VBA code to calc a check sum for a string variable?

[twgonder]

I don't want to reinvent this wheel in VBA.
I've got a long text field in a table, that I don't want users or other developers to modify.
It's a legal notice.

I'm looking for a simple checksum procedure to validate that the long text hasn't changed.
It can be in VBA, but since one can't hide certain code in a projext module (.accdb) then it might work better
if it was some kind of call outside Access, but a call that is standard enough in Windows that there won't be .dll problems in the future.



Got any ideas?

[Bulzie]

Not sure outside of Access, maybe this for VBA (not my code)

Function Checksum(text As String) As Long
Checksum = 0
For x = 1 To Len(text)
Checksum = Checksum + (13 * Asc(Mid(text, x, 1)))
Next x

End Function

[twgonder]

@ Bulzie, #2 Thanks, it's a start I'll see what happens with a long string. It'll be a little more complicated with having a copyright year in the long string that needs to be removed first, and I'll see how big the long number gets.

[CJ_London]

Depends on how long the text is but in principle you could hash the string and hide the result away somewhere - perhaps as a property. A simple comparison between the hash of the current string and the hidden away value will tell you it has changed - much the same way you would verify a password

[twgonder]

@ CJ post #4

hide the result away somewhere - perhaps as a property

Okey, I'll bite. I had planned to save in a table, but that could easily be changed by a user.
How does one save data like this in a property? And then use it later?
It's string data since I have to parse it for language and the checksum for each language.

[CJ_London]

Not worth providing an example as properties can be attached to numerous objects - Google ‘ access vba create property’ to give you some idea

I use them to store commented sql (attached to a querydef) licensing (attached to the fe) authorisation (attached to a table) etc

[twgonder]

@CJ #6 Thanks for that hint, here's what I found:
Database.CreateProperty method (DAO) | Microsoft Learn

If it remains "persistent" as claimed in the Remarks, it just might be the ticket. I'm guessing one runs the code once to create the property, and then it remains through new opens of the .accdx (my idea of persistent).

I tried the code in the MS sample, it's obviously quite old. And it dies with a RTE in my Access 2021.
Also missing is the way to read just one property that I might set.

Seen any better documentation that the MS one that falls quite short for a full explanation?

Post note: I found this: Microsoft Access - Playing With Database Properties (youtube.com)

[CJ_London]

then it remains through new opens of the .accdx

don't know what you mean by that. If you mean open a db, create the property, close the db. The property is available when you next open it.

I tried the code in the MS sample, it's obviously quite old. And it dies with a RTE in my Access 2021.

Without knowing what the error actually is, unable to comment

Also missing is the way to read just one property that I might set.

in the same way you read any property

objectname.propertyname

or

objectname.properties("propertyname").value

[twgonder]

@ All This is a good video I found:

https://youtu.be/hnyC8uYgJBU?si=6roLH9Mkn15OUf-2

One might consider the simple approach at 20:30 of the video.

[isladogs]

I had planned to save in a table, but that could easily be changed by a user.

Tables can be made read only using constraints