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Problem with 'Mid' and/or 'Left' functions

 
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MarkDM2

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Joined: 19 Dec 2015
Posts: 7
Location: Flanders
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PostPosted: Fri Apr 11, 2025 8:55 pm    Post subject: Problem with 'Mid' and/or 'Left' functions Reply with quote
They don't work like before. I am updating a 5 years old Bascom-Avr program. Is does not work anymore.
I isolated the problem in a testprogram.
The 3 Print-statements should give the same output.
Not anymore now.

Quote:

Dim Buf(50) As Byte
Dim Bufc As String * 50 At Buf Overlay

Bufc = "$P"
Mid(Bufc,3,2) = "1;"
Mid(Bufc,5,2) = "$T"
Print left(Bufc,6)

Mid(Bufc,1,2) = "$Q"
Mid(Bufc,3,2) = "2;"
Mid(Bufc,5,2) = "$T"
Print left(Bufc,6)

Mid(Bufc,1,6) = "$Q3;$T"
Print left(Bufc,6)

Bufc = "$R4;$T"
Print left(Bufc,6)


In the previous version of my program (5 years ago) I used the first compilation of the string. It worked fine, the AVR printed all the 6 character. Now, it prints only 2 chars.
What can be wrong ?



(BASCOM-AVR version : 2.0.8.6 )
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albertsm

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Joined: 09 Apr 2004
Posts: 6173
Location: Holland
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PostPosted: Sat Apr 12, 2025 8:10 am    Post subject: Reply with quote
the output is correct. in older versions where you get different output there was a bug which was fixed.
MID statement may not write beyond the length of the string and that is what you do.
the reason is that it is potential unsafe. VB will not allow it either.
To fix your code simple use + SomeString = Somestring + "QQ"
Or make the string filled with spaces.
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MarkDM2

Bascom Member



Joined: 19 Dec 2015
Posts: 7
Location: Flanders
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PostPosted: Sat Apr 12, 2025 8:56 pm    Post subject: Reply with quote
Thank you for the reply.

I modified the first line of the testprogram:

Quote:
Bufc = "$P3456"

Then I overwrite with 'mid' function.

It works fine.
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