how to use arrays before assigning values in vb

Question

I am trying to fill an array using a loop in VB. It basically read a .txt file and store all the line in an array. Im getting this error. "Array is used before it has been assigned values".

Dim fileEntries As String() = Directory.GetFiles(folderDIR, "*.txt")
Dim fileName As String
Dim fileReader As StreamReader
Dim strReadFile As String
Dim arrLines() As String
Dim i As Integer = 0
For Each fileName In fileEntries
    fileReader = File.OpenText(fileName)
    Do Until fileReader.Peek = -1
        strReadFile = fileReader.ReadLine()
        arrLines(i) = strReadFile
        i += 1
    Loop
Next

Is there any way I could do this, without pre-defining length of the array? I want the length of array to be number of lines in txt files. Hope i explained this well. Thank you in advance.

score 0 · Answer 1 · answered Aug 01 '14 at 11:11

0

There is quite a while, in vb6, I used ReDim to dynamically add a new entry in the array in the loop. Inconvenient: slow down the process. Better to count the occurrences needed from the file before creating the array. Hope that helps.

answered Aug 01 '14 at 11:11

Jeremy

1

Or, better yet, use one of the automatic collection classes. I can't remember if VB 6 had any of them (I think it did), but VB.NET certainly does. A *way* better option than `ReDim` if you don't know the size ahead of time. – Cody Gray - on strike Aug 01 '14 at 11:22

score 0 · Answer 2 · edited Aug 01 '14 at 11:24

0

you can declare arrlines as list:

Dim arrLines As New List(Of String)()

then you can convert to arrLines to array :

arrLines.ToArray()

try this:

Dim fileEntries As String() = Directory.GetFiles(folderDIR, "*.txt")
Dim fileName As String
Dim fileReader As StreamReader
Dim strReadFile As String
Dim arrLines As New List(Of String)()
Dim i As Integer = 0
For Each fileName In fileEntries
    fileReader = File.OpenText(fileName)
    Do Until fileReader.Peek = -1
        strReadFile = fileReader.ReadLine()
        arrLines.Add(strReadFile)
    Loop
Next
arrLines.ToArray()

edited Aug 01 '14 at 11:24

SysDragon

9,692
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answered Aug 01 '14 at 11:19

renis

171
7
16

2

You do not need an array at all here. A List can do everything that an array can do. The `arrLines.ToArray()` conversion is pointless. – Cody Gray - on strike Aug 01 '14 at 11:22
I agree. I just want to mention lists convert to array. – renis Aug 01 '14 at 11:28

score 0 · Accepted Answer · answered Aug 01 '14 at 11:45

You can do something like this:

Dim fileEntries As String() = Directory.GetFiles(folderDIR, "*.txt")
Dim fileName As String
Dim fileReader As StreamReader
Dim strReadFile As String
Dim arrLines() As String = {} 'Added this
'Dim i As Integer = 0 'Removed this
For Each fileName In fileEntries
    fileReader = File.OpenText(fileName)
    Do Until fileReader.Peek = -1
        strReadFile = fileReader.ReadLine()
        If arrLines.Length = 0 Then ReDim arrLines(0 To 0) Else ReDim Preserve arrLines(0 To arrLines.Length)
        arrLines(arrLines.Length - 1) = strReadFile
        i += 1
    Loop
Next

Or so...

how to use arrays before assigning values in vb

3 Answers3