相关疑难解决方法(0)

[ 跟进检查boost :: log过滤器明确？ ]

以下示例使用Boost Log中的普通记录器.它输出1,显示expensive()只调用一次.它是如何工作的？为什么expensive()不叫？

Live On Coliru

#include <iostream>

#include <boost/log/expressions.hpp>
#include <boost/log/trivial.hpp>

int count = 0;

int expensive()
{
    return ++count;
}

int main()
{
    boost::log::core::get()->set_filter(
        boost::log::trivial::severity >= boost::log::trivial::warning
    );

    BOOST_LOG_TRIVIAL(error) << expensive();
    BOOST_LOG_TRIVIAL(info) << expensive();

    std::cout << count << '\n';

    return 0;
}

输出:

[2018-05-21 14:33:47.327507] [0x00007eff37aa1740] [error]   1
1