Timezone information with text file backend

[KennethBuijssen]

We're currently working on adding logging to our application and trying to get a log file in the following format: test_20230607T165634+0200.log

With the following code however, the resulting log file is test_20230607T165634.log. After reading the documentation is seems that boost log does not support any of the time zone flags, since it uses ptime internally (https://www.boost.org/doc/libs/1_82_0/doc/html/date_time/date_time_io.html#date_time.format_flags). Could support for this be added?

#include <boost/log/trivial.hpp>
#include <boost/log/utility/setup/file.hpp>

void init_logger(const std::string& filename)
{
  auto sink = boost::log::add_file_log(boost::log::keywords::file_name = filename + "_%Y%m%dT%H%M%S%q.log");
}

int main(int, char**)
{
  init_logger("test");

  BOOST_LOG_TRIVIAL(info) << "Hello, World!";
}

[Lastique]

This is not easy to do, since Boost.DateTime does not allow to create a time zone object that reflects the time zone set on the system. There doesn't seem to be a portable way to obtain this information either, at least I'm not aware of one. I reported this to Boost.DateTime, but the chances for this to be implemented soon are rather slim, unfortunately.

[otopetrik]

It could be useful to have configuration option to use UTC time for file names.

Instead of having log file names with times in unknown time zone, the timezone would be known.
Especially useful if already using attributes::utc_clock for TimeStamp

Looks like local_time_traits::get_clock() is hardcoded, with no way to use utc_time_traits

log/src/text_file_backend.cpp

Line 242 in ae9bf80

m_Facet.put(sbuf_it, m_Stream, m_Stream.fill(), boost::log::attributes::local_time_traits::get_clock());