What is object reference not set to an instance of an object?

[sweehin18]

Do While lcp_objReader.Peek() <> -1

            str\_lcp\_Tmp = lcp\_objReader.ReadLine()

            str\_lcp\_data(a) = str\_lcp\_Tmp.Split(lcp\_delimiter, StringSplitOptions.RemoveEmptyEntries)



            If str\_lcp\_data(a).Length > 0 Then


                For index As Integer = 0 To str\_lcp\_data(a).Length - 1

                    Console.Write(str\_lcp\_data(a)(index) + "|")
          
                Next

                Console.Write(vbCrLf)
                a += 1

            End If

        Loop

i would like to print out the row 120, so i put

Console.Write(str_lcp_data(120)(index) + "|")

After debug, it gave the message "object reference not set to an instance of an object". How come it become like this? If i want to print the rows after row 120 (from 121 until end of the file), should i initialise a to 120 before do while loop?

[Tom Deketelaere]

this usualy accurs when you forget the initialize the object (the new keyword) for example: Dim ll As List(Of String) ll.Add("test") --> will give you're error Dim ll As new List(Of String) ll.Add("test") --> will not give the error so in you're case I think you forgot to initialize the str_lcp_data object

[sweehin18]

i got initialise str_lcp_data object

dim str_lcp_data (1000)() as string

[Tom Deketelaere]

that is not initialized (I think correct me if I'm wrong) that is declared to initialize the variable you need to enter data try this (just to see if this is the problem) str_lcp_data(120)="test" and then run and see if you still get the error if not you've found the cause wich is that there was no data to display if you still get the error then I don't really know what is going on

[TwoFaced]

You've created a jagged array (an array of arrays). When you do this each element points to another array. The array's initially aren't created. I think this is why you get the error. Take this for example

    Dim data(5)() As String
    data(0) = New String() {"Data1", "Data2", "Data3"}

    Console.WriteLine(data(0)(0))

    ' The next line will throw an error because the 2nd element
    ' doesn't point to an array yet.
    Console.WriteLine(data(1)(0))

What's probably happening is you are only reading x number of rows, so only the first x elements have been initialized properly. Trying to read beyond x will throw an error. You could initialize all the elements first like so:

    For i As Integer = 0 To data.Length - 1
        data(i) = New String() {}
    Next

Or you can just make sure you don't read beyond the number of lines read.