How to get out bytes and get number from byte array

Question

I read a binary file of 900 bytes with much informations inside.
Like this:

     Dim myFile As String = txt_mydir.Text + "\MY_FILE.BIN"
     If IO.File.Exists(myFile) Then
        Dim fInfo As New FileInfo(myFile)
        Dim numBytes As Long = fInfo.Length
        Dim fStream As New FileStream(myFile, FileMode.Open, FileAccess.Read)
        Dim br As New BinaryReader(fStream)
        Dim data As Byte() = br.ReadBytes(CInt(numBytes))

All bytes finishes in bytearray 'data'.

Now I have to read a numbers written with VB6 structs into that file. Structs are mine and I know what is what and where is what. For example I need a VB.NET 'short' number which is at bytes 81 and 82. Among that I have all other basic number types to get out.

How to take out desired number of bytes from 'data' from specific location, with exact length and get a proper number from it (short, int, double...)?

Examples of the array, what values you need from it? The inputs? Surely you can give some. — Oded
– Oded, Commented Dec 20, 2012 at 18:34

Olivier Jacot-Descombes · Accepted Answer · 2012-12-20 18:01:23Z

1

Use the methods of the BinaryReader to get the fields of your original struct

Dim i As Integer = br.ReadInt32()
Dim d As Double = br.ReadDouble()
Dim s As String = br.ReadString()

And so on. You must read the fields in exactly the same order as they were written to the file.

Embed it into a loop like this

While br.BaseStream.Position() <> inFile.BaseStream.Length()
    ...
End While

edited Dec 20, 2012 at 18:01

answered Dec 20, 2012 at 17:55

Olivier Jacot-Descombes

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4 Comments

Wine Too Over a year ago

Very interesting Olivier, and works. But I would have to seek somehow over half of file because I have to pass more than 200 variables which is not needed.

Olivier Jacot-Descombes Over a year ago

You can fist seek to the desired position and then use an appropriate read-method.

Wine Too Over a year ago

That can be a solution. I am new to vb.net, so can you please show how to seek to desired position?

Wine Too Over a year ago

I find ;), thank you very much "fStream.Seek(417, SeekOrigin.Begin)"

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