# &Qt; and Licensing questions

What is &Qt;, by the way?

&Qt; is a C++-based class library to build user interfaces. It also includes many utility classes like string classes and classes to handle input and output. It provides most of the widgets you will see in a &kde; application: menus, buttons, sliders, &etc;. &Qt; is a cross-platform library that allows you to write code that will compile on &UNIX; systems as well as &Windows; and embedded devices. You can learn more about &Qt; at http://www.qtsoftware.com.

Why does &kde; use &Qt;?

&Qt; is a very sophisticated toolkit that provides everything that is needed to build a modern user interface. &Qt; is written in C++, thus allowing object-oriented development which ensures efficiency and code reuse in a project the size and scope of &kde;. In our opinion there is no better toolkit available for &UNIX; systems and that it would have been a grave mistake to try to build &kde; on anything but the best.

Why does &kde; not use GTK, XForms, Xlib, whatever?

There are a number of toolkits available. To provide a consistent user interface and to keep used resources such as memory to a minimum, &kde; can use only one of them. &Qt; was selected for the reasons mentioned above.

But &Qt; isn't free, is it?

It is! As of September 4, 2000, version 2.2 of the &Qt; libraries were licensed under the GPL, thereby fulfiling all aspects of free software. Since version 4.5.0 Qt is also available under the LGPL.

Can I write commercial software for &kde;?

You can use the &kde; libraries to write commercial and closed source as well as commercial and open source software. If you want to write open source software you can use the &Qt; free edition. But if you intend to write closed source software you may not use the &Qt; free edition; you need to obtain the &Qt; professional edition from Qt Software.

If you want more information, please contact Qt Software directly.