What is the best way to iterate through an array in Classic Asp VBScript?

Question

Is:

For i = LBound(arr) To UBound(arr)

The best way?

What is the point in asking for LBound? Surely that is always 0 isn't it?

Answer 1

Probably it comes from VB6. Because with Option Base statement in VB6, you can alter the lower bound of arrays like this:

Option Base 1

Also in VB6, you can alter the lower bound of a specific array like this:

Dim myArray(4 To 42) As String

Answer 2

Option Base doesn't seem to work in ASP - nor does Dim( 4 To 42 )

Answer 3

Option Base doesn't seem to work in ASP

Yes it only does in VB6 like I said. My point is that this usage comes from VB6 programmers who are also ASP (VBScript) programmers.

Answer 4

I've always used For Each...

Answer 5

There is a good reason NOT to use "For i = LBound(arr) To UBound(arr)"

"dim arr(10)" allocates eleven members of the array, 0 through 10 (assuming the VB6 default Option Base).

Many VB6 programmers assume the array is one-based, and never use the allocated arr(0). You can remove a potential source of bugs by using "For i = 1 To UBound(arr)" or "For i = 0 To UBound(arr)", because then it is clear whether arr(0) is being used.

"For each" makes a copy of each array element, rather than a pointer. This has two problems. First, when you try to assign a value to an array element, it doesn't happen. This code assigns a value of 47 to the variable i, but does not affect the elements of arr.

for each i in arr
  i = 47
next i

Second, you don't know the index of an array element in a "for each," and you are not guaranteed the sequence of elements (although it seems to be in order.)

Answer 6

LBound may not always be 0. Whilst it is not possible to create an array that has anything other than a 0 Lower bound VBScript it is still possible to retrieve an array of variants from a COM component which may have specified a different LBound.

That said I've never come across one that has done anything like that.

Answer 7

It is actually a matter of taste. For i ... UBound is a tad faster, but ForEach is cleaner.