[Qt-interest] Legal question: Qt IOS static linking

[Ross Bencina]

On 3/09/2011 4:32 AM, NoRulez wrote:
> Why I must distribute my app. I thought that it would be a problem
> when I change the sources from Qt, but when I create static libraries
> then I don't touch the sources, so for my understanding I doesn't need
> to distribute anything from my app.

My (limited) understanding is that there are really two "freedom" issues 
with unmodified LGPL:

1. As you suggest above, if you change the sources to Qt you are 
requeired to release those changes. You are also, in some sense, 
required to ensure that your end-users can access the Qt sources whether 
you changed them or not.

2. The end-user needs to be able to take your modified Qt sources, fix a 
bug in them, and then relink your app with the modified and user-patched 
sources. In other words, you get to keep your source code closed, but 
people still need to be able to link your object code with their own 
modified LGPL sources.

So to answer your question: case (2) is why you must distribute .o files 
from your app if you don't support dynamic linking of GPL code.

Obviously the easiest way to support case (2) is to use standard dynamic 
linking mechanisms. The alternative, providing .o files to support 
static re-linking is also allowed (I think, IANAL though).


If you don't like this, you *could* buy a commercial licence... except 
that now there is some LGPL code even in the commercial tree so you need 
to be careful.

Ross.