How do I optimize my code - vb.net - vb.net

Question

I have a working program, but it's like Frankenstein - parts of other programs put together, that may be redundant. Here's what I'm trying to do:
Find a string inside a binary file & from that location to the EOF dump the contents into a string.
Here is my code:
Imports System.IO
Public Class Form1
Dim b() As Byte = IO.File.ReadAllBytes("C:\data.bin")
Dim encodme As New System.Text.ASCIIEncoding
Dim SearchString As String = "xyzzy"
Dim bSearch As Byte() = encodme.GetBytes(SearchString)
Dim bFound As Boolean = True
Dim oneByte As Byte
Dim fileData As New IO.FileStream("C:\data.bin", FileMode.Open, FileAccess.Read)
Dim strMessage As String
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
For i As Integer = 0 To b.Length - bSearch.Length - 1
If b(i) = bSearch(0) Then
bFound = True
For j As Integer = 0 To bSearch.Length - 1
If b(i + j) <> bSearch(j) Then
bFound = False
Exit For
End If
Next
If bFound Then
fileData.Seek(i + 5, SeekOrigin.Begin)
strMessage = ""
For r As Integer = (i + 5) To fileData.Length() - 1
oneByte = fileData.ReadByte()
strMessage = strMessage + Chr(oneByte)
Next r
MsgBox(strMessage)
Else
MsgBox("File Doesn't have string")
Exit Sub
End If
End If
Next
End Sub
End Class

Answer 1

When looking for performance, it is best to avoid trying to walk through this kind of thing byte by byte. Instead you should use the facilities .NET provides you with. This example uses RegEx to find all matches of a string in any file, returning each match with everything that follows it until the next match or the end of the file in a UTF-8 string:
Imports System.IO
Imports System.Text
Imports System.Text.RegularExpressions
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim matches = FindStringMatchesInFile("C:\Infinite Air\snowboarding.exe", "data")
For Each m In matches
...
Next
End Sub
Private Function FindStringMatchesInFile(filename As String,
searchString As String) As List(Of String)
Dim output As New List(Of String)
Dim reader = New StreamReader(filename, Encoding.UTF8)
Dim re = New Regex(String.Format("{0}(?:(?!{0}).)*", searchString),
RegexOptions.Singleline Or RegexOptions.IgnoreCase,
Regex.InfiniteMatchTimeout)
Dim matches = re.Matches(reader.ReadToEnd())
For Each m As Match In matches
output.Add(m.ToString())
Next
Return output
End Function
End Class
The RegEx pattern definition is the following:
Matches the characters {searchString} literally (case insensitive)
Non-capturing group (?:(?!{searchString}).)*
* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Negative Lookahead (?!{searchString})
Assert that the Regex below does not match
Matches the characters {searchString} literally (case insensitive)
. matches any character
Global pattern flags
g modifier: global. All matches (don't return after first match)
s modifier: single line. Dot matches newline characters
i modifier: case insensitive.