ZLIB(3)                FreeBSD Library Functions Manual                ZLIB(3)

NAME

     zlib - compression/decompression library

SYNOPSIS

     [see zlib.h for full description]

DESCRIPTION

     The zlib library is a general purpose data compression library.  The code
     is thread safe, assuming that the standard library functions used are
     thread safe, such as memory allocation routines.  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 may be added later
     with the same stream interface.

     Compression can be done in a single step if the buffers are large enough
     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 the 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 test/example.c and test/minigzip.c, as well as other
     examples in the examples/ directory.

     Changes to this version are documented in the file ChangeLog that
     accompanies the source.

     zlib is built in to many languages and operating systems, including but
     not limited to Java, Python, .NET, PHP, Perl, Ruby, Swift, and Go.

     An experimental package to read and write files in the .zip format,
     written on top of zlib by Gilles Vollant (info@winimage.com), is
     available at:

            https://www.winimage.com/zLibDll/minizip.html and also in the
            contrib/minizip directory of the main zlib source distribution.

SEE ALSO

     The zlib web site can be found at:

            https://zlib.net/

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

            https://datatracker.ietf.org/doc/html/rfc1950 (for the zlib header
            and trailer format)
            https://datatracker.ietf.org/doc/html/rfc1951 (for the deflate
            compressed data format)
            https://datatracker.ietf.org/doc/html/rfc1952 (for the gzip header
            and trailer format)

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

            https://zlib.net/nelson/

REPORTING PROBLEMS

     Before reporting a problem, please check the zlib web 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 zlib FAQ at:

            https://zlib.net/zlib_faq.html

     before asking for help.  Send questions and/or comments to zlib@gzip.org,
     or (for the Windows DLL version) to Gilles Vollant (info@winimage.com).

AUTHORS AND LICENSE

     Version 1.3.2

     Copyright (C) 1995-2026 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.

     Permission is granted to anyone to use this software for any purpose,
     including commercial applications, and to alter it and redistribute it
     freely, subject to the following restrictions:

     1. The origin of this software must not be misrepresented; you must not
        claim that you wrote the original software. If you use this software
        in a product, an acknowledgment in the product documentation would be
        appreciated but is not required.

     2. Altered source versions must be plainly marked as such, and must not
        be misrepresented as being the original software.

     3. This notice may not be removed or altered from any source
        distribution.

     Jean-loup Gailly        Mark Adler
     jloup@gzip.org          madler@alumni.caltech.edu

     The deflate format used by zlib was defined by Phil Katz.  The deflate
     and zlib specifications 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
     (rodgers@nlm.nih.gov).

                                  17 Feb 2026                          ZLIB(3)