[SOLVED]Freely distribute the Qt shared libraries (DLLs)?



  • Hi, all!
    I've developed an application using the LGPL version of Qt. I've went over the LGPL license (http://www.gnu.org/licenses/lgpl-2.1.html), but am looking for a little clarification on some things.

    I've used the Qt library without any modification, and the executable that will be shipped will be built with MSVC on Windows. The application will be dynamically linked to the Qt library. The source code of the application is proprietary.

    Now, when I ship my application, I would need to include the Qt DLLs:

    • QtCore4.dll
    • QtGui4.dll
    • ...
      My understanding of the license is that I can freely distribute these DLLs, and only need to provide a copy of the LGPL license and a location (i.e., qt.nokia.com) to download the source code of the library from. Is this Correct?

    Can I keep my application's source code proprietary, and freely distribute the Qt shared libraries (DLLs)?
    Any help are welcome.
    Thanks!!



  • Yes, you are correct. LGPL allows you to keep the source code of your application closed.



  • Thanks for reply!
    The key point is: Can I freely distribute the Qt shared libraries (DLLs)?



  • Yes, you can.



  • Yes, you can. And if i understand i have to provide a way to update the library if the user want this, right?



  • ... which you already do by using dynamic linking: the user will just have to drop in the replacements.



  • Yes, but some user don't know this simple procedure and i have to write a minimal guide for this.
    User != technician :P

    [quote author="peppe" date="1292403048"]... which you already do by using dynamic linking: the user will just have to drop in the replacements.[/quote]





  • [quote author="stuk" date="1292403168"]Yes, but some user don't know this simple procedure and i have to write a minimal guide for this.
    User != technician :P

    [quote author="peppe" date="1292403048"]... which you already do by using dynamic linking: the user will just have to drop in the replacements.[/quote]

    [/quote]
    As far as I know, the LGPL does not require you to explain how to do it. Just to make it possible to do so. I don't think writing a manual that states that you can drop in newer versions of the Qt library files is needed.



  • [quote author="stuk" date="1292403168"]Yes, but some user don't know this simple procedure and i have to write a minimal guide for this.
    User != technician :P

    [quote author="peppe" date="1292403048"]... which you already do by using dynamic linking: the user will just have to drop in the replacements.[/quote]
    [/quote]

    The LGPL doesn't require you to make your users smarter :-)



  • This 'allow updates' requirement is a way to guarantee your proprietary application does not depend on modifications you did in the library - it must be possible for the software to be linked with a newer version of the LGPL library (Qt, in this case :-P), not only to your Qt version. So, if you modify Qt (what is not you case, as you said), to respect LGPL you must submit the changes upstream.

    I'm not a lawyer [1], please correct me if I'm wrong

    [1] In 100% of the license discussions, someone must say this sentence, at least once =P



  • Thanks a lot!!



  • [quote author="anselmolsm" date="1292412214"]I'm not a lawyer [1], please correct me if I'm wrong

    [1] In 100% of the license discussions, someone must say this sentence, at least once =P[/quote]

    You're absolutely right. Was thinking if this should be some kind of FAQ: "Never ever ask for legal advice on forums, mailing lists, IRC and whatsoever. Consult an IT lawyer." (?)



  • [quote author="peppe" date="1292457362"]You're absolutely right. Was thinking if this should be some kind of FAQ: "Never ever ask for legal advice on forums, mailing lists, IRC and whatsoever. Consult an IT lawyer." (?)
    [/quote]

    That might not help either. If you ask three of these guys you will get four opinions....



  • [quote author="Volker" date="1292492418"][quote author="peppe" date="1292457362"]You're absolutely right. Was thinking if this should be some kind of FAQ: "Never ever ask for legal advice on forums, mailing lists, IRC and whatsoever. Consult an IT lawyer." (?)
    [/quote]

    That might not help either. If you ask three of these guys you will get four opinions....[/quote]

    Haha, ok, point taken, but at least they're supposed to know the matter and you sign agreements with them, whilst on forums you have no guarantees whatsoever.



  • [quote author="peppe" date="1292493548]Haha, ok, point taken, but at least they're supposed to know the matter and you sign agreements with them, whilst on forums you have no guarantees whatsoever.[/quote]

    That's true. It's in most cases better to ask a specialized lawyer than a forum with all that "I believe that..." answers.



  • But if you ask 3 lawyers, you perhaps get also 4 answers.
    Perhaps the Trolls can make a definite statement? That could then also be put to FAQ?



  • Hi, All, Another question that is can i distribute all files (e.g. my apps, Qt DLLs) use one package (e.g. one NSIS install package, or one zip/7z/tar.gz package) ?
    Many thanks!



  • Sure you can*!

    *) Opinion of a non-lawer.



  • Change state to SOLVED.
    Thanks all!


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