Boost::log:基于级别的不同格式(HTML 格式)

Question

我正在从这里研究基本的提升示例。我正在配置应用程序所需的内容，但我卡住了。这就是我现在所处的位置：

#include <fstream>
#include <iomanip>
#include <boost/date_time/posix_time/posix_time_types.hpp>
#include <boost/log/support/date_time.hpp>
#include <boost/smart_ptr/shared_ptr.hpp>
#include <boost/smart_ptr/make_shared_object.hpp>
#include <boost/log/core.hpp>
#include <boost/log/trivial.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/sources/record_ostream.hpp>
#include <boost/log/utility/setup/common_attributes.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/date_time/posix_time/posix_time_io.hpp>
namespace logging = boost::log;
namespace src = boost::log::sources;
namespace expr = boost::log::expressions;
namespace sinks = boost::log::sinks;
namespace keywords = boost::log::keywords;
void init()
{
    typedef sinks::synchronous_sink<sinks::text_ostream_backend> text_sink;
    boost::log::core::get()->add_global_attribute("TimeStamp", boost::log::attributes::utc_clock());
    boost::shared_ptr<text_sink> sink = boost::make_shared<text_sink>();
    sink->locked_backend()->add_stream(
        boost::make_shared<std::ofstream>("log.html"));
    sink->set_formatter
    (
        expr::stream
            << expr::format_date_time<boost::posix_time::ptime>("TimeStamp", "%Y.%m.%d-%H:%M:%S-UTC")
            << ": <" << logging::trivial::severity << "> " << expr::smessage
    );
    logging::core::get()->add_sink(sink);
}

int main(int, char*[])
{
    std::cout<<"Start"<<std::endl;
    init();
    logging::add_common_attributes();
    using namespace logging::trivial;
    src::severity_logger< severity_level > lg;
    BOOST_LOG_SEV(lg, trace) << "A trace severity message";
    BOOST_LOG_SEV(lg, debug) << "A debug severity message";
    BOOST_LOG_SEV(lg, info) << "An informational severity message";
    BOOST_LOG_SEV(lg, warning) << "A warning severity message";
    BOOST_LOG_SEV(lg, error) << "An error severity message";
    BOOST_LOG_SEV(lg, fatal) << "A fatal severity message";
    std::cout<<"End"<<std::endl;
    return 0;
}

我希望格式取决于严重性级别。这是因为我的日志记录输出是 HTML。例如，我在主要打印的消息应该像这样输出到文件中：

<font color='black'>A trace severity message</font>
<font color='gray'>A debug severity message</font>
<font color='blue'>An informational severity message</font>
<font color='orange'>A warning severity message</font>
<font color='red'>An error severity message</font>
<strong><font color='red'>A fatal severity message</font></strong>

我那里的简单模型可以做到这一点吗？需要什么？

将if条件插入sink->set_formatter() 。我也不能在那里使用 C++11 lambda。

Answer 1

有很多

方法可以做你想做的事。最直接的方法是使用条件格式化程序：

sink->set_formatter
(
    expr::stream
        << expr::if_(logging::trivial::severity <= logging::trivial::severity_level::trace)
           [
               expr::stream << "<font color='black'>"
           ]
           .else_
           [
               expr::stream << expr::if_(logging::trivial::severity <= logging::trivial::severity_level::debug)
               [
                    // ...
               ]
           ]
        << expr::format_date_time<boost::posix_time::ptime>("TimeStamp", "%Y.%m.%d-%H:%M:%S-UTC")
        << ": <" << logging::trivial::severity << "> " << expr::smessage
);

但是，这种方法可能相当乏味，并且性能欠佳。

更好的解决方案是将函数注入格式化程序。下面是一个示例：

boost::string_view prefix_formatter(
    logging::value_ref< logging::trivial::severity_level, logging::trivial::tag::severity > const& level)
{
    if (level)
    {
        switch (level.get())
        {
        case logging::trivial::severity_level::trace:
            return "<font color='black'>";
        case logging::trivial::severity_level::debug:
            return "<font color='gray'>";
        // ...
        }
    }
    return boost::string_view();
}
boost::string_view suffix_formatter(
    logging::value_ref< logging::trivial::severity_level, logging::trivial::tag::severity > const& level)
{
    if (level)
    {
        switch (level.get())
        {
        case logging::trivial::severity_level::trace:
            return "</font>";
        // ...
        }
    }
    return boost::string_view();
}
sink->set_formatter
(
    expr::stream
        << boost::phoenix::bind(&prefix_formatter, logging::trivial::severity.or_none())
        << expr::format_date_time<boost::posix_time::ptime>("TimeStamp", "%Y.%m.%d-%H:%M:%S-UTC")
        << ": <" << logging::trivial::severity << "> " << expr::smessage
        << boost::phoenix::bind(&suffix_formatter, logging::trivial::severity.or_none())
);

在这里，如果日志记录中不存在该属性，or_none会使value_ref为空，因此需要在 prefix_formatter 和 suffix_formatter 中检查它。

最后，由于您正在编写 HTML，因此您可能希望自动将输出中的保留字符转换为转义序列。XML字符装饰器可以帮助您解决此问题。

Answer 2

我能够像这样做，使用自定义格式化程序：

#include <fstream>
#include <iomanip>
#include <boost/smart_ptr/shared_ptr.hpp>
#include <boost/smart_ptr/make_shared_object.hpp>
#include <boost/log/core.hpp>
#include <boost/log/trivial.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/sources/record_ostream.hpp>
#include <boost/log/utility/setup/common_attributes.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/date_time/posix_time/posix_time_io.hpp>
#include "boost/log/utility/setup.hpp"
#include "boost/log/support/date_time.hpp"
#include <boost/log/expressions/formatters/xml_decorator.hpp>
namespace b_logging = boost::log;
namespace b_srcs = b_logging::sources;
namespace b_expr = b_logging::expressions;
namespace b_sinks = b_logging::sinks;
b_logging::formatting_ostream& severity_wrap_prefix(b_logging::formatting_ostream& strm, const b_logging::trivial::severity_level& sev)
{
    if     (sev == b_logging::trivial::severity_level::trace)
        strm << "<font color='gray'>";
    else if(sev == b_logging::trivial::severity_level::debug)
        strm << "<font color='#808080'>";
    else if(sev == b_logging::trivial::severity_level::info)
        strm << "<font color='green'>";
    else if(sev == b_logging::trivial::severity_level::warning)
        strm << "<font color='orange'>";
    else if(sev == b_logging::trivial::severity_level::error)
        strm << "<font color='red'>";
    else if(sev == b_logging::trivial::severity_level::fatal)
        strm << "<strong><font color='red'>";
    else
        strm << "<UNKNOWN SEVERITY LEVEL>";
    return strm;
}
b_logging::formatting_ostream& severity_wrap_suffix(b_logging::formatting_ostream& strm, const b_logging::trivial::severity_level& sev)
{
    if     (sev == b_logging::trivial::severity_level::trace)
        strm << "</font><br>";
    else if(sev == b_logging::trivial::severity_level::debug)
        strm << "</font><br>";
    else if(sev == b_logging::trivial::severity_level::info)
        strm << "</font><br>";
    else if(sev == b_logging::trivial::severity_level::warning)
        strm << "</font><br>";
    else if(sev == b_logging::trivial::severity_level::error)
        strm << "</font><br>";
    else if(sev == b_logging::trivial::severity_level::fatal)
        strm << "</strong></font><br>";
    else
        strm << "<UNKNOWN SEVERITY LEVEL>";
    return strm;
}
std::string ptime_to_string(const boost::posix_time::ptime& time)
{
    std::stringstream str;
    boost::posix_time::time_facet *facet = new boost::posix_time::time_facet("%d.%m.%Y-%H:%M:%S-UTC");
    str.imbue(std::locale(str.getloc(), facet));
    str << time;
    return str.str();
}
void init()
{
    b_logging::core::get()->add_global_attribute("TimeStamp", b_logging::attributes::utc_clock());
    typedef b_sinks::synchronous_sink<b_sinks::text_ostream_backend> text_sink;
    boost::shared_ptr<text_sink> sink = boost::make_shared<text_sink>();
    sink->locked_backend()->add_stream(
        boost::make_shared<std::ofstream>("sample.htm"));
    sink->set_formatter([&](b_logging::record_view const& rec, b_logging::formatting_ostream& strm)
    {
        const b_logging::trivial::severity_level& sev = *b_logging::extract<b_logging::trivial::severity_level>("Severity", rec);
        const boost::posix_time::ptime &pt = *b_logging::extract<boost::posix_time::ptime>("TimeStamp", rec);
        severity_wrap_prefix(strm,sev);
        strm << ptime_to_string(pt) << ": "
                     << rec[b_expr::smessage];
        strm << b_expr::xml_decor[b_expr::stream << b_expr::smessage];
        severity_wrap_suffix(strm,sev);
    });
    b_logging::core::get()->add_sink(sink);
}

int main(int, char*[])
{
    std::cout<<"Start"<<std::endl;
    init();
    b_logging::add_common_attributes();
    using namespace b_logging::trivial;
    b_srcs::severity_logger< severity_level > lg;
    BOOST_LOG_SEV(lg, trace) << "A trace severity message";
    BOOST_LOG_SEV(lg, debug) << "A debug severity message";
    BOOST_LOG_SEV(lg, info) << "An informational severity message";
    BOOST_LOG_SEV(lg, warning) << "A warning severity message";
    BOOST_LOG_SEV(lg, error) << "An error severity message";
    BOOST_LOG_SEV(lg, fatal) << "A fatal severity message";
    std::cout<<"End"<<std::endl;
    return 0;
}

Andrey 的解决方案对我不起作用，因为显然string_view是新的东西，我在 Debian Jessie 附带的 Boost 1.55 中找不到它。