Retrieving position of a byte within a Hex file using vb.net

[toddw607]

Hello everyone,
I am trying to retrieve a byte within a hex document. I am looking for the position of 'R', which I have found but I need the hex value located 28 spaces before the position of 'R'. Here is the code I have been using to find the 'R' value:

         Dim byteRead As Byte
          Dim j As Integer
          For j = 0 To br.BaseStream.Length() - 1
              byteRead = br.ReadByte
              count = count + 1
              If (byteRead = 82) Then
                  bw.Write(byteRead)
              End If
          Next  

The loop searches for 82 (R) in a file and writes it to a file but I need to know what occurs at the position R-28. Any thoughts would be greatly appreciated.

[Plater]

Read in the entire stream into a Byte[] first.
Then itterate through it's index looking for 'R'(82) then you will have an index number for it (say you called it IDX)
So if mybytearray[IDX]=='R' then you could say mybytearray[IDX-28] is the byte you want

[toddw607]

Hi Plater,
I have tried that so many different ways but the syntax only clicked in my head when you posted your response. Everything works fine but considering the following code:

                                  Dim byteRead As Byte
          Dim j As Integer
          For j = 0 To br.BaseStream.Length() - 1
              byteRead = br.ReadByte
              bytes(j) = byteRead
              count = count + 1
              If (byteRead = 82) Then
                  bw.Write(byteRead)
              End If
          Next
 
          For k = 0 To count
              If (bytes(k) = 36) Then
                  bv.Write(bytes(k - 28))
              End If
          Next
 

I want to return the substring between k-28 to k-20, would I need a 2D array for this or is there any simpler way? Thanks again for the insight.

[Plater]

Well you have your array that is full of all the data.
And you know your start and stop points (count-28) - (count-20)

so do a for loop from the start spot to end spot and write the data where you want it

[toddw607]

Thanks a lot. Most times I know what to do but I work all alone and it just takes someone it bounce it off from before I know the idea of what I need to do. Here is what i used just in case it may help out someone if they're in the same situation:

 For k = 0 To count
              If (bytes(k) = 164) Then
                  For z = -19 To -12
                      bv.Write(bytes(k + z))
                  Next
              End If
          Next 

Once again, thanks for giving me ideas!