Regarding Block level Scope & Variable Life Time

  • Thread starter Thread starter ElanKathir .S.N
  • Start date Start date
E

ElanKathir .S.N

Hi all !

VB.NET adds the ability to create variables that are visible only within
a block. A block is any section of code that ends with one of the words
End , Loop , or Next . This
means that For...Next and If...End If blocks can have their own
variables.

So,

While y>6
Dim x as interger
......
End while

But x have lifetime of procedure level. Means,
Dim x as interger -- This line geting eff. at first time only. is it
right ?


Thanks & Regards

Elankathir,
B'lore,
India.
 
if you are asking how to use vars in loops i would say
(pseudo)
private sub bla
dim x as object
loop
x = new object
end loop
end sub

local in a for could also be

for i as integer = 0 to 100 step 1
array(i). bla = bla
next i

yust some thoughts

eric
 
Hi Elan,

Yes and they overrule the variables declared on a higher level outside the
method.

However you can not declare variables more times inside a method

It is in every block too every block from a try catch error block by
instance.

I hope this helps?

Cor
 
Cor Ligthert said:
Yes and they overrule the variables declared on a higher level
outside the method.

However you can not declare variables more times inside a method

It is in every block too every block from a try catch error block
by instance.
Click to expand...

Sorry Cor, but I really don't understand the last sentence. What do you
mean? Maybe the OP understands it but I'm really also interested.
 
Elankathir and everybody else,

Here's a sample:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim i As Short
For i = 1 To 10
Dim x As Short
x = 1
Next
Dim x As Short
MessageBox.Show("x = " & x)
End Sub

As shown, I get an error at the first declaration of x, saying that x hides
a variable declared in the enclosing block. This is interesting, since the
declaration is after the For loop. This appears to show that all
declarations happen before any code in a block is executed, regardless of
where the Dim statements are. Is that correct?

When I comment out the second declaration, I get an error in the message box
line saying that x is not accessible in this context because it is private.
It cannot be changed to protected or public.

I haven't tried it, but I'm pretty durn sure that in C++, a similar
construct would be perfectly acceptable. The inner x would be used in the
for loop, and the message box would show a random value because the outer x
would never have been initialized. There is no check for whether a variable
declaration in one scope hides a declaration in another scope. At most, a
warning, not an error, would have been generated.

I tried commenting out the inner declaration and leaving the outer
declaration. I got an error saying that x cannot be used before it is
declared.

Ah, well. This doesn't seem to be an issue I'm going to need to worry about
much in real life.

Rob
 
Seeing the message from Rob, I see I did not write it clear (I did want to
simplivy it)

I made a mistake in my message I see when I see your message, this is
allowed

for i as integer = 0 to 100
dim x =1
next
for i as integer = 0 to 100
dim x = 1
next

however this
dim x as integer
for i as integer = 0 to 100
dim x =1
next
for i as integer = 0 to 100
dim x = 1
next
will give an error

Cor
 
Hi Armin,

I saw too this was a very quick written message.
The same behaviour is for every kind of block, by instance too for a Try,
Catch, End Try block.

I hope this makes it even without the rest of the text more clear?

(I do not know why I write the last days try catch error block, now i see I
have to watch for that, I did that more times)

Thanks for making me attent on this

Cor
 
Cor Ligthert said:
Hi Armin,

I saw too this was a very quick written message.
Click to expand...

Now I understand. Your "too" was confusing me. :-)

"I saw (that) this was a very quickly written message, too."
"I also saw (that) this was a very quickly written message."

:-))

(I really hope that this is correct *g*)

The same behaviour is for every kind of block, by instance too for a
Try, Catch, End Try block.

I hope this makes it even without the rest of the text more clear?

(I do not know why I write the last days try catch error block, now i
see I have to watch for that, I did that more times)
Click to expand...

Sorry for correcting you, but I think this is allowed on Fridays at this
time (you (and everybody else) can correct me, too). ;-)))) The time should
be at the start or end of the sentence.

"I do not know why I write try catch error block (in) the last(past?) days,
now i see I have to watch for that, I did that many times"

Should only be a little hint because I'm often sitting in front of your
messages a long time. :-))) But don't care about me as long as everybody
else understands you. ;-)
 
"I saw (that) this was a very quickly written message, too."
"I also saw (that) this was a very quickly written message."
Click to expand...
I saw as well that this was a very quickly written message.

However let us not do to much correction in this sense, we loose it anytime
from a lot of others here.

:-))

Cor
 
Cor Ligthert said:
I saw as well that this was a very quickly written message.

However let us not do to much correction in this sense, we loose it
anytime from a lot of others here.

:-))
Click to expand...

Sorry, I don't understand you. ;-))
 
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