[delphizip] Re: Very slow to delete files from ZIP file
- From: Roger Aelbrecht <Roger.Aelbrecht@xxxxxxxxx>
- To: delphizip@xxxxxxxxxxxxx
- Date: Tue, 16 Oct 2007 18:14:53 +0200
Lewis wrote:
> Thank you James, here are the detail information
>
> 1) The zip file is 247MB and it contains 277 files
> 2) Delete a single file takes about 20 seconds
> 3) It's on the local drive
>
> Before delete the file I shutdown the antivirus software.
>
> Do you mean ZIPMaster also need to copying required files to a new zip
> file? If so, I believe that's why it's so slow to delete a file.
>
> And, do you have any documents about why program can't simply delete a
> file from a ZIP file like hard disk? I want to know more information
> about it. Thanks!
>
> Lewis Tian
>
The structure of a zip file is such that you cannot simply delete a file
from it.
Each file has a local directory structure and has an entry in the
central directory structure.
Both contain information about the offset of the beginning of the file
from the start of the archive.
All these offset needs to be recalculated and all local and central
directories have to be re-written, that's why the whole file needs to be
re-written.
If course all these directory structures need to be read first from the
original file.
--
Roger Aelbrecht
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