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Quick Overview
zlib is a widely-used, free, general-purpose compression library that provides high-quality data compression and decompression functions. It is the basis for many compression utilities and file formats, including gzip, PNG, and ZIP. The library is designed to be compact, fast, and portable across various platforms.
Pros
- High performance and efficient compression/decompression
- Cross-platform compatibility and wide adoption
- Small footprint and easy integration into other projects
- Well-maintained and stable codebase with a long history
Cons
- Limited to DEFLATE algorithm, which may not be optimal for all use cases
- Not designed for streaming or parallel processing out of the box
- Documentation could be more comprehensive for advanced usage
- Lacks some modern features found in newer compression libraries
Code Examples
- Compressing data:
#include <zlib.h>
const char* data = "Hello, zlib!";
uLong sourceLen = strlen(data) + 1;
uLong destLen = compressBound(sourceLen);
Bytef* compressed = (Bytef*)malloc(destLen);
if (compress(compressed, &destLen, (const Bytef*)data, sourceLen) != Z_OK) {
// Handle error
}
- Decompressing data:
#include <zlib.h>
uLong uncompressedLen = /* known or estimated length */;
Bytef* uncompressed = (Bytef*)malloc(uncompressedLen);
if (uncompress(uncompressed, &uncompressedLen, compressed, compressedLen) != Z_OK) {
// Handle error
}
- Using zlib with streams:
#include <zlib.h>
z_stream strm;
strm.zalloc = Z_NULL;
strm.zfree = Z_NULL;
strm.opaque = Z_NULL;
deflateInit(&strm, Z_DEFAULT_COMPRESSION);
// Set input and output buffers
strm.avail_in = inputLen;
strm.next_in = input;
strm.avail_out = outputLen;
strm.next_out = output;
deflate(&strm, Z_FINISH);
deflateEnd(&strm);
Getting Started
To use zlib in your project, follow these steps:
- Download the zlib source from the official repository.
- Build the library using the provided build scripts or integrate it into your build system.
- Include the zlib header in your source files:
#include <zlib.h>
-
Link your project with the zlib library (e.g.,
-lz
on Unix-like systems). -
Use zlib functions in your code, such as
compress()
,uncompress()
, or the more advanced streaming functions likedeflateInit()
,deflate()
, anddeflateEnd()
.
Remember to check the return values of zlib functions for proper error handling.
Competitor Comparisons
miniz: Single C source file zlib-replacement library, originally from code.google.com/p/miniz
Pros of miniz
- Single-file implementation, making it easier to integrate into projects
- Designed for simplicity and ease of use
- Smaller codebase, potentially easier to understand and modify
Cons of miniz
- May not be as optimized for performance as zlib
- Less extensively tested and battle-hardened compared to zlib
- Fewer features and configuration options than zlib
Code Comparison
zlib:
int deflate(z_streamp strm, int flush);
int inflate(z_streamp strm, int flush);
miniz:
int mz_deflate(mz_streamp pStream, int flush);
int mz_inflate(mz_streamp pStream, int flush);
The function signatures are very similar, with miniz using the mz_
prefix for its functions and types. This similarity allows for relatively easy porting between the two libraries.
Both libraries provide compression and decompression functionality, but zlib offers a more extensive API with additional features and optimizations. miniz focuses on simplicity and ease of integration, making it a good choice for projects that prioritize quick implementation over maximum performance or advanced features.
While zlib is the more established and widely used option, miniz can be an attractive alternative for developers looking for a lightweight, single-file compression solution.
Extremely Fast Compression algorithm
Pros of lz4
- Significantly faster compression and decompression speeds
- Better suited for real-time applications and scenarios requiring low latency
- Simpler API, making it easier to integrate into projects
Cons of lz4
- Lower compression ratio compared to zlib
- Less widespread adoption and ecosystem support
- Fewer advanced features and customization options
Code Comparison
zlib:
z_stream strm;
deflateInit(&strm, Z_DEFAULT_COMPRESSION);
deflate(&strm, Z_FINISH);
deflateEnd(&strm);
lz4:
LZ4_stream_t lz4Stream;
LZ4_resetStream(&lz4Stream);
int compressedSize = LZ4_compress_fast_continue(&lz4Stream, src, dst, srcSize, dstCapacity, 1);
Summary
zlib and lz4 are both popular compression libraries, each with its own strengths. zlib offers better compression ratios and wider adoption, making it suitable for general-purpose compression tasks. lz4, on the other hand, excels in speed and simplicity, making it ideal for applications where performance is critical. The choice between the two depends on the specific requirements of the project, balancing compression ratio, speed, and ease of use.
Zstandard - Fast real-time compression algorithm
Pros of zstd
- Higher compression ratios, especially for larger files
- Significantly faster decompression speeds
- More flexible with adjustable compression levels
Cons of zstd
- Slightly slower compression speeds at higher levels
- Larger library size and more complex implementation
- Less widespread adoption compared to zlib's ubiquity
Code Comparison
zlib:
z_stream strm;
deflateInit(&strm, Z_DEFAULT_COMPRESSION);
deflate(&strm, Z_FINISH);
deflateEnd(&strm);
zstd:
ZSTD_CCtx* cctx = ZSTD_createCCtx();
ZSTD_compressCCtx(cctx, dst, dstCapacity, src, srcSize, compressionLevel);
ZSTD_freeCCtx(cctx);
Summary
zstd offers superior compression ratios and decompression speeds, making it ideal for scenarios where file size and quick access are crucial. However, zlib remains widely adopted and may be preferable for simpler implementations or when compatibility with older systems is necessary. The choice between the two depends on specific project requirements, with zstd excelling in performance-critical applications and zlib offering tried-and-true reliability and broad support.
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ZLIB DATA COMPRESSION LIBRARY
zlib 1.3.1.1 is a general purpose data compression library. All the code is thread safe. The data format used by the zlib library is described by RFCs (Request for Comments) 1950 to 1952 in the files http://tools.ietf.org/html/rfc1950 (zlib format), rfc1951 (deflate format) and rfc1952 (gzip format).
All functions of the compression library are documented in the file zlib.h (volunteer to write man pages welcome, contact zlib@gzip.org). A usage example of the library is given in the file test/example.c which also tests that the library is working correctly. Another example is given in the file test/minigzip.c. The compression library itself is composed of all source files in the root directory.
To compile all files and run the test program, follow the instructions given at the top of Makefile.in. In short "./configure; make test", and if that goes well, "make install" should work for most flavors of Unix. For Windows, use one of the special makefiles in win32/ or contrib/vstudio/ . For VMS, use make_vms.com.
Questions about zlib should be sent to zlib@gzip.org, or to Gilles Vollant info@winimage.com for the Windows DLL version. The zlib home page is http://zlib.net/ . Before reporting a problem, please check this site to verify that you have the latest version of zlib; otherwise get the latest version and check whether the problem still exists or not.
PLEASE read the zlib FAQ http://zlib.net/zlib_faq.html before asking for help.
Mark Nelson markn@ieee.org wrote an article about zlib for the Jan. 1997 issue of Dr. Dobb's Journal; a copy of the article is available at https://marknelson.us/posts/1997/01/01/zlib-engine.html .
The changes made in version 1.3.1.1 are documented in the file ChangeLog.
Unsupported third party contributions are provided in directory contrib/ .
zlib is available in Java using the java.util.zip package. Follow the API Documentation link at: https://docs.oracle.com/search/?q=java.util.zip .
A Perl interface to zlib and bzip2 written by Paul Marquess pmqs@cpan.org can be found at https://github.com/pmqs/IO-Compress .
A Python interface to zlib written by A.M. Kuchling amk@amk.ca is available in Python 1.5 and later versions, see http://docs.python.org/library/zlib.html .
zlib is built into tcl: http://wiki.tcl.tk/4610 .
An experimental package to read and write files in .zip format, written on top of zlib by Gilles Vollant info@winimage.com, is available in the contrib/minizip directory of zlib.
Notes for some targets:
-
For Windows DLL versions, please see win32/DLL_FAQ.txt
-
For 64-bit Irix, deflate.c must be compiled without any optimization. With -O, one libpng test fails. The test works in 32 bit mode (with the -n32 compiler flag). The compiler bug has been reported to SGI.
-
zlib doesn't work with gcc 2.6.3 on a DEC 3000/300LX under OSF/1 2.1 it works when compiled with cc.
-
On Digital Unix 4.0D (formerly OSF/1) on AlphaServer, the cc option -std1 is necessary to get gzprintf working correctly. This is done by configure.
-
zlib doesn't work on HP-UX 9.05 with some versions of /bin/cc. It works with other compilers. Use "make test" to check your compiler.
-
For PalmOs, see http://palmzlib.sourceforge.net/
Acknowledgments:
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; they are too numerous to cite here.
Copyright notice:
(C) 1995-2024 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:
- 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.
- Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
- This notice may not be removed or altered from any source distribution.
Jean-loup Gailly Mark Adler jloup@gzip.org madler@alumni.caltech.edu
If you use the zlib library in a product, we would appreciate not receiving lengthy legal documents to sign. The sources are provided for free but without warranty of any kind. The library has been entirely written by Jean-loup Gailly and Mark Adler; it does not include third-party code. We make all contributions to and distributions of this project solely in our personal capacity, and are not conveying any rights to any intellectual property of any third parties.
If you redistribute modified sources, we would appreciate that you include in the file ChangeLog history information documenting your changes. Please read the FAQ for more information on the distribution of modified source versions.
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