Saving data to a random file using a fixed array element error

Question

The file structure is fine for retrieving data from the file  but when I go to write data to the elements and hit any of the fixed array elements,  I get an exception error. this has got to be a sytax problem I am just not seeing. Maybe someone could point me in the right direction.

It seems that I am not addressing the  array member correctly yet the same logic pulls it properly from existing records on file.

in a Module I have the structure as follows:

 Structure INVOICE
        <VBFixedString(6)> Public NUM As String
        <VBFixedString(2)> Public SYMBOL As String
        Public FAC_ID As Short
        Public CORP_ID As Short
        Public DTE As Integer
        <VBFixedString(10)> Public INV_NO As String
        <VBFixedString(10)> Public PO As String
        <VBFixedString(2)> Public FILLER1 As String
        Public DELETE As Short
        <VBFixedArray(19)> Public ID() As Short
        <VBFixedArray(19)> Public QTY() As Integer
        <VBFixedArray(19)> Public COST() As Integer
        <VBFixedString(1)> Public TRANSFER As String
        Public TRAIL As Integer
        <VBFixedString(20)> Public FILLER As String


    End Structure

Public WRK() As INVOICE

Class Review
sub send_rec
ReDim Wrk(0 To 1)


        FileClose(4)
        FileOpen(4, "D:\myDB\TMP\INVOICE.TMP", OpenMode.Random, , OpenShare.Shared, Len(WRK(1)))
        PTR = LOF(4) / Len(WRK(1))
        PTR = PTR + 1





for j as int = 0 to 19
            x = 5

      Wrk(1).QTY(j) = X  (error occurs here: Object reference not set to an instance of an object.)

next j

      If ITR > 0 And ITR <= PTR Then
                 FilePut(4, WRK(1), ITR)       
     end if        
    fileclose(4)

End sub

End Class

Answer 1

I actually discovered my own answer on this.  I have to define an external array for each arrayed item in the structure and pass it along to the data structure as a complete unit.  (I wish this stuff was explained better!) I can manipulate each of the pieces of the array  pulled out of the data record but going in MUST be a a complete unit.

 sub send_rec
      ReDim Wrk(0 To 1)     
       ReDim qty1(0 To 19)
        ReDim cst1(0 To 19)
        ReDim id1(0 To 19)

        For J As Int32 = 0 To 19
            If Val(Grid1.Rows(J).Cells(1).Value) > 0 Then
                qty1(J) = CInt(Grid1.Rows(J).Cells(1).Value) * 100 
                cst1(J) = Int(CDbl(Grid1.Rows(J).Cells(3).Value) * 100)
                 id1(J) = CInt(Grid1.Rows(J).Cells(4).Value) 
            End If
        Next J
        wrk(1).QTY = qty1 ' have to pass the information across as a whole array'
               'In VB6 this is how this was stated to pass along an array value to data structure' 
               'not <>     wrk(1).QTY(j) = qty1(j)'         wrk(1).ID = id1 ' have to pass the information across as a whole array'
        wrk(1).COST = cst1 ' have to pass the information across as a whole array'

Answer 2

 sub send_rec
      ReDim Wrk(0 To 1)            ReDim qty1(0 To 19)
        ReDim cst1(0 To 19)
        ReDim id1(0 To 19)

        For J As Int32 = 0 To 19
            If Val(Grid1.Rows(J).Cells(1).Value) > 0 Then
                qty1(J) = CInt(Grid1.Rows(J).Cells(1).Value) * 100 
                cst1(J) = Int(CDbl(Grid1.Rows(J).Cells(3).Value) * 100)                 id1(J) = CInt(Grid1.Rows(J).Cells(4).Value) 
            End If
        Next J
        wrk(1).QTY = qty1 ' have to pass the information across as a whole array'               'In VB6 this is how this was stated to pass along an array value to data structure'                'not <>     wrk(1).QTY(j) = qty1(j)'         wrk(1).ID = id1 ' have to pass the information across as a whole array'
        wrk(1).COST = cst1 ' have to pass the information across as a whole array'

There's no requirement to pass the whole array to the variable, although often that is the most convenient way to do it.  If you initialise the array correctly you can reference individual elements.

        ReDim Wrk(1).COST(19)
        ReDim Wrk(1).QTY(19)
        ReDim Wrk(1).ID(19)
        For J As Int32 = 0 To 19
            If Val(Grid1.Rows(J).Cells(1).Value) > 0 Then
                Wrk(1).QTY(J) = CInt(Grid1.Rows(J).Cells(1).Value) * 100
                Wrk(1).COST(J) = Int(CDbl(Grid1.Rows(J).Cells(3).Value) * 100)
                Wrk(1).ID(J) = CInt(Grid1.Rows(J).Cells(4).Value)
            End If
        Next J

Answer 3

So do you have to redim the fixed array separately or above and beyond rediming the whole array?

I had Redim wrk(0 to 1)  at the beginning of the subroutine. That doesn't reset the fixed array portion at the same time?  Just trying to understand the difference because redimming the whole structure (or Type ..... End Type) did that in VB6. I don't care which way it is done ...just trying to understand.

Answer 4

Hi,

Here is an example of Random File Access.>>

http://social.msdn.microsoft.com/Forums/en/vbgeneral/thread/50d7b930-edd3-4ba4-92fe-2c16e5235e51

 Would you like me to try an example with your STRUCTURE?

 Try the following just after your ReDim

Work(0) = New Invoice

Work(1) = New Invoice

That should get rid of the error "Object reference not set to an instance of an object."

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Answer 5

I had Redim wrk(0 to 1)  at the beginning of the subroutine. That doesn't reset the fixed array portion at the same time?  Just trying to understand the difference because redimming the whole structure (or Type ..... End Type) did that in VB6. I don't care which way it is done ...just trying to understand.

You have two sets of array - the array of invoices and the arrays within the structure - and both need to be correctly initialised before the array elements can be referenced.  You can do this by DIMming the arrays (as per my example) or by setting the array to a new array created for the purpose (as per your solution) but the preferable option in my opinion is to do the initialiation as part of the process of constructing the structure instance, so it happens automatically.

Structure INVOICE
        Public NUM As String
<vbfixedstring(2)Public SYMBOL As String
        Public FAC_ID As Short
        Public CORP_ID As Short
        Public DTE As Integer
        <vbfixedstring(10)> Public INV_NO As String
        <vbfixedstring(10)> Public PO As String
        <vbfixedstring(2)> Public FILLER1 As String
        Public DELETE As Short
        <vbfixedarray(19)> Public ID() As String
        <vbfixedarray(19)> Public QTY() As Integer
        <vbfixedarray(19)> Public COST() As Integer
        <vbfixedstring(1)> Public TRANSFER As String
        Public TRAIL As Integer
        <vbfixedstring(20)> Public FILLER As String
        Public Sub New(ByVal COUNT As Integer)
            ReDim ID(COUNT)
            ReDim QTY(COUNT)
            ReDim COST(COUNT)
        End Sub
    End Structure
    Public WRK() As INVOICE
    Class Review
        Sub send_rec()
            Dim WRK(1)
            WRK(1) = New INVOICE(19)
            FileClose(4)
FileOpen(4, "D:\myDB\TMP\INVOICE.TMP", OpenMode.Random, ,  OpenShare.Shared, Len(WRK(1))) PTR = LOF(4) / Len(WRK(1)) PTR = PTR + 1
            For j As Integer = 0 To 19
  Dim x As Integer = 5 WRK(1).QTY(j) = x
            Next j
            If ITR > 0 And ITR <= PTR Then
                FilePut(4, WRK(1), ITR)
            End If
            FileClose(4)
        End Sub
    End Class