Re: [boost] [iostreams] array and gzip_decompressor

Subject: Re: [boost] [iostreams] array and gzip_decompressor
From: Chris Hamilton (chamilton_at_[hidden])
Date: 2010-03-01 07:43:54

> On 2/23/2010 10:48 PM, Nikolay Mladenov wrote:
>>
>> Is there another way I should be creating gzipped stream into memory?
>> Or maybe the arrays could be made peekable?
>>
> 
> Perhaps you could read it into a stringstream.
> 
> namespace io = boost::iostreams;
> 
> io::filtering_istream in;
> in.push(io::gzip_decompressor());
> in.push(io::file_source(fileName.c_str(), std::ios_base::in |
> std::ios_base::binary));
> std::stringstream    memStream;
> memStream << in.rdbuf();

If you don't know before-hand how big the output can be, you can write
into a std::vector relatively easily.  The following creates an
ovectorstream object:

template<typename Ch>
struct basic_vector_sink
{
  typedef Ch char_type;
  typedef bio::sink_tag category;

  typedef std::vector<char_type> vector_type;

  basic_vector_sink( vector_type& vector ):
    _vector(vector)
  {
  }

  std::streamsize write( const char_type *buf, std::streamsize n )
  {
    if ( n <= 0 ) return n;
    size_t s = _vector.size();
    _vector.resize( s + n );
    memcpy( (void*)((&_vector[0])+s), (const void*)buf,
n*sizeof(char_type) );
    return n;
  }

  vector_type& _vector;
};
typedef basic_vector_sink<char> vector_sink;
typedef bio::stream<vector_sink> ovectorstream;

In my mind, something like arraystream (but for vectors) would be useful
in boost::iostreams.  The above is a pale imitation of the full
functionality offered by an arraystream (bidirectional, seekable, etc),
but it does the job for me.

Cheers,

Chris