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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.

Description

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,

Examples

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:

Strings:

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

Buffers:

void* pBuffer; // a memory buffer
int len;       // size in bytes of the memory buffer
// writing buffer
gzip.WriteBuffer(pBuffer,len);

When done, you must close the file:

gzip.Close();

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
gzip.ReadBuffer(&pBuffer,&len);
// 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
gzip.ReadBufferSize(pBuffer,len);

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
//jloup@gzip.org          madler@alumni.caltech.edu


//The data format used by the zlib library is described by RFCs (Request for
//Comments) 1950 to 1952 in the files ftp://ds.internic.net/rfc/rfc1950.txt
//(zlib format), rfc1951.txt (deflate format) and rfc1952.txt (gzip format).

License

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

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About the Author

Jonathan de Halleux
Engineer
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 (http://research.microsoft.com/pex).

Comments and Discussions

 
GeneralRe: Conflicts with MFC program PinmemberJonathan de Halleux6-Aug-03 23:07 
GeneralArchive multiple files Pinmemberadityad12-Jun-03 9:18 
GeneralRe: Archive multiple files PinmemberJonathan de Halleux12-Jun-03 9:30 
GeneralJust great! PinmemberEugene Plokhov7-Jun-03 21:29 
GeneralRe: Just great! PinmemberJonathan de Halleux31-Jul-03 12:23 
GeneralArchiving Multiple Files PinmemberAnimesh Pandeya27-Jan-03 2:19 
GeneralTar PinmemberJonathan de Halleux27-Jan-03 2:53 
Generalbuffer to buffer treatment Pinmemberrowby14-Jan-03 7:23 
I want to be able to compress/decompress from one buffer to another. Is this possible? I have no file system to work with. further more, is it possible to unzip a certain number of bytes only?
GeneralRe: buffer to buffer treatment PinmemberJonathan de Halleux15-Jan-03 22:46 
GeneralRe: buffer to buffer treatment PinmemberJonathan de Halleux27-Jun-03 1:38 
QuestionWhere is the code? Pinmemberpeter.ward@chasseral.com13-Jan-03 1:45 
AnswerCode = gzip.h, gzip.cpp PinmemberJonathan de Halleux13-Jan-03 2:41 
GeneralRe: Code = gzip.h, gzip.cpp PinmemberEvilTed14-Aug-03 8:13 
QuestionHow can I unzip a file which tarred ? Pinmembervanta8-Jan-03 21:09 
AnswerTar files PinmemberJonathan de Halleux15-Jan-03 22:41 
GeneralRe: Tar files Pinmembervanta15-Jan-03 23:06 
GeneralRe: Tar files PinmemberJonathan de Halleux15-Jan-03 23:40 
GeneralBetter CGzipFile PinsussPaul Andreassen2-Jan-03 17:30 
GeneralRe: Better CGzipFile PinmemberPaul Selormey2-Jan-03 18:01 
QuestionSo, GZIP class can gzip,ungzip the SINGLE file ? Pinmembervanta29-Dec-02 19:55 
AnswerUntar PinmemberJonathan de Halleux15-Jan-03 22:42 
GeneralGZip and GUnzip PinmemberPaul Selormey23-Dec-02 3:21 
Generala possible solution PinmemberJonathan de Halleux23-Dec-02 3:37 
GeneralRe: a possible solution PinmemberPaul Selormey23-Dec-02 3:52 
GeneralSanta si here PinmemberJonathan de Halleux23-Dec-02 5:17 

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