4
在过去的三个小时里，我被以下编译错误彻底搞糊涂了。有人能告诉我这里发生了什么吗？Boost Log - 为什么不编译？
我试图将log :: formatter（标记如下）定义为自己的变量，所以它可以在几个地方重新使用。但是，尝试重新使用它时会出现编译错误。
但是，如果我完全摆脱了这个变量，而是复制并粘贴代码，它会编译。有没有搞错？有什么办法可以做我想做的事吗？
boost::shared_ptr<log::core> logger = log::core::get();
logger->set_logging_enabled(enabled);
logger->set_filter(trivial::severity >= level);
logger->add_global_attribute(
"TimeStamp", attr::local_clock());
logger->add_global_attribute(
"ProcessID", attr::current_process_id());
logger->add_global_attribute(
"ThreadID", attr::current_thread_id());
// want this to be it's own variable
log::formatter fmt = expr::stream
<< "[" << expr::format_date_time<boost::posix_time::ptime>("TimeStamp", "%d.%m.%Y %H:%M:%S.%f") << "] "
<< "[" << expr::attr<attr::current_process_id::value_type>("ProcessID") << "] "
<< "[" << expr::attr<attr::current_thread_id::value_type>("ThreadID") << "] "
<< "[" << expr::attr<std::string>("Channel") << "] "
<< "[" << expr::attr<severity_level>("Severity") << "]: "
<< expr::smessage
;
// so it can be reused here, but this is a compiler error
log::add_console_log(
std::clog, keywords::format=fmt);
// and here, too. But this is also a compiler error
log::add_file_log(
"test.log", keywords::format=fmt);
编译错误（用铛++）是：
In file included from ../src/util/logging/Logging.cpp:34:
In file included from /opt/boost-1.54.0/include/boost/log/utility/setup/console.hpp:22:
/opt/boost-1.54.0/include/boost/log/detail/sink_init_helpers.hpp:107:21: error: no matching function for call to 'acquire_formatter'
s.set_formatter(aux::acquire_formatter(args[keywords::format]));
^~~~~~~~~~~~~~~~~~~~~~
/opt/boost-1.54.0/include/boost/log/utility/setup/console.hpp:76:5: note: in instantiation of function template specialization 'boost::log::v2_mt_posix::aux::setup_format
boost::log::v2_mt_posix::sinks::synchronous_sink<boost::log::v2_mt_posix::sinks::basic_text_ostream_backend<char> >, boost::parameter::aux::tagged_argument<boost::log::v2
posix::keywords::tag::format, boost::log::v2_mt_posix::basic_formatter<char> > >' requested here
aux::setup_formatter(*pSink, args,
^
/opt/boost-1.54.0/include/boost/log/utility/setup/console.hpp:136:12: note: in instantiation of function template specialization 'boost::log::v2_mt_posix::aux::add_consol
g<char, boost::parameter::aux::tagged_argument<boost::log::v2_mt_posix::keywords::tag::format, boost::log::v2_mt_posix::basic_formatter<char> > >' requested here
return aux::add_console_log(strm, arg1);
^
../src/util/logging/Logging.cpp:121:2: note: in instantiation of function template specialization 'boost::log::v2_mt_posix::add_console_log<char, boost::parameter::aux::t
d_argument<boost::log::v2_mt_posix::keywords::tag::format, boost::log::v2_mt_posix::basic_formatter<char> > >' requested here
log::add_console_log(
^
/opt/boost-1.54.0/include/boost/log/detail/sink_init_helpers.hpp:80:33: note: candidate template ignored: failed template argument deduction
inline basic_formatter<CharT> acquire_formatter(const CharT* formatter)
^
/opt/boost-1.54.0/include/boost/log/detail/sink_init_helpers.hpp:85:33: note: candidate template ignored: failed template argument deduction
inline basic_formatter<CharT> acquire_formatter(std::basic_string< CharT, TraitsT, AllocatorT > const& formatter)
^
/opt/boost-1.54.0/include/boost/log/detail/sink_init_helpers.hpp:91:5: note: candidate template ignored: disabled by 'enable_if' [with FormatterT = boost::log::v2_mt_posi
asic_formatter<char>]
phoenix::is_actor<FormatterT>,
^
但是，如果我代替它更改为此，它编译：
boost::shared_ptr<log::core> logger = log::core::get();
logger->set_logging_enabled(enabled);
logger->set_filter(trivial::severity >= level);
logger->add_global_attribute(
"TimeStamp", attr::local_clock());
logger->add_global_attribute(
"ProcessID", attr::current_process_id());
logger->add_global_attribute(
"ThreadID", attr::current_thread_id());
// copy and paste the expression
log::add_console_log(
std::clog,
keywords::format =
(
expr::stream
<< "[" << expr::format_date_time<boost::posix_time::ptime>("TimeStamp", "%d.%m.%Y %H:%M:%S.%f") << "] "
<< "[" << expr::attr<attr::current_process_id::value_type>("ProcessID") << "] "
<< "[" << expr::attr<attr::current_thread_id::value_type>("ThreadID") << "] "
<< "[" << expr::attr<std::string>("Channel") << "] "
<< "[" << expr::attr<severity_level>("Severity") << "]: "
<< expr::smessage
)
);
// copy and paste the expression again
log::add_file_log(
"test.log",
keywords::format =
(
expr::stream
<< "[" << expr::format_date_time<boost::posix_time::ptime>("TimeStamp", "%d.%m.%Y %H:%M:%S.%f") << "] "
<< "[" << expr::attr<attr::current_process_id::value_type>("ProcessID") << "] "
<< "[" << expr::attr<attr::current_thread_id::value_type>("ThreadID") << "] "
<< "[" << expr::attr<std::string>("Channel") << "] "
<< "[" << expr::attr<severity_level>("Severity") << "]: "
<< expr::smessage
)
);