DataStreamPtr FileSystemArchive::open(const String& filename) const
    {
        String full_path = concatenate_path(mName, filename);

        // Use filesystem to determine size 
        // (quicker than streaming to the end and back)
        struct stat tagStat;
        int ret = stat(full_path.c_str(), &tagStat);
        assert(ret == 0 && "Problem getting file size" );

        // Always open in binary mode
        static std::vector<wchar_t>    s_wchar_buf((size_t)128);
        size_t lengthUnicode = MultiByteToWideChar(CP_ACP, 0, full_path.c_str(), full_path.size(), NULL, 0);
        if (s_wchar_buf.size() < lengthUnicode + 1)
        {
            s_wchar_buf.resize(lengthUnicode * 2);
        }
        wchar_t* szUnicode = &s_wchar_buf[0];
        MultiByteToWideChar(CP_ACP, 0, full_path.c_str(), full_path.size(), szUnicode, lengthUnicode);
        szUnicode[lengthUnicode] = 0;
        std::ifstream* origStream = new std::ifstream();
        origStream->open(szUnicode, std::ios::in | std::ios::binary);

        // Should check ensure open succeeded, in case fail for some reason.
        if (origStream->fail())
        {
            delete origStream;
            OGRE_EXCEPT(Exception::ERR_FILE_NOT_FOUND,
                "Cannot open file: " + filename,
                "FileSystemArchive::open");
        }

        /**//// Construct return stream, tell it to delete on destroy
        FileStreamDataStream* stream = new FileStreamDataStream(filename,
            origStream, tagStat.st_size, true);
        return DataStreamPtr(stream);
    }