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I am using Qt4 to build an application and for some reason I want to keep it proprietary. Qt4 is released under LGPL, does that force me to release the code to my application. I ask this question because I am finding it difficult to understand the LGPL license.

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As far as I know, Qt relatively recently underwent licensing changes that allowed you to use it in close source commercial products. It didn't used to be okay, which is why a great many folks used to prefer GTK – RobotHumans Sep 28 '12 at 2:46
@aking1012: Not that recent. Mathematica has been using Qt for a few years at least. – Mechanical snail Sep 28 '12 at 4:45
@Mechanicalsnail IIRC it had to do with cost of licensing previously. January 2009 or so is when it went LGPL according to this blog post:… for the decade previous it was pay to be used commercially. – RobotHumans Sep 28 '12 at 4:54
So you all are saying I can use it to make my own commercial product but the catch is I need to have the LGPL Licence with my binary? – Alwin Doss Oct 1 '12 at 2:31
Indeed. Note also that the binary can not have Qt statically linked, as that would mean it is considered a derivative work instead of something using it - which would mean that you would have to either open-source your app, or pay for the proprietary-licensed Qt version. Dynamic linking and including the LGPL is all you need to do. – user64152 Oct 4 '12 at 6:50


"The main difference between the GPL and the LGPL is that the latter allows the work to be linked with (in the case of a library, 'used by') a non-(L)GPLed program, regardless of whether it is free software or proprietary software.


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This is a great answer. To make it even better, you can try to expand with more examples. – hexafraction Nov 23 '12 at 13:46

In addition to @user64152's answer I have to add one more thing. If along with proprietary you also intend to make a commercial product and modify the Qt libraries, you have to buy the Qt Commercial License in order to be able to sell your product.

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This is not true. LGPL (which Qt is released) Allows commercial/closed source applications as long as you do not modify the qt libraries or if you do making them available to the public. But just the LGPL'd libraries. – VassilisGr Feb 9 '15 at 10:40
Yes, I didn't express myself clear enough. Will add this to my answert. Thanks! – rbaleksandar Feb 9 '15 at 13:28

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