Text file Handling

[insomnia]

Hi there, need to be able to create a text file that stores information like so :
this i have managed with a stream writer/append

1
aaaa
bbbbb
ccccccc
dddddddd
------------------
2
aaaa
bbbbb
cccccc
dddddddd

My problem is now i have to "Edit" an individual line within the text file.
e.g. The user enters number "2" in to a text box to verify which record they wish to access. (the streamreader needs to locate that record) The user then needs to change the entry details for "bbbbb" to "xxxxx" for that record only.

Any ideas on how to search a file for the identification number e.g. 2 and then modify the 2nd line down within that record.

thanks in advance

[Frinavale]

Hi there, need to be able to create a text file that stores information like so :
this i have managed with a stream writer/append

1
aaaa
bbbbb
ccccccc
dddddddd
------------------
2
aaaa
bbbbb
cccccc
dddddddd

My problem is now i have to "Edit" an individual line within the text file.
e.g. The user enters number "2" in to a text box to verify which record they wish to access. (the streamreader needs to locate that record) The user then needs to change the entry details for "bbbbb" to "xxxxx" for that record only.

Any ideas on how to search a file for the identification number e.g. 2 and then modify the 2nd line down within that record.

thanks in advance

Have you checked MSDN?
There's an article on How To Read Text From A File. It tells you how to grab the lines from the text file...

One possible solution would be to take all of the lines from the text file and add them to an ArrayList. Then, depending on what the user has entered, edit that String (at that index array)...after your finished editing, over write the text file with the contents of the ArrayList....

There are many other ways to solve this problem.
Give it a try and then get back to us if you get stuck on something more specific.

-Frinny

[balabaster]

Are we talking a flat file storage format of a DataTable?

I'd probably create a DataTable of x columns, where the first is the primary key and the remaining items (before the -------) are the other fields. Then I'd create a DataRow of the same amount of columns parsing each item (before the -------) into one of the fields in the DataRow. As each DataRow is completed, I'd add it to the DataTable. Once all of the data is in the DataTable it's far easier to query and thus making further coding simpler and more efficient as you are now querying memory instead of relaying to/from disk for each read.

My save would then iterate the DataTable writing each DataRow back to the file...you could choose just to write the rows/fields that have changed, or you could write the whole file... depending on the file size and how much data has changed depends on which method you're likely to choose. If the amount of data is small or a large portion of the data changes each time, then it's mostly likely more efficient to write the whole table back to the file, otherwise you may wish to just write the changed fields.

Just my humble 2 cents... if this is purely a file read/write exercise, then I'm most likely complicating the issue for you - even though from a code standpoint it's far more elegant/efficient.

[insomnia]

One possible solution would be to take all of the lines from the text file and add them to an ArrayList. Then, depending on what the user has entered, edit that String (at that index array)...after your finished editing, over write the text file with the contents of the ArrayList....
-Frinny

This was the idea i had in mind, grabbing the lines from the text file and putting them in to an array.

So do you recommend reading the entire text file and turning it in to an arraylist?



Thanks Balablaster but yes it is a simple read/write/ammend task.
im trying to make a very simple mini database to store records using a text file



This is what i was trying to do before, although it now clearly rubbish, I will try and give the arraylist idea a go:

 
 Dim FILE_NAME As String = "C:\sample.txt"
 
 
        Dim LineIn As String
 
        If File.Exists(FILE_NAME) = True Then
 
            ' Open and read my file 
 
            oRead = File.OpenText(FILE_NAME)
            While oRead.Peek <> -1
                LineIn = oRead.ReadLine()
 
 
'If the line found matches the ID number the user entered
 
                If LineIn = membersearch.Text Then 
 
'HERE IS WHERE I WANT TO CHANGE fields
 
                    oRead.Close()
 
 
' Gets messy after
 
                    MsgBox(LineIn & " Found.")
 
                    ' Write to an existing file 
                    oWrite = File.AppendText(FILE_NAME)
 
'wanted then these lines to write within that record
 
                    oWrite.WriteLine(changetime.Text)
                    oWrite.WriteLine(changelevel.Text)
                    oWrite.WriteLine("---------")
                    oWrite.Flush()
                    oWrite.Close()
                    Exit While
                End If
 
 
 

[Frinavale]

Make one function for reading the file into your ArrayList.

Once the file's read into the array, then make the changes to the strings at whatever spot they should be modified.

After this is finished (or if you fail), call another function that opens the file again and overwrites it with the modified data.

[insomnia]

ok thanks ill give it a go

[balabaster]

Not sure if this is any use...it's a different method than the one you're using - it may provide more flexibility down the road:

Function InitDataStructure() As DataTable
        Dim Data As New DataTable
        Dim oKeyCol As New DataColumn("DataKey", GetType(Integer))
        oKeyCol.AutoIncrement = True
        oKeyCol.Unique = True
        Data.Columns.Add(oKeyCol)
        Data.Columns.Add(New DataColumn("Field1", GetType(String)))
        Data.Columns.Add(New DataColumn("Field2", GetType(String)))
        Data.Columns.Add(New DataColumn("Field3", GetType(String)))
        Data.Columns.Add(New DataColumn("Field4", GetType(String)))
        Dim oPrimaryKey() As DataColumn = {Data.Columns("DataKey")}
        Data.PrimaryKey = oPrimaryKey
        Return Data
End Function
 
Function WriteDataToDisk(ByVal Data As DataTable, ByVal FileName As String) As Boolean
        Dim sOut As String = ""
        For iRow As Integer = 0 To Data.Rows.Count - 1
            For iCol As Integer = 0 To Data.Columns.Count - 1
                sOut &= Data.Rows(iRow).Item(iCol) & ControlChars.CrLf
            Next
            If Not iRow = Data.Rows.Count - 1 Then
                sOut &= "------------------" & ControlChars.CrLf
            End If
        Next
        System.IO.File.WriteAllText(FileName, sOut)
End Function
 
Function ReadDataFromDisk(ByVal FileName As String) As DataTable
        Dim oTable As DataTable = InitDataStructure()
        Dim sLines() As String = System.IO.File.ReadAllLines(FileName)
        Dim oData As New ArrayList
        For i As Integer = 0 To sLines.Length - 1
            If Not (sLines(i).StartsWith("-")) Then
                oData.Add(sLines(i))
            End If
            If (sLines(i).StartsWith("-")) Or (i = sLines.Length - 1) Then
                oTable.Rows.Add(oData.ToArray)
                oData.Clear()
            End If
        Next
        Return oTable
End Function
 
Sub Main()
        Dim DataFolder As String = System.Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory)
        Dim DataFile As String = DataFolder & "\TestDB.txt"
        Dim oDT As DataTable = ReadDataFromDisk(DataFile)
 
        Dim iCurrentSelection As Integer = 2 'Currently selected record is 2
        oDT.Rows(iCurrentSelection).Item("Field1") = "MyTestChange" 'Here is my change to the record
 
        If WriteDataToDisk(oDT, DataFile) Then MsgBox("Update successfully saved.") 'Save the data back to my datafile - or another datafile if you choose...
 
End Sub

Adding a new record to your database would be as simple as:

Dim NextRec As Integer = oDT.Rows(oDT.Rows.Count - 1).Item(0) + 1
Dim NewData() As String = {NextRec, "Test1", "Test2", "Test3", "Test4"}
oDT.Rows.Add(NewData)

And deleting a record from your database would be as simple as:

Dim iKeyToDelete As Integer = 4
oDT.Rows.Find(iKeyToDelete).Delete()

Sorting your records is also a piece of cake:

oDT.DefaultView.Sort = "Field2 Desc" 'for Field2 descending
'Or
'oDT.DefaultView.Sort = "DataKey Asc" 'for datakey ascending

[Frinavale]

Not sure if this is any use...it's a different method than the one you're using - it may provide more flexibility down the road:
...

I like your solution Balabaster :)
I have a feeling it's a bit too complicated for what this OP is looking for but I'm sure that it will help other people who are looking for this type of solution :)

-Frinny

[balabaster]

I like your solution Balabaster :)
I have a feeling it's a bit too complicated for what this OP is looking for but I'm sure that it will help other people who are looking for this type of solution :)

-Frinny

Thanks - I have a feeling it's a bit too complex too...

I wasn't going to post the code, but I thought I'd do it as an exercise to raise the point that there's usually more than one way to skin a cat and that sometimes a different approach will pay dividends when it comes to extending the software.

Lots of programmers get blinkered in and spend tonnes of time trying to code around issues that could be avoided with some extra forethought. A reminder to think outside the box that is the design-brief ;o)

[insomnia]

Balablaster thanks for that.

And how would you ammend an existing record in your data base ?

The problem i am having with my data base at the moment is.

I cant AMMEND an existing record within the text file.
Ive just started looking at arrays as suggested before, but i am quite a novice.

 
 
 
        reader = File.OpenText("C:\sample.txt")
 
        aryText = (reader.ReadToEnd.ToCharArray())
 
        reader.Close()
 
        MsgBox(aryText)
 
 

Now the whole file is in an array how do i search and ammend ?

[balabaster]

Balablaster thanks for that.

And how would you ammend an existing record in your data base ?

Lines 50/51 of my original code show you how to change a record - the code below should be easier to follow - this is how you would edit the field called "Field4" in the record having the primary key of 3

Dim iKeyToChange As Integer = 3
Dim oDR As DataRow = oDT.Rows.Find(iKeyToChange)
oDR.Item("Field4") = "This is my new test value"
'Don't forget to write the data table back to the file when we're done making changes
WriteDataToDisk(oDT, DataFile)