I have a string (of some fixed length), which I need to compress and then compare the compressed lengths (as a proxy for redundancy in the data or as a rough approximation to the Kolmogorov complexity). Currently, I am using boost::iostreams for compression, which seems working well. However, I don't know how to obtain the size of the compressed data. Can someone help, please?
The code snippet is
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/filtering_stream.hpp>
#include <boost/iostreams/copy.hpp>
#include <boost/iostreams/filter/gzip.hpp>
#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/filesystem.hpp>
#include <string>
#include <sstream>
namespace io = boost::iostreams;
int main() {
std::string memblock;
std::cout << "Input the string to be compressed:";
std::cin >> memblock;
std::cout << memblock << std::endl;
io::filtering_ostream out;
out.push(io::gzip_compressor());
out.push(io::file_descriptor_sink("test.gz"));
out.write (memblock.c_str(), memblock.size());
std::cout << out.size() << std::endl;
return 0;
}
You can try adding boost::iostreams::counter to you chain between the compressor and sink and then calling it's characters() member to get number of bytes that went through it.
This works for me:
#include <boost/iostreams/filter/counter.hpp>
...
io::filtering_ostream out;
out.push(io::counter());
out.push(io::gzip_compressor());
out.push(io::counter());
out.push(io::file_descriptor_sink("test.gz"));
out.write (memblock.c_str(), memblock.size());
io::close(out); // Needed for flushing the data from compressor
std::cout << "Wrote " << out.component<io::counter>(0)->characters() << " bytes to compressor, "
<< "got " << out.component<io::counter>(2)->characters() << " bytes out of it." << std::endl;