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Posted 17 Nov 2002

CGZip, a C++ wrapper for gzip methods

, 9 Dec 2002
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A minimal class for handling gzip methods included in the zlib library.


This documents present CGZip, C++ class wrapper for the gzip methods, which are included in the zlib library. The intention of this class is to have a simple class for zipping-unzipping buffers.

The main features of the class are:

  • Compress, decompress LPCTSTR to file
  • Compress, decompress memory buffer to file
  • Non-MFC
  • Hides zlib so you don't have to distribute the zlib headers
  • UNICODE compliant,


In the examples, we shall consider the following code snippet to be present on top:

// CGZip is in the zlib namespace
using namespace zlib;
CGZip gzip;

Zipping a memory buffer or a string

First of all, let's open a file for writing:

if(!gzip.Open(_T("myFile.gz"), CGZip::ArchiveModeWrite)))
        // the file could not be opened...

As you can see, Open returns true if success and false otherwise. All the methods (almost) have this behavior.

Now we can send data and strings to the file:


LPCTSTR szString = _T("This is a test string\n");
// writing string


void* pBuffer; // a memory buffer
int len;       // size in bytes of the memory buffer
// writing buffer

When done, you must close the file:


Note that if gzip goes out of scope, it is automatically closed.

Unzipping a buffer or a string

The reading behaves pretty much like the writing. First of all, open a file for reading:

if(!gzip.Open(_T("myFile.gz"), CGZip::ArchiveModeRead)))
        // the file could not be opened...

Now, you can read a buffer with fixed length or the whole file:

The whole file:

void* pBuffer=NULL;
int len=0;
// reads and unzip the hole file, len contains the resulting size of pBuffer
// pBuffer now contains len read bytes
// don't forget to delete pBuffer
if (pBuffer)
   delete[] pBuffer;

A fixed length buffer:

  int len;
char* pBuffer[len];
// reads and unzip the hole file, len contains the resulting size of pBuffer

Class reference

A detailed class reference is available as compressed HTML (generated by Doxygen).

GZip license

This piece of code is totally, utterly free for commercial and non-commercial use. However, it uses zlib so you should check the zlib license before using it. It is included in the source code but here it is:

//zlib.h -- interface of the 'zlib' general purpose compression library
//version 1.1.4, March 11th, 2002

//Copyright (C) 1995-2002 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

//The data format used by the zlib library is described by RFCs (Request for
//Comments) 1950 to 1952 in the files
//(zlib format), rfc1951.txt (deflate format) and rfc1952.txt (gzip format).


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Jonathan de Halleux
United States United States
Jonathan de Halleux is Civil Engineer in Applied Mathematics. He finished his PhD in 2004 in the rainy country of Belgium. After 2 years in the Common Language Runtime (i.e. .net), he is now working at Microsoft Research on Pex (

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Comments and Discussions

QuestionHow can I unzip a file which tarred ? Pin
vanta8-Jan-03 22:09
membervanta8-Jan-03 22:09 
AnswerTar files Pin
Jonathan de Halleux15-Jan-03 23:41
memberJonathan de Halleux15-Jan-03 23:41 
GeneralRe: Tar files Pin
vanta16-Jan-03 0:06
membervanta16-Jan-03 0:06 
GeneralRe: Tar files Pin
Jonathan de Halleux16-Jan-03 0:40
memberJonathan de Halleux16-Jan-03 0:40 
GeneralBetter CGzipFile Pin
Paul Andreassen2-Jan-03 18:30
sussPaul Andreassen2-Jan-03 18:30 
GeneralRe: Better CGzipFile Pin
Paul Selormey2-Jan-03 19:01
memberPaul Selormey2-Jan-03 19:01 
QuestionSo, GZIP class can gzip,ungzip the SINGLE file ? Pin
vanta29-Dec-02 20:55
membervanta29-Dec-02 20:55 
AnswerUntar Pin
Jonathan de Halleux15-Jan-03 23:42
memberJonathan de Halleux15-Jan-03 23:42 
Untarring a file is another problem (untar is part of GNU)

Sorry, I do not have the time to look at it...

Jonathan de Halleux.

GeneralGZip and GUnzip Pin
Paul Selormey23-Dec-02 4:21
memberPaul Selormey23-Dec-02 4:21 
Generala possible solution Pin
Jonathan de Halleux23-Dec-02 4:37
memberJonathan de Halleux23-Dec-02 4:37 
GeneralRe: a possible solution Pin
Paul Selormey23-Dec-02 4:52
memberPaul Selormey23-Dec-02 4:52 
GeneralSanta si here Pin
Jonathan de Halleux23-Dec-02 6:17
memberJonathan de Halleux23-Dec-02 6:17 
GeneralRe: Santa si here Pin
Paul Selormey23-Dec-02 14:14
memberPaul Selormey23-Dec-02 14:14 
GeneralMore details Pin
Jonathan de Halleux24-Dec-02 3:20
memberJonathan de Halleux24-Dec-02 3:20 
GeneralRe: More details Pin
Paul Selormey24-Dec-02 14:46
memberPaul Selormey24-Dec-02 14:46 
GeneralStop party , start reading Pin
Jonathan de Halleux30-Dec-02 0:57
memberJonathan de Halleux30-Dec-02 0:57 
GeneralIStream Pin
Jonathan de Halleux2-Jan-03 2:14
memberJonathan de Halleux2-Jan-03 2:14 
GeneralRe: IStream Pin
Paul Selormey2-Jan-03 18:48
memberPaul Selormey2-Jan-03 18:48 
GeneralAllelulia Pin
Jonathan de Halleux3-Feb-03 1:27
memberJonathan de Halleux3-Feb-03 1:27 
GeneralRe: Allelulia Pin
Paul Selormey3-Feb-03 1:47
memberPaul Selormey3-Feb-03 1:47 
GeneralCan't compile demo in release mode Pin
Thomas Haase6-Dec-02 1:40
memberThomas Haase6-Dec-02 1:40 
GeneralFix in update... Pin
Jonathan de Halleux6-Dec-02 2:32
memberJonathan de Halleux6-Dec-02 2:32 
GeneralSorry Pin
George O.3-Dec-02 4:40
sussGeorge O.3-Dec-02 4:40 
Generalyes and on Pin
Jonathan de Halleux6-Dec-02 2:32
memberJonathan de Halleux6-Dec-02 2:32 
GeneralGood work Pin
Nishant S24-Nov-02 16:16
editorNishant S24-Nov-02 16:16 

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