Really need help for copy memory..

[jwm]

I want to move data from a byte array to some kind of udt. I used copy memory to do it. But got some prob, really can't figure out why the result is like this:

Here is the code and the result:

Private Type MyUdt1
    count  As Byte      'length of udt
    c(4)   As Byte
    d      As Byte
End Type
Private Type MyUdt2
    count  As Byte      'length of udt
    a      As Byte
    b()    As Byte
End Type
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
(pDst As Any, pSrc As Any, ByVal ByteLen As Long)

Private Sub Command1_Click()
    Dim arr(6) As Byte
    Dim udt1 As MyUdt1
    Dim udt2 As MyUdt2
    arr(0) = 5
    arr(1) = 1
    arr(2) = 2
    arr(3) = 3
    arr(4) = 4
    arr(5) = 5

    CopyMemory udt1, arr(0), 6
    Debug.Print udt1.c(2) '=3,ok
    Debug.Print udt1.d    '=0, why??? (it should be 5)
    
    ReDim udt2.b(0 To 2)
    CopyMemory ByVal udt2, arr(0), 6
    Debug.Print udt2.a    '=1, ok
    Debug.Print udt2.b(0) 'script out of range.???
End Sub

please help me out. Your answer would be greatly appreciated.!!!

[jwm]

can somebody help?

[ccoder]

Originally posted by jwm
I want to move data from a byte array to some kind of udt. I used copy memory to do it. But got some prob, really can't figure out why the result is like this:

    CopyMemory udt1, arr(0), 6
    Debug.Print udt1.c(2) '=3,ok
    Debug.Print udt1.d    '=0, why??? (it should be 5)

A byte array is defined as vbArray + vbByte. Therefore, there is an extra byte between c(3) and d.

    ReDim udt2.b(0 To 2)
    CopyMemory ByVal udt2, arr(0), 6
    Debug.Print udt2.a    '=1, ok
    Debug.Print udt2.b(0) 'script out of range.???
End Sub

I can't say for sure what is happening here. I never use variable length variables in a UDT. For example, if you declare a string in a UDT, 4 bytes are allocated to hold a pointer to the actual string. If you declare a string as String * 8, 16 bytes are allocated to hold the string.

Here is the output from some testing that I did some time ago. The UDT and its type defines are:

Private Type dclLogRec
             UserId As String * 8
             PassWd As String * 8
             UserOK As Integer
        End Type

Dim Login    As dclLogRec          ' the IPC structure

The code in the DataArrival sub to get the received data is:

   ReDim bTBuff(bytesTotal)
   tcpClient.GetData bTBuff, vbArray + vbByte, bytesTotal
   CopyMemory Login, bTBuff(0), Len(Login)

Debug.Print output is:

Login VarPtr=1689292
Login.Userid VarPtr=1242488, StrPtr=1552148
Login.PassWd VarPtr=1242488, StrPtr=1625324
Login.UserOK VarPtr=1689324
Login Len = 18
Login LenB = 34
 99  99  111  100  101  114  32  32  98  121  116  101  109  101  32  32  2  0

The last line of numbers shows the value of each byte in the UDT.

[jwm]

Thanks lot.

I got some idea.