Deflate and inflate for PDF, using zlib C++ - c++

Question

I am trying to implement the "zlib.h" deflate and inflate functions to compress and decompress streams in PDF-file.
Input: compressed stream from PDF-file. I implemented inflate function -- it's all right, I have uncopressed stream, after that I try to compress this stream again with deflate function, as output I have compressed stream, but it is not equal to input compressed stream and they are not equal to the length. What I'm doing wrong? This is a part of my code:
size_t outsize = (streamend - streamstart) * 10;
char* output = new char[outsize]; ZeroMemory(output, outsize);
z_stream zstrm; ZeroMemory(&zstrm, sizeof(zstrm));
zstrm.avail_in = streamend - streamstart + 1;
zstrm.avail_out = outsize;
zstrm.next_in = (Bytef*)(buffer + streamstart);//block of date to infalte
zstrm.next_out = (Bytef*)output;
int rsti = inflateInit(&zstrm);
if (rsti == Z_OK)
{
int rst2 = inflate(&zstrm, Z_FINISH);
if (rst2 >= 0)
{
cout << output << endl;//inflated data
}
}
char* deflate_output = new char[streamend - streamstart];
ZeroMemory(deflate_output, streamend - streamstart);
z_stream d_zstrm; ZeroMemory(&d_zstrm, sizeof(d_zstrm));
d_zstrm.avail_in = (uInt) (strlen(output)+1);
d_zstrm.avail_out = (uInt) (streamend - streamstart);
d_zstrm.next_in = (Bytef*)(output);
d_zstrm.next_out = (Bytef*)(deflate_output);
int rsti1 = deflateInit(&d_zstrm, Z_DEFAULT_COMPRESSION);
if (rsti1 == Z_OK)
{
int rst22 = deflate(&d_zstrm, Z_FINISH);
out << deflate_output << endl << "**********************" << endl;
//I try to write deflated stream to file
printf("New size of stream: %lu\n", (char*)d_zstrm.next_out - deflate_output);
}

Answer 1

There is nothing wrong. There is not a unique compressed stream for a given uncompressed stream. All that is required is that the decompression give you back exactly what was compressed (hence "lossless").
It may simply be caused by different compression parameters, different compression code, or even a different version of the same compression code.
If you can't reproduce the original compressed data, so what? All that matters is that you can make a valid PDF file that can be decompressed and has the content that you want.