boost log format single attribute with logging::init_from_stream

Question

When I set up format params in code, to format date time output I can use something like this

logging::formatter simpleFormat(expr::format("%1% %2%") %
   expr::format_date_time<boost::posix_time::ptime>("TimeStamp", "%H:%M:%S") %
   expr::smessage
);

But when I initialize logger with a config file, I can specify format only in attributes position notation, not their format details.

so, this line in a boost log config file

Format="[%TimeStamp%]: %Message%"

produces output:

[2015-Feb-06 09:32:27.401496]: blah blah blah

I want to reduce timestamp to something like this

[06.02.2015 09:32:27]

How can it be described in boost log config file, ot it cant be done at all?

Answer 1

Preamble

My answer is valid for boost 1.55 (haven't tested with latest one). And it was only tested with MSVC 2013 compiler.

Answer

Looks like you need custom formatter_factory for TimeStamp attribute to be able to specify it's format. This works for me:

#include <fstream>
#include "boost/shared_ptr.hpp"
#include "boost/log/trivial.hpp"
#include "boost/log/expressions.hpp"
#include "boost/log/utility/setup.hpp"
#include "boost/log/support/date_time.hpp"

class timestamp_formatter_factory :
    public boost::log::basic_formatter_factory<char, boost::posix_time::ptime>
{
    public:
        formatter_type create_formatter(boost::log::attribute_name const& name, args_map const& args)
        {
            args_map::const_iterator it = args.find("format");
            if (it != args.end())
                return boost::log::expressions::stream << boost::log::expressions::format_date_time<boost::posix_time::ptime>(boost::log::expressions::attr<boost::posix_time::ptime>(name), it->second);
            else
                return boost::log::expressions::stream << boost::log::expressions::attr<boost::posix_time::ptime>(name);
        }
};

int main()
{
    // Initializing logging
    boost::log::register_formatter_factory("TimeStamp", boost::make_shared<timestamp_formatter_factory>());
    boost::log::add_common_attributes();
    std::ifstream file("settings.ini");
    boost::log::init_from_stream(file);
    // Testing
    BOOST_LOG_TRIVIAL(info) << "Test";
    return 0;
}

And now it your settings file you can specify format argument for TimeStamp attribute. Like this:

[Sinks.ConsoleOut]
Destination=Console
AutoFlush=true
Format="[%TimeStamp(format=\"%Y.%m.%d %H:%M:%S\")%]: %Message%"