DotNet Visual Basic: Yet Another StreamReader q

• dminder / 104 / Fri, 27 Mar 2009 21:27:00 GMT / Comments (5)
• I am searching through thread after thread and not coming up with the answer....
  
  I open a streamreader and point it to a logfile. Done, Cool no problem. If I have not opened this file before I read the whole thing in at once to get to the end of stream, again no problem. I get/save the position by getting the .Length of the stream (not sure if this is best practice, only way I could figure how to do it). Once the filesystemwatcher triggers it comes back in and is supposed to move the last known position and read the next line. All I am getting is the last 2 characters of the line and the line is alot longer than that. What am I overlooking or not doing correctly here??
  
  Here is what I have gotten so far:
  
  Dim currLogFile As String=""
  Dim filepos As Long=0
  
  Private Sub ReadLogFile()
  If currLogFile = "" Then Exit Sub
  Dim fs As StreamReader = File.OpenText(currLogFile)
  Dim s As String
  
  Try
  'Check to see if there is a position
  If filepos = 0 Then
  filepos = fs.ReadToEnd().Length
  Exit Sub
  End If
  
  'Get to the last position in the file
  fs.BaseStream.Seek(filepos, SeekOrigin.Begin)
  
  'Read the last line added
  s = fs.ReadLine()
  
  'used for testing purposes to see what was read in
  MsgBox(s)
  
  Catch ex As Exception
  ShowErrorMessage(ex.ToString)
  Finally
  fs.Close()
  fs.Dispose()
  End Try
  End Sub
  
  Also, I need to know is this the best way to do this? This log file is a high volume log file and can be updated sometimes up to 20 times a second. I am only reading from it so that I can detect specific messages. I have little to no control over the size of the file or how fast it updates and it could be as large as 75 MB or so.
  
  Thanks all!
  
  D
• Keywords:

  streamreader, dotnet, visual basic, vb, .net

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• 1. Nice code.
     
     Are you saying that each time the file is updated you want a message box to appear showing only the new data that has appended to the end?
     
     If so everything looks good but you might want to change your code to this.
     
     s = fs.ReadToEnd
     
     I have know idea how efffecient this code is but hopefully it will help be able to move forward.

     cpcishere | Tues, 04 Dec 2007 13:38:00 GMT |

  2. I think the stream and basestream positions are not synchronised, try having a look at this it may help;
     
     http://msdn2.microsoft.com/en-us/library/system.io.streamreader.discardbuffereddata.aspx

     tinbeard | Tues, 04 Dec 2007 13:39:00 GMT |

  3. I implemented both suggestions plus also added in an update for the file position so it would take into account things that would be added. I am still only getting the last 2 characters of the last line of data. :( :cry:
     
     'Shows that I am importing the correct namespace :)
     Imports System.IO
     
     'Globals
     Dim currLogFile As String = ""
     Dim filepos As Long = 0
     
     Private Sub ReadLogFile()
     If currLogFile = "" Then Exit Sub
     Dim fs As StreamReader = File.OpenText(currLogFile)
     Dim s As String = ""
     
     Try
     'Check to see if there is a position
     If filepos = 0 Then
     filepos = fs.ReadToEnd.Length
     End If
     
     'Get the end of the file
     fs.DiscardBufferedData()
     fs.BaseStream.Seek(filepos, SeekOrigin.Begin)
     
     'Read the last line added
     s = fs.ReadToEnd.ToString
     
     'Used for testing purposes to see what was read in
     MsgBox(s)
     
     'Reset filepos to reflect added info
     filepos = fs.ReadToEnd.Length
     
     Catch ex As Exception
     ShowErrorMessage(ex.ToString)
     Finally
     fs.Close()
     fs.Dispose()
     End Try
     End Sub
     
     Private Sub EQ2LogFileWatcher_Changed(ByVal sender As Object, _
     ByVal e As System.IO.FileSystemEventArgs) Handles EQ2LogFileWatcher.Changed
     'This is where it sets the path for the log file to be read from
     Try
     If currLogFile = "" Then currLogFile = e.FullPath.ToString
     ReadLogFile()
     Catch ex As Exception
     ShowErrorMessage(ex.ToString)
     End Try
     End Sub

     dminder | Tues, 04 Dec 2007 13:40:00 GMT |

  4. Ok, I took a slightly different approach and I am not sure how much it will impact performance but it does the trick for now.
     
     Private Sub ReadLogFile()
     If currLogFile = "" Then Exit Sub
     Dim fs As StreamReader = File.OpenText(currLogFile)
     Dim s As String = ""
     Dim i As Long
     
     Try
     'Get a total Line Count from the GetGo
     If linecount = 0 Then
     Do While Not fs.EndOfStream
     fs.ReadLine()
     linecount += 1
     Loop
     linecount -= 1
     Else
     'move to LineCount
     Do While i < linecount
     fs.ReadLine()
     i += 1
     Loop
     End If
     
     'Read the last line added
     s = fs.ReadToEnd.ToString
     
     'Add 1 to LineCount
     linecount += 1
     
     'Used for testing purposes to see what was read in
     MsgBox(s)
     
     Catch ex As Exception
     ShowErrorMessage(ex.ToString)
     Finally
     fs.Close()
     fs.Dispose()
     End Try
     End Sub
     
     If anybody knows what I was doing incorrectly on the original code, please let me know. Just to give you an idea on how these log files can grow that I am working on. I took a snippet of one and it is 2876 lines of text to go through. To have to read every line for a live one, that I would guess is in excess of 100,000 lines would be ludicrous!!
     
     Thank you all again as always your input is muchly appreciated.
     
     D

     dminder | Tues, 04 Dec 2007 13:41:00 GMT |

  5. I think I might have figured it out.
     This works for me.
     
     Dim currLogFile As String=""
     Dim filepos As Long=0
     
     Private Sub ReadLogFile()
     If currLogFile = "" Then Exit Sub
     Dim fs As StreamReader = File.OpenText(currLogFile)
     Dim s As String
     
     Try
     'Check to see if there is a position
     If filepos = 0 Then
     filepos = fs.ReadToEnd().Length
     Exit Sub
     End If
     
     'Get to the last position in the file
     fs.BaseStream.Seek(filepos, SeekOrigin.Begin)
     
     'Read the last line added
     s = fs.ReadToEnd
     
     'used for testing purposes to see what was read in
     MsgBox(s)
     filepos += s.Length
     Catch ex As Exception
     ShowErrorMessage(ex.ToString)
     Finally
     fs.Close()
     fs.Dispose()
     End Try
     End Sub

     cpcishere | Tues, 04 Dec 2007 13:42:00 GMT |