RLog provides a flexible message logging facility for C++ programs
and libraries.  It is subscription based, meaning you can subscribe
to messages of your choice in an number of ways: by hierarchical
channel name (e.g. "debug", "debug/ special", "error", etc.), or
file name, component name, etc.  Log messages are individually enabled.
It is meant to be fast enough to leave in production code - even
where it may be called many times, as both the GCC and Intel compilers
reduce the logging overhead a few clock cycles if they are dormant
(with no subscribers).  Other add-on components can extend subscriptions
to external programs, allowing you to enable and collect debugging
messages remotely.

WWW: https://www.arg0.net/rlog
WWW: https://github.com/anastmag/rlog