Re: [Boost-users] count compressed bytes

Subject: Re: [Boost-users] count compressed bytes
From: Philipp Kraus (philipp.kraus_at_[hidden])
Date: 2010-06-11 10:13:56

On 2010-06-11 15:45:42 +0200, Roland Bock said:

> Philipp Kraus wrote:
> On 2010-06-11 13:06:46 +0200, Philipp Kraus said: 
> 
> On 2010-06-11 09:41:40 +0200, Roland Bock said: 
> 
> Kraus Philipp wrote: 
> Hi, 
> 
> I have implemented this litte code to compress a file 
> 
> bio::filtering_streambuf< bio::input > l_deflate; 
> switch (m_compress) { 
> case gzip   : l_deflate.push( bio::gzip_compressor() );     break; 
> case bzip2Â  : l_deflate.push( bio::bzip2_compressor() );Â Â Â  break; 
> } 
> 
> 
> 
> l_deflate.push( bio::file_source(p_str, BOOST_IOS::binary) ); 
> 
> 
> I need only the number of compressed bytes of l_deflate. I try to 
> 
> use l_deflate.size() but it returns only a fixed number. 
> 
> 
> How I can read the number of compressed bytes? 
> 
> 
> Thanks 
> 
> 
> Phil 
> 
> 
> The only method I know is to add a small filter which counts the Bytes. 
> 
> I have found this 
> http://www.boost.org/doc/libs/1_43_0/boost/iostreams/filter/counter.hpp 
> Can I use this class? I don't know how I can use the class (must I only 
> create a new object and push it to my l_deflate) ? 
> 
> I have add this code: 
> 
> Â Â Â Â Â Â  bio::filtering_streambuf< bio::input > l_deflate; 
> Â Â Â Â Â Â  switch (m_compress) { 
>            case gzip   : l_deflate.push( bio::gzip_compressor() );     break; 
> Â Â Â Â Â Â Â Â Â Â  case bzip2Â  : l_deflate.push( bio::bzip2_compressor() );Â Â Â  break; 
> Â Â Â Â Â Â  } 
> 
> Â Â Â Â Â Â  // create counter structures 
> Â Â Â Â Â Â  bio::counter l_counter; 
> Â Â Â Â Â Â  l_deflate.push( boost::ref(l_counter) ); 
> Â Â Â Â Â Â  l_deflate.push( bio::file_source(p_str1, BOOST_IOS::binary) ); 
> 
> but l_counter.characters() returns always zero. At next I have declared 
> a filter_ostream and copy l_deflate to the ostream in which I pushed 
> the l_counter. At this I run into a bus error. 
> For testing I've copy the l_deflate to std::cout and I can see the 
> compressed data. 
> 
> Thanks for help 
> 
> Hi,
> 
> I haven't actually used this filter myself, but here are some thoughts:
> 
>>>> 	1.	when you get the counter to work, it will probably count the 
>>>> uncompressed bytes. You should add it before the compressor, so that 
>>>> bytes travel from source to compressor to counter.

I swapped the lines

>>>> 	2.	If l_counter.characters() is always zero, I'd suspect that the 
>>>> filter is copied, when it is pushed to the stream. I haven't found 
>>>> respective information in the documentation at once, so I would suggest 
>>>> to add some debug code to the filter class, to 
>>>>>>> 	â—¦	see if the characters are actually finding their way through the filter
>>>>>>> 	â—¦	make sure that the filter is not copied
> Once you figure out what went wrong, maybe you could create a 
> documentation ticket containing the relevant information.

I tested both examples
http://www.boost.org/doc/libs/1_43_0/libs/iostreams/doc/classes/counter.html#examples
but 

in both the character-methods returns alway zero.
In the second example there is also an error:
io::filtering_ostreams out; is wrong it sould be io::filtering_ostream 
out; without "s".

At this time it is a very bad situtation. 

Thanks