XLL+ 6.2 contains a logging framework, cpplog, which helps you to write diagnostic and other information to log files and to the Visual Studio console window.

You can use a configuration file to control what is logged, the destination for the log statements, and what level of detail is recorded. By default nothing is written to the log, and the performance cost of log statements is extremely low.

See Logging in the User Guide for details. The class reference for the framework header files is here: cpplog.h.