Structure Sizes for Interoperability Not Adding Up 1

[bustell]

I am having trouble creating a structure that I can send to a Delphi 5 DLL. The DLL is expecting a structure containing 9 bytes containing 1 Byte and 2 Int32's.

If I create a structure with just the one byte field, the Marshal.SizeOf() equals 1.

If I create a structure with the two Int32 fields, the Marshal.SizeOf() equals 8.

However, if I create the structure with all three fields, the Marshal.SizeOf() equals 12. This does not add up, it should be equal to 9.

I have tried using a structure attribute of <StructLayout(layoutkind.Sequential)> and it did not help.

I tried using a structure attribute of <StructLayout(layoutkind.Explicit)> with <FieldOffset> attributes on the fields and it did not help.

I really need the structure to be 9 bytes. I hope someone has run into this and can help.

Here's the Code:

Private Sub btn1_Click(ByVal sAs System.Object, ByVal e As System.EventArgs) Handles btn1.Click

  Dim myTest1 as TTest1
  Dim myTest2 as TTest2
  Dim iSize1, iSize2 as Int32
  iSize1 = Marshal.SizeOf(myTest1)
  iSize2 = Marshal.SizeOf(myTest2)
	
End Sub
	
Public Structure TTest1             '          Size
  Public ActiveMessage As Int32     'PChar     004
  Public ActiveMessageSize As Int32 'Integer   004
End Structure
	
Public Structure TTest2             '          Size
  Public Active As Byte             'Boolean   001
  Public ActiveMessage As Int32     'PChar     004
  Public ActiveMessageSize As Int32 'Integer   004
End Structure

Pat B

 

[chiph]

Did you try LayoutKind.Sequential with the Pack option of 0?

Chip H.


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[bustell]

Chip,

You are my hero! Though setting Pack to 0 did not fix it. Setting it to 1 did fix it. Zero sets it to the OS default.

Thanks so much for pointing me in the right direction.




Pat B

 

[chiph]

Ooops.
But glad you got it to work.

Chip H.


____________________________________________________________________
Click here to learn Ways to help with Tsunami Relief
If you want to get the best response to a question, please read FAQ222-2244 first