Does a company writing C++ apps have to share its source code if it calls unmodified QT or Ubuntu libraries?

Question

What is the relationship between Ubuntu and QT and Canonical? The coming Ubuntu phone looks interesting. Ubuntu seems to be interwoven with QT. If my company wants to write commercial C++ apps calling QT (or Ubuntu) libraries that my company has not modified, then I do NOT have to provide my company created source code with the app, correct? Thanks!

Answer 1

Well, Qt is owned by Digia, not related to Ubuntu/Canonical.

Qt itself is licensed under the GNU Lesser General Public License (LGPL) version 2.1. This allows you to create and redistribute your closed source apps very well, as long as you're dynamically linking to Qt, or adhere to the limitations of statically linking.

See also these Q&A on SO:

• Use LGPL libraries in closed source software?
• QT, LGPL, Commercial closed-source application

While your question is specifically about Qt, keep in mind that in case you are using other libraries in addition to it you will need to check the terms on those as well. Another library may require you to release the source, but Qt does not.

Answer 2

Qt is available in 3 diffrent licenses:

1. GPL: Suitable for open source programs, because you should release source code of your app.

2. LGPL: Suitable for both open source and closed source programs. You need not release source code of your app. But if you created some changes in the qt library, you should release modified sourcecode.

3. Commercial license: Suitable for closed source programs, You can make any change in qt libs and kept it as secret, and you can use any license for your app. But you should purchase license from Digia

In most of the cases LGPL license is enough. If your app's source code is very critical contact a lawyer before choosing the license.