License to use a DLL base on Qt
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Hi,
Team A plan to develop a DLL based on QtCore.
This DLL will provide fluid simulations (this DLL is not a Qt wrapper of course).Team B use this DLL to develop an application. This application does not directly use Qt.
If Team A use Qt commercial license, does Team B need also a Qt license if it does not use Qt ?
Jean-Marie.
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Hi,
Team A plan to develop a DLL based on QtCore.
This DLL will provide fluid simulations (this DLL is not a Qt wrapper of course).Team B use this DLL to develop an application. This application does not directly use Qt.
If Team A use Qt commercial license, does Team B need also a Qt license if it does not use Qt ?
Jean-Marie.
@Jean-Marie said in License to use a DLL base on Qt:
Hi,
Team A plan to develop a DLL based on QtCore.
This DLL will provide fluid simulations (this DLL is not a Qt wrapper of course).Team B use this DLL to develop an application. This application does not directly use Qt.
If Team A use Qt commercial license, does Team B need also a Qt license if it does not use Qt ?
Yes it does, if commercial license is necessary (since it's a DLL you can probably fulfill LGPL license terms quite easily, so maybe commercial license is not needed).
Although technically speaking, if Team A is a client of Team B, then Team B needs commercial license and Team A does not.
I am not a lawyer and all that. You can ask Qt Company, too.
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@Jean-Marie said in License to use a DLL base on Qt:
Hi,
Team A plan to develop a DLL based on QtCore.
This DLL will provide fluid simulations (this DLL is not a Qt wrapper of course).Team B use this DLL to develop an application. This application does not directly use Qt.
If Team A use Qt commercial license, does Team B need also a Qt license if it does not use Qt ?
Yes it does, if commercial license is necessary (since it's a DLL you can probably fulfill LGPL license terms quite easily, so maybe commercial license is not needed).
Although technically speaking, if Team A is a client of Team B, then Team B needs commercial license and Team A does not.
I am not a lawyer and all that. You can ask Qt Company, too.
@sierdzio said in License to use a DLL base on Qt:
Although technically speaking, if Team A is a client of Team B, then Team B needs commercial license and Team A does not.
I am not sure if I agree with this statement. Maybe the information is too little to properly understand it. Here is my interpretation:
If I develop an application under the commercial Qt license I can sell that application and the user does not need a Qt license. In the same sense, if I develop a DLL under the commercial Qt license and provide the DLL, the user of the DLL does not need a Qt license. If I (team A) don't have a commercial Qt license I can only develop under the GPL or LGPL. If team B does not recompile my DLL code they can only use Qt under the same license. I don't see a way to upgrade the license retroactively. It is most likely not allowed to first develop under the LGPL and later switch to a commercial license. At least Qt is claiming this is not allowed.
You can convert from developing under open source to commercial terms and conditions by contacting the Qt Company. The commercial license does not by default allow using of code created under open source license, thus you will need to contact the Qt Company to help you with the transition.
Source: https://www.qt.io/faq/tag/qt-commercial-licensing
This is based on my understanding that every developer that employs Qt needs a commercial Qt license. This is the people on team A and not team B.
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@sierdzio said in License to use a DLL base on Qt:
Although technically speaking, if Team A is a client of Team B, then Team B needs commercial license and Team A does not.
I am not sure if I agree with this statement. Maybe the information is too little to properly understand it. Here is my interpretation:
If I develop an application under the commercial Qt license I can sell that application and the user does not need a Qt license. In the same sense, if I develop a DLL under the commercial Qt license and provide the DLL, the user of the DLL does not need a Qt license. If I (team A) don't have a commercial Qt license I can only develop under the GPL or LGPL. If team B does not recompile my DLL code they can only use Qt under the same license. I don't see a way to upgrade the license retroactively. It is most likely not allowed to first develop under the LGPL and later switch to a commercial license. At least Qt is claiming this is not allowed.
You can convert from developing under open source to commercial terms and conditions by contacting the Qt Company. The commercial license does not by default allow using of code created under open source license, thus you will need to contact the Qt Company to help you with the transition.
Source: https://www.qt.io/faq/tag/qt-commercial-licensing
This is based on my understanding that every developer that employs Qt needs a commercial Qt license. This is the people on team A and not team B.
I've asked Qt Company about this many times, they most often say the end client (the company ordering the code to be written) needs to buy licenses. That company needs to buy licenses for all developers working on the project, even if they come from a different company (contractor, sub-contractor). Sounds insane? Sure does, but that's what I've been told multiple times.
OP should consult with Qt Company, too, I think. Maybe the rules have changed, or perhaps they will meet some exceptional sales rep who will say otherwise (I have got conflicting answers from Qt Company many times as well).
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I've asked Qt Company about this many times, they most often say the end client (the company ordering the code to be written) needs to buy licenses. That company needs to buy licenses for all developers working on the project, even if they come from a different company (contractor, sub-contractor). Sounds insane? Sure does, but that's what I've been told multiple times.
OP should consult with Qt Company, too, I think. Maybe the rules have changed, or perhaps they will meet some exceptional sales rep who will say otherwise (I have got conflicting answers from Qt Company many times as well).
@sierdzio In my case, Team A and B are in the same company. Team B does not use Qt in its code (no #include <QtWidgets> or equivalent), no call to the Qt API. Team B just needs the Qt redistributable to run the DLL delivered by team A. This is why, I wonder if Team B needs Qt commercial license. Of sure Team A need it.
