Reverse entries in a text file

[SkennyR]

Hi all..
I have a program I wrote that outputs abnormal program activity to a text file.
Example: Say user tries to choose a non-existant path:
message= "Path error encountered."
Goes to a sub called logme:
sub logme
open "errorlog.txt" for append as #1
print #1, message
close 1

Pretty simple I know.
But what if I wanted to limit the errorlog.txt file size to 100 entries?
Is there a simple way to delete entry #1 when entry #101 is made?

Currently program counts the number of lines in the file before writing to it. If over 100 then it copies everything except entry #1 to another file (erorlog.tmp). It then adds entry 101 to errorlog.tmp.
It then deletes errorlog.txt, renames errorlog.tmp to errorlog.txt. This results in 100 entries, first in-first out.
There has got to be a cleaner way to do this, and I know you are the guys to ask.
Thanks.

 

[fredericofonseca]

no better way with sequential files.

But creating a temp file is really not required (although benefic for a safeguard point of view).
You can load the whole file into a array, add your new entry, and then open the original file as output, and write your 2-101 entries to it again.



Regards

Frederico Fonseca
SysSoft Integrated Ltd

http://www.syssoft-int.com

 

[SkennyR]

Thanks,,
That is an idea.
But wont that take a huge chunk of memory?
And after I read my post, i think I need to clarify the title.
SEQ files write first on top, last on the bottom of the file.
I was wondering if there is anyway to reverse this order.
I think it would be easier to remove the bottom line of the file than it would be to remove the top line.

 

[dilettante]

There will be some sort of cost no matter what you do. 100 records in memory is nothing really if they aren't extremely long. It does have a clumsy feel to it though.

One alternative might be a fixed-length record random file. Let the first record contain a "last entry" record index field and the next 100 records hold log entries. You just write to LastUsed + 1, wrapping back to the beginning in a circular fashion when you get past the last slot.

Yes you'll need to have a "log viewer" program, or at least something that can unroll the log file into a sequential "log report" textile.


Of course at that point you may as well have a "viewer/reporter" that does the trimming back to 100 entries on viewing.

But there isn't anything that will impose some alternative structure on a stream file for "free." It's a case of "pay me now or pay me later.

 

[SkennyR]

Thanks for the input.
Could you give me a sample of using the random file?

 

[Swi]

Take a look at the below thread:

thread222-689374

Swi

 

[dilettante]

There is a bit of work to it, but you only need to write the code once. Here's a combined logger/viewer:

Option Explicit
'
'Logs events up to LOG_MAX entries and then recycles
'log records.
'
'Form has 4 controls:
'
'   1 multiline textbox txtLog
'   3 command buttons cmdLogA, cmdLogB, & cmdViewLog
'
'cmdViewLog displays log entries "newest to oldest"
'

Private Const LOG_FILE As String = "appevents.log"
Private Const LOG_MAX As Long = 10

Private Type LogControl
    LastEntry As Long
End Type

Private Type LogEntry
    Timestamp As String * 24
    EventClass As String * 1 'vbNullChar for unused records
    Description As String * 100
End Type

Private Function FilePresent(ByVal FileName As String) As Boolean
    On Error Resume Next
    FileLen FileName
    FilePresent = Err.Number = 0
End Function

Private Sub LogEvent(ByVal EventClass As String, _
                     ByVal Description As String)
    Dim blnNoFile As Boolean
    Dim intFile As Integer
    Dim leRecord As LogEntry
    Dim lcRecord As LogControl
    
    With leRecord
        .Timestamp = Format$(Now(), "yyyy/mm/dd \@ hh:nn:ss AM/PM")
        .EventClass = EventClass
        .Description = Description
    End With
    
    blnNoFile = Not FilePresent(LOG_FILE)
    intFile = FreeFile(0)
    Open LOG_FILE For Random As #intFile Len = Len(leRecord)
    If blnNoFile Then
        lcRecord.LastEntry = 1
    Else
        Get #intFile, LOG_MAX + 1, lcRecord
        lcRecord.LastEntry = (lcRecord.LastEntry Mod LOG_MAX) + 1
    End If
    Put #intFile, LOG_MAX + 1, lcRecord
    Put #intFile, lcRecord.LastEntry, leRecord
    Close #intFile
End Sub

Private Sub cmdLogA_Click()
    LogEvent "A", "Testing, testing"
End Sub

Private Sub cmdLogB_Click()
    LogEvent "B", "The quick brown fox jumped over the lazy dog"
End Sub

Private Sub cmdViewLog_Click()
    Dim intFile As Integer
    Dim lcRecord As LogControl
    Dim lngRec As Long
    Dim leRecord As LogEntry
    
    If FilePresent(LOG_FILE) Then
        intFile = FreeFile(0)
        Open LOG_FILE For Random As #intFile Len = Len(leRecord)
        Get #intFile, LOG_MAX + 1, lcRecord
        lngRec = lcRecord.LastEntry
        txtlog.Text = ""
        Do
            Get #intFile, lngRec, leRecord
            With leRecord
                If .EventClass <> vbNullChar Then
                    txtlog.Text = txtlog.Text _
                                & .Timestamp & " " _
                                & .EventClass & " " _
                                & RTrim$(.Description) & vbNewLine
                End If
            End With
            lngRec = ((lngRec + LOG_MAX - 2) Mod LOG_MAX) + 1
        Loop While lngRec <> lcRecord.LastEntry _
               And leRecord.EventClass <> vbNullChar
        Close #intFile
    Else
        txtlog.Text = "*no entries*"
    End If
End Sub

This example puts the "control" record after the log entry records (set to just 10 here).