Developing Commercial Software in Qt



  • I am developing a program in Qt that will hopefully end up commercial, I am still learning Qt and I am new to how licenses work.

    What are the implications if I want to make a program I have made with Qt proprietary? Are there any major limitations I need to be aware of?

    Or if I do keep it open source, how do I ensure that it won't just be forked, rebranded and re-released and sold (Or 100% free unlike my commercial software) by somebody else claiming it to be his own work and essentially stealing both months of work and potential cash income from me by doing so?



  • My understanding is as follows:

    1. If you make it Open Source, you have no guarantees.

    2. With regards to commercial use, Qt can be used under the LGPL which only affects your distribution, not your code (i.e. your source can be closed, but you have to distribute the Qt libraries you use with your application amongst other things).

    I suggest you read up on LGPL licensing in detail and involve a lawyer if you really are very serious about this.



  • So then I can keep my source closed as long as I re-distribute all the Qt libraries I use with the program and keep their source readily available to ensure that any modifications I made to Qt itself will remain open source, right?



  • Hi.

    you can go through the following link of The Qt Company(a subsidiary of DIGIA plc.)

    "from here":http://www.qt.io/licensing/



  • [quote author="rabcor" date="1414994395"]So then I can keep my source closed as long as I re-distribute all the Qt libraries I use with the program and keep their source readily available to ensure that any modifications I made to Qt itself will remain open source, right?[/quote]

    That is my understanding, yes. You might want to just make 100% sure that modifications you make to Qt source does not need to get pushed upstream again...I have never needed to modify Qt source so have not bothered reading up on those aspects of the LGPL in too much detail.


  • Lifetime Qt Champion

    Hi,

    The only real good answer is: ask a lawyer.

    The link provided by IamSumit is worth reading as a starting point. However, for all legal aspects of licensing, contact a professional.

    The FSF can also help answer your questions.



    1. You can pay Digia for a commercial licence

    2. You can distribute in accordance with LGPL v2.1

    If you distribute in accordance with LGPL v2.1 you must “Use a suitable shared library mechanism for linking with the Library.” (I.e. you must dynamically link to the Qt Libraries, which of course means that you have to re-distribute them). If you don’t do that, then you must release the object code and/or source code for your application.



  • Thanks guys :)


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