My company uses Qt 4.7.4 under LGPL for a commercial proprietary application.
We had to put two changes into the source code of Qt and re-build its DLLs to resolve some issues. What should we now do under LGPL? Are we to expose our source code? or do we just need to expose the Qt files we've changed? What is the nature of this "exposure"? posting them on a website?
how does that work?
LGPL is mainly meant for libraries and means that you can use Qt with "closed-source" applications, i.e. ones you do not have to divulge their source code.
Would Qt be GPL, you would have had to open-source your own app, too.
Now, LGPL also means that if you modify the sources of the library, you have to make these modifications open and public.
How this is done is not fixed in stone. If your modifications is of general interest, you should submit a patch to Code Review. see Contribute to Qt for more info.
If it is very specific to your needs, publishing the patch on your website should be sufficient.