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Groups > microsoft.public.excel.programming > #110679

Re: Problem getting a pointer to a User Defined Type (UDT)

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"Desmond Walsh" <deasmhuinbreathnach@gmail.com> wrote in message
On Friday, May 25, 2018 at 4:34:39 AM UTC-4, Peter T wrote:
> "Desmond Walsh"  wrote in message
>
In my test code (in GetUdtPointer), I changed the value of the bmember2 
property
first using the pointer marray(2).amember1.bmember2 and then using the 
pointer GetUdtPointer.bmember2.   Locals Window clearly showed 2 distinct 
UDTb's being updated in the scope of GetUdtPointer. This led me to believe 
that I could not return a pointer to a specific UDTb. But,  when I switched 
to a class definition of UDTb, I got the pointer I wanted.

Maybe I am missing a point.  Could you modify the GetUdtPointer code to 
return a pointer to a specific UDTb.  That is all I was trying to do.

>==============

I think you're missing the point about pointers!

Rather than explain maybe this illustrates using your UDTs -

' ' normal module
Private Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" ( _
                               ByRef Destination As Any, _
                               ByRef Source As Any, _
                               ByVal Length As Long)
' this API needs adapting for use in 64bit Excel

Public Type Udtb
    bmember1 As Integer  ' 2 bytes
    bmember2 As Integer  ' 2 bytes
End Type                 ' total 4 bytes

Public Type Udta_v1
    index As Integer     'bytes 1 to 2
    amember1 As Udtb     'bytes 3 to 6
    amember2 As Udtb     'bytes 7 to 10
End Type  '    total 10 bytes


Sub test()
Dim bigU As Udta_v1, ba() As Byte, i As Long

    bigU.index = 1
    bigU.amember1.bmember1 = 2
    bigU.amember1.bmember2 = 3
    bigU.amember2.bmember1 = 4
    bigU.amember2.bmember2 = 5

    foo bigU, ba
    Debug.Print bigU.amember1.bmember1  ' 5623
    Debug.Print bigU.amember1.bmember2  ' 8223
    Debug.Print bigU.amember2.bmember1  ' 10793
    Debug.Print bigU.amember2.bmember2  ' 13363

    For i = 0 To UBound(ba)
        Debug.Print ba(i);
    Next
' 1  2  21  22  31  32  41  42  51  52

End Sub

Sub foo(bigU As Udta_v1, ba() As Byte)
Dim uB1 As Udtb, n As Integer

    bigU.index = 1 + 256 * 2

    uB1.bmember1 = 21 + 256 * 22    ' 5623
    uB1.bmember2 = 31 + 256 * 32    ' 8223

    n = 41 + 256 * 42            ' 10793

    CopyMemory ByVal VarPtr(bigU) + 2, uB1, 4
    CopyMemory ByVal VarPtr(bigU) + 6, n, 2
    CopyMemory ByVal VarPtr(bigU) + 8, (51 + 256 * 52), 2

    ReDim ba(0 To LenB(bigU) - 1)  '  0 to 10 -1
    CopyMemory ByVal VarPtr(ba(0)), bigU, LenB(bigU)

End Sub
' ' end code

While this is all straightforward with this set of UDTs with all declared 
numeric members, be careful as with variants, strings (particularly if any 
unicode) and arrays in UDTs internally, the data may not line up as simply 
as in this example.

Your "GetUdtPointer" function is misnamed, it doesn't return a pointer. Also 
there isn't a "pointer to a specific Utdb" as the specific Utdb you're 
talking about doesn't exist until reconstructed, merely the relevant byte 
offset from the main udt's pointer as illustrated. Just as series of bytes 
any portion of which could be reconstrated to say a byte array or somthing 
else.

If you explain the real objective for all this maybe there is a different 
sort of answer.

Peter T

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Thread

Problem getting a pointer to a User Defined Type (UDT) Desmond Walsh <deasmhuinbreathnach@gmail.com> - 2018-05-17 06:01 -0700
  Re: Problem getting a pointer to a User Defined Type (UDT) Ulrich Möller <knobbi38@arcor.de> - 2018-05-17 16:02 +0200
    Re: Problem getting a pointer to a User Defined Type (UDT) Desmond Walsh <deasmhuinbreathnach@gmail.com> - 2018-05-18 04:28 -0700
      Re: Problem getting a pointer to a User Defined Type (UDT) Ulrich Möller <knobbi38@arcor.de> - 2018-05-18 13:59 +0200
        Re: Problem getting a pointer to a User Defined Type (UDT) Desmond Walsh <deasmhuinbreathnach@gmail.com> - 2018-05-19 13:31 -0700
  Re: Problem getting a pointer to a User Defined Type (UDT) "Peter T" <askformy@gmail.com> - 2018-05-25 09:34 +0100
    Re: Problem getting a pointer to a User Defined Type (UDT) Desmond Walsh <deasmhuinbreathnach@gmail.com> - 2018-05-26 14:28 -0700
      Re: Problem getting a pointer to a User Defined Type (UDT) "Peter T" <askformy@gmail.com> - 2018-05-27 12:08 +0100

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