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Qt licensing

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  • A Offline
    A Offline
    AndrzejB
    wrote on last edited by
    #1

    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?

    jsulmJ 1 Reply Last reply
    0
    • mrjjM Offline
      mrjjM Offline
      mrjj
      Lifetime Qt Champion
      wrote on last edited by
      #2

      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.

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      • A 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?

        jsulmJ Offline
        jsulmJ Offline
        jsulm
        Lifetime Qt Champion
        wrote on last edited by
        #3

        @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

        https://forum.qt.io/topic/113070/qt-code-of-conduct

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        • SGaistS Offline
          SGaistS Offline
          SGaist
          Lifetime Qt Champion
          wrote on last edited by
          #4

          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.

          Interested in AI ? www.idiap.ch
          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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