boost::log

1.最平常的写日志

#include <boost/log/trivial.hpp>int main(int, char*[]){BOOST_LOG_TRIVIAL(trace) << "A trace severity message";BOOST_LOG_TRIVIAL(debug) << "A debug severity message";BOOST_LOG_TRIVIAL(info) << "An informational severity message";BOOST_LOG_TRIVIAL(warning) << "A warning severity message";BOOST_LOG_TRIVIAL(error) << "An error severity message";BOOST_LOG_TRIVIAL(fatal) << "A fatal severity message";return 0;}

  信息会打印到控制台，类似std::cout，但有如下优势：
  1).不光有日志信息，输出还包含时间戳，当前线程标识，安全等级；
  2).不同线程同时写日志是安全的；
  3).可以应用过滤。

   添加过滤日志：

void init(){logging::core::get()->set_filter(    logging::trivial::severity >= logging::trivial::info);}int main(int, char*[]){init();BOOST_LOG_TRIVIAL(trace) << "A trace severity message";BOOST_LOG_TRIVIAL(debug) << "A debug severity message";BOOST_LOG_TRIVIAL(info) << "An informational severity message";BOOST_LOG_TRIVIAL(warning) << "A warning severity message";BOOST_LOG_TRIVIAL(error) << "An error severity message";BOOST_LOG_TRIVIAL(fatal) << "A fatal severity message";return 0;}

   等级大于info的才会输出，其他的忽略。

2. Setting up sinks

  sink由两个类组成：
    1).frontend:负责所有sink的各种常见任务，如线程同步模型，过滤，针对text-based sink的格式化；
    2).backend:实现特定sink的所有事情，如写到一个文件。

  synchronous_sink：支持多线程同时写日志，必要时会自动阻塞。

  text_ostream_backend类可以将格式化的日志项写到STL兼容的stream。例：

#include <boost/core/null_deleter.hpp>// We have to provide an empty deleter to avoid destroying the global stream objectboost::shared_ptr< std::ostream > stream(&std::clog, boost::null_deleter());sink->locked_backend()->add_stream(stream);

  text_ostream_backend支持添加多个流。对于这个sink来说这种方式可以复制输出到控制台和文件，而这个过程中对于每个日志项过滤/格式化和其他类库只有一次开销。
locked_backend成员函数调用sink的backend。它被用来得到一个对backend的线程安全的调用，所有sink fronteds可以提供改成员函数。这个函数返回一个智能指针，并且只要它存在，backend就是被锁的。只有一个例外，unlocked_sink frontend，它不是同步的，而且只是简单返回一个未锁的指向backend的指针。

3.Creating loggers and writing logs

创建logger对象
    src::logger lg;
    类库提供了两个版本的logger：线程安全/非线程安全。非线程安全的logger当使用不同logger实例写日志时是安全的。也就也意味着每个线程都要建立一个logger实例。线程安全的logger可以多个线程同时写，但是这个过程会包含锁，降低效率。线程安全的logger类型都带有_mt后缀。

全局logger对象
    BOOST_LOG_INLINE_GLOBAL_LOGGER_DEFAULT(my_logger, src::logger_mt)
    src::logger_mt& lg = my_logger::get();    //get本身是线程安全的，不用添加同步

写日志

logging::record rec = lg.open_record();if (rec){logging::record_ostream strm(rec);strm << "Hello, World!";strm.flush();lg.push_record(boost::move(rec));}

或者使用宏定义

BOOST_LOG(lg) << "Hello, World!";

全部例子

/* *          Copyright Andrey Semashev 2007 - 2015. * Distributed under the Boost Software License, Version 1.0. *    (See accompanying file LICENSE_1_0.txt or copy at *          http://www.boost.org/LICENSE_1_0.txt) */#include <boost/move/utility.hpp>#include <boost/log/sources/logger.hpp>#include <boost/log/sources/record_ostream.hpp>#include <boost/log/sources/global_logger_storage.hpp>#include <boost/log/utility/setup/file.hpp>#include <boost/log/utility/setup/common_attributes.hpp>namespace logging = boost::log;namespace src = boost::log::sources;namespace keywords = boost::log::keywords;BOOST_LOG_INLINE_GLOBAL_LOGGER_DEFAULT(my_logger, src::logger_mt)void logging_function1(){src::logger lg;//[ example_tutorial_logging_manual_logginglogging::record rec = lg.open_record();if (rec){    logging::record_ostream strm(rec);    strm << "Hello, World!";    strm.flush();    lg.push_record(boost::move(rec));}//]}void logging_function2(){src::logger_mt& lg = my_logger::get();BOOST_LOG(lg) << "Greetings from the global logger!";}int main(int, char*[]){logging::add_file_log("sample.log");logging::add_common_attributes();logging_function1();logging_function2();return 0;}

编译链接：

c++ -g -std=c++11 -Wall -DBOOST_ALL_DYN_LINK -DBOOST_LOG_DYN_LINK -o ./main.o -c ./main.cc  c++ -g -std=c++11 ./main.o -o main  -rdynamic -lpthread -lboost_log_setup  -lboost_log -lboost_filesystem  -lboost_system -lboost_thread

4. Adding more information to log: Attributes

logging::add_common_attributes();

    添加LineID,TimeStamp,ProcessID,ThreadID

其相当于如下代码：

void add_common_attributes(){boost::shared_ptr< logging::core > core = logging::core::get();core->add_global_attribute("LineID", attrs::counter< unsigned int >(1));core->add_global_attribute("TimeStamp", attrs::local_clock());// other attributes skipped for brevity}

可以为参数定义占位符

BOOST_LOG_ATTRIBUTE_KEYWORD(line_id, "LineID", unsigned int)BOOST_LOG_ATTRIBUTE_KEYWORD(severity, "Severity", severity_level)BOOST_LOG_ATTRIBUTE_KEYWORD(tag_attr, "Tag", std::string)BOOST_LOG_ATTRIBUTE_KEYWORD(scope, "Scope", attrs::named_scope::value_type)BOOST_LOG_ATTRIBUTE_KEYWORD(timeline, "Timeline", attrs::timer::value_type)

5. Log record formatting
Lambda-style formatters 示例1：

void init(){logging::add_file_log(    keywords::file_name = "sample_%N.log",    // This makes the sink to write log records that look like this:    // 1: <normal> A normal severity message    // 2: <error> An error severity message    keywords::format =    (        expr::stream            << expr::attr< unsigned int >("LineID")            << ": <" << logging::trivial::severity            << "> " << expr::smessage    ));}

示例2

void init(){typedef sinks::synchronous_sink< 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.log"));sink->set_formatter(    expr::stream           // line id will be written in hex, 8-digits, zero-filled        << std::hex << std::setw(8) << std::setfill('0') << expr::attr< unsigned int >("LineID")        << ": <" << logging::trivial::severity        << "> " << expr::smessage);logging::core::get()->add_sink(sink);}

Boost.Format-style formatters
示例1：

void init(){    typedef sinks::synchronous_sink< 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.log"));    // This makes the sink to write log records that look like this:    // 1: <normal> A normal severity message    // 2: <error> An error severity message    sink->set_formatter    (        expr::format("%1%: <%2%> %3%")            % expr::attr< unsigned int >("LineID")            % logging::trivial::severity            % expr::smessage    );    logging::core::get()->add_sink(sink);}

6. Filtering revisited

示例：

BOOST_LOG_ATTRIBUTE_KEYWORD(line_id, "LineID", unsigned int)BOOST_LOG_ATTRIBUTE_KEYWORD(severity, "Severity", severity_level)BOOST_LOG_ATTRIBUTE_KEYWORD(tag_attr, "Tag", std::string)void init(){// Setup the common formatter for all sinkslogging::formatter fmt = expr::stream    << std::setw(6) << std::setfill('0') << line_id << std::setfill(' ')    << ": <" << severity << ">\t"    << expr::if_(expr::has_attr(tag_attr))       [           expr::stream << "[" << tag_attr << "] "       ]    << expr::smessage;// Initialize sinkstypedef sinks::synchronous_sink< 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 >("full.log"));sink->set_formatter(fmt);logging::core::get()->add_sink(sink);sink = boost::make_shared< text_sink >();sink->locked_backend()->add_stream(    boost::make_shared< std::ofstream >("important.log"));sink->set_formatter(fmt);sink->set_filter(severity >= warning || (expr::has_attr(tag_attr) && tag_attr == "IMPORTANT_MESSAGE"));logging::core::get()->add_sink(sink);// Add attributeslogging::add_common_attributes();}void logging_function(){src::severity_logger< severity_level > slg;BOOST_LOG_SEV(slg, normal) << "A regular message";BOOST_LOG_SEV(slg, warning) << "Something bad is going on but I can handle it";BOOST_LOG_SEV(slg, critical) << "Everything crumbles, shoot me now!";{    BOOST_LOG_SCOPED_THREAD_TAG("Tag", "IMPORTANT_MESSAGE");    BOOST_LOG_SEV(slg, normal) << "An important message";}}int main(int, char*[]){init();logging_function();return 0;}

示例中初始化了两个sink，两个设置了相同的记录格式。第二个设置了过滤，要求级别大于warning或者包含tag参数，且参数为IMPORTANT_MESSAGE。在调用logger对象写日志的时候可以用BOOST_LOG_SCOPED_THREAD_TAG("Tag", "IMPORTANT_MESSAGE");设置tag。

总结：

一般init的流程

1.新建backend；

2.新建sink，将backend添加到sink；

3.配置sink并将添加到core中。

一般调用的流程

1.定义全局变量

2.调用全局变量