Member Avatar for yongj

I have a textfile I need to open and I need to put each line into the array. What is the simplest way to add the elements/each line's data into the array while increasing the array as it reads each line? This is blowing my mind right now...

I thought about using a counter and then redim-ing the array (while preserving of course). If so, how would that be constructed? Thanks!

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  • Latest Post Latest Post by GeekByChoiCe

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If you truly need an array, consider reading lazily and only materializing once at the end. File.ReadLines streams the file line-by-line (unlike ReadAllLines, which loads the entire file at once), so it is memory-friendly for large inputs. You can also normalize or filter as you go:

Dim path As String = "C:\path\file.txt"
Dim lines As String() =
    System.IO.File.ReadLines(path).
        Select(Function(s) s.Trim()).
        Where(Function(s) s <> "").
        ToArray()

This avoids repeatedly resizing an array. ReDim Preserve reallocates and copies the array each time, which is O(n^2) overall and gets slow as the file grows; see the VB reference for details on how Preserve copies elements ReDim Statement. For very large files, you can also process each line without creating an array at all: iterate File.ReadLines(path) and handle each line inside the loop, which keeps memory usage flat. If you need a specific text encoding (for example, UTF-8 with BOM or Windows-1252), use the encoding overload of ReadLines or open a StreamReader with the proper Encoding. Docs: File.ReadLines, and for resource cleanup when manually using readers, the VB Using statement.

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Member Avatar for Member #857553

I would use a list(Of T)

Heres 2 ways you could do that.

'Add with list(Of T)
        Dim fStream As New System.IO.FileStream("c:\text.txt", IO.FileMode.Open)
        Dim sReader As New System.IO.StreamReader(fStream)

        Dim List As New List(Of String)
        Do While sReader.Peek >= 0
            List.Add(sReader.ReadLine)
        Loop

        'to go back to an array
        Dim thisArray As String() = List.ToArray

        fStream.Close()
        sReader.Close()


        'with Array
        fStream = New System.IO.FileStream("c:\text.txt", IO.FileMode.Open)
        sReader = New System.IO.StreamReader(fStream)

        Dim sArray As String()
        Dim Index As Integer = 0

        Do While sReader.Peek >= 0
            ReDim Preserve sArray(Index)
            sArray(Index) = sReader.ReadLine
            Index += 1
        Loop

        fStream.Close()
        sReader.Close()
Edited by Member #857553 because: n/a
Member Avatar for Member #857553

Keep in mind you can use a List(of T) the same way as an array.

'You can use the List(Of T) the same way as an array.
        Dim thisLine As String
        For i = 0 To List.Count - 1
            thisLine = List(i)
        Next

        For Each S As String In List
            thisLine = S
        Next


        'And if you wanted your array to be 1 based then you could
        'get rid of the index.
        Dim sArray(0) As String
        Do While sReader.Peek >= 0
            ReDim Preserve sArray(sArray.Length)
            sArray(UBound(sArray)) = sReader.ReadLine
        Loop
Member Avatar for GeekByChoiCe

why not just:

Dim lines() As String = IO.File.ReadAllLines("C:\myFie.txt")
For Each line As String In lines
	'do what you want with each single line
Next
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