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I have a question about the use of Qt and its licenses because i'm so confused with it. I want to make an application (Commercial and its own source code as private) in C++ which uses Qt and its libraries for the GUI (I don't want to modify it) and I want to use it in the Open Source version (not the commercial one).

The Qt Core libraries use a LGPL license as I can read from multiple forums and the official website, so if I publish only the part of the Qt code (maintain the mine as private) and follow the LGPL restrictions, for example with a template like that: https://marketplace.qt.io/products/qt-lgpl-app-template will be any problem?.

For the other side, I want to make the GUI with the tool Qt Creator, because it is easier for me. But on the property website: https://www.qt.io/product/features?hsLang=en if you choose the LGPL license the Qt Creator is disabled except if you check in the filters for a GPLv3 license. But as I can read in their own GitHub repository: https://github.com/qt-creator/qt-creator/blob/master/LICENSE.GPL3-EXCEPT (in the Exception 1) and in other posts similar to mine: Using Qt Designer to create UI design for closed source application.

Can I use it for a private commercial application?.

(EDIT: I read here (https://embeddeduse.com/2023/01/06/using-qt-5-15-and-qt-6-under-lgplv3/) I can use the Qt Creator IDE to make my own files, I suppose '.ui' also are in this consideration...Without any restrictions of GPL, have I understood it correctly?)

Another question is...If I should follow the GPL rights in case of using Qt Creator...Can I do my application as private and commercial, but with the option to access the source code if you buy it, or the application should be free (inclusive if you don't modify the Qt libraries).

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    Your question has so many parts! Have you looked at this: opensource.stackexchange.com/questions/12849/… and this opensource.stackexchange.com/questions/7709/… ? Feb 15, 2023 at 12:39
  • Thanks to both! Sorry for the long text, i have so many question with this... With the first two links of planetmaker: It confirms that I can use the free option of the tool with a LGPL license as long as the libraries are through a link, right?. With the other two of @Martin_in_AUT, yes i read it, i understand for it that with the Exception no.1 of the second link, i can use qt creator? Feb 15, 2023 at 13:09
  • The sub-question about .ui files is related to the "moc" (the Meta-Object Compiler). Maybe that deserves a separate question if you want it answered (the question should be further developed first though, with more details about what you want to do). I see that's been discussed elsewhere in forums, but I don't see it adressed on this StackExchange site yet.
    – Brandin
    Apr 18, 2023 at 9:50

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With respect, this is not a great first question. It has, as has been noted, way too many parts, and nearly all of them have already been answered here. It looks rather as if you're after not information but legal advice, which we can't provide (and which you should go and pay for, if you're betting a business on this). Nevertheless, in the hope of answering the question promptly:

You may use the Qt libraries in a proprietary application, under the LGPL, provided that you honour the requirements of the LGPL; see eg this question for more details.

You may use the Qt Creator under the terms of GPL to write a de novo application which you then distribute under terms of your choice; see eg this question for more details. Those terms may include fully-proprietary, GPL-with-paid-exceptions, and fully GPL.

If, after reading the linked questions fully, that leaves you with any remaining issues, could I ask you to be clear and explicit about them?

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  • Thanks! I had a lot of interrogatives with this licenses and this different parts of Qt, but with your second paragraph now I have a more clear idea. Feb 16, 2023 at 8:33

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