Question

how to redimension array

Asked by: jmarkfoley

I have the following:

ReDim Preserve jobCodes(0 To jbMax) As String

and when I compile I get the compile error: Array Already Dimensioned

The message is true: my array *was* previously dimensioned. This is my frist shot at using dynamic arrays, so I'm sure I'm doing something wrong, but I thought one was supposed to use the "Preserve" when the arrary was previously dimensioned. What am I doing wrong?

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Asked On
2009-02-24 at 10:47:33ID24173130
Tags

VBA ARRAY REDIM

Topic

Access Forms

Participating Experts
3
Points
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Comments
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Answers

 

by: LSMConsultingPosted on 2009-02-24 at 11:00:20ID: 23724974

How was your array dimensioned originally? Was it also an array of Strings?

 

by: harfangPosted on 2009-02-24 at 11:15:40ID: 23725198

The initial declaration must be made without dimensions. You use 'Preserve' to enlarge a dynamic array which has already been dimensioned once dynamically, if you want to keep the values already entered.

(°v°)

    Dim jobCodes() As String   ' initial declaration for dynamic arrays
    
    ReDim jobCodes(0 to 3)   ' run-time dimensioning of array
    jobCodes(2) = "foobar"   ' using  the array
    ReDim Preserve jobCodes(0 To jbMax)   ' preserving the first 4
                                              
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by: TextReportPosted on 2009-02-24 at 13:01:43ID: 23726441

The Preserve keyword is used when you want to "Preserve" the values already assigned to your Array elements and only works if you are increasing the elements.

You do not need to DIM an array, the ReDim does the job for you.

The following example will print A to F in the Immediate window, if you take out the PRESERVE then you will get 5 blank lines followed by E and F.

Are you changing the defined type, say to string from variant?

Finally, what version of Access are you using my tests were in Access 2007 but I am fairly sure the previous versions were the same.

Cheers, Andrew

Dim cnt As Long
ReDim arya(0 To 4) As String
Dim jbmax As Long
 
    
    For cnt = 0 To 4
        arya(cnt) = Chr(65 + cnt)
    Next cnt
    
    jbmax = 6
    ReDim Preserve arya(0 To jbmax) As String
    For cnt = 5 To jbmax
        arya(cnt) = Chr(65 + cnt)
    Next cnt
 
    For cnt = 0 To jbmax
        Debug.Print arya(cnt)
    Next cnt
                                              
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by: harfangPosted on 2009-02-24 at 14:15:50ID: 23727382

> You do not need to DIM an array

That is true. Option Explicit will not catch the problem. Formally (from the VB help file), you should not use it that way:

The ReDim statement is used to size or resize a dynamic array that has already been formally declared using a Private, Public, or Dim statement with empty parentheses (without dimension subscripts).

The problem becomes apparent in the snippet. The typo isn't identified, and the code breaks only at run-time. I don't know why the VB compiler was made to imply Dim when reading ReDim, these are quite different operations, and no other language makes that particular confusion. Anyway, you are right:

    ReDim Something(12) As String

Is interpreted as

    Dim Something() As String
    ReDim Something(12)

Stupid, but there you go...

(°v°)

Sub Manipulate(pvarMyArray() As Variant)
 
    ReDim pvarMyAray(12)
    pvarMyArray(12) = "something"
 
End Sub
 
Sub ShowProblem()
 
    Dim Values() As Variant
    Manipulate Values
 
End Sub
                                              
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by: TextReportPosted on 2009-02-24 at 14:27:22ID: 23727495

harfang, I always use Option Explicit and would always recoment it's use for trapping the logic error that are caused by a stupid typo. Everyone should have this option turned ON in your VBA Options (goodnes knows why the default is OFF)
Cheers, Andrew

 

by: jmarkfoleyPosted on 2009-09-16 at 14:03:46ID: 31550717

didn't implement any solutions

20120131-EE-VQP-002

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