编译用于创建boost.log格式的代码时出错

Error compiling code for creating boost.log format

本文关键字：代码 出错 格式 log 用于 创建 boost 编译      更新时间：2023-10-16

我正试图在Ubuntu 18.04 LTS上使用gcc 7.3.0编译以下代码，选项为-std=c++14:

auto createLogFormatter()
{
boost::log::expressions::stream_type stream;
stream  << boost::log::expressions::format_date_time<boost::posix_time::ptime>("TimeStamp", "%Y-%m-%d %H:%M:%S  ")
<< boost::log::expressions::attr<int>("Severity")
<< " " // ERROR HERE
<< boost::log::expressions::attr<boost::log::attributes::current_thread_id::value_type>("ThreadID")
<< " "
<< boost::log::expressions::smessage;
return stream;
}

并得到奇怪的错误：

Log.cpp:51:13: error: no match for ‘operator<<’ (operand types are ‘boost::log::v2_mt_posix::expressions::aux::make_output_actor<boost::phoenix::actor<boost::log::v2_mt_posix::expressions::aux::attribute_output_terminal<boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::phoenix::argument<2> >, 0> >, boost::posix_time::ptime, boost::log::v2_mt_posix::fallback_to_none, boost::log::v2_mt_posix::aux::light_function<void(boost::log::v2_mt_posix::basic_formatting_ostream<char>&, const boost::posix_time::ptime&)> > >, boost::log::v2_mt_posix::expressions::attribute_actor<int, boost::log::v2_mt_posix::fallback_to_none, void, boost::phoenix::actor>, int, false>::type {aka boost::phoenix::actor<boost::log::v2_mt_posix::expressions::aux::attribute_output_terminal<boost::phoenix::actor<boost::log::v2_mt_posix::expressions::aux::attribute_output_terminal<boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::phoenix::argument<2> >, 0> >, boost::posix_time::ptime, boost::log::v2_mt_posix::fallback_to_none, boost::log::v2_mt_posix::aux::light_function<void(boost::log::v2_mt_posix::basic_formatting_ostream<char>&, const boost::posix_time::ptime&)> > >, int, boost::log::v2_mt_posix::fallback_to_none, boost::log::v2_mt_posix::to_log_fun<void> > >}’ and ‘const char [2]’)
stream  << boost::log::expressions::format_date_time<boost::posix_time::ptime>("TimeStamp", "%Y-%m-%d %H:%M:%S  ")
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<< boost::log::expressions::attr<int>("Severity")
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<< " "
^~~~~~

根据Boost的例子，这样的东西应该是有效的：

expr::stream
<< expr::attr< unsigned int >("LineID")
<< ": <" << logging::trivial::severity
<< "> " << expr::smessage

但我犯了这样的错误。我做错了什么？

编译器错误可能是由缺少include引起的。Lambda表达式运算符由Boost.Fenix在boost/phoenix/operator.hpp中提供。或者您可以只包含boost/log/expressions.hpp，它提供所有Boost.Log表达式节点以及运算符。

但除此之外，createLogFormatter函数是不正确的，因为它丢弃了整个格式化程序表达式。您不应该创建并返回stream对象，它只是启动格式化程序表达式的终端。您需要返回作为lambda表达式结果创建的函数对象。

auto createLogFormatter()
{
auto fmt = stream  << boost::log::expressions::format_date_time<boost::posix_time::ptime>("TimeStamp", "%Y-%m-%d %H:%M:%S  ")
<< boost::log::expressions::attr<int>("Severity")
<< " " // ERROR HERE
<< boost::log::expressions::attr<boost::log::attributes::current_thread_id::value_type>("ThreadID")
<< " "
<< boost::log::expressions::smessage;
return fmt;
}

如果您想要一个稳定的返回类型，可以使用boost::log::formatter来包装表达式。

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