Qt Open Source Project License

beecksche

Hi,
i'm planning to start an open source library with Qt. I want to use the LGPLv3 license, but i'm not sure of my obligations and freedoms. I'm not planning to modify the source code of Qt.

So i hope you can help me with those questions:

Obviosly, to compile/use the library the Qt libraries are needed. Do i have to use the dynamic linked libraries or is this only necessary, if you want to keep the application source code private? Or is it even allowed to copy the source code of the needed modules to the project? So its statically linked.
The LGPLv3 says that you have to give prominent notice with the combined library that you use a LGPL licensed library. So it is sufficient to add a notice in the documentation? Or should i add this notice in every file?
Are there more things to follow?

Thanks!

SGaist

Hi,

WARNING I'm not a lawyer and this is no legal advices.

The only real good answer is: Check with a lawyer.

To comply with the LGPL, the users of your library should be able to swap the provided Qt version with another which excludes the use of static build.
AFAIK, there's usually a file in the sources which lists the dependencies used as well as their licence(s). And a note in the documentation is also good.

Again, for more exact information, consult a lawyer.

Eeli K

@beecksche : @SGaist said in Qt Open Source Project License:

To comply with the LGPL, the users of your library should be able to swap the provided Qt version with another which excludes the use of static build.

More exactly: if you distribute your binaries which are dynamically linked to LGPL'ed library you can keep your source code closed. Then the users can swap the Qt version. If you distribute statically linked binaries you have to open the source code so that the users can recompile with another Qt version.

But I'm not sure if I understand you question correctly. If you're planning an open source library, why do you ask about keeping the application source code private? Do you mean your library code or the code of the possible developer who uses your library?

(Also IANAL warning)

beecksche

@SGaist
@Eeli-K

Thanks for the replies.

No sorry, i do not want to keep the source code of the library private. I want to use the LGPLv3 license so developer who use the library are able to keep their code private.

I reviewed the Qt Webinar "Qt Licensing & What You Need to Know" https://www.qt.io/event/qt-licensing-need-know/. Static linking and LGPLv3 do not fit together!