VarPtr and arrays..???

[Torben Marcussen]

Ok, here is a weird one....

The following code WILL work correctly,,, But why..?

Type StationRecord
Number As String * 5
sData(1600 To 2100, 12) As Double
End Type

Function PbMain()

Dim Station As StationRecord
Dim RainArr() as double

'--- Add some data to Station ----

ReDim RainArr(1600 to 2200, 12) as double At VarPtr(Station.sData(1500,0))

End Function


OK, Why do I have to ReDim at 1500 rather than 1600 to get the data in the right spot...?????

TIA
Torben

[Semen Matusovski]

Torben --
What do you name "correctly" ?
RainArr(x, 0) and Station.sData(x,0) will have different location (like expected)

  #Compile Exe
  #Dim All
  #Register None
  Type StationRecord
     Number As String * 5
     sData(1600 To 2100, 12) As Double
  End Type
  Function PbMain() As Long
     Dim Station As StationRecord
     Dim RainArr() As Double
     '--- Add some data to Station ----
     ReDim RainArr(1600 To 2200, 12) As Double At VarPtr(Station.sData(1500,0))
     MsgBox Format$(VarPtr(RainArr(1700, 0))),, Format$(VarPtr(Station.sData(1700,0)))
  End Function

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[Torben Marcussen]

Semen,

I mean that the data I put in Station.sData(1800,1)
will only appear in RainArr(1800,1) if I ReDim the RainArr at 1500 rather than 1600...

I presume it has something to do with the fact that I am also trying to extend the ReDim'ed array at the same time. ie, I am increasing the UBOUND from 2100 to 2200. But what I don't understand is why does that mean I have to bring the LBOUND back the same amount...????

Torben


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[Semen Matusovski]

Torben --
imagine following
Redim Ar1(1 : 100, 1 : 6) At x
Redim Ar2(1 : 200, 1 : 3) At x

Elements are located
Ar1(1, 1) ... Ar1(100, 1) Ar1(1, 2) ... Ar1(100, 2)
Ar2(1, 1) ... Ar2(200, 1) Ar2(1, 2) ... Ar1(200, 2)

This means that address of Ar1(1, 3) is the same as Ar2(1, 2)
Probably, if you will calculate addresses for your case, you will understand, what happends.

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[Lance Edmonds]

Multi-dimensional arrays are stored in "column-major" order... see ARRAY SORT() for more information on how arrays are stored internally.



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Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>