C# Array of objects, can't set values

Question

class City
{
    string name;

    public string getName()
    {
        return name;
    }

    public void setName(String value)
    {
        name = value;
    }
}

static void Main(string[] args)
{
    City[] arr = new City[1];
    arr[0].setName("New York");
}

The problem is that I get "System.NullReferenceException", "Object reference not set to an instance of an object." at the line where I set the name to New York. If I do:

City city = new City();
city.setName("New York");

I don't get any errors but I want to use an array, since I will be adding more objects. Is this possible in C# because it is in C++? Is the only way to declare 5 objects, set their names and then create an array and put them inside?

you define the array, but you have to initialize the objects too — İsmet Alkan, Dec 04 '14 at 15:18
For the duplicate, see section `Array` and `Array Elements`. — Patrick Hofman, Dec 04 '14 at 15:20
On a side note you should look into using a `Name` [property](http://msdn.microsoft.com/en-us/library/x9fsa0sw.aspx) instead of `getName` and `setName` methods. — juharr, Dec 04 '14 at 15:30

score 4 · Accepted Answer · answered Dec 04 '14 at 15:18

4

You are creating an empty array. You have to initialise the object before assigning it:

City[] arr = new City[1];
arr[0] = new City();
arr[0].setName("New York");

answered Dec 04 '14 at 15:18

Ludovic Feltz

11,416
4
47
63

Thanks. Guess it's some sort of saving memory, to not declare all the objects unless I actually declare and use them. – ivanpop Dec 04 '14 at 15:36
@user2765257 It's because sometimes an empty constructor doesn't exist on class you want to put in an array. That's why you have to call it manually. – Ludovic Feltz Dec 04 '14 at 15:38

score 1 · Answer 2 · answered Dec 04 '14 at 15:19

1

This line just creates an array with one element.

City[] arr = new City[1];

The element is null.

You need to assign it a value

arr[0] = new City();

Then you can access it.

arr[0].setName("New York");

answered Dec 04 '14 at 15:19

Ben Robinson

21,601
5
62
79

C# Array of objects, can't set values

2 Answers2