How to read a specific line from a text file in VB

vb.net

Solution

You will have to read all lines up to the one you're interested in. For example:

Function ReadLineWithNumberFrom(filePath As String, ByVal lineNumber As Integer) As String
    Using file As New StreamReader(filePath)
        ' Skip all preceding lines: '
        For i As Integer = 1 To lineNumber - 1
            If file.ReadLine() Is Nothing Then
                Throw New ArgumentOutOfRangeException("lineNumber")
            End If
        Next
        ' Attempt to read the line you're interested in: '
        Dim line As String = file.ReadLine()
        If line Is Nothing Then
            Throw New ArgumentOutOfRangeException("lineNumber")
        End If
        ' Succeded!
        Return line 
    End Using
End Function

This is because lines of text are variable-length records, and there is no way to guess the exact file offset where a specific line begins — not without an index.

If you frequently need to load a specific line, you have some more options:

Load the complete text file into memory, e.g. by using `File.ReadAllLines("Foobar.txt")`. This returns a `String()` array which you can access by line number directly.

Create a line number index manually. That is, process a text file line by line, and fill a `Dictionary(Of Integer, Integer)` as you go. The keys are line numbers, and the values are file offsets. This allows you to `.Seek` right to the beginning of a specific line without having to keep the whole file in memory.

Problem

I am creating a program that is supposed to write text into a text file, and should be able to read specific lines from a text file in VB (so if i needed to read a specific name I could select line 5 and it would display in the textbox). I am able to read the text from the text file but I do not know how to control a specific line. Here is my code: ``` Public Class Form1 Private Sub btnSubmit_Click(sender As System.Object, e As System.EventArgs) Handles btnSubmit.Click Dim writer As New System.IO.StreamWriter("/text.txt", True) writer.WriteLine(txtFirstName.Text) writer.WriteLine(txtLastName.Text) writer.WriteLine("-------------------------------------") writer.Close() End Sub Private Sub btnRead_Click(sender As System.Object, e As System.EventArgs) Handles btnRead.Click Dim reader As New System.IO.StreamReader("/text.txt") Dim FirstName, LastName As String FirstName = reader.ReadLine() LastName = reader.ReadLine() reader.Close() txtFirstName.Text = FirstName txtLastName.Text = LastName End Sub Private Sub btnClear_Click(sender As System.Object, e As System.EventArgs) Handles btnClear.Click txtFirstName.Clear() txtLastName.Clear() End Sub End Class ``` Any help would be appreciated. Thanks!

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