Weird behavior with streamreader. How do I fix?

Question

I have a ~ 1 GB text file containing a line of text followed by 100 million lines each containing a prime number followed by a last line with a zero. I've used (read with streamreader) this file in several VB (2010) programs without problem.  This morning,
I tried writing a simple program which would tell me what the greatest gap is between any two of the primes in the file. After I debugged (due to some silly logic errors which shouldn't be relevant) the program's behavior changed. It was reading the file but
now all it does is find a single line, rather than 100 million lines AND the single line is the filename rather that what the first text line actually is.
I open the file in Form1_Load sub as follows:
Dim fr As System.IO.Streamreader
Dim s As string
fr = New System.IO.Streamreader("filename.txt")
s = fr.readline
and from that point I ran into problems when I used a RichTextBox to display (via .AppendText) the output using a While fr.peek >0 loop. I've previously run into the problem that writing to textboxes and richtextboxes take enormous amounts of time to
run (hours, if not days)  while the same logic but directed to an output file runs in a couple of minutes. So, I closed the program (forced closed) and rewrote output to a streamwriter to a new filename. Since then, I can't get any real output from the
file, even when I change output back to a textbox. The text file name is Primes1E9.txt and the first line is:> This file contains 102886524 primes, the largest is 2099999983 < and the second line is 2 then 3, 5, 7, etc up to 2099999983 followed by a
line containing a 0. Here is the problem: when I attempt to read past the first line, the program causes an error (I can catch error in catch try block) or if I don't use a catch block then I get an unhandled error. AND the first readline tells me that the
first line is Primes1e9.txt, which it is NOT. (again, that is the filename, not the first line of text). I've tried closing VS2010, shutting off my PC and rebooting, and deleting and replacing the copy of the text file, all to no avail: I continue to get the
erroneous behavior. Windows explorer confirms the first 20,000 or so lines are correct in the textfile, but my VB2010 program isn't seeing it correctly for some reason. Any ideas?
I use VS2010 on Win7 (64bit), files are on my E: drive (E:\<root> , specifically) with executables in the usual subdirectory (bin\debug).
David E. Nalepa

Answer 1

Hi
The code below took 144 seconds on my system to read and fill a similar amount of data to the RTB.
' Form1 with RichTextBox1
Option Strict On
Option Infer Off
Option Explicit On
Public Class Form1
Dim sw As New Stopwatch
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
' WriteDummyData()
sw.Start()
FillRTB()
sw.Stop()
Me.RichTextBox1.AppendText("Time: " & sw.ElapsedMilliseconds.ToString & "ms" & "(" & sw.ElapsedMilliseconds \ 1000 & "sec)")
' on my system it took 144 seconds to fill the RTB
End Sub
Private Sub FillRTB()
Me.RichTextBox1.LoadFile(Application.StartupPath & "\Data\MyFile.txt", RichTextBoxStreamType.PlainText)
End Sub
Public Sub WriteDummyData()
' this created approx 1GB data text file
Dim fn As String = Application.StartupPath & "\Data\MyFile.txt"
Dim pp As String = My.Computer.FileSystem.GetParentPath(fn)
If IO.Directory.Exists(pp) Then
Using sr As IO.StreamWriter = New IO.StreamWriter(fn, False)
For r As Integer = 1 To 100000000
sr.WriteLine(r.ToString)
Next
End Using
Else
My.Computer.FileSystem.CreateDirectory(pp)
WriteDummyData()
End If
End Sub
End Class
Regards Les, Livingston, Scotland