c++ - boost 日志 : Why it is showing duplicate the message?

Question

我正在学习 Boost.Log 库。我想将消息发送到文件和 std::clog。我有以下类(class):

class logger
{
    public:
        explicit logger(
            const std::string& tag,
            const std::string& file,
            bool console
        )
        {
            boost::log::register_simple_formatter_factory< boost::log::trivial::severity_level, char >("Severity");

            std::string the_format = "[%TimeStamp%] (%LineID%) [%Severity%]";
            if(!tag.empty()) {
                m_log_.add_attribute(
                    "Tag",
                    boost::log::attributes::constant< std::string >( tag )
                );
                the_format += " [%Tag%]";
            }

            the_format += ": %Message%";

            if(console) {
                boost::log::add_console_log(
                    std::clog,
                    boost::log::keywords::auto_flush = true,
                    boost::log::keywords::format = the_format
                );
            }

            if(!file.empty()) {
                boost::log::add_file_log(
                    boost::log::keywords::file_name = file,
                    boost::log::keywords::auto_flush = true,
                    boost::log::keywords::open_mode = (std::ios::out | std::ios::app),
                    boost::log::keywords::format = the_format
                );
            }

        }

        ~logger(void)
        { }

        void log(
            const std::string& msg
        )
        {
            BOOST_LOG_SEV ( m_log_, boost::log::trivial::info ) << msg;
        }

    private:
        boost::log::sources::severity_logger< boost::log::trivial::severity_level > m_log_;

}; // logger

我有以下 main() 函数:

void x()
{
    logger lg("omega", "", true);
    lg.log( "Goodbye" );
}

int main(int argc, char** argv)
{
    logger lg( "alfa", "", true );
    lg.log( "Hello world!!!");
    x();
    return 0;
}

我不明白为什么会显示重复的消息:“Hello world!!!”:

[2016-Aug-23 17:51:36.852912] (1) [info] [alfa]: Hello world!!!
[2016-Aug-23 17:51:36.853359] (2) [info] [omega]: Goodbye
[2016-Aug-23 17:51:36.853359] (2) [info] [omega]: Goodbye

更新:抱歉，示例不完整。

Answer 1

logger 的构造函数正在调用 add_console_log() 和 add_file_log()。如果你两次构造logger，这些函数也会被调用两次。由于它们添加了全局接收器，因此每个日志条目都将在控制台和您的文件中复制两次。

int main(int argc, char** argv)
{
    logger lg1("1", "", true);
    logger lg2("2", "", true);
    logger lg3("3", "", true);
    logger lg4("4", "", true);

    lg1.log("test");
}

这将输出:

[2016-Aug-23 13:25:56.468382] (1) [info] [1]: test
[2016-Aug-23 13:25:56.468382] (1) [info] [1]: test
[2016-Aug-23 13:25:56.468382] (1) [info] [1]: test
[2016-Aug-23 13:25:56.468382] (1) [info] [1]: test

您可能需要某种引用计数或标志来仅调用这些函数一次。