@SGaist said in Can I charge customer to use Software if I have created Software using open source Qt?:

Also, if you do any changes to Qt for one reason or another, you have to publish these changes.

In addition to what @SGaist said: You need to have the source code of the Qt version that you used. You can either provide a written offer valid for at least 3 months for your customer to request the Qt source code (not your own source code). Or you provide the Qt source code in the same way as your software (if your software can be downloaded, place a download link to the Qt source code in the same place). A download link to someone else hosting the same Qt source code does not count. You have to host it in the same place as your software.

Furthermore, the LGPL requires that the user is able to relink with a different Qt version. If you are using Qt's DLLs this is taken care of already as the user can just replace the DLLs.

You never have to publish (i.e. making it public to everyone) your code. At least that depends on the mode of distribution.

The GPL only places requirements on you when you give your software to someone else. Everyone who receives your software is also eligible to your source code (under GPL, not under LGPL). So, if you give your software to one or two people you also have to give them the source code. If they decide to further give the software to somebody else, they also have to provide the source code to those people. If you put up your software for everyone to download on the internet, then you need to actually publish your source code. This all only applies to GPL. LGPL only means that this applies to the library (Qt in this particular case) and not your own source code. Also, you can provide a written offer valid for at least three? months to provide the source code to everyone who receives your software instead of giving them the source code directly.

Everything that is private and stays private does not have any requirements on the source code.

@AnneRanch said in General question about open source development:

@JKSH So if the "author" has no obligation to publish - how does that "protect" the user ?
If it is bad product I can see the "protection" , but it should be up to the user to decide.

In any case - there is something amiss in the concept of "free licensing" - it is like writing a book and not publish it. Silly.

You'll find there's nothing amiss when you understand its goals.

If an application/executable is a house, and the source code is the blueprints, then a traditional commercial license is like a property developer that says: "Pay me money and you can live in this house. But you are not allowed to look at the blueprints, you are not allowed to renovate or repair the house, and you are not allowed to replace even a single lightbulb."

Now, suppose someone invents a fancy home automation system.

If this system is released under the GPL, it says to the property developer, "You can use my system in the houses that you build. In return, you must give your buyers the blueprints (including the schematics of my automation system) and give them permission to renovate/repair/replace all parts of the house." If this system is released under the Lesser GPL, it says to the property developer, You can use my system in the houses that you build. In return, you must give your buyers access to the schematics of my automation system and give them permission to tinker with and replace the automation system.

So, when the inventor releases the home automation system under the GPL/LGPL, they are encouraging property developers to give the homebuyers more freedom.

Please take a lok if the 'Next' button is really grayed out - I also got a red warning and did not notice that the 'Next' button is available.

Hi,

What version of macOS are you using ?

You don't need to login to get the Open Source version of Qt.

The /Application folder is protected because it's shared among all computer users. You should rather keep the default installation path in your user's folder.

There's no need to select everything especially if you intend to only develop on macOS. Just select the macOS build.

What exactly did the Kit page show once you had that message in Qt Creator ?

By the way, it's Qt, QT stands for Apple's QuickTime which is likely not what you want to develop with.

@VRonin you probably need a software copyright layer to answer that :)

My totally layman understanding (and now I take my work hat off, as this is code owned by my employer) is that in Finland (and probably most of the EU) you would be safe if the code you are copying is practically the only way to do it, and it is so simple that it is the only reasonable solution to your problem, and that the part you are copying is short enough that could simply re-write it anytime, and you aren't copy pasting anything else from the same work.

The problem is that everything I'm saying above is way too hand-wavy to be of any use. It's always a case-by-case situation.

Linking has nothing to do with it. It is a question of does the copy-pasted material automatically bring it's license with it to your code.

If you wanted to be utterly safe, you would ask your friend, who has not seen the Qt code to implement a paintEvent once, and then use that. He probably would come up with about the same seven to ten lines of code. (clean room is the only way to be totally sure)

I found qtlicense, i deleted this file. But nothing happens.

Then i create a new account on Qt installer, and re-install the open source version.
That did the trick. Many thanks Dheerendra.

Regards, Nahuel.

Hi,

Currently the QtQuickCompiler is a licensed product, you should rather contact the Qt Company for these questions.

Hi and welcome to devnet,

Looks interesting ! Thanks for sharing !

Hi @mrjj & @JulienMaille,

Thanks to both of you for your comments. I was clear on publishing my changes done in Qt sources if working with LGPL license.

What I misunderstood was the licensing for applications developed using Qt. I was under the impression that an application used for proprietary usage (irrespective of linkage - dynamic or static) requires purchase of license.

The truth is that if an application is developed using dynamic linkage with Qt libraries, then purchasing of license is not required. Please correct me if I still got it wrong.

Regards,
Anant Agrawal

Are you sure all available modules were built ?