How to log for a ClassLibrary project, but not a Console Application project?

[Qiu-xia . Zhang]

Hi
I have tried logging for Console Application project. It goes well.
And I also tried logging in Class Library project (with code like"Logger.Debug("...");")  called by a Console Application project (with .config). This is allright too.
But If I only applied log4net in a Class Library project, or a Class Library project called by a Windows Application project, it didn't run well.
Can log4net  be applied to Windows Application? Class Library?
How should I config it?
Thanks in advance.

Qiu-xia