Qt License for Commercial Application

Jignesh Patel

I want to start a cross-platform project. I had my research and i want to use QT in my application,but i have some question about QT license.
I am working on Embedded board which already has QT library installed on image that is open source.

can i use my application as commercial and non open source?

jsulm

@Jignesh-Patel I'm not a lawyer!
As long as your app links against dynamic Qt libraries it is fine (LGPL allows this).
You just need to mention somewhere in your app that it uses Qt.
But if you want to use static Qt libs then you need a commercial license.

Jignesh Patel

Yes, I understand and we can display that our application is created using QT.
But question here is : Do we have to make our source available to the customer for that application?

ad1170

No, if you have a commercial license, you not need to make your source code available.

mrjj

Hi
I might misread this
"has QT library installed on image that is open source."

But it seems you have open source Qt so all you need to do is just use
the Qt "dlls" and all be fine. ( as @jsulm says)

michaelL

Hi,
so if i use Qt Open Source and do dynamic linking do i still have to make my source code available?

mrjj

@michaelL
Nope. You do not.

michaelL

@mrjj When i download Qt Opensource and use Qt Creator and leave everything as default, does it dynamic link the libs by its self or do i have to do it myself?

mrjj

@michaelL
Hi, its dynamic pr default. To use static , you would have to make a static version so its not something
you would ever do by accident. :)

michaelL

@mrjj So what is the advantages of commercial license anyway?

SGaist

Hi,

Static Qt build for closed source application.
Support from the Qt Company.
Prioritisation of your bug reports.
No need to publish your Qt modifications if you did any (although it would be very nice).
Some additional tools and modules that you may find useful that are not in the OpenSource project.

Jignesh Patel

I want to verify what understood by me.
I am developing my application using embedded board which already have open source distribution with QT library.
GUI will develop using QT creater-open source and it will display "application is created using QT".

I think above effort does not require to make source open for QT GUI Application.
Am i right?

Hung Tran

@Jignesh-Patel Yes, For your case, don't care about license.

Jignesh Patel

@Hung-Tran Thanks,
understand the QT license for open source distribution, I have one question for customise distribution.
I have customised Linux distribution to remove unnecessary package and make minimal, We are ready for keep source open of new customise Linux distribution.
I am developing my application using embedded board and install my customise Linux image.
Now, In above scenario. can i use my application as commercial and non open source?

Thanks.

mrjj

@Jignesh-Patel
Yes you can be closed source as long as you dynamic link to Qt.

The license model of the customized Linux distribution is not important in this matter.

SGaist

And unlike what @Hung-Tran wrote: care about the license, using GPL or LGPL also has implications.

tekojo

Hi @Jignesh-Patel
As long as you dynamically link to (Qt or anything else) LGPL libraries you can keep your source closed and still comply with the LGPL. However if there are GPL licensed libraries that you are linking to, your code needs to be GPL, and thus you need to share your source.