[Boost-users] [iostreams] Flushing problems with :filtering_ostream

Subject: [Boost-users] [iostreams] Flushing problems with :filtering_ostream
From: Bo Jensen (jensen.bo_at_[hidden])
Date: 2011-04-18 11:31:22

I had some older code which used to work before, but seem to have
flushing problems now.

The problem is I can not make boost::iostreams::filtering_ostream
flush properly. Here is a snippet of my code, which is not compilable
in the current form, since I just pulled it out of my own code. Here
it goes :

/* Helper class for writing gzipped files */
  class gzip_sink
  {
    public:
      typedef char                           char_type;
      typedef boost::iostreams::sink_tag     category;

      Log                                    &Logger_;   /* Logger */
      boost::iostreams::filtering_ostream    sink_;      /* Sink used
to push filters */
      SlmOfstream                            outifstr_;  /* Write
stream to be pushed into sink */
      std::wstring                           name_;      /* Store name
of attached file */

      /* Constructor */
      gzip_sink(const wchar_t *filename,Log &logger)
        SlmExcStartConstructor :
        Logger_(logger),
        name_(filename)
      {
        /* Open for write */
        SlmOpenWriteFile(Logger_,
                         name_.c_str(),
                         outifstr_);

        /* Push gzip compressor */
        sink_.push(boost::iostreams::gzip_compressor());
      }
      SlmExcStopConstructor

      gzip_sink(const gzip_sink &rhs)
        SlmExcStartConstructor :
        Logger_(rhs.Logger_),
        name_(rhs.name_)
      {
        /* Open for write */
        SlmOpenWriteFile(Logger_,
                         name_.c_str(),
                         outifstr_);

        /* Push gzip compressor */
        sink_.push(boost::iostreams::gzip_compressor());
      }
      SlmExcStopConstructor

      void Close()
      {
        sink_.reset();
      }

      ~gzip_sink()
      {
        sink_.reset();
      }

      /* Write function */
      std::streamsize write( const char * s, std::streamsize n )
      {
        /* Push write stream */

        /* THIS IS THE HACK !!! WE NEED TO PUSH AND POP EACH TIME
OTHERWISE SOME FLUSH IS NOT DONE!! */
        sink_.push(outifstr_);

        sink_.write(s,n);

        sink_.pop();

        return n;
      }
  };

I have to push and pop the stream on to the sink each time I write,
which should only be done once in the constructor. It is clearly some
flushing issue, but I have tried flushing in all places and no luck,
any help ?

If you think it looks a bit odd, it's because I use it together with
boost::iostreams::code_converter<gzip_sink> to be able to use gzip
with wide streams.