You will see I asked this earlier above, because I did not know about it. This is not stated anywhere in the LGPL v3. However, I am still unsure where the 3 years come from. Not that I wish to knock them, they are here to make money. Qt will always tell you that it is safest to get the commercial license. Keeping the source of Qt for another 3 years certainly helps legally, but as I said I can't find it in the official license said in QT Commercial vs Open Source: Though I am not a lawyer and so I don't know for sure. I would assume that you need to provide the source code of Qt for the versions of the software you are still distributing. If you comply with this the Qt company can't force you into buying the commercial license. In theory (though this has never been legally tested), you can also statically link with Qt as long as you provide (upon request) the object files of your own software (and in special cases the linker as well) so that your client could relink your object files with a different Qt version. The second point is easily achieved by dynamically linking to Qt (i.e. that you provide your client with everything he needs to relink your software.that you keep a copy of the source code (Qt in this case) that you can provide your clients with (you have to have a copy it is not sufficient that there is an official download page).The obligations that the LGPL states are: And also Qt wants to make money, so they will always tell you to buy the commercial license. This is where some uncertainty comes from. There are a few things in the LGPL (especially in back in version 2 previously used by Qt) that have never been fought in court (for any software or library). LGPL requires you to do it only for your clients (people using your app). LGPL does not apply to every human being in existence :-) You don't have to publish Qt and your patches online for everybody. LGPL requires you to do it only for your clients (people using your said in QT Commercial vs Open Source: And if you patch Qt (for example, change something in QString code), these patches need to be under LGPL and you have to make them available to your clients. In practice it means you should have a copy of Qt source code somewhere on your PC/ server for 3 years (just in case that official Qt archive goes offline or something). So you have to provide Qt source code to your clients if they ask for it. Your code is not bound by LGPL license (unless you decide to ship your code under LGPL as well). No problem, that's what this forum is for :-)ĮDIT: I think I have to make my software with the source code public for 3 years. Please pardon me for being a total ignorant newbie here The choice between LGPL and GPL is arbitrary - you choose which license you want Qt to be under (unless you chose some module which is not available under LGPL, like QtCharts, Lottie etc.). If you have installed Qt without paying the commercial license, it is safe to assume you are using the open source version -) How can i check my QT license? from the Update Manger? That's why you have to inform your users that you are using Qt and that they can replace Qt with their own version if they want to. Yes, but LGPL applies only to Qt not to your code. What do I have to worry here? I heard that the Open Source license can be copied by anyone? But I can say that if you make sure you don't break LGPL, Qt Company won't have any basis to "chase" you. So, It is possible for me to get a confirmation from the QT sales team that they will not come after me if I released a proprietary software that I developed on my own?Īsk Qt Company then :-) I'm not their employee.
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