Re: More GPL questions

[David Kastrup]

"Alfred M. Szmidt" <ams@gnu.org> writes:

>    This example program would dynamically link to both Qt and my sdk's
>    library.
>
> This would make this non-free SDK library a derivate of Qt and the
> example program.

Of course this is nonsense.  Alfred confuses several different issues
that lead to a particular result.

While the SDK library is not derived from Qt, the complete example
program is derived from both SDK library and Qt.  The licensing
conditions of Qt are the GPL, and they require releasing the whole
under the GPL or not at all.  Releasing your example program as a
whole under the GPL requires releasing the SDK library which it
integrates under the GPL as well.

So the net effect is that you have a problem, even though it is
different from the problem Alfred proposes.

>    Does including this example source code in my distrubuted tarball
>    put the entire thing, including the sdk, under the GPL?
>
> Yes.  See section 2(b) of the GNU GPL.

It does not "put the entire thing under the GPL".  You can use such a
combination for your own private use.  You are just not permitted to
distribute versions of it unless you do so under the GPL.

>    If it does, I'll be forced to leave out the Qt example source,
>    altogether, and that seems silly to me.

If the code paths are disjunct, such that one can either link with Qt,
_or_ with the SDK library, but not both, you can dual-license your
code under the GPL and a license fit for linking with the SDK library.
Anybody who would build a binary would then have to discard the part
of the dual-license that is incompatible with the library that got
used.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum