Frequently Asked Technical Questions

Table of contents

How do I add a custom level to Apache log4cxx?

This is a common topic for all the Apache logging frameworks and typically motivated to try to categorize events by functionality or audience. An common request is to add an AUDIT level so that the user can configure AUDIT level messages to go to a specific appender. However, the logger name was designed explicitly to support routing of messages by topic or audience. The common pattern of using classnames for logger names obscures the more general capability of logger name to represent the topic or audience of the logging request. The easiest approach to solve the underlying issue is to use a logger names like “” that allow all AUDIT messages to be routed to a particular appender. If you attempted to use a level for that then you would lose the ability to distinguish between different significances within the audit messages.

My application on Windows crashes on shutdown?

Apache log4cxx API calls use C++ Standard Template Library string parameters. If the caller is using a different instance or type of the C Runtime Library that log4cxx, then it is very likely that some memory that was originally allocated by log4cxx would be freed by the caller. If log4cxx and the caller are using different C RTL's, the program will likely crash at the point. Use “Multithread DLL” with release builds of log4cxx and “Multithread DLL Debug” with debug builds.

Does Apache log4cxx support Unicode?

Multiple string flavors

Yes. Apache log4cxx exposes API methods in multiple string flavors const char*, std::string, wchar_t*, std::wstring, CFStringRef et al. const char* and std::string are interpreted according to the current locale settings. Applications should call setlocale(LC_ALL, "") on startup or the C RTL will assume US-ASCII. Before being processed internally, all these are converted to the LogString type which is one of several supported Unicode representations selected by the --with-logchar option. When using methods that take LogString as arguments, the macro LOG4CXX_STR() can be used to convert ASCII literals to the current LogString type. FileAppenders support an encoding property which should be explicitly specified to UTF-8 or UTF-16 for XML files.

Example of wrong non-English logging

For example, here is some Hebrew text which says “People with disabilities”:

נשים עם מוגבלות

If you are to log this information on a system with a locale of en_US.UTF-8, the log message might look something like the following, because the given characters can't be converted to US-ASCII:

loggername - ?????????? ???? ??????????????

Executing std::setlocale(LC_ALL, "") either before actually logging the text above or at the app- startup will allow the message to be logged appropriately. See issue LOG4CXX-483 for more information.