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How to repair zip files?

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techidave:
+1 to Shades and Ath's response.  i was getting this same error while using the Win 7 built in utility.  :(  Then on a suggestion from a friend I tried 7-zip and it was able to uncompress it without any problems at all.   :)

I believe they used a newer utillty to compress it the win 7 tool just couldn't handle it.

Renegade:
As above...

Most good ZIP utilities will either make this invisible to you or prompt you to repair an archive. If they don't work, you're hosed.

Most ZIP programs include a lot of error finding code to fix common problems and some not-so-common problems. However, as noted above, ZIP files do not contain recovery information, so if a utility can't recover it, the data is lost (without massive effort that probably isn't worth it).

IainB:
Interesting. I would usually remove WinZip from the XP and let the standard system ZIP functionality in Windows Explorer do the work - mainly because Search/Index could read files in Windows-created ZIP archives, but not necessarily in ZIP archives created by proprietary ZIP archiving tools.
I never had a "corrupt" ZIP file, and I do not see how such corruption could occur, or even that it should (other things being equal and no system problems). However, I did find that sometimes ZIP archives created by proprietary ZIP archiving tools could not be read by Windows Explorer, but could be opened by (say) 7-ZIP without any difficulty.

Similarly, using Win7, I have never had any difficulty with the standard system ZIP functionality.

There was a post made earlier - a couple of days ago - in this thread that I think might have been deleted as spam, or something, but actually it seemed helpful and pointed to some good references, so I have copied it below. Malwarebytes didn't ring any alarms when I followed the link given. The notes seem genuine enough.
[email protected]
Dear friend,
Corrupted zip files can be repaired with the help of manual solution using WinRar application. It has inbuilt tool that repairs your damaged file and makes it accessible. Visit the link given below to know the steps required to execute:

http://nalavadebela.wordpress.com/2014/04/05/how-to-repair-a-corrupted-archive-file/

These steps are very easy and no such technical knowledge is required to execute this manual process. You can also read detailed description about corruption and solution to repair file in this blog post.

--- End quote ---

xtabber:
WinRAR can create RAR files with an internal recovery record that slightly increases the archive size, but lets you to recover the contents of damaged RAR archives when the corrupted or missing segment is no larger than the size of the recovery record.

However, according to the WinRAR help file, "ZIP archive format does not support the recovery record."

IainB:
^^ Good point re WinRAR and the "recovery record". I vaguely recall that as being amongst its list of features when I used to use it some time ago.

I just now did a DuckGo search on "Repair corrupt ZIP" and came up with several hits, including this interesting one about ZIP Repair Pro:
Repair Zip Files using Zip Repair
Zip Repair
Zip Repair is a utility that will repair corrupt Zip files. Usually a corrupt Zip file gives the error message:

"Cannot open file: it does not appear to be a valid archive"

Zip Repair creates an error free backup of your original file for instant access, or you can extract files directly from a corrupt ZIP file to your hard drive. No special skills required. A simple user interface with full install / uninstall support.

Version 5:

* New: Repair a Zip file or extract files directly from the ZIP
* New: Zip Repair will fix CRC errors in .zip files so that data can still be uncompressed
* New: Zip Repair supports spanned zip volumes. You can now repair and extract from a spanned zip set even if part of the set is missing
* New: Full support for the Zip64 format
* New: Support for huge file sizes 2GB+ (as long as you have the disk space)
* New: Batch repair multiple ZIP files
--- End quote ---

It doesn't say whether it can recover all of a corrupted ZIP file's contents 100% of the time, but it could be worth a try if you are stuck with a truly corrupted file that (say) 7-ZIP cannot open/read or where other approaches suggested above have drawn a blank.

A year or so past, I downloaded a corrupted executable install file for Stickies. It executed fine but wouldn't install properly - the install got stuck in a program loop. So I asked the author (Tom Revell of Zhorn Software) about it and he was mystified. He sent me a ZIP file (which installed just fine) and asked me to send him a copy of the installer file that I had downloaded. It turned out that it had a different checksum to the one on the download server, so it must have got corrupted in transmission, somehow, and yet it still executed with no error message.
After that experience, I now usually look for the checksum of downloaded executable and other archive files, for file verification, and also - just in case - try to open and test them using 7-ZIP.

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