Here is a bullet point run-down of what I take to be the salient features of libcwd, John Torjo's Proposed Boost.Log library, and what I can glean from skimming Preston's "Mantra" Logger implementations. These lists are by no means complete but I hope this helps to move the discussion along. libcwd (see http://libcwd.sourceforge.net/www/features.html): * Part of a larger, mature library that provides logging, memory allocation tracing and other debugging facilities. * Thread-safe. Provides a separate libcwd_r for use in MT apps. * Uses ostreams for formatting * Supports "severity" levels on each message. * Suggested API is macro-based. All logging code can thereby be excluded from a build by ensuring the macro CWDEBUG is not defined. * Output divided up into channels; user can create any number of new namespace-protected channels; somewhat tortured syntax for doing so (they must be in a namespace called "dc" nested inside a user-defined namespace) * Output directed to channel objects by passing them to a macro (e.g. Dout (dc::notice, ...)) Torjo (need gmane URLs) * Uses ostreams to format messages * No concept of a message severity or level (suggested to use different Log instances) * Messages are directed to Logs. Logs have Modifiers and Appenders associated with them. The set of Modifiers and Appenders in use is up to the user. * Modifiers are functors that take Messages and alter them (e.g. prepend a timestamp, thread ID, append a newline, etc.). * Appenders are functors that take the modified messages and do something with them (e.g. write them to a file, syslog, etc). * Logs must be declared in a header, defined in a different TU. Helper macros provided to assist with this [this is the one feature I most dislike] * Log names may use namespace::name style * "Appenders" are used to direct log messages to a file/device/etc. Appenders are associated with one or more logs using a wild-cardable string name * Includes several Appender implementations including file, Win32 debug window, size/date-based rolling logs * Output directed to Log objects by passing them to BOOST_LOG macro (e.g. BOOST_LOG(ldebug) << ostream stuff) Mantra (http://www.neuromancy.net/viewcvs/Mantra-I/include/mantra/log/?root=mantra) * Part of a larger library ("Mantra") that provides networking, file operations, persistence, and a bunch ofther stuff I'm sure I missed. Much of this is built using Boost facilities. The Logger portion does not seem to be tightly coupled to the rest. * Logger paramaterized on charT type. Allows for wide-character output. * Some of the Logger implementations depend on Boost.Thread to provide MT safety * Uses Boost.Format for message formatting and also provides a hex-dump output method. * Messages include a "severity" level; Loggers are set to emit messages of a specific severity or greater. Severity levels not pluggable ATM. * Provides a special hook for use when a Fatal message is logged. * Includes several Logger implementations including file (with automatic rollover based on size), socket, syslog * No helper macros provided for "performance optimized" logging (e.g. not formatting messages which won't get logged; compiling-out logging code). This is surely easy to add however. * Output directed to Loggers using logger.Write (LogLevel, boost::format object) -- Caleb Epstein caleb dot epstein at gmail dot com