I've had log4cxx recommended to me as a good way of generating log messages from C++ applications. However, plain old UNIX syslog() calls do let me output to files, or over the network, and have all the usual DEBUG/INFO/WARN/ERROR levels.
log4cxx is clearly more modular/customizable, but I really just want to log to a file so can't imagine needing to write any custom output functionality. I feel like I must be missing something: what does log4cxx give me over and above using plain syslog? Performance? Robustness? Portability?
Portability.
If one day you chose to move your application to a windows environment or somewhere else that doesn't provide syslog(), you won't have to rewrite your logger.