Boost log - formatting with severity_channel_logger

I have seen several examples with formatters, but those used custom defined attributes.

How do I specify format for the severity_channel_logger? What I get now is:

[2015-07-20 11:53:09.879305] [0x00007f047b525740] [trace]   Bla, bla bla, bla bla bla.
[2015-07-20 11:53:09.879370] [0x00007f047b525740] [trace]   Bla, bla bla, bla bla bla.
[2015-07-20 11:53:09.879376] [0x00007f047b525740] [fatal]   Bla, bla bla, bla bla bla.

logger.h

#ifndef LOGGER_H_
#define LOGGER_H_

#include <boost/log/trivial.hpp>
#include <boost/log/core.hpp>
#include <boost/log/sources/global_logger_storage.hpp>
#include <boost/log/sources/record_ostream.hpp>
#include <boost/log/sources/channel_feature.hpp>
#include <boost/log/sources/severity_channel_logger.hpp>

#include <string>

namespace Logging {

typedef boost::log::sources::severity_channel_logger<boost::log::trivial::severity_level,std::string> LoggerType;

BOOST_LOG_GLOBAL_LOGGER(clogger,LoggerType)

} // namespace Logging

#endif

logger.cpp

#include "logger.h"
#include <memory>

#include <boost/log/core/core.hpp>
#include <boost/log/expressions/formatters/date_time.hpp>
#include <boost/log/expressions.hpp>
#include <boost/log/sinks/sync_frontend.hpp>
#include <boost/log/sinks/text_ostream_backend.hpp>
#include <boost/log/sources/severity_logger.hpp>
#include <boost/log/support/date_time.hpp>
#include <boost/core/null_deleter.hpp>
#include <boost/log/utility/setup/common_attributes.hpp>
#include <boost/make_shared.hpp>
#include <boost/shared_ptr.hpp>

using namespace Logging;

BOOST_LOG_GLOBAL_LOGGER_INIT(clogger, LoggerType)
{
    boost::log::sources::severity_channel_logger< boost::log::trivial::severity_level, std::string > lg;
    return lg;
}

main.cpp

#include "logger.h"
#include <boost/log/attributes/named_scope.hpp>
using namespace Logging;

int main()
{
    BOOST_LOG_FUNCTION();
    BOOST_LOG(clogger::get()) << "Bla, bla bla, bla bla bla.";
    BOOST_LOG_CHANNEL(clogger::get(),"standard") << "Bla, bla bla, bla bla bla.";
    BOOST_LOG_CHANNEL_SEV(clogger::get(),"standard",boost::log::trivial::fatal) << "Bla, bla bla, bla bla bla.";
}

Solution

You need to set a formatter to your sink. The formatter can be defined in multiple ways but the bottom line is that it extracts attribute values from log records and put them into a string. It doesn't matter whether the attributes are defined by user or library - you just need the attribute name and the type of its values.

The severity_channel_logger is a composite logger that inserts both severity level and a channel in log records made through that logger. As such, you'll know from the docs that the attribute names are "Severity" and "Channel", respectively, and the attribute value types are the types you specify as the logger template parameters - boost::log::trivial::severity_level and std::string in your case.

Now you are able to set the formatter you want to your sink. For example:

namespace expr = boost::log::expressions;

sink->set_formatter(
    expr::stream
        << expr::attr< boost::log::trivial::severity_level >("Severity")
        << " [" << expr::attr< std::string >("Channel") << "]: "
        << expr::smessage;
);