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Thread: Qt, Lgpl

  1. #1
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    Smile Qt, Lgpl

    Hi,

    We are evaluating Qt for future symbian application development. I read the faq for Qt and LGPL.
    But many things are not clear to me. Please answer the following questions

    1. Can the LGPL version be used to create commercial closed source applications for s60 and
    other platforms ?

    2. What are the restrictions that the LGPL license impose ? I read, the libraries needs to be linked
    dynamically. What does this actually mean. All Qt libraries are dlls and anyway, they can be only
    linked dynamically. What are the other restrictions ?

    3. Why should one choose for a commercial license when LGPL available ?

    4. Is the commercial license really meant for companies who want to change the Qt source
    code and keep the changes themselves, thus extending Qt to suit their own requirements
    like various device manufacturers ?

    Regards,
    Jaak

  2. #2
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    Re: Qt, Lgpl

    1. Can the LGPL version be used to create commercial closed source applications for s60 and
    other platforms ?
    Yes.

    2. What are the restrictions that the LGPL license impose ? I read, the libraries needs to be linked
    dynamically. What does this actually mean. All Qt libraries are dlls and anyway, they can be only
    linked dynamically. What are the other restrictions ?
    Correct, the dynamic linking restriction isn't such a big issue on S60, but it might be on other platforms. You really need to read the LGPL carefully to make sure you know the restrictions - there are lots of lay-person type explanations on the internet, but you can't rely on those, it's the wording of the license that's important. Anything I wrote here to summarise would be similarly incomplete.

    3. Why should one choose for a commercial license when LGPL available ?

    4. Is the commercial license really meant for companies who want to change the Qt source
    code and keep the changes themselves, thus extending Qt to suit their own requirements
    like various device manufacturers ?
    The answer to 4 is yes, which also answers 3. Another part of the answer is technical support, although you can also purchase that separately for the LGPL version. One final point is if you can't live with one of the other conditions of the LGPL, for which see my answer to 2.

    Sorry that isn't very complete but these licensing issues are one that you really need to understand fully for yourself. If you have some doubt about what a particular bit of the license means then please do come back and ask for clarification.

    Mark

  3. #3
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    Smile Re: Qt, Lgpl

    Hi,

    Thanks for the reply. That clears my immediate doubts. Anyway, I will go through the lgpl doc.
    But I think there is no problem with dynamic linking on s60, windows and linux. Is it a problem on Mac ?
    I read some times earlier that Qt is also to be ported to the s40 platform. Is it true ?

    Regards,
    Jaak

  4. #4
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    Re: Qt, Lgpl

    Quote Originally Posted by 1xuname1x View Post
    Hi,
    I read some times earlier that Qt is also to be ported to the s40 platform. Is it true ?
    Qt has not been made available for or on an S40 device so far.

  5. #5
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    Re: Qt, Lgpl

    Unfortunately there's nothing concrete that can be communicated regarding Qt support on S40 at this stage.

    Cheers,
    Jack

  6. #6
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    Smile Re: Qt, Lgpl

    Hi,

    Another question. What about the .lib files that Qt uses ? They are statically linked to the
    the executable. Where does they fit in the lgpl scheme ?

    Regards,
    Jaak

  7. #7
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    Re: Qt, Lgpl

    Technically static libs are a bit dodgy here. Generally Qt is dynamically linked, most of the .lib files are just the import libraries for the dynamic libs, which are fine but I think the new entry point is implemented as a static library, this code should really be separately licensed, under BSD or similar, to avoid all doubt, but you can be fairly sure that including a standard entry point does not make your code a derivate work, so it should be fine under the LGPL too.

    Mark

  8. #8
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    Smile Re: Qt, Lgpl

    Hi,

    Thanks for the reply. One final question. Is Qt mobile extensions available on Windows mobile also or is
    it for s60 only ?

    Regards,
    Jaak

  9. #9
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    Re: Qt, Lgpl

    The technology preview is available only for S60.

    Cheers,
    Jack

  10. #10
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    Smile Re: Qt, Lgpl

    Is there plan to support other platforms ?

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