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.

Thanks for the reply , yeah I was thinking same to contact sales team.

@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.

@rktech
How you write it does not matter. You must observe the LGPL terms of (most of, assuming you stick to that) Qt. Which means that you don't have to publish your sources, and if you do not alter the Qt sources you don't need to publish them either.

I am not a lawyer. This is an opinion, not legal advice.

@VRonin said in Qt 5.15 licensing update:

I think this is a requirement of GPL not of LGPL

It's what I thought for a long time as well. There was another discussion in this forum about this. Finally, we figured out that as of version 3 the LGPL starts by including the GPL and granting a few more rights. It does not rephrase the requirements for distributing the source code.

Maybe I was a little bit unclear (if that is the confusion): You only need to provide the source code of Qt. In no case do you need to provide the source code of your own software when using Qt under the LGPL.

@SGaist Hi, Thank you for your reply. I understand your point, so I set this topic solved.

I just realized that C:\Qt\Licenses\LISENSE do not include the GPL v3 exception stated above. Hence, the argument above does not hold.

@jordanbaucke Sure, since you have commercial license you can bring the point directly to support.

@VRonin Thanks for the answer.
Just to be sure, this is my output when I run otool -L on my .app
Does that look ok?

@executable_path/../Frameworks/libopencv_core.3.1.dylib (compatibility version 3.1.0, current version 3.1.0) @executable_path/../Frameworks/libopencv_imgcodecs.3.1.dylib (compatibility version 3.1.0, current version 3.1.0) @executable_path/../Frameworks/libopencv_highgui.3.1.dylib (compatibility version 3.1.0, current version 3.1.0) @executable_path/../Frameworks/libopencv_imgproc.3.1.dylib (compatibility version 3.1.0, current version 3.1.0) @executable_path/../Frameworks/libopencv_objdetect.3.1.dylib (compatibility version 3.1.0, current version 3.1.0) @rpath/QtWidgets.framework/Versions/5/QtWidgets (compatibility version 5.6.0, current version 5.6.0) @rpath/QtGui.framework/Versions/5/QtGui (compatibility version 5.6.0, current version 5.6.0) @rpath/QtCore.framework/Versions/5/QtCore (compatibility version 5.6.0, current version 5.6.0) /System/Library/Frameworks/OpenGL.framework/Versions/A/OpenGL (compatibility version 1.0.0, current version 1.0.0) /System/Library/Frameworks/AGL.framework/Versions/A/AGL (compatibility version 1.0.0, current version 1.0.0) /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 120.1.0) /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)

@Spirrwell Yep, that would be a good option indeed :)

Thank you, @tekojo, for your answer.

Qt's sources are covered by the same set of license, GPL, LGPL and Commercial. There's no one widget with a license and another with another license.

You have to choose which license you want to use with your project and then abide by its rules. The commercial license being only available once you bought it.

Para resumir: se sua aplicação depende das DLL's/shared librarys, você pode manter seu fonte fechado e vender. Se você "consumir" o Qt estaticamente (.lib), aí você quebrou a LGPL.

Resumo: É possível vender minha aplicação usando o LGPL?

Para Windows: é possível.
Para Linux: é possível.
Para MacOS: é possível.
Para Android: é possível.
Para IOS: não é possível. Isso pq a AppStore não permite shlib. Logo sua aplicação deve ser compilada com o Qt estático.

Como o mundo mobile gira em torno de Android/IOS.......

@mcosta Thanks. It would help to have a link to Commercial Features & Benefits instead of the main download page.

@SGaist said:

Where did you got these informations ?

Nowhere. I just wanted to make certain that this was not true. Your extra information about the Apple Store is very useful -- thanks.

No you don't, again, just check what the LGPL license requires and conform to it, then you'll be good.

@scrolling said:

But, what does "dynamic linking" means?

It applies only to Qt linking. This means that you can use LGPL version for closed source software only if you link dynamically QT libraries

Thanks Huulivoide and Jeroen3.
I carefully read your reply and I study LGPL license and Qt license FAQ again.
So I got some conclusions：

provide the Qt source code use dynamic link library notified the user: the application is used by LGPL license provide the LGPL licensed contents