Change just one line in a text file? - vb.net

Question

I have a text file with the format:
(title,price,id#)
CD1,11.00,111111
CD2,12.00,222222
CD3,13.00,333333
CD4,14.00,444444
CD5,15.00,555555
CD6,16.00,666666
What is the best way to go change the price of the appropriate CD if I'm given the id# and new price?
I'm sure it has something do to with getting the line and splitting it, but I'm not sure how I edit just one line and not mess up the whole file.

Answer 1

You can't rewrite a line without rewriting the entire file (unless the lines happen to be the same length). For such a small file it's probably the easiest to change the line in memory and then rewrite all to the file:
Dim idToFind = "444444"
Dim newPrice = "100"
Dim lines = IO.File.ReadAllLines(path)
For i = 0 To lines.Length - 1
Dim line = lines(i)
Dim fields = line.Split(","c)
If fields.Length > 2 Then
Dim id = fields(2)
If id = idToFind Then
Dim title = fields(0)
lines(i) = String.Format("{0},{1},{2}", title, newPrice, id)
Exit For
End If
End If
Next
IO.File.WriteAllLInes(path, lines)

Answer 2

Okay, now we know it's a short file, life becomes much easier:
Load the file into an array of lines using File.ReadAllLines
Find the right line using string.Split to split each line into the constituent parts, and check the ID.
When you've found the right line, replace it with the complete new line
Write the file back with File.WriteAllLines
That should be enough to get you going.

Answer 3

If its just a file with like 25 lines, you could do a simple input-transform-output routine and update the price per line.
Something like this (Using Streamreader / writer ).
Sub UpdatePrice(ByVal pricesToUpdate As Dictionary(Of Integer, String), ByVal inputPath As String)
If Not IO.File.Exists(inputPath) Then Return
Try
Using inputStream = New IO.StreamReader(inputPath, System.Text.Encoding.UTF8, True)
Using outputStream = New IO.StreamWriter(inputPath + ".tmp", False, System.Text.Encoding.UTF8)
While Not inputStream.EndOfStream
Dim inputLine = inputStream.ReadLine
Dim content = inputLine.Split(","c)
If Not content.Length >= 3 Then
outputStream.WriteLine(inputLine)
Continue While
End If
Dim id As Integer
If Not Integer.TryParse(content(2), id) Then
outputStream.WriteLine(inputLine)
Continue While
End If
If Not pricesToUpdate.ContainsKey(id) Then
outputStream.WriteLine(inputLine)
Continue While
End If
content(1) = pricesToUpdate(id)
outputStream.WriteLine(String.Join(",", {content(0), content(1), content(2)}))
End While
End Using
End Using
If IO.File.Exists(inputPath + ".tmp") Then
IO.File.Delete(inputPath)
IO.File.Move(inputPath + ".tmp", inputPath)
End If
Catch ex As IO.IOException
If IO.File.Exists(inputPath + ".tmp") Then IO.File.Delete(inputPath + ".tmp")
End Try
End Sub