boost zlib problem

Question

I'm having a problem with the zlib libraries in boost under VS 2010. I built the libraries and the appropriate dlls/libs were generated in the boost/stage/lib folder. I added the .dlls into my programs debug folder and linked in the matching.lib.

But I'm running into problems when I actually try to use the zlib streams. Heres an example:

#include <cstring>
#include <string>
#include <iostream>
#include <boost\iostreams\filter\gzip.hpp>
#include <boost\iostreams\filtering_streambuf.hpp>
#include <boost\iostreams\copy.hpp>
std::string DecompressString(const std::string &compressedString)
{
    boost::iostreams::filtering_streambuf<boost::iostreams::input> in;
    in.push(boost::iostreams::zlib_decompressor());
    in.push(compressedString);
    std::string retString = "";

    copy(in, retString);
    return retString;
}



when I try to compile thise though, I get multiple errors including:
error C2039: 'char_type' : is not a member of 'std::basic_string<_Elem,_Traits,_Ax>'    c:\program files (x86)\boost\boost_1_46_0\boost\iostreams\traits.hpp
error C2208: 'boost::type' : no members defined using this type c:\program files (x86)\boost\boost_1_46_0\boost\iostreams\traits.hpp
error C4430: missing type specifier - int assumed. Note: C++ does not support default-int   c:\program files (x86)\boost\boost_1_46_0\boost\iostreams\traits.hpp

If I change my code to the following:

std::string DecompressString(const std::string &compressedString)
{

    boost::iostreams::filtering_streambuf<boost::iostreams::input> in;
    in.push(boost::iostreams::zlib_decompressor());
    std::string retString = "";
    return retString;

}

It compiles, meaning the problem is with the in.push for compressedString and the copy to the retString. Am I doing something wrong? Am I not allowed to use strings like this?

Thanks in advance

Answer 1

Try this:

#include <string>
#include <iostream>
#include <sstream>
#include <boost\iostreams\filter\zlib.hpp>
#include <boost\iostreams\filtering_streambuf.hpp>
#include <boost\iostreams\copy.hpp>

std::string DecompressString(const std::string &compressedString)
{
    std::stringstream src(compressedString);
    boost::iostreams::filtering_streambuf<boost::iostreams::input> in(src);
    std::stringstream dst;
    boost::iostreams::filtering_streambuf<boost::iostreams::output> out(dst);
    in.push(boost::iostreams::zlib_decompressor());

    boost::iostreams::copy(in, out);
    return dst.str();
}

The basic problem seems to be that you're trying to use boost::iostreams::copy() on string types rather than stream types. Also, including zlib.hpp instead of gzip.hpp probably doesn't hurt either.