c++ - 为每条记录设置严重性和 channel

Question

我正在使用组合的严重性和 channel 记录器来获取日志输出的某种范围。

问题是我想为整个项目使用单个日志记录对象，因此希望能够为特定记录设置 channel ，但我无法同时设置严重性和 channel 。我可以设置其中一个或，但不能同时设置两者。

示例代码:

#include <iostream>
#include <boost/log/trivial.hpp>
#include <boost/log/sources/severity_channel_logger.hpp>
#include <boost/log/utility/manipulators/add_value.hpp>
#include <boost/log/utility/setup/common_attributes.hpp>
#include <boost/log/expressions.hpp>
#include <boost/log/sinks/sync_frontend.hpp>
#include <boost/log/sinks/text_ostream_backend.hpp>
#include <boost/log/support/date_time.hpp>
#include <boost/core/null_deleter.hpp>

namespace logging = boost::log;

using logger_type = logging::sources::severity_channel_logger_mt<logging::trivial::severity_level>;

int main()
{
    logging::add_common_attributes();

    using text_sink_type = logging::sinks::synchronous_sink<logging::sinks::text_ostream_backend>;
    auto sink = boost::make_shared<text_sink_type>();

    sink->locked_backend()->add_stream(boost::shared_ptr<std::ostream>(&std::clog, boost::null_deleter()));

    sink->set_formatter(
        logging::expressions::stream
            << logging::expressions::format_date_time<boost::posix_time::ptime>("TimeStamp", "%Y-%m-%d %H:%M:%S.%f") << " :: "
            << '[' << logging::trivial::severity << " - " << logging::expressions::attr<std::string>("Channel") << "] "
            << logging::expressions::smessage
    );

    logging::core::get()->add_sink(sink);


    logger_type logger;

    auto rec = logger.open_record(logging::keywords::severity = logging::trivial::info);
    if (rec)
    {
        // This do not work
        rec.attribute_values()["Channel"] = logging::attributes::make_attribute_value(std::string{"bar"});

        logging::record_ostream ros{rec};

        // This do not work either
        ros << logging::add_value("Channel", std::string{"foo"});

        ros << "Some message";
        ros.flush();
        logger.push_record(std::move(rec));
    }
}

上面的代码将会输出

2016-09-27 10:25:38.941645 :: [info - ] Some message

As seen, the channel name is not in the output.

I can easily set the channel name when opening the record:

auto rec = logger.open_record(logging::keywords::channel = std::string{"channel"});

但是我无法设置正确的严重性。

有没有办法为单个记录设置严重性和 channel ？或者我是否必须使用多个记录器对象，每个 channel 一个？

我可以轻松地为每个输出创建新的日志记录对象，但即使对于少量的日志记录，这也似乎过多。

Answer 1

open_record() 采用一组属性。后者是通过重载的逗号运算符构建的。但是，为了禁止将逗号解释为函数参数分隔符，您必须添加一对额外的括号。

auto rec = logger.open_record( (logging::keywords::channel = std::string{"channel"}, logging::keywords::severity = logging::trivial::info) );