Question

I want to extract some specific lines from a text file to other text file. i am using the following code

    Imports System.IO



Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim Tr As IO.TextReader = System.IO.File.OpenText("C:\Assignment.txt")
        For c As Integer = 1 To 10

            If c = 7 Then
                Dim MyFileLine As String = Split(Tr.ReadToEnd(), vbCrLf)(c) & vbCrLf
                Tr.Close()



                Dim TW As System.IO.TextWriter
                'Create a Text file and load it into the TextWriter 
                TW = System.IO.File.CreateText("C:\Assignment1.txt")
                TW.WriteLine(MyFileLine)
                'Flush the text to the file 
                TW.Flush()
                'Close the File 
                TW.Close()
            End If

        Next c
    End Sub
End Class

But this code extract only the line no 7 where i want to extract the 8th,9th,10th,14th,15th,16th, lines also . Please guide me the right solution. Thank u in advance.

Answer 1

There seems to be several issues here. I will correct them and then explain below:

Imports System.IO

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim currentLine As String
        Dim lineCounter As Integer = 1
        Dim lineNumbersRequired As List(Of Integer) = New List(Of Integer)
        lineNumbersRequired.Add(7)
        lineNumbersRequired.Add(8)
        lineNumbersRequired.Add(9)
        lineNumbersRequired.Add(10)
        lineNumbersRequired.Add(14)
        lineNumbersRequired.Add(15)
        lineNumbersRequired.Add(16)

        Dim TW As System.IO.TextWriter
        'Create a Text file and load it into the TextWriter 
        TW = System.IO.File.CreateText("C:\Assignment1.txt")

        Using Tr As IO.TextReader = New IO.StreamReader("C:\Assignment.txt")
            While Not Tr.EndOfStream
                If lineNumbersRequired.Contains(lineCounter) Then
                    Dim MyFileLine As String = Split(currentLine, vbCrLf)(c) & vbCrLf
                    TW.WriteLine(MyFileLine)
                End If
                lineCounter = lineCounter + 1
            End While
        End Using

        TW.Flush()
        'Close the File 
        TW.Close()

    End Sub
End Class

NOTE: Code not tested, but should be pretty close if you do get a few compile errors!

Ok then, just a quick rundown of what I did here:

1. Changed the For Loop into a while because you had the for loop running from 1 To 10, so even if it worked, then you would have never read past the 10th line in your file. So I have changed it to a while loop that will end when the TextReader has read all lines in the file. Also the current line read from the file has been added to a new variable called currentLine.
2. The new currentLine variable is now used to populate the lines of your writing file.
3. I have added a list of Integers that will hold the line numbers you want to keep, then within the while loop I have a counter that counts each line as it is processed and if this counter is inside the list of line numbers you want to save into your output file, then it will output the current line.

Let me know how you get on, and if you need more of an explanation on any of it then please ask.