C# Object reference not set to an instance of an object.

Question

I have the following piece of code that is suppose to extract some info from a file.

private string[][] users;
private string userID;

public void getInfo()
{

    string[] lines = System.IO.File.ReadAllLines(@"U:\Final Projects\Bank\ATM\db.txt");

    for (int i = 0; i < lines.Count(); i++ )
    {
        string[] values = lines[i].Split(',');
        for (int b = 0; b < 5; b++ )
        {

            users[i][b] = values[b];

        }


    }
}

the line users[i][b] = values[b]; returns the error : " Object reference not set to an instance of an object. " but I am not sure why. the code is suppose to read each line and split the line by , and create 2 dimensional array from the info.

Seems like a homework, anyway, try initializing users variable — Abdul Munim, Dec 03 '11 at 13:17
What is the value of i and b when the exception is thrown? Either users[i][b] or values[b] is causing the exception -- can you tell which one? — Keith, Dec 03 '11 at 13:18
@Munim its a final project, but I am not asking you to do it for me :) just need help with, is that against the rules? — Ahoura Ghotbi, Dec 03 '11 at 13:20
@Keith its value `b` and the value is 0 when the error appears — Ahoura Ghotbi, Dec 03 '11 at 13:21
See [What is a NullReferenceException in .NET?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net) — Keith, Dec 03 '11 at 13:28

score 2 · Answer 1 · answered Dec 03 '11 at 13:19

2

I think you need to allocate space for the array

string[,] users = new string[M,N];

answered Dec 03 '11 at 13:19

parapura rajkumar

22,951
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is that the way you create a 2 dimensional array in C#?? because I was under the impression that its `string[][] users` – Ahoura Ghotbi Dec 03 '11 at 13:23
1

That just declares the array you need to use new before you can [dereference it](http://msdn.microsoft.com/en-us/library/aa288453(v=vs.71).aspx) – parapura rajkumar Dec 03 '11 at 13:24
do i need to specify `M` and `N`?? is it not possible to have it dynamically grow as I add new values?? – Ahoura Ghotbi Dec 03 '11 at 13:25
If sizes are not known you can use `List< List >` – parapura rajkumar Dec 03 '11 at 13:44
See this question for info on creating dynamic arrays: [Dynamic array in C#](http://stackoverflow.com/questions/594853/dynamic-array-in-c-sharp) – Keith Dec 03 '11 at 14:02

score 0 · Answer 2 · answered Dec 03 '11 at 13:17

0

Unless there's code you've not shown us, you never actually created the array. Therefore, users will be null, so attempt to dereference it doesn't make sense. Hence, the exception.

answered Dec 03 '11 at 13:17

Kent Boogaart

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oh sorry the method is part of a class, so I call it in the start of the program to gather the data – Ahoura Ghotbi Dec 03 '11 at 13:20

score 0 · Answer 3 · answered Dec 03 '11 at 13:38

0

You need to allocate users:

string[][] users = new string[n][];
for(int i = 0; i < n; i++)
{
    users[i] = new string[m];
}

n and m can be variables.

answered Dec 03 '11 at 13:38

Tudor

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C# Object reference not set to an instance of an object.

3 Answers3