I have a bunch of questions but will list a few.

I referenced the Applebaum book and looked at examples, but some of the basics confound me.

I'm trying to write VB6 code to interface with a "C/C++" DLL.

In a VB6 module1.bas I have the following:

Public Type STA_PROPS
    cbSize As Long
    STA_DPROP_DEVADDR As String   '-  Device Address    08
    STA_DPROP_GATEWAY As String   '-  Gateway Address   10
    STA_DPROP_NETMASK As String   '-  Network Mask      20
    STA_DPROP_MASK As String    'Mask of used props     38
   
Which are chosen from:

' STA_DPROP_DATETIME   '0x00000001  ///< Date/Time
' STA_DPROP_DEVID      '0x00000002  ///< Device ID
' STA_DPROP_ALIAS      '0x00000004  ///< Alias
' STA_DPROP_LOCATION   '0x00000004  ///< Location ID (same as Alias - compatibility)
' STA_DPROP_DEVADDR    '0x00000008  ///< Device Address
' STA_DPROP_GATEWAY    '0x00000010  ///< Gateway Address
' STA_DPROP_NETMASK    '0x00000020  ///< Network Mask

ETC

' STA_DPROP_MASK       '0x00FFFFFF  ///< Mask of Used DevProp flags

In my VB Form;

Is the DPRPOP_MASK calculated correctly ? and would it be specified as

Dim DPROP_MASK As String, or as long

DPROP_MASK = &H38,  or "0x00000038" or what

How would I DIM the string mystring = "abcdefghij"

Dim mystring As string * 10

or mystring * &HA

or mystring

How do I calculate the cbsize (Size of the structure)

what if the structure had 2 LONG variables, and the above string, how would I calculate the size?

Thanks for any help?

Spsp_1981: spsp_1981[remove.this]@tutopia.com

I don't understand the response.

How can variable = Len(Structure) if structure isn't defined yet.  The SIZE of the structure is part of the definition of the structure.

Or am I really missing something simple here?

First of all I want to state that for structure I understood UDT as commonly called between VB programmers. Tell me if I'm wrong because my mother language is not English and sometimes I misunderstand some concepts.

When reading about the Windows' API, I found a lot of functions that require an structure as a parameter (SHELL_NOTIFYICON for example) and a commonly used coding standard in the API requieres the structure to have a field where to store its size, so if a function has multiple versions using different structures, the function can know from the size of the structure, which version to implement. So that, when you want to store the mentioned size in the field, you use Len() which returns the size of it from the declaration. Example:

Public Type EXAMPLE_UDT
  Name   As String
  Age    As Integer
  Height As Long
End Type 'EXAMPLE_UDT

Each field has a predefined Data-Type which has a predefined size given by VB itself. So when you write: Len(EXAMPLE_UDT) what VB does is look the UDT's fields' data types and calculates the amount of memory it uses, and thats the information the function needs to know. Hope you understand what I hardly tried to explain. I can't remember exactly where I read about it but I believe it must have been in Bruce McKinney's HardCore Visual Basic book which comes with Visual Studio 6 MDSN

Spsp_1981: spsp_1981[remove.this]@tutopia.com

Here's my problem. Your example is:

Public Type EXAMPLE_UDT
  Name   As String
  Age    As Integer
  Height As Long
End Type 'EXAMPLE_UDT

But my DLL requires a change to your example

Public Type EXAMPLE_UDT

  ExampleSize As Long

  Name As String

  Age As Integer

  Height As Long

End Type ‘EXAMPLE_UDT


Dim MyData As EXAMPLE_UDT

With MyData

  .Name = "Spsp_1981"

  .Age = 22

  .Height = 1.82

  .ExampleSize = Len(MyData)

End With ‘MyData

Spsp_1981: spsp_1981[remove.this]@tutopia.com

That example cleared it up. 

I tried it, and the routine came up with the number I expected.  I think that also cleared up another question I had.  Apparently, the string size is not related to the size of the string, it is just a pointer to the string, so it has the same length as any other LONG.

Thanks for the help

Your welcome

Spsp_1981: spsp_1981[remove.this]@tutopia.com