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
– Abdul Munim, Commented Dec 3, 2011 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
– Keith, Commented Dec 3, 2011 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
– Ahoura Ghotbi, Commented Dec 3, 2011 at 13:20
@Keith its value b and the value is 0 when the error appears — Ahoura Ghotbi
– Ahoura Ghotbi, Commented Dec 3, 2011 at 13:21

parapura rajkumar · Accepted Answer · 2011-12-03 13:19:24Z

2

I think you need to allocate space for the array

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

answered Dec 3, 2011 at 13:19

parapura rajkumar

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5 Comments

Ahoura Ghotbi Over a year ago

is that the way you create a 2 dimensional array in C#?? because I was under the impression that its string[][] users

parapura rajkumar Over a year ago

That just declares the array you need to use new before you can dereference it

Ahoura Ghotbi Over a year ago

do i need to specify M and N?? is it not possible to have it dynamically grow as I add new values??

parapura rajkumar Over a year ago

If sizes are not known you can use List< List<string> >

Keith Over a year ago

See this question for info on creating dynamic arrays: Dynamic array in C#

Kent Boogaart · Accepted Answer · 2011-12-03 13:17:49Z

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 3, 2011 at 13:17

Kent Boogaart

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1 Comment

Ahoura Ghotbi Over a year ago

oh sorry the method is part of a class, so I call it in the start of the program to gather the data

Tudor · Accepted Answer · 2011-12-03 13:38:17Z

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 3, 2011 at 13:38

Tudor

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