What's new in VB.NET Arrays?
There are few differences between VB6 and VB.NET arrays. Let's find out
how VB.NET arrays differ from the VB6 arrays. The main difference between VB.NET
and VB6 based arrays are VB.NET arrays always starts from the element zero
(Arrays in .NET enabled languages are inherited from the System.Array class). We
have the option of setting the array index with "Option Base" statement in VB6.
Option Base statement is obsolete in VB.NET (This is going to be a major problem
when we are porting out code from VB6 to VB.NET. This change is critically
required to give interoperability between other .NET-enabled languages). The
next major difference was, when we declare an array in VB.NET with 4 elements
it’ll have only 4 elements unlike vb6, which will have 5 elements. This was
only with Beta1 and Microsoft revert the changes in Beta2 to be consistent with
VB6 arrays. See the eWeek Article
on this.
In VB6 we'll get 5
elements raging from 0 to 4 in the array (Assuming we are not overriding the
lower boundary of the array to 1 by the Option Base statement). But in the
VB.NET we'll only get 4 elements raging from 0 to 3. If we try to access the 4th
element we'll get the "IndexOutOfRangeException". So when accessing the VB.NET
array always lower one element from the upper bound of the array like this.
Dim Ary(4) As Integer
Dim i As Integer
For i
= 0 to Ary.GetUpperBound(0) 'Or
UBound(Ary)
Ary(i) = i
Next
The GetUpperBound method is equivalent to the UBound
statement in VB6 (The GetUpperBound method is accessible by all the .NET-enabled
languages). Still the UBound statement works in VB.NET.
In VB.NET there is no
concept of fixed length arrays. For example we can declare a fixed length array
in VB6, which can't be changed by the ReDim statement.
Dim Ary(0 to 4) as Integer
But in VB.NET
we can mimic the same declaration like this,
Dim Ary(4) As Integer
OR
Dim Ary As Integer = New Integer(4)
{}
We can even have a default value for arrays like this,
Dim Ary As Integer = New Integer(4)
{0, 1, 2, 3}
OR
Dim Ary(4) As Integer =
{0, 1, 2, 3}
We can change the
above VB.NET array with the ReDim statement.
Dim Ary(4) As Integer
ReDim Ary(10)
OR
Dim Ary(4) As Integer
ReDim Preserve Ary(10)
VB.NET allows
declaring multi dimensional arrays. For example, the following statement
declares three-dimensional array in VB.NET.
Dim Ary(,,) As Integer
Then we can use the
ReDim statement to declare the size of the array like this.
ReDim Ary(5,5,5)
Dim x,
y, z As Integer
For x
= 0 to 4
For y
= 0 to 4
For z
= 0 to 4
Ary(x,y,z) = x + y + z
Next
Next
Next
We all should know the
one limitation of the ReDim statement. The ReDim statement can't dynamically
change the number of dimensions the array has. For example if we've a
three-dimensional array we can redim it in to a four or two-dimensional array.
All we can do is, we can change the lost dimension array of the array with the
ReDim statement.
In VB.NET we can
compare an array with the keyword nothing to make sure the array is
un-initialized, which is not possible with VB6.
Dim ary() As Integer
If ary
= Nothing then
Response.Write("The array is
un-initialized")
Else
Response.Write("The array is
initialized")
End if
Summary
I this article, I've pointed out few key differences between VB6 and VB.NET
arrays. I hope you'll find the article helpful and interested.
Until next time, Happy Programming!