There are 3 C++ equivalents to log4j:
- log4cxx - recently became an Apache project, active after looking dormat for a while.
- log4cpp - dormant for ages but it looks like it's active again this year
- log4cplus - looks like it hasn't been touched for years. Something like 4 users subbed to its mailing list.
I'm using log4cxx, mainly because I read some comments that it's closer to log4j's API and supports log4j-style config files etc. Its connection to Apache is also a plus. I have no idea which is best, though.