如何查询boost::log严重性？
如何查询boost::log严重性？
提问于 2016-12-14 21:44:20
我正在使用boost::log库的简单日志记录，并且我想根据当前设置的记录器严重性来执行一些代码。仅当日志消息将被输出时，才需要它来构造日志消息。但是我找不到正确的方法来查询严重性。代码必须类似于：
if (boost::log::trivial::severity <=
boost::log::trivial::severity_level::trace)
{
// construct log message
BOOST_LOG_TRIVIAL(trace) << message;
}此外，可能有一些方法，当我知道消息将被输出，以避免双重检查严重度，并直接输出它，而不是使用BOOST_LOG_TRIVIAL宏？
回答 2
Stack Overflow用户
回答已采纳
发布于 2016-12-14 21:55:36
它不是那样工作的。您需要提供一个筛选器函数来boost::log::trivial，如下文档所示：
http://www.boost.org/doc/libs/1_61_0/libs/log/doc/html/log/tutorial/trivial_filtering.html
void init()
{
logging::core::get()->set_filter
(
// here they've used a constant but you could use a global or
// a function
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;
}传递给logging::core::set_filter的对象的类型为boost::log::filter
你可以很容易地写出：
auto filt = logging::filter(logging::trivial::severity >= logging::trivial::info);
logging::core::get()->set_filter(filt);filt是一个轻量级函数对象，它的任务是检查发送给它的属性，并返回是否所有针对这些属性的测试都返回true。在本例中，只有一个测试- logging::trivial::severity >= logging::trivial::info。
日志记录器的工作是构造属性集，并在boost::log::core想要发出某些内容时将其传递给它。
总而言之，您必须在自己的变量中跟踪日志记录级别。这里有一种方法：
#include <iostream>
#include <boost/log/core.hpp>
#include <boost/log/trivial.hpp>
#include <boost/log/expressions.hpp>
namespace logging = boost::log;
int main(int, char*[])
{
// track your own variable here
logging::trivial::severity_level my_log_level = logging::trivial::trace;
// with this filter
auto filt = logging::filter(logging::trivial::severity >= my_log_level);
logging::core::get()->set_filter(filt);
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";
// now you have control
if (my_log_level <= logging::trivial::trace)
{
std::cout << "tracing\n";
}
return 0;
}Stack Overflow用户
发布于 2018-09-05 08:15:23
这里有一个选项，它添加了另一层日志记录宏，并包装了要在提供给这些宏的lambda函数中有条件调用的代码。只有当满足严重级别约束时，才会计算lambda函数。
据我所知，这个方法是线程安全的，但我对boost::log is...limited的理解是。我还没有在多线程环境中测试过。
//g++ -std=gnu++11 -DBOOST_LOG_DYN_LINK main.cpp -lboost_log -lpthread -o lambda_demo
#include <boost/log/core.hpp>
#include <boost/log/trivial.hpp>
#include <boost/log/expressions.hpp>
namespace logging = boost::log;
#define LOG_TRACE(ARG) BOOST_LOG_TRIVIAL(trace) << ARG;
#define LOG_INFO(ARG) BOOST_LOG_TRIVIAL(info) << ARG;
const std::string complicated_function(const std::string &message)
{
std::cout << "\nInside complicated_function.\n" << std::flush;
return "Returning from complicated_function (" + message + ").\n";
}
int main(int, char*[])
{
std::cout << "\n" << complicated_function("called from std::cout") << "\n" << std::flush;
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\n";
LOG_TRACE ("Coming up: a trace message with a lambda function:");
LOG_TRACE (
[=]() {
return complicated_function("(called from LOG_TRACE");
}()
);
logging::core::get()->set_filter
(
logging::trivial::severity >= logging::trivial::info
);
BOOST_LOG_TRIVIAL(trace) << "After setting filter, another trace severity message";
BOOST_LOG_TRIVIAL(debug) << "After setting filter, another debug severity message";
BOOST_LOG_TRIVIAL(info) << "After setting filter, another informational severity message";
BOOST_LOG_TRIVIAL(warning) << "After setting filter, another warning severity message";
BOOST_LOG_TRIVIAL(error) << "After setting filter, anothern error severity message";
BOOST_LOG_TRIVIAL(fatal) << "After setting filter, another fatal severity message\n";
LOG_TRACE ("Coming up: a trace message with a lambda function:");
LOG_TRACE (
[=]() {
return complicated_function("called from LOG_TRACE");
}()
);
LOG_INFO ("Coming up: an info message with a lambda function:");
LOG_INFO (
[=]() {
return complicated_function("called from LOG_INFO");
}()
);
return 0;
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/41144163
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