The archives have typically some file management involved. That is not part of zlib.
Some useful information you may find here [qt-project.org]

How to compress data with Qt?

Qt uses the zlib library to provide compression. This means that you can compress and decompress your bytearrays of data using Qt. See the documentation on qUncompress() [qt.nokia.com]

Note that this does not produce file archives that can be opened by other applications, to do that you will need to write it yourself using Qt’s custom file handling system [qt.nokia.com] or use a 3rd party library.

i didn’t want to use something that is not in the default library.. but it seems i will.. i will try to use Quazip.. if i find any difficulties i will post in this thread.. :)

zlib != zip

zip usually does contain meta information about files stored which is not handled at all by qUncompress, which just takes a chunk of memory and returns another chunk that is compressed.

Go with Quazip.