reading a text file to an array - problem

[shadowfyre]

This seems so easy, but I'm pulling my hair out because I can't figure it out. Maybe some fresh eyes will be able to spot my glaringly simple mistake that I just can't find.

I want to read a text file in, line by line, sort the lines, and write back to the same text file. But I'm having problems assigning the line that is read from the file to an element of the array. Here's my code:

If File.Exists(outputpath & dir.ToLower & ".txt") Then
                'append to file
                sr = File.AppendText(outputpath & dir.ToLower & ".txt")
                sr.WriteLine(filename & ";" & filedate & ";" & dir & ";" & filesize)
                sr.Close()
                ' Sort file by filename
                Dim sortfile() As String
                Dim inputfile As New StreamReader(outputpath & dir.ToLower & ".txt")
                Dim inputstring As String
                inputstring = inputfile.ReadLine()
                Dim i As Integer = 0
                While (inputstring <> Nothing)
                    Try
                        sortfile(i) = inputstring
                    Catch ex As Exception
                        MessageBox.Show(ex.Message, "Caught Exception")
                    End Try
 
                    i = i + 1
                    inputstring = inputfile.ReadLine()
                End While
                inputfile.Close()
                System.Array.Sort(sortfile)
                Dim outputfile As New StreamWriter(outputpath & dir.ToLower & ".txt")
                Dim j As Integer = 0
                While j < sortfile.Length
                    outputfile.WriteLine(sortfile(j))
                    j = j + 1
                End While
                outputfile.Close()
            Else
                'create new file
                sr = File.CreateText(outputpath & dir.ToLower & ".txt")
                sr.WriteLine(filename & ";" & filedate & ";" & dir & ";" & filesize)
                sr.Close()

I keep getting the exception

Object reference not set to an instance of an object

when reading the file in, right at the line:

sortfile(i) = inputstring

Is this not allowed?

[nemaroller]

You haven't set the size of the array SortFile, only its reference.

Therefore, you have only declared to the compiler to set aside 2 bytes to point to a spot in memory where to begin the array.

But the array size is never declared, therefore, it fails.

You have to declare the size of the array when you declare the reference.

Dim SortFile(myinputfile.Lines) As String

So you will need a way to count the number of lines in your file to continue on the approach you are using.

[shadowfyre]

Ok, I see.

Is there a better way to go about this? I'm going to have to do something similar, yet slightly different (so I can't reuse this exact code) later in the program.

[shadowfyre]

I seem to have found a way around this.

Just before the assignment statement, sortfile(i) = inputstring, I put in Redim Preserve sortfile(i), so that it looks like this (Note the Try/Catch statement):

If File.Exists(outputpath & dir.ToLower & ".txt") Then
                'append to file
                sr = File.AppendText(outputpath & dir.ToLower & ".txt")
                sr.WriteLine(filename & ";" & filedate & ";" & dir & ";" & filesize)
                sr.Close()
                ' Sort file by filename
                'Dim sortfile() As String
                Dim inputfile As New StreamReader(outputpath & dir.ToLower & ".txt")
                Dim inputstring As String
                Dim sortfile() As String
                inputstring = inputfile.ReadLine()
                Dim i As Integer = 0
                While (inputstring <> Nothing)
                    Try
                        ReDim Preserve sortfile(i)      'I just added this
                        sortfile(i) = inputstring
                    Catch ex As Exception
                        MessageBox.Show(ex.Message, "Caught Exception")
                    End Try
 
                    i = i + 1
                    inputstring = inputfile.ReadLine()
                End While
                inputfile.Close()
                System.Array.Sort(sortfile)
                Dim outputfile As New StreamWriter(outputpath & dir.ToLower & ".txt")
                Dim j As Integer = 0
                While j < sortfile.Length
                    outputfile.WriteLine(sortfile(j))
                    j = j + 1
                End While
                outputfile.Close()
            Else
                'create new file
                sr = File.CreateText(outputpath & dir.ToLower & ".txt")
                sr.WriteLine(filename & ";" & filedate & ";" & dir & ";" & filesize)
                sr.Close()
            End If

This works. I get a sorted text file, but is this the best way to do it, or is there a more elegant way?