zlib - compression/decompression library


[see zlib.hfor full description]


The zliblibrary is a general purpose data compression library. The code is thread safe. It provides in-memory compression and decompression functions, including integrity checks of the uncompressed data. This version of the library supports only one compression method (deflation) but other algorithms will be added later and will have the same stream interface.

Compression can be done in a single step if the buffers are large enough (for example if an input file is mmap'ed), or can be done by repeated calls of the compression function. In the latter case, the application must provide more input and/or consume the output (providing more output space) before each call.

The library also supports reading and writing files in gzip (1) (.gz) format with an interface similar to that of stdio.

The library does not install any signal handler. The decoder checks the consistency of the compressed data, so the library should never crash even in case of corrupted input.

All functions of the compression library are documented in the file zlib.h . The distribution source includes examples of use of the library in the files example.cand minigzip.c .

Changes to this version are documented in the file ChangeLogthat accompanies the source, and are concerned primarily with bug fixes and portability enhancements.

A Java implementation of zlibis available in the Java Development Kit 1.1:


A Perl interface to zlib , written by Paul Marquess (), is available at CPAN (Comprehensive Perl Archive Network) sites, including:


A Python interface to zlib , written by A.M. Kuchling (), is available in Python 1.5 and later versions:


A zlibbinding for tcl (1), written by Andreas Kupries (), is availlable at:


An experimental package to read and write files in .zip format, written on top of zlibby Gilles Vollant (), is available at:

http://www.winimage.com/zLibDll/unzip.html and also in the contrib/minizipdirectory of the main zlibweb site.


The zlibweb site can be found at either of these locations:


The data format used by the zlib library is described by RFC (Request for Comments) 1950 to 1952 in the files:

http://www.ietf.org/rfc/rfc1950.txt (concerning zlib format)
http://www.ietf.org/rfc/rfc1951.txt (concerning deflate format)
http://www.ietf.org/rfc/rfc1952.txt (concerning gzip format)

These documents are also available in other formats from:


Mark Nelson () wrote an article about zlibfor the Jan. 1997 issue of Dr. Dobb's Journal; a copy of the article is available at:



Before reporting a problem, please check the zlibweb site to verify that you have the latest version of zlib ; otherwise, obtain the latest version and see if the problem still exists. Please read the zlibFAQ at:


before asking for help. Send questions and/or comments to , or (for the Windows DLL version) to Gilles Vollant ().


Version Copyright (C) 1995-2006 Jean-loup Gailly () and Mark Adler ().

This software is provided "as-is," without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software. See the distribution directory with respect to requirements governing redistribution. The deflate format used by zlibwas defined by Phil Katz. The deflate and zlibspecifications were written by L. Peter Deutsch. Thanks to all the people who reported problems and suggested various improvements in zlib ; who are too numerous to cite here.

UNIX manual page by R. P. C. Rodgers, U.S. National Library of Medicine ().