Reading a binary file created with VB6

8 Jun 2006 10:39 AM

Mr X

One of my employer's products, written in VB6, reads and writes binary
files. We are shortly going to port to VB.NET (framework version 2.0) and
will need to be able to read and write these binary files from .NET. The
file format cannot be changed, so the .NET code will need to mimic the
read/write VB6 stuff.

I am am using a BinaryReader to read the data in .NET. In VB6, the data is
read with "Get" and retrieved with "Put", in a file opened/created in binary
mode.

I am having trouble working out how VB6 stores certain types of data. Below
is some VB6 code that mimics the write behaviour:

Option Explicit

Private Type MyAttrib
sId As String
End Type

Private Type MyType
Attribs() As MyAttrib
End Type

Private Sub Form_Load()
Dim ff As Integer
ff = FreeFile()

On Error Resume Next
Kill "C:\test.txt"
On Error GoTo 0

Open "C:\test.txt" For Binary As ff

Dim count As Integer
count = 2

Dim mt As MyType
ReDim mt.Attribs(count)

Dim i As Integer
For i = 0 To count - 1
mt.Attribs(i).sId = "Identifier " & CStr(i)
Next

Put #ff, , mt

Close ff
End Sub

Note that the MyType type has an array of "MyAttrib"s. There can be any
number of "MyAttrib"s.

Question: how does VB6 store this array?

Looking at a hex editor gives this:

01 00 03 00 00 00 00 00 00 00 0C 00 49 64 65 6E 74 69 66 69 65 72 20 30 0C
00 49 64 65 6E 74 69 66 69 65 72 20 31 00 00

The strings "Identifier 0" starts with the 49 64 65 sequence. It is
preceded by two bytes that indicate the length of the string.

Presumably the "01 00 03 00 00 00 00 00 00 00" sequence tells VB6 how long
the array is.

How can I use this information from .NET to work out the length of the
array?

Perhaps:

Bytes 2 and 3 (03 00) less bytes 0 and 1 (01 00) = 2 = number of members of
array.

Any help would be appreciated. Sorry for the length of this post.

8 Jun 2006 3:54 PM

AMDRIT

Perhaps you can make use of this article:
http://www.codeproject.com/csharp/fastbinaryfileinput.asp and modify it to
your needs.

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"Mr X" <some***@somewhere.com> wrote in message
news:Om1HgfuiGHA.4660@TK2MSFTNGP03.phx.gbl...
> One of my employer's products, written in VB6, reads and writes binary
> files. We are shortly going to port to VB.NET (framework version 2.0) and
> will need to be able to read and write these binary files from .NET. The
> file format cannot be changed, so the .NET code will need to mimic the
> read/write VB6 stuff.
>
> I am am using a BinaryReader to read the data in .NET. In VB6, the data
> is read with "Get" and retrieved with "Put", in a file opened/created in
> binary mode.
>
> I am having trouble working out how VB6 stores certain types of data.
> Below is some VB6 code that mimics the write behaviour:
>
> Option Explicit
>
> Private Type MyAttrib
> sId As String
> End Type
>
> Private Type MyType
> Attribs() As MyAttrib
> End Type
>
> Private Sub Form_Load()
> Dim ff As Integer
> ff = FreeFile()
>
> On Error Resume Next
> Kill "C:\test.txt"
> On Error GoTo 0
>
> Open "C:\test.txt" For Binary As ff
>
> Dim count As Integer
> count = 2
>
> Dim mt As MyType
> ReDim mt.Attribs(count)
>
> Dim i As Integer
> For i = 0 To count - 1
> mt.Attribs(i).sId = "Identifier " & CStr(i)
> Next
>
> Put #ff, , mt
>
> Close ff
> End Sub
>
>
> Note that the MyType type has an array of "MyAttrib"s. There can be any
> number of "MyAttrib"s.
>
> Question: how does VB6 store this array?
>
> Looking at a hex editor gives this:
>
> 01 00 03 00 00 00 00 00 00 00 0C 00 49 64 65 6E 74 69 66 69 65 72 20 30 0C
> 00 49 64 65 6E 74 69 66 69 65 72 20 31 00 00
>
> The strings "Identifier 0" starts with the 49 64 65 sequence. It is
> preceded by two bytes that indicate the length of the string.
>
> Presumably the "01 00 03 00 00 00 00 00 00 00" sequence tells VB6 how long
> the array is.
>
> How can I use this information from .NET to work out the length of the
> array?
>
> Perhaps:
>
> Bytes 2 and 3 (03 00) less bytes 0 and 1 (01 00) = 2 = number of members
> of array.
>
> Any help would be appreciated. Sorry for the length of this post.
>
>