如何解决如何将boost :: log :: expressions格式化程序对象插入流以格式化时间戳记 或者
我正在遵循有关Boost.log记录格式的教程,并且我试图格式化时间戳以仅在小数秒部分显示2位数字。 9年前在这里how to customize "TimeStamp" format of Boost.Log提出了相同的问题,但是该解决方案似乎不适用于更新版本的Boost。这是我尝试过的与上述解决方案类似的方法,但是使用的是format_date_time< boost::posix_time::ptime >
而不是date_time<boost::posix_time::ptime>
:
namespace expr = boost::log::expressions;
auto ts = expr::format_date_time< boost::posix_time::ptime >("TimeStamp","%Y-%m-%d %H:%M:%s.");
auto ts_fractional = expr::format_date_time< boost::posix_time::ptime >("TimeStamp","%f");
auto ts_fractional_short = (expr::format("%.2s") % ts_fractional);
auto strm = expr::stream
<< '[' << ts << '.'
<< ts_fractional_short << ']' //error here. ts_fractional would work
<< '[' << logging::trivial::severity << ']'
<< " " << expr::smessage;
sink->set_formatter(strm);
似乎相关的错误是:
/path/to/boost_1_73_0/boost/log/utility/formatting_ostream.hpp:921:19: note: 'boost::log::v2s_mt_posix::basic_formatting_ostream<char>::ostream_type {aka std::basic_ostream<char>}' is not derived from 'boost::log::v2s_mt_posix::basic_formatting_ostream<CharT,TraitsT,AllocatorT>'
strm.stream() << value;
...
/path/to/boost_1_73_0/boost/log/utility/formatting_ostream.hpp:921:19: note: cannot convert 'value' (type 'const boost::log::v2s_mt_posix::aux::basic_format<char>::pump') to type 'const id& {aka const boost::log::v2s_mt_posix::aux::id<boost::log::v2s_mt_posix::aux::process>&}'
strm.stream() << value;
是否可以将expr::format()
返回的对象转换为可以注入expr::stream
的对象?
更新
我找到了一个解决方案,该解决方案是使用使用formatting_ostream
和record_view
的自定义格式器,并从记录中提取时间戳。然后,我使用local_date_time
对象和output_facet
s进行格式化,最后使用小数秒字符串上的boost::format
将其写回到ostream。这很丑。必须有更好的方法。
void formatter(const boost::log::record_view &rec,boost::log::formatting_ostream &os)
{
auto pt = logging::extract< boost::posix_time::ptime >("TimeStamp",rec);
using namespace boost::local_time;
using namespace boost::gregorian;
stringstream ss;
auto output_facet = new local_time_facet();
auto input_facet = new local_time_input_facet();
ss.imbue(locale(locale::classic(),output_facet));
ss.imbue(locale(ss.getloc(),input_facet));
local_date_time ldt(not_a_date_time);
ss << pt;
ss >> ldt; //yuck...
output_facet->format("%Y-%m-%d %H:%M:%s");
ss.str("");
ss << ldt;
auto ts = ss.str();
output_facet->format("%f");
ss.str("");
ss << ldt;
auto ts_fractional = ss.str();
os << boost::format("[%1%.%2%][%3%] %4%")
% ts
% (boost::format("%.3s") % ts_fractional)
% logging::extract< boost::log::trivial::severity_level >("Severity",rec)
% rec[expr::smessage];
}
int main(int argc,char *argv[]) {
...
sink->set_formatter(&formatter);
...
}
更新2
以防万一有人偶然发现这个问题并想在C ++ 11编译器中使用@sehe的format_f
:
struct format_f {
std::string format_str;
template<typename T1,typename... Ts>
string operator()(T1 const& t1,Ts const&... ts) const {
return consume_arg((boost::format(format_str) % t1),ts...).str();
}
template<typename T1>
T1 consume_arg(T1 &t1) const {
return t1;
}
template<typename T1,typename T2,typename... Ts>
T1 consume_arg(T1 &t1,T2 const& t2,Ts const&... ts) const {
return consume_arg(t1 % t2,ts...);
}
};
解决方法
您想延期使用应收帐款。
从this older answer of mine轻松地借用Xfrm
,我建议做一个完整日期时间的子字符串:
static constexpr Xfrm Left24 { [](std::string const& s) { return s.substr(0,24); } };
logging::formatter formatter = expr::stream
<< line_id
<< " | "
<< Left24 [ expr::stream << expr::format_date_time(timestamp,"%Y-%m-%d,%H:%M:%S.%f") ]
<< " [" << logging::trivial::severity << "]"
<< " - " << expr::smessage;
3 | 2020-08-15,11:37:30.128 [warning] - this is a warning message
4 | 2020-08-15,11:37:30.129 [error] - this is an error message
5 | 2020-08-15,11:37:30.129 [fatal] - this is a fatal error message
提取值
您可能希望提取真实数据,而不是进行文本后处理。我发现这比我希望的要难,但无论如何都要展示,以防万一:
boost::phoenix::function<milliseconds_f> milliseconds;
logging::formatter formatter = expr::format(
"%1% | %2%.%3% [ %4% ] - %5%")
% line_id
% expr::format_date_time(timestamp,%H:%M:%S")
% milliseconds(expr::attr<boost::posix_time::ptime>("TimeStamp").or_throw())
% logging::trivial::severity
% expr::smessage;
现在,milliseconds_f
被定义为:
struct milliseconds_f {
auto operator()(logging::value_ref<boost::posix_time::ptime> const& v) const {
auto f = v.get().time_of_day().fractional_seconds();
std::string s = std::to_string(f / 1000);
while (s.length()<3) s += '0';
return s;
}
};
3 | 2020-08-15,12:27:38.870 [ warning ] - this is a warning message
4 | 2020-08-15,12:27:38.870 [ error ] - this is an error message
5 | 2020-08-15,12:27:38.870 [ fatal ] - this is a fatal error message
替代:更接近您的期望
您可以创建一个惰性函数来进行有效的格式化:
boost::phoenix::function<format_ex> format;
logging::formatter formatter = expr::format(
"%1% | %2%.%3% [ %4% ] - %5%")
% line_id
% expr::format_date_time(timestamp,%H:%M:%S")
% format(std::string("%.3s"),expr::format_date_time(timestamp,"%f"))
% logging::trivial::severity
% expr::smessage;
哪里
struct format_ex {
template<typename... T>
auto operator()(std::string const& format_str,T const&... v) const {
return (boost::format(format_str) % ... % v);
}
};
由于渗漏的抽象,您需要通过引用确保format-string不是char []文字。您还可以强制衰减(难看,但较不冗长):
% format(+"%.3s","%f"))
要避开整个问题,可以将Phoenix Bind与格式化程序分开使用:
using boost::phoenix::bind;
logging::formatter formatter = expr::format(
"%1% | %2%.%3% [ %4% ] - %5%")
% line_id
% expr::format_date_time(timestamp,%H:%M:%S")
% bind(format_f{"%.3s"},"%f"))
% logging::trivial::severity
% expr::smessage;
使用
struct format_f {
std::string format_str;
template<typename... T>
std::string operator()(T const&... v) const {
return (boost::format(format_str) % ... % v).str();
}
};
同时看到这两个 Live On Wandbox
混合
尝试通过以下方式将expr::stream
与format
混合:
boost::phoenix::function<format_f> left24 = format_f{"%.24s"};
logging::formatter formatter = expr::stream
<< line_id << " | "
<< left24(expr::format_date_time(timestamp,%H:%M:%S.%f"))
<< " [ " << logging::trivial::severity
<< " ] - " << expr::smessage;
使用与上面相同的format_f
: Live On Wandbox ,打印:
3 | 2020-08-15,12:55:39.426 [ warning ] - this is a warning message
4 | 2020-08-15,12:55:39.426 [ error ] - this is an error message
5 | 2020-08-15,12:55:39.426 [ fatal ] - this is a fatal error message
或者
boost::phoenix::function<format_ex> format;
logging::formatter formatter = expr::stream
<< line_id << " | "
<< format(+"%.24s",%H:%M:%S.%f"))
<< " [ " << logging::trivial::severity
<< " ] - " << expr::smessage;
3 | 2020-08-15,12:59:35.964 [ warning ] - this is a warning message
4 | 2020-08-15,12:59:35.965 [ error ] - this is an error message
5 | 2020-08-15,12:59:35.965 [ fatal ] - this is a fatal error message
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