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From: Tony Toews [MVP] on 23 May 2010 16:43
MM <kylix_is(a)yahoo.co.uk> wrote:

>I use the free bincomp.exe. Here's how I call it from my VB6 front-end
>app:

Thanks for the suggestion however I want to contain everything within
my single VB 6 exe. It uses a drag and drop deploy so I'm trying to
keep things exceedingly simple.

Tony
--
Tony Toews, Microsoft Access MVP
Tony's Main MS Access pages - http://www.granite.ab.ca/accsmstr.htm
Tony's Microsoft Access Blog - http://msmvps.com/blogs/access/
For a convenient utility to keep your users FEs and other files
updated see http://www.autofeupdater.com/
Granite Fleet Manager http://www.granitefleet.com/
From: Tony Toews [MVP] on 23 May 2010 16:51
Jason Keats <jkeats(a)melbpcDeleteThis.org.au> wrote:

>I've used the following for SHA1:
>http://vb.wikia.com/wiki/SHA-1.bas
>
>It seems to be faster than the CRC32 implementation you're using, is
>less likely to produce duplicate values (if that's important) and it's
>certainly more secure (only important if you're going to use it with
>passwords, etc.).

Ah, interesting. I'll do some timing tests. I've got a 300 Mb Access
file which would be suitable for such. <smile>

The concern is about unspecified and unknown oddities happening
between the file server and the client PC when copying down files.
Which is the primary purpose of my utility. These oddities should
never happen. Of course. <smile> If the file server, network, and
client PC are working just fine. And they probably will 99.99999% of
the time.

Tony
--
Tony Toews, Microsoft Access MVP
Tony's Main MS Access pages - http://www.granite.ab.ca/accsmstr.htm
Tony's Microsoft Access Blog - http://msmvps.com/blogs/access/
For a convenient utility to keep your users FEs and other files
updated see http://www.autofeupdater.com/
Granite Fleet Manager http://www.granitefleet.com/
From: Nobody on 24 May 2010 01:39
Tested routine, but slow for large files:

' Returns 0 when identical in size and contents
Public Function CompareFiles(fn1 As String, fn2 As String) As Long
Dim i As Long
Dim fs1 As Long
Dim fs2 As Long
Dim f1 As Long
Dim f2 As Long
Dim b1 As Byte
Dim b2 As Byte

CompareFiles = 0 ' Assume identical

On Error Resume Next

fs1 = FileLen(fn1)
If Err.Number <> 0 Then
Err.Clear
CompareFiles = 1 ' File 1 not found
Exit Function
End If
fs2 = FileLen(fn2)
If Err.Number <> 0 Then
Err.Clear
CompareFiles = 2 ' File 2 not found
Exit Function
End If
If fs1 <> fs2 Then
CompareFiles = 3 ' File size is not the same
Exit Function
End If

f1 = FreeFile
Open fn1 For Binary Access Read Shared As f1
If Err.Number <> 0 Then
Err.Clear
CompareFiles = 4 ' Error opening file 1
Exit Function
End If

f2 = FreeFile
Open fn2 For Binary Access Read Shared As f2
If Err.Number <> 0 Then
Err.Clear
CompareFiles = 5 ' Error opening file 2
Close f1
Exit Function
End If

On Error GoTo 0

For i = 1 To fs1
Get f1, , b1
Get f2, , b2
If b1 <> b2 Then
CompareFiles = 6 ' Contents don't match
Debug.Print "CompareFiles: Mismatch at byte position " &
Seek(f1) - 1
Exit For
End If
Next

Close f2
Close f1

End Function


From: Tony Toews [MVP] on 24 May 2010 15:16
"Nobody" <nobody(a)nobody.com> wrote:

>Tested routine, but slow for large files:

One of the files to be compared will always be on a network file
share. Thus I'd prefer to compute the CRC/hash once when it changes.

Tony
--
Tony Toews, Microsoft Access MVP
Tony's Main MS Access pages - http://www.granite.ab.ca/accsmstr.htm
Tony's Microsoft Access Blog - http://msmvps.com/blogs/access/
For a convenient utility to keep your users FEs and other files
updated see http://www.autofeupdater.com/
Granite Fleet Manager http://www.granitefleet.com/
From: Dee Earley on 25 May 2010 07:44
On 23/05/2010 04:56, Tony Toews [MVP] wrote:
> Folks
>
> I've had a request to double check that files which my utility as
> copied from the network server to the client PC has been copied
> correctly. Presumably by using a CRC although it looks like I could
> also use SHA or MD5..
>
> Any comments on Calculating CRC32 With VB
> http://www.vbaccelerator.com/home/vb/code/libraries/CRC32/article.asp
>
> Any better algorithms out there?

If it works... :)

Bear in mind that doing the calculations on the copying end means it
needs to transfer the data twice, possibly showing the same or different
corruption each time.

You would really need something else (ideally the server) to generate
the checksums that you then check against on the client.

--
Dee Earley (dee.earley(a)icode.co.uk)
i-Catcher Development Team

iCode Systems

(Replies direct to my email address will be ignored.
Please reply to the group.)
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