Trying to find substring efficiently.

[Rob S]

Hi,
I am not sure where I am going wrong with this code.
It seems to work fine for a small text file but when I use files larger than 100MB it does not give me an accurate count.
The program is pretty simple. It should return the number of occurences of a substring from within a text file. I look for a match to the first character of the substring and if found then my code should test to see if the whole substring exists.
I have run several tests but for some reason I am not getting an accurate result. I used the windowsupdate.l og file. My code trturned 34596 hits but when I used MS Word to find the number of occurences it returned 50096. Obviously there is something wrong with my code but I cant seem to figure it out.
Any help would be highly appreciated. Thanks a lot.
Rob

here is the code:

Imports System.IO
Imports System.Diagnostics
Imports System.Threading.Tasks
Imports System.Text
 
 
 
Module Module1
 
    Sub Main()
        Dim sw As New Stopwatch
        sw.Start()
        Dim fs As New FileStream("C:\mpi\windowsupdate.log", FileMode.Open, FileAccess.Read)
        Dim br As New StreamReader(fs)
        Dim searchterm As String = "WINDOWS"
        Dim bytesTerm As Byte() = Encoding.ASCII.GetBytes(searchterm)
        Dim WordLen As Integer = searchterm.Length - 1
        Dim matchcount As Integer = 0
        Dim matches As Boolean = False
        Dim c As Byte
        Console.WriteLine("Processing...")
        While br.Peek <> -1
            c = br.Read
            If c = bytesTerm(0) Then
                matches = True
                For i = 1 To WordLen
                    c = br.Read
                    If c = bytesTerm(i) Then
                        matches = True
                    Else
                        matches = False
                    End If
                Next
                If matches = True Then
                    matchcount += 1
                    matches = False
                End If
            End If
        End While
        sw.Stop()
        Console.WriteLine("Total matches:" & matchcount)
        Console.WriteLine("Total time:" & sw.Elapsed.Seconds)
        Console.ReadLine()
        br.Close()
        fs.Close()
 
    End Sub
 
End Module
 

[Rabbit]

A couple of things. You need to exit out of that For loop once you hit a False. Otherwise, if the last letter matches, it's going to return a hit. Second, you're only matching on capital letters, what about lowercase?

[Rob S]

Hey Rabbit,
Thanks a lot for your quick response. I made the changes you suggested and it works fine now. As you noticedthe search is case sensetive and will only return an exact hit which is what i was looking for anyways. I might modify the algorithm at some point to work with regular expressions as well.
By the way, have you ever worked with MPI or any kind of distributed applications?
Take care.
Rob

[Rabbit]

Sorry, can't say that I have.