Licensing confusion with Qt5... [solved]



  • Hello,
    First of all let me clear that I am a Mechanical Engineering student & have an avid interest in C++ programing. Around September 2012 I came across Qt. I have been developing a program in Qt Creator 4.8 (LGPL version) which I will be releasing as Open Source.
    However I have also been planning to develop another program which will be free to use but will be closed source. Since I will devote huge time & resources in it I plan to earn money by folllowing methods:

    1. Provide an option for users to donate me money as per their wish.
    2. Earn money through advertisement on website & the program itself will feature advertisements.
    3. Should be able to sell the program (source code & all) to a company if they are interested in buying my program.
    4. Charge for Cutomisation to individual users
    5. Charge for plug-ins/add-ons.

    Now here's the problem:
    Until Qt was with Nokia i.e. till 4.8 version under LGPL I could do the same without any legal objections. But now with Qt 5 if i want to develop closed source application (even though free to use) I have to use the commercial version of Qt.

    bq. The commercial license of Qt is the correct license to use for the development of proprietary and/or commercial software with Qt where you need to safeguard your development investment to secure your competitive advantage.

    So if i don't move to Qt 5 & continue with Qt 4.8 will I be able to do the above mentioned points?
    Thank You!
    PS: Sorry if my question is common or stupid. I tried searching on internet but couldnt find precise facts outlining my situation.
    Also I have no interest in modifying Qt & want to use it as is. In addition, I have no problem in saying that I have developed the application in Qt on my products website & its documentation!



  • What makes you think that the licensing options have changed for Qt5?



  • I have updated the question.
    Please see the quotes from download page of Qt.
    Thank You for replying.



  • This is misleading. The licensensing options for Qt5 are still GPL, LGPL and Commercial.

    Feel free to release your proprietary, closed-source commercial application as long as you adhere to the terms of the LGPL (which basically means no static linking).

    IANAL.



  • ok. can you please be specific by what you mean by

    bq. as long as you adhere to the terms of the LGPL.

    I have mentioned my situation above. So basically I can earn money from applications developed in Qt 5 even though I use LGPL version of Qt as long as:

    1. I dont modify the source code of Qt
    2. I dont say that "I have not used Qt & developed complete program by myself"

    Can you please clear that for me?



  • You can use Qt to create a commercial, closed-source application as long as you

    • do not statically link against the Qt libraries and
    • provide any modifications you have done to Qt under the terms of the LGPL

    IANAL.



  • Care to classify "any modification" - does this only include altering existing functionality, or also includes adding new?

    In the case of the latter, would that mean that adding a new class method classifies as a modification, but implementing the same functionality as a free function does not?

    Also, doesn't the LGPL mandate to somehow mention the application uses Qt?


  • Moderators

    [quote author="utcenter" date="1358968562"]Care to classify "any modification" - does this only include altering existing functionality, or also includes adding new?

    In the case of the latter, would that mean that adding a new class method classifies as a modification, but implementing the same functionality as a free function does not?
    [/quote]
    All this probably depends where you place it. My interpretation is anything linked statically with Qt means open source. So, if the new functionality is part of a new QtCore.dll you cannot keep close. If the new part with extending functionality is in your own application or your own dll (which does not holds any Qt stuff) it should be fine.

    IANAL :-)



  • God, I wish people stop using that acronym, it sounds like a perverted sex toy, manufactured by Apple...



  • [quote author="utcenter" date="1358968562"]Care to classify "any modification" - does this only include altering existing functionality, or also includes adding new?[/quote]You will have to provide any modifications which are required to link your application against an official Qt.

    [quote author="utcenter" date="1358968562"]In the case of the latter, would that mean that adding a new class method classifies as a modification, but implementing the same functionality as a free function does not?[/quote]Yes. If you modify or extend any classes in the Qt libraries you will have to provide the modifications, if you just use them, you do not have to, as long as it is no derivative work (which means you cannot take Qt, modify it, call it Ut and deny the providing of the modifications, as it is your work).

    [quote author="utcenter" date="1358968562"]Also, doesn't the LGPL mandate to somehow mention the application uses Qt?[/quote]Yes, you "...must give prominent notice with each copy of the work that the Library is used in it and that the Library and its use are covered by this License. You must supply a copy of this License. If the work during execution displays copyright notices, you must include the copyright notice for the Library among them, as well as a reference directing the user to the copy of this License...".


  • Moderators

    [quote author="Lukas Geyer" date="1359013865"]
    [quote author="utcenter" date="1358968562"]In the case of the latter, would that mean that adding a new class method classifies as a modification, but implementing the same functionality as a free function does not?[/quote]
    Yes. If you modify or extend any classes in the Qt libraries you will have to provide the modifications, if you just use them, you do not have to, as long as it is no derivative work (which means you cannot take Qt, modify it, call it Ut and deny the providing of the modifications, as it is your work).
    [/quote]

    Also note that you can use LGPL-EXCEPTION to make small modifications to Qt itself without breaking the license see LGPL_EXCEPTION.txt in QTDIR.

    [quote]So basically I can earn money from applications developed in Qt 5 even though I use LGPL version of Qt[/quote]

    You can earn money with GPL, too. Both GPL and LGPL do not say anything about charging for the application. They're concerned with the source code availability only.



  • [quote author="sierdzio" date="1359017260"]
    You can earn money with GPL, too. Both GPL and LGPL do not say anything about charging for the application. They're concerned with the source code availability only.[/quote]

    So what is the difference between the two?

    Basically, I work in a big software company as a QA guy. I want to develop a small app for our customers. However our company doesn't use Qt (any version). So I didn't want to give my company any legal hassles, as I am developing in consultation with my Manager at our local level. We are not in talks with the legal team which is present in HQ of our company, as it is a very lengthy procedure.
    As you may have totally understood my situation can you suggest which version I should I use?



  • [quote author="Lukas Geyer" date="1358967890"]You can use Qt to create a commercial, closed-source application as long as you

    • do not statically link against the Qt libraries and
    • provide any modifications you have done to Qt under the terms of the LGPL

    IANAL.[/quote]

    That was pretty helpful!
    Thanks :)


  • Moderators

    With GPL you have to publish entire source code of the whole application. Qt under LGPL allows you to choose your own license for your part of the code (so, you can keep source code secret, just need to inform it uses Qt etc.).

    Again, this does not say a thing about money. Earning money is allowed for both licenses (but with GPL you distribute the source code, so your clients can compile themselves). Note that by "publish the source code" GPL does not force you to publish to the whole world - you can distribute the source to your clients only. But those are tiny details, don't bother yourself too much - choose LGPL :)



  • [quote author="sierdzio" date="1359119583"]With GPL you have to publish entire source code of the whole application. Qt under LGPL allows you to choose your own license for your part of the code (so, you can keep source code secret, just need to inform it uses Qt etc.).

    Again, this does not say a thing about money. Earning money is allowed for both licenses (but with GPL you distribute the source code, so your clients can compile themselves). Note that by "publish the source code" GPL does not force you to publish to the whole world - you can distribute the source to your clients only. But those are tiny details, don't bother yourself too much - choose LGPL :)[/quote]

    Thank You so much man!
    That was some pure English which I can understand... ;)
    I can now heave a sigh of relief....phew.
    You mark this as answered, as I cannot find an option for the same.


  • Moderators

    Just edit your first post here - there will be an option to change topic. Add "[Solved]" there. Bit of a manual work around here :)


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