Loop dim confusion

[VBAHole22]

Maybe I'm having a brain fart from too much turkey but answer me this. Look at the following code:

 

Dim i As Integer

For i = 0 To 30

Dim stuff, huh As String

stuff = "43524525"

huh = "3452345"

Next

 

Now if I put a break on the 'stuff=' line and run it; the first time around stuff will be equal to nothing. But what about the second time around?

[Mike_R]

The best way to know is to test it!

 

But the answer is that the Scope of your 'stuff' variable is local to that block, but its Lifetime will persist until the Sub or Function is exited. That is, it will only be 'Dimmed' but once, even if it loops multiple times. So the 2nd time through your loop, the line:

Dim stuff, huh As String

will be ignored for it already has been Dimentioned, that is, allocated space on the Stack, etc. So the 2nd time through, you'll find that the value of 'stuff' will already = "43524525".

 

You should test this yourself though to see. More interesting might be to use an Integer variable in the same manner, incrementing it each time through the loop. You'll notice that the variable is sort of "Static", in that it's value from the previous time is maintained. It will be maintained until the Sub or Function istelf is exited. (But it is not *truly* static, for a Static var maintains its value between calls to the Sub or Function.)

 

Also note that by dimming within the block, this value is not accessible outside that block. That is, the variable's Scope is limited to within this block.

[VBAHole22]

Those are precisely the results I observed. It is the same with int or string.

I'm shocked. You think you know someone, you let them in your home, and then they do this to you!

Can anyone confirm if this behavior existed in VB6?

[Mike_R]

It's the *same* within VB6, however VB6 has sloppier Scoping rules. For example:

Private Sub Form_Load()
   Dim i As Integer
   For i = 0 To 30
       Dim stuff, huh As String
       stuff = "43524525"
       huh = "3452345"
   Next
   
   MsgBox stuff  'Returns "3452345"
End Sub

Note that the final MsgBox returns the value for 'stuff' even though stuff is declared within a block. VB6 does not care about where a variable is declared. VB.Net is tighter with the scoping rules; witness the following:

Private Sub Form1_Load(ByVal sender As System.Object, _
                      ByVal e As System.EventArgs) Handles MyBase.Load
   Dim i As Integer
   For i = 0 To 30
       Dim stuff, huh As String
       stuff = "43524525"
       huh = "3452345"
   Next

   MessageBox.Show (stuff) ' <-- CTE: "Name 'stuff' is not declared."
End Sub

Try copying the above into your VB.Net and it won't even run. You'll get a Compile-Time Error stating "Name 'stuff' is not declared."

 

But the internals within the loop are basically the same.

[donnacha]

The golden rule in .Net is never assume anythong and always init your variables to a default value.....

[VBAHole22]

and in this case resest each variable for every turn in the loop

 

Dim i As Integer
For i = 0 To 30
Dim stuff, huh As String
stuff= string.empty
huh = string.empty
stuff = "43524525"
huh = "3452345"
Next