adobe Photoshop Album, VirtualBox and OPIE. It is produced by the Norwegian company Qt Software, formerly known as Trolltech, a wholly owned subsidiary of Nokia since June 17, 2008.[2]

Qt uses C++ with several non-standard extensions implemented by an additional pre-processor that generates standard C++ code before compilation. Qt can also be used in several other programming languages; via language bindings. It runs on all major platforms, and has extensive internationalization support. Non-GUI features include SQL database access, XML parsing, thread management, network support and a unified cross-platform API for file handling.

Distributed under the terms of the GNU Lesser General Public License (among others), Qt is free and open source software.


[edit] Varieties

Qt is released by Trolltech on the following platforms:

Qt software on October 20, 2008 announced a version of Qt on S60 platform.[4][5][6][7][8][9][10][11]

There are four editions of Qt available on each of these platforms, namely:

  • Qt Console – edition for non-GUI development
  • Qt Desktop Light – entry level GUI edition, stripped of network and database support
  • Qt Desktop – complete edition
  • Qt Open Source Edition – "complete" edition, with some exceptions,[12] for free software/open source developers

[edit] License

Until version 1.45, source code for Qt was released under the FreeQt license — which was viewed as not compliant with the open source principle by the Open Source Initiative and the free software definition by Free Software Foundation, because while the source was available it did not allow the redistribution of modified versions.

With the release of version 2.0 of the toolkit, the license was changed to the Q Public License (QPL), a free software license but one regarded by the Free Software Foundation as incompatible with the GPL. Compromises were sought between KDE and Trolltech whereby Qt would not be able to fall under a more restrictive license than the QPL, even if Trolltech were bought out or went bankrupt. This led to the creation of the KDE Free Qt foundation, which guarantees that Qt would fall under a BSD-style license should no free software/open source version of Qt be released during 12 months.

Later Qt became available under a dual license, the GPL v2 or v3 with special exception[13] and a proprietary commercial license on all supported platforms. The commercial license allows the final application to be licensed under various free software/open source licenses such as the LGPL or the Artistic License, or a proprietary software license.

As announced on January 14, 2009, Qt version 4.5 adds another option, the LGPL, [14] which should make Qt more suitable for non-GPL open source projects and for commercial users.[15]

All editions support a wide range of compilers, including the GCC C++ compiler and the Visual Studio suite.

[edit] Current

Trolltech released Qt 4 on June 28, 2005 and introduced five new technologies in the framework:

  • Tulip A set of template container classes.
  • Interview A model/view architecture for item views.
  • Arthur A 2D painting framework.
  • Scribe A Unicode text renderer with a public API for performing low-level text layout.
  • MainWindow A modern action-based main window, toolbar, menu, and docking architecture.

Qt 4.1, released on December 19, 2005, introduced integrated SVG Tiny support, a PDF backend to Qt's printing system, and a few other features.

Qt 4.2, released on October 4, 2006, introduced Windows Vista support, introduced native CSS support for widget styling, as well as the QGraphicsView framework for efficient rendering of thousands of 2D objects onscreen, to replace Qt 3.x's QCanvas class.

Qt 4.3, released on May 30, 2007, improved Windows Vista support, improved OpenGL engine, SVG file generation, added QtScript (ECMAScript scripting engine based on QSA).[16]

Qt 4.4, released on May 6, 2008. Features included are improved multimedia support using Phonon, enhanced XML support, a concurrency framework to ease the development of multi-threaded applications, an IPC framework with a focus on shared memory, and WebKit integration.

Qt 4.5, released on March 3, 2009. Major included features are QtCreator, improved graphical engine, improved integration with WebKit, OpenDocument Format read support and new licensing options. Mac OS X Cocoa Framework support.

[edit] Bindings

Qt has a range of bindings for various languages which implementing some or all of widget set.

[edit] Migration tools

[edit] History

Haavard Nord and Eirik Chambe-Eng (the original developers of Qt and the CEO and President, respectively, of Trolltech) began development of "Qt" in 1991, three years before the company was incorporated as Quasar Technologies, then changed the name to Troll Tech, and then to Trolltech.

The toolkit was called Qt because the letter Q looked appealing in Haavard's Emacs font, and "t" was inspired by Xt, the X toolkit.[17]

Controversy erupted around 1998 when it became clear that KDE was going to become one of the leading desktop environments for Linux. As KDE was based on Qt, many people in the free software movement worried that an essential piece of one of their major operating systems would be proprietary.

This gave rise to two efforts: the Harmony toolkit, which sought to duplicate the Qt Toolkit under a free software license, and the GNOME desktop, which intended to supplant KDE entirely. The GNOME Desktop uses the GTK+ toolkit, which was originally written for the GIMP, and primarily uses the C programming language.

The first two versions of Qt had only two flavours: Qt/X11 for Unix and Qt/Windows for the Windows platform. The Windows platform was only available under the proprietary license which meant free/open source applications written in Qt for X11 could not be ported to Windows without purchasing the QPL edition. In the end of 2001, Trolltech released Qt 3.0 which added support for the Mac OS X platform. The Mac OS X support was available only in the proprietary license, until June 2003, where Trolltech released Qt 3.2 with Mac OS X support available under the GPL.

In 2002 members of the KDE on Cygwin project began porting the GPL licensed Qt/X11 code base to Windows.[18] This was in response to Trolltech's refusal to license Qt/Windows under the GPL on the grounds that Windows was not a free software/open source platform.[19][20] The project achieved reasonable success although it never reached production quality.

This was resolved when Trolltech released Qt/Windows 4 under the GPL in June 2005. Qt 4 now supports the same set of platforms in the free software/open source editions as in the proprietary edition, so it is now possible to create GPL-licensed free/open source applications using Qt on all supported platforms.

In June 2008 Nokia acquired Trolltech ASA to enable the acceleration of their cross-platform software strategy for mobile devices and desktop applications, and to develop its Internet services business. On September 29, 2008 Nokia renamed Trolltech to Qt Software.

[edit] Training and Consulting Partners

Region Company
Flag of the United States North America ICS, KDAB,SCS
 Europe BasysKom, Digia, KDAB
 Japan SRA International
 Poland ARISE
 India GTE

[edit] Design

The innovation of Qt when it was first released relied on a few key concepts.

[edit] Use of native UI-rendering APIs

Qt used to emulate the native look of its intended platforms, which occasionally led to slight discrepancies where that emulation was imperfect. Recent versions of Qt use the native APIs of the different platforms to draw the Qt controls, and so do not suffer from such issues.[21]

[edit] Meta object compiler

Known as the moc, this is a tool that is run on the sources of a Qt program prior to compiling it. The tool will generate C++ code with "Meta Information" about the classes used in the program. This meta information is used by Qt to provide programming features not available natively in C++: The signal/slot system (which has also been implemented in native C++ by other parties), introspection and asynchronous function calls.

[edit] Criticism

The use of an additional tool has been criticized for making Qt programming different from pure C++ programming. In particular, the choice of an implementation based on macros has been criticized for its absence of type safety and pollution of the namespace.[1] Trolltech viewed this as a necessary trade-off to provide introspection and the dynamically generated slot and signal mechanism.[2]

[edit] QtScript ECMAScript interpreter

Qt Script for Applications is a cross-platform toolkit that allows developers to make their Qt/C++ applications scriptable using an interpreted scripting language: Qt Script (based on ECMAScript/JavaScript).

From Qt 4.3.0 onward, the scripting API [22], which is based on QSA [23] is integrated as a core part of Qt and is no longer a separate library.

[edit] Qt hello world

#include <QtGui/QApplication>
#include <QtGui/QLabel>
int main(int argc, char *argv[])
    QApplication app(argc, argv);
    QLabel label("Hello, world!");
    return app.exec();

[edit] Compiling and executing Qt hello world program

1. Create a folder named Hello
2. Copy paste the above program as Hello.cpp in folder Hello
3. At Hello folder run

 a. qmake -project
 b. qmake 
 c. make/gmake/nmake - as needed by OS and your compiler setups

4. Exeute ./release/Hello (Or release/Hello.exe in Windows)

[edit] Applications built using Qt

Popular examples of applications which use Qt include:

[edit] See also

[edit] References

  1. ^ http://video.google.com/videoplay?docid=-1435432529445611697
  2. ^ Nokia acquired Trolltech
  3. ^ Qt for Windows CE Technology Preview Download — Trolltech
  4. ^ Nokia - Nokia enriches application development with Qt for S60
  5. ^ Qt for S60 - Forum Nokia Wiki
  6. ^ Symbian - Nokia enriches application development with Qt for S60
  7. ^ All About Symbian - Nokia Announce Technology preview of Qt on S60
  8. ^ ars technica - Nokia releases first Qt preview for Symbian S60
  9. ^ Qt Labs Blogs - We’re porting Qt to S60!
  10. ^ Qt Software - Technology Preview - Qt for S60
  11. ^ Qt Sftware - How to get Qt running on your S60 phone
  12. ^ The ActiveQt class for ActiveX on Windows, for example, is not available in the Open Source Edition
  13. ^ Nokia Corporation Qt GPL Exception Version 1.3
  14. ^ LGPL License Option Added to Qt January 14, 2009
  15. ^ ICS Whitepaper on the Implications of Qt under LGPL for Commercial and Government users
  16. ^ Trolltech: What’s New in Qt 4.3
  17. ^ "A Brief History of Qt". http://safari.oreilly.com/0131872494/pref04. Retrieved on 2007-12-20. 
  18. ^ Q../Windows Edition history, 5 June 2006
  19. ^ E-mail to the kde-cygwin mailing list by Chris January, 4 February 2003
  20. ^ Qt Non-commercial FAQ, 5 October 2003
  21. ^ Products - Qt – A cross-platform application and UI framework 'Qt uses the native graphics APIs of each platform it supports, taking full advantage of system resources and ensuring that applications have native look and feel.'
  22. ^ Qt 4.3: QtScript Module
  23. ^ QSA 1.2: Qt Script for Applications
  24. ^ Adobe Photoshop Elements® Album – Qt Software
  25. ^ TOra uses the Qt library

[edit] External links

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