Qt licensing

[AndrzejB]

If I write open source program using Qt, I must licence it to GPL or LGPL?
I must link only dynamic, not static with Qt libraries?

[mrjj]

Hi
Disclaimer, im not a a lawyer.
Qt is (mostly) LGPLv3
https://www.qt.io/faq/
If you dynamic link to Qt, its possible to use Qt with a closed source app.
However, if you app is open source, you can use static linking as users are still then free to change Qt as
they see fit as source is public.

[jsulm]

@AndrzejB Since Qt is LGPL3 you don't have to use GPL/LGPL for your open source application when linking dynamically.
Static linking: no need to release your app as GPL or LGPL, but see https://www.gnu.org/licenses/gpl-faq.en.html#LGPLStaticVsDynamic

[SGaist]

Hi,

Same disclaimers as my fellows apply

For LGPL and static linking, you have to provide your users with a mean to re-build the executable/library against a different version of Qt. Which means it could be enough to provide them with the build artefacts of all your project objects (on each platform you support).

In practice it's way simpler to have the sources at their disposal because you would have to keep the artefacts for each and every release you do.