Writing libraries for applications

[kornicameister]

I've recently posted that I had some problems with my firsts library that I'd written for my application so as I could have better possibilities to support it.

I have noticed that I can create QObject derived objects from my application (declarations along with definitions are held in my library) because debugger noticed me that this was impossible.

I know now that some things are impossible, some should be avoided etc., but I need some good source of knowledge (tutorials) to work with, to learn from, so if you were so kind, it would be absolutely helpful...

[high_flyer]

I have noticed that I can create QObject derived objects from my application

I guess you meant can't and not can.
The only restriction is that you can't multi inherit QObjects, but you can definitively have QObjects in your lib.
There are no other restrictions AFAIK, except those imposed by C++ itself.
And the QObject restriction is in the documentation.