Commercial and LGPL

**bnilsson** · 2nd August 2009, 09:36

I am making a commercial app using Qt4.5.

If I understand correctly, I can do this under LGPL if I distribute the unmodified Qtcore and Qtgui with the installation and the proper readme's. Is this correct?

I also need the QtSingleApplication class, http://www.qtsoftware.com/products/a...gleapplication.
Do I have to distribute it as a library, or can I compile into my code?
It is tempting to do that since the number of files is small.

I have to say the LGPL license text is not making it easy for the reader!
It seems the more 'legally clear' such a text is, the more difficult it is to understand for us commoners.

**franz** · 2nd August 2009, 17:46

For usage of LGPL you have to distribute unmodified dlls or release your modifications under the same license. Especially in the latter case you will have to supply the changed source code with your distribution.

The single application solution is also LGPL and therefore the same rules apply to it as to the Qt libraries. That means you can't compile it into your application.

**rexi** · 2nd August 2009, 18:58

Originally Posted by bnilsson

I have to say the LGPL license text is not making it easy for the reader!
It seems the more 'legally clear' such a text is, the more difficult it is to understand for us commoners.

As a rule of thumb (I'm no expert on this, either, but I had my share of dealing with the peculiarities of the most common licenses): you can link anything, be it open or closed source, against a LGPL library. But it must be possible for the user to replace that library with another one. So it is out of the question to statically link against LGPL code, unless you release your code under LGPL, too (or any other license that's compatible with it). In your case, this means that you have to use dynamic libraries.

And I totally agree with your observation regarding understandability

. "Legal Speak" is a foreign language to most of us who haven't studied law. But I guess this is the price you have to pay when you want to express your intentions unambiguously. Common speech is just full of ambiguity, surely thats why legal experts define every single word they use (sometimes counterintuitively, but at least it is well defined. Much like us programmers do, isn't it?

)