Using qt for a commercial application on windows (LGPL)

jsulm

@Jo-Jo said in Using qt for a commercial application on windows (LGPL):

Do I understand correctly that it is enough to provide a link to download the Qt source code, for example, to the GitHub repository?

No, it means the opposite, because you cannot be sure that GitHub will be there al long as you distribute your software. That's why you should have the source code of the Qt version you're using and provide it on request.

Jo Jo

@jsulm said in Using qt for a commercial application on windows (LGPL):

No, it means the opposite, because you cannot be sure that GitHub will be there al long as you distribute your software. That's why you should have the source code of the Qt version you're using and provide it on request.

Should it be a web hosting under my control? Even then, the hosting may stop working. Any Internet resource may eventually close down.

jsulm

@Jo-Jo It doesn't matter how you store the source code. What is required is that you can provide Qt source code to whoever asks for it. It does not have to be an URL, it can also be an USB stick or what ever.

Jo Jo

@jsulm Do you mean to provide the Qt source code on demand? But am I not obliged to provide access to the Qt source code even without user requests?

jsulm

@Jo-Jo said in Using qt for a commercial application on windows (LGPL):

But am I not obliged to provide access to the Qt source code even without user requests?

You are as far as I know, read again what @SimonSchroeder wrote

Jo Jo

@jsulm I have read it. As far as I understand, I am obliged to provide a download link plus a guarantee that if the link stops working, I will be able to transfer the Qt sources in an alternative way. To do this, I must store the Qt sources somewhere on my own. Right?

jsulm

@Jo-Jo said in Using qt for a commercial application on windows (LGPL):

To do this, I must store the Qt sources somewhere on my own.

Yes, that's what I wrote

Jo Jo

@jsulm Thank you!

Jo Jo

Sorry, do I need to additionally provide the text of the LGPL license in software or on the some web page?

SGaist

Yes, with the software. Also ~~QMainWindow~~ QApplication has an aboutQt method that shows this information.

Jo Jo

@SGaist
I can't find the QMainWindow::aboutQt method in the documentation. Can you provide a link? I found QApplication::aboutQt but it gives us general information about Qt licensing (not specific to LGPL)

One more question: can anyone provide me with a link to a commercial Windows application that uses Qt under the LGPL license? I need such a program as an example

SGaist

@Jo-Jo My bad it was QApplication::aboutQt

zvoopz

@Jo-Jo said in Using qt for a commercial application on windows (LGPL):

can anyone provide me with a link to a commercial Windows application that uses Qt under the LGPL license? I need such a program as an example

I dont know which type of license does Viber use. I cant find any information about licenses inside this application but I see a bunch of Qt`s dlls here
C:\Users\username\AppData\Local\Viber
No Qt mention as well

Jo Jo

@zvoopz said in Using qt for a commercial application on windows (LGPL):

No Qt mention as well

Probably they are using commercial license but I am interested in example of app which releases under LGPL (no payment for Qt license, but commercial app)

Pl45m4

@Jo-Jo said in Using qt for a commercial application on windows (LGPL):

I am interested in example of app which releases under LGPL (no payment for Qt license, but commercial app)

I think it might be hard to tell, because to know this, you have to get the source code, which commercial app developers would not publish.
And AFAIK commercial Qt users can link Qt statically while keeping the code hidden. So as "customer" you are not able to tell whether such app even uses Qt.
Meanwhile, commercial LGPL developed apps you also have to buy first to inspect the files that are shipped with it.
(I don't have any apps I paid for, that were developed using Qt)

You could check the Windows App Store. Maybe there you find apps tagged with "Qt" (if there is such feature).
Or look into the Showcase subforum here. Maybe you find links to commercial apps that were developed by open source users here in the forum.

Jo Jo

@Pl45m4 ok, thank you!

SimonSchroeder

BTW, any app needs to comply with the same rules when using Qt under the GPL or LGPL. It doesn't matter if it's commercial or not. As soon as you distribute a binary (even if it is open source) you need to follow these rules. So, open source apps using Qt will suffice as example. Just note that just because someone else isn't doing something (e.g. not providing a download link for the Qt sources) doesn't mean this is the correct way to do it.

jsulm

@SimonSchroeder said in Using qt for a commercial application on windows (LGPL):

It doesn't matter if it's commercial or not

I disagree with this statement. As far as I know as commercial user you do not have to follow GPL/LPLG as you get Qt under commercial license, not GPL/LGPL (dual licensing).

SGaist

@jsulm said in Using qt for a commercial application on windows (LGPL):

@SimonSchroeder said in Using qt for a commercial application on windows (LGPL):

It doesn't matter if it's commercial or not

I disagree with this statement. As far as I know as commercial user you do not have to follow GPL/LPLG as you get Qt under commercial license, not GPL/LGPL (dual licensing).

I think @SimonSchroeder meant that when using Qt under GPL/LGPL, the fact that the application is commercial or open source does not change anything with regard to respecting these licenses constraints.

Jo Jo

So, guys, what should I do then? We don't have an example on hand that would prove that all these messages in this topic work effectively in practice. I'm tormented by the question: what if it turns out that following all these rules is not enough to use qt for free? After all, we don't have real examples of anyone who did this and didn't have any problems