Boost :: log：基于级别的不同格式（HTML格式）

Question

我正在研究基本的boost example from here。我正在配置我的应用程序所需的内容，但我被卡住了。这里是我现在的位置：

#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; 
} 

我想要的格式取决于严重程度。这是因为我的日志输出是HTML。例如，这些消息我在主那里应该输出打印这样的文件：

<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> 

这可能与简单的模型我在那里？需要做些什么？

插入if条件到sink->set_formatter()。我不能在那里使用C++ 11 lambda。

Answer 1

有很多方法可以做你想做的事情。最直接的方法是使用conditional formatter：

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，这种方法可以是相当繁琐的，并且具有最佳性能。

更好的解决方案是将你的函数注入格式化程序。这里有一个例子：

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()) 
); 

这里，or_none使得value_ref是空的，如果属性不存在的日志记录，因此需要检查它在prefix_formatter和suffix_formatter。

最后，由于您正在编写HTML，因此您可能希望将输出中的保留字符自动转换为转义序列。 XML character decorator可以帮助你。

Answer 2

我能够像这样做，使用自定义格式：

#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; 
} 

安德烈的解决方案并没有为我工作，因为显然string_view是新的东西，在我提升我找不到它是附带Debian Jessie，Boost 1.55。