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Bug when using the classes to write zip files

, 8 May 2004 CPOL
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Describes an issue when writing a binary file into a zip file using the classes


I was writing a little .NET app in C# and was looking for a small library that would let me read and write zip files. That's when my first Google search gave me a link to Using the Zip Classes in the J# Class Libraries to Compress Files and Data with C#. Great! - that was my first reaction, but it didn't last too long. You can read zip files alright, but when you write zip files, if you have binary files (as you most often will), the generated zip file will be corrupt and you can't read it back. Funnily, WinZip does open it (ignoring the header errors) and the suggested solution by a Microsoftie in the one of the MS NGs was to extract all files using WinZip and then to zip it back. LOL. Why'd anyone want to use the zipping libraries at all if they had the option of bringing WinZip into the picture?

There is not even a KB article on this bug - bad! I lost about half a day when I was using these classes because I initially thought it was something wrong in my code. Anyway, this is a warning to everyone. Do not use the J# class libraries for zipping/unzipping if you are using the BCL 1.1 version. Heath Stewart (C# MVP and CodeProject Editor) has informed me that the BCL 2.0 includes zipping functionality - so that's really good news. And until that comes out, a very good free alternative to the J# classes is SharpZipLib which I very strongly recommend.

Bug demo

  1. Create a new C# console app project
  2. Add a reference to vjslib (...Microsoft.NET\Framework\v1.1.4322\vjslib.dll)
  3. Copy/paste the following code into your main cs file :-
    using System;
    using System.IO;
    class MainClass
      static void Main(string[] args)
      static void BugDemo()
        //Write zip file
        ZipOutputStream os = new ZipOutputStream(
        ZipEntry ze = new ZipEntry("gluk.gif");
        os.putNextEntry(ze); fs = 
        sbyte[] buff = new sbyte[1024];
        int n = 0;
        while ((,0,buff.Length))>0)
        Console.WriteLine("Okay, the zip has been written.");
        //Read zip file
          //Bug will occur here
          ZipFile zf = new ZipFile("");  
          Console.WriteLine("Bug confirmed!");
  4. Now make sure you have a gluk.gif in the same folder as the executable.

  5. Compile and run.


There is no real workaround to the problem. You can use the alternative library I mentioned above or wait for Whidbey.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Nish Nishant
United States United States
Nish Nishant is a Software Architect/Consultant based out of Columbus, Ohio. He has over 16 years of software industry experience in various roles including Lead Software Architect, Principal Software Engineer, and Product Manager. Nish is a recipient of the annual Microsoft Visual C++ MVP Award since 2002 (14 consecutive awards as of 2015).

Nish is an industry acknowledged expert in the Microsoft technology stack. He authored
C++/CLI in Action for Manning Publications in 2005, and had previously co-authored
Extending MFC Applications with the .NET Framework for Addison Wesley in 2003. In addition, he has over 140 published technology articles on and another 250+ blog articles on his
WordPress blog. Nish is vastly experienced in team management, mentoring teams, and directing all stages of software development.

Contact Nish : You can reach Nish on his google email id voidnish.

Website and Blog

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GeneralAlternative (with code) Pin
Elmue17-Nov-05 2:30
memberElmue17-Nov-05 2:30 

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