How do you Deflate data and put it into a vector? - c++

Question

With zstr, a header-only C++ zlib wrapper library, I’m trying to Deflate a std::string and put it into a std::vector<unsigned char>.
zstr::ostream deflating_stream(std::cout);
deflating_stream.write(content.data(), content.size());
The above code works: it prints the Deflate’d. The problem is, I’m not familiar with C++ streams and I cannot get it into a std::vector. Tried several times in vain with std::ostringstream, std::ostream, std::istringstream, std::istreambuf_iterator, std::streambuf, .rdbuf(), et cetera, and the only thing that came out was an emptiness output (.tellp() == 0).
How do I Deflate a std::string and put it into a std::vector<unsigned char>?
The following is some of my tries. I have no idea how to access the Deflate’d data.
std::istringstream is;
std::ostream ss(is.rdbuf());
zstr::ostream deflating_stream(ss);
deflating_stream.write(
uncompressed_string.data(),
uncompressed_string.size()
);
the_vector.insert(
the_vector.cend(),
std::istreambuf_iterator<char>(is),
std::istreambuf_iterator<char>()
);
std::ostringstream oss;
zstr::ostream deflating_stream(oss);
deflating_stream.write(
uncompressed_string.data(),
uncompressed_string.size()
);
const std::string deflated = oss.str();
the_vector.insert(
the_vector.cend(),
deflated.cbegin(),
deflated.cend()
);
std::stringstream ss;
zstr::ostream deflating_stream(ss);
deflating_stream.write(
uncompressed_string.data(),
uncompressed_string.size()
);
std::string deflated = ss.str();
std::cout << deflated.size(); // Says 0.

Answer 1

Something like this works:
#include <iostream>
#include <sstream>
#include <vector>
#include <string>
#include <algorithm>
#include "zstr.hpp"
int main() {
std::string text{"some text\n"};
std::stringbuf buffer;
zstr::ostream compressor{&buffer};
// Must flush to get complete gzip data in buffer
compressor << text << std::flush;
// It's probably easier to use just the string...
auto compstr = buffer.str();
std::vector<unsigned char> deflated;
deflated.resize(compstr.size());
std::copy(compstr.begin(), compstr.end(), deflated.begin());
std::cout.write(reinterpret_cast<char *>(deflated.data()), deflated.size());
return 0;
}
After compiling:
$ ./a.out | zcat
some text