LGPL question

[tommy]

Hi,

I have a simple question. If I use Qt 4.5 under LGPL, can I then sell my own programs written with Qt 4.5 as closed source proprietary programs if I don't make any changes in the original Qt software. If the answer is yes, then why would anyone ever get a Qt license and pay for it?
Thanks.

[Lykurg]

If the answer is yes, then why would anyone ever get a Qt license and pay for it?

bacause under gpl you are not allowed to link static. The compiled must be runable by linking against the original libraries. So you can't change the libraries without open your code. Further with a license you also get support of the Qt stuff.

[wysota]

I'm also quite sure it is very difficult to deploy a software using LGPL components on embedded systems as (as I see it) you have to allow the user to change the LGPL components to some equivalents which involves direct (and often priviledged) access to the device's internals.

[tommy]

Sorry, but I'm still not absolutely clear about this LGPL.

So the only difference is that with LGPL you have to give the user the provided *.dll files and you cannot compile your program so that all components of your program are in one file??

But can you still sell software made with LGPL as a closed source software?

Thanks again!

[Lykurg]

So the only difference is that with LGPL you have to give the user the provided *.dll files and you cannot compile your program so that all components of your program are in one file??

Simplified yes. But think, if you are a company you may want to hide your source and you don't want that people know what you are directly doing in your program. When you deliver a software under LGPL it must as said be runable by linking against the original library files. Now if I had much time I could rewrite the whole Qt thing and log actions. E.g. I could change the constructor of QString to generate an output like "A QString with the value xyz was initialized." and so on. That is dangerous if you really have to hide your data. Think forward, encrypted databases makes no sens anymore because you only have to modify the QSql* and voila you get the database + password...

So companies will still need a license. And by the way, if you earn money with any open source product, you should be honest and give that projects some money. They deserve it. (It hasn't be much. Just a little bit.)

EDIT: Your last question: yes you can sell it. And Nokia hasn't released Qt 4.5 under the LGPL just of humanity. They surely hope to get a better position on the market, that Qt becomes a "standard". Then more companies will buy licenses, because the users demand for Qt software.

P.s.: At the time I am very angry with an product written in Qt. It has such a poor quality that it really sucks. Now I will write that company and complain that and ask them for what I have payed 50€ for a program which I could better program by myself (in 2 days!). And that even if I am not an information scientist. So they get "forced" to develop better applications => they obviously can't => they need help => they by support from Nokia.