如何在Boost :: Log中使用压缩器Boost :: Iostreams过滤器作为接收器

Question

我正在尝试通过利用来即时压缩使用Boost Log库创建的日志文件boost::iostreams::gzip_compressor.因此,当我打电话时BOOST_LOG(),输出会即时压缩.这是我到目前为止所尝试的:

#include <fstream>
#include <iostream>

#include <boost/iostreams/filtering_stream.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/filter/gzip.hpp>

#include <boost/smart_ptr/shared_ptr.hpp>
#include <boost/smart_ptr/make_shared_object.hpp>

#include <boost/log/core.hpp>
#include <boost/log/trivial.hpp>
#include <boost/log/sinks/sync_frontend.hpp>
#include <boost/log/sinks/text_ostream_backend.hpp>
#include <boost/log/sources/logger.hpp>

void init()
{
    // Construct the sink
    typedef boost::log::sinks::synchronous_sink< boost::log::sinks::text_ostream_backend > text_sink;
    boost::shared_ptr< text_sink > sink = boost::make_shared< text_sink >();

    boost::shared_ptr< std::ofstream > file = boost::make_shared< std::ofstream >( 
            "sample.gz", std::ios_base::out | std::ios_base::binary );
    boost::iostreams::filtering_ostream out;
    out.push( boost::iostreams::gzip_compressor() );
    out.push( *(file.get()) );

    for( int i = 0; i < 10; i++ ) {
        out << "Hello world! " << i << std::endl; // compresses OK
    }

    sink->locked_backend()->add_stream( file );

    // Register the sink in the logging core
    boost::log::core::get()->add_sink( sink );
}

int main( )
{
    init();

    boost::log::sources::logger lg;
    for( int i = 0; i < 10; i++ ) 
        BOOST_LOG(lg) << "Bye world!" << std::endl; // Does not compress

    return 0;
}

我觉得我应该以某种方式1)将整个filtering_ostream作为接收器,而不仅仅是file或

2)以某种方式推动记录器接收器而不是file在filtering_ostream.

有人能指出我正确的方向吗？谢谢!

Answer 1

我想你想传递filtering_ostream你的记录器流.你需要做两件事:

1. 制作一个shared_ptr包含你的filtering_ostream,和
2. 确保延长输出文件流的生命周期,直到关闭过滤流.

您可以使用自定义shared_ptr删除器来完成此操作.删除器是传递给shared_ptr构造函数的可选函数对象,将被调用以释放指针.您可以在删除器中存储一个shared_ptrto file,以确保文件存在,只要该流存在.在C++ 11中,你可以使用这样的lambda:

boost::shared_ptr<boost::iostreams::filtering_ostream> out(
   new boost::iostreams::filtering_ostream,
   [file](std::ostream *os) { delete os; });

out->push(boost::iostreams::gzip_compressor());
out->push(*file);

sink->locked_backend()->add_stream(out);

[file]lambda 的一部分保持一直shared_ptr到ofstream调用删除器.

如果你没有C++ 11编译器,你可以用普通的仿函数做同样的事情,比如(未编译和未经测试):

struct MyDeleter {
   boost::shared_ptr<std::ofstream> file_;

   MyDeleter(const boost::shared_ptr<std::ofstream>& file)
      : file_(file) {
   }

   void operator()(std::ostream *os) {
      delete os;
   }
};

...

boost::shared_ptr<boost::iostreams::filtering_ostream> out(
   new boost::iostreams::filtering_ostream,
   MyDeleter(file));