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

       zlib - compression/decompression library

       [see zlib.h for full 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 available in Java using the package:


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


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


       zlib is built into tcl:


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

     and also in the
              contrib/minizip directory of the main zlib source distribution.

       The zlib web site can be found at:


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

     (for the zlib header and
              trailer format)
     (for the deflate compressed
              data format)
     (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:


       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


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

       Version 1.2.7 Copyright (C) 1995-2012 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 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

                                  2 May 2012                           ZLIB(3)


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