c++ - 通过 boost::iostreams 压缩字符串的长度

Question

我有一个字符串(固定长度)，我需要对其进行压缩，然后比较压缩后的长度(作为数据冗余的代理或作为 Kolmogorov 复杂度的粗略近似值)。目前，我正在使用 boost::iostreams 进行压缩，这似乎运行良好。但是，我不知道如何获取压缩数据的大小。有人可以帮忙吗？

代码片段是

#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;

}

Answer 1

您可以尝试将 boost::iostreams::counter 添加到压缩器和接收器之间的链中，然后调用它的 characters() 成员来获取字节数经历过。

这对我有用:

#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;