log4cplus::FileAppender::FileAppender (
const log4cplus::tstring & filename,
LOG4CPLUS_OPEN_MODE_TYPE mode = LOG4CPLUS_FSTREAM_NAMESPACE::ios::trunc,
bool immediateFlush = true
)


Immediate flush means that the underlying writer or output stream will be flushed at the end of each append operation.

Immediate flush is slower but ensures that each append request is actually written. If immediateFlush is set to false, then there is a good chance that the last few logs events are not actually written to persistent media if and when the application crashes.

The immediateFlush variable is set to true by default.