How to output TimeStamp and ThreadID attributes with custom boost::log formatter?

Question

I'm using custom boost::log formatter for color coding the output log message, but I'm failing to find the proper way to add TimeStamp and ThreadID attributes to the log. When I'm using file logging I just write keywords::format = "[%TimeStamp%] [%ThreadID%] [%Severity%]: %Message%" as logging::add_file_log parameter. I want to have similar effect in the following custom formatter:

void coloring_formatter(const logging::record_view& record,
                        logging::formatting_ostream& stream)
{
  auto severity = record[logging::trivial::severity];
  assert(severity);

  stream << "\e[1m";

  switch (severity.get())
  {
  case logging::trivial::severity_level::trace:
    stream << "\e[97m";
    break;
  case logging::trivial::severity_level::debug:
    stream << "\e[34m";
    break;
  case logging::trivial::severity_level::info:
    stream << "\e[32m";
    break;
  case logging::trivial::severity_level::warning:
    stream << "\e[93m";
    break;
  case logging::trivial::severity_level::error:
    stream << "\e[91m";
    break;
  case logging::trivial::severity_level::fatal:
    stream << "\e[41m";
    break;
  }

  stream // << output TimeStamp
         // << output ThreadID
         << "[" << severity << "] "
         << record[logging::expressions::smessage]
         << "\e[0m";
}

Belch

Answer 1

Given that you have added these attributes to log records, there are multiple ways to extract them. The simplest way is to use keywords. First you declare keywords for the attributes:

BOOST_LOG_ATTRIBUTE_KEYWORD(a_timestamp, "TimeStamp", attrs::local_clock::value_type)
BOOST_LOG_ATTRIBUTE_KEYWORD(a_thread_id, "ThreadID", attrs::current_thread_id::value_type)

Note that the third parameter is the value type of the corresponding attribute. In this example I assumed that the attributes you used were local_clock and current_thread_id.

Now you can use these keywords to extract the value from log records.

stream << record[a_timestamp] << " "
       << record[a_thread_id]
       << " [" << severity << "] "
       << record[logging::expressions::smessage]
       << "\e[0m";

Reluctivity

How could you apply format_date_time<boost::posix_time::ptime> on that timestamp attribute? – Anaesthesiology

Given that format_date_time is a formatter expression node, you'd have to construct a function object like expressions::stream << format_date_time<...>(...) (saving it in an auto variable or in a basic_formatter wrapper) and then invoke it with record and stream arguments. But that would be rather inefficient, you're better off with strftime or snprintf. – Reluctivity

Spasiba Andrey, could you provide some examples on that? How may I record a custom timestamp? I tried with boost::log::formatting_ostream os; const boost::log::formatter TSF(boost::log::expressions::stream << boost::log::expressions::format_date_time<boost::posix_time::ptime>("TimeStamp","%H:%M:%S.%f")); os << TSF; but it fails compiling – Anaesthesiology

@PatrizioBertoni See here. – Reluctivity