Qt Open Source Version License

pavll · wrote on 18 Mar 2021, 19:38

Hi, I've downloaded Qt Creator Open Source and am rewriting one of my desktop applications. If I now want to sell the program in an online store for free or maybe for 1 or 2€, then I just have to offer users a copy of the Qt source code, right? however my program source code can be closed source so private, or did I misunderstand?

SGaist · wrote on 18 Mar 2021, 19:44

Hi and welcome to devnet,

It depends on the licence you select for your project.

pavll · wrote on 18 Mar 2021, 19:48

If I have closed source code is it important if I add a license to it?

SGaist · wrote on 18 Mar 2021, 19:52

I meant the Qt license (and the ones of the other libraries you might be using).

pavll · wrote on 18 Mar 2021, 20:02

At the moment I only use Qt C++ in my project I think if I can choose which version of qt open source I use, I would use GPL v3 because most official qt extensions are available for it.

SGaist · wrote on 18 Mar 2021, 20:04

In that case, you will have to make your code source available to your users.

pavll · wrote on 18 Mar 2021, 20:16

Ok i just found this:

Contribution via Open Source
When selecting an open source license for your project, you contribute to free and open source software development by using Qt under any of the following licenses: LGPL version 3, GPL version 2 and GPL version 3.

Basic Premises of the Qt Open Source Model

GPL – All users have the rights to obtain, modify and redistribute the full source code of your application. Your users are granted rights founded on the four freedoms of the GNU General Public License.

LGPL – Any modification to a Qt component covered by the GNU Lesser General Public License must be contributed back to the community. This is the primary open source Qt license, which covers the majority of Qt modules.

Please note that there are parts of Qt that are only provided under GPL for open source users that will require you to license your application under a GPL compatible license. Qt also ships with third party open source components that might require respective licensing compliancy, if used. See details of other licenses inside Qt .

on the downloads page.

This means if I use LGPL I don't have to make my source code public, am I right?

But if I select LGPL v3 on this page: [https://www.qt.io/product/features#js-6-3](Qt product features) It says I cannot use the Qt Creator. Is this right? But I can use JetBrains clion if my qt project uses cmake instead of qmake? And what should i do with UI files generate by qt designer? can i use them?

SGaist · wrote on 18 Mar 2021, 20:21

No you don't however your user shall be able to switch the Qt version you used for another one.

You got the filters wrong on that page. You can use Qt Creator without any problem.

pavll · wrote on 18 Mar 2021, 20:30

Ok is it right like that? So all modules which aren't grayed out I can use in my project?

SGaist · wrote on 18 Mar 2021, 20:42

If you selected "Develop" in the filters, you should have the information your are looking for.

pavll · wrote on 18 Mar 2021, 20:46

Ok, thank you for your advice. But if I use this tool and select target platform windows then the license model switches from LGPL v3 to commercial without doing anything.

SGaist · wrote on 18 Mar 2021, 20:49

Then check the documentation of the modules you are interested in, the license will be explained there as well.