qt-copy and Qt 4.3

[Cyrille Berger]

On Friday 23 March 2007, Clarence Dang wrote:
> On Friday 23 March 2007 16:48, Thiago Macieira wrote:
> > Clarence Dang wrote:
> > >My understanding is that if people develop kdelibs with a GPL Qt/Windows
> > > and then commit changes to kdelibs, those changes must be under the
> > > GPL, which would be problematic.
> >
> > No. Your code is licensed using the license *you* choose. Neither
> > Trolltech nor anyone else can impose a license on the code you're about
> > to write.
>
> Because dynamically linking against a library results in a derived work, a
> condition of using that library might be that you license your code under a
> particular licence or else, don't use the library at all.
>
> I thought linking against a GPL-only library requires licensing anything
> you developed, while linked to the library, as GPL.  IANAL but I think this
> is 2.b) in GPLv2: "b) You must cause any work that you distribute or
> publish, that in whole or in part contains or is derived from the Program
> or any part thereof, to be licensed as a whole at no charge to all third
> parties under the terms of this License."

As Thiago said, linking against a GPL-only library only requires to use a 
GPL-compatible licence.

See:
http://www.gnu.org/licenses/gpl-faq.html#WhatIsCompatible

In fact to link against a GPL library only requires that you work can also be 
released with the GPL. But you can release your work with an other licence 
(like BSD), but what GPL requires is that if you link against some GPL 
library, anyone can take your program and release it also as a whole (your 
program + Qt) under GPL.

(even if it seems to be contradicted by 
http://www.gnu.org/licenses/gpl-faq.html#IfLibraryIsGPL but it's the only 
item of the list where they don't use GPL-compatible probably an error)

> As far as I understand, QPL versions of Qt allow you to license your code
> under most opensource licenses as you describe, including LGPL.  However,
> I'm reading that the free Windows version of Qt is GPL-only, with no QPL
> option (please correct me if I'm wrong).

Yes QPL is less restrictive, but nowdays most opensoure licenses are GPL 
compatible (including BSD and LGPL).

-- 
Cyrille Berger