IndexOutOfRange in Constructor C#

Question

I've got simple class, something like this:

public class myClass
{
    public static readonly string[] stringArray= { "one", "two" };
    private string myString;

    public myClass (int _index)
    {
       if(_index > (stringArray.Length - 1) || _index < 0)
       {
           throw new IndexOutOfRangeException("Bad index.");
       }
       else
       {
           myString = stringArray[_index];
       }
    }

}

I'm running simple constructor: myClass example = myClass(5); and I've got error. It shouldn't leave constructor without trying create new object?

I don't understand how throw works there.

Edit: Sorry, I made a mistake. There should be stringArray.Length -1 in if section.

This is not a duplicate. The OP has a type in his code and he needs help. — Black Frog, Dec 04 '14 at 18:34
Do you not understand why your exception is being thrown, or why throwing an exception in the constructor will cause the object to not be initialized? — juharr, Dec 04 '14 at 18:37
I just want something like that: myClass example = myClass(1); -> It's ok, I've my object myClass example = myClass(5); -> Write error in Console. — user3692826, Dec 04 '14 at 18:38
What is the question here: why myClass example = myClass(5); throws an expcetion ? — mybirthname, Dec 04 '14 at 18:43

score 3 · Answer 1 · answered Dec 04 '14 at 18:31

3

myString is null, so you are getting a NullReferenceException when you access the Length property.

My guess is that you want:

if(_index > (stringArray.Length - 1) || _index < 0)

answered Dec 04 '14 at 18:31

John Koerner

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My guess would be your guess as well. – Brad Christie Dec 04 '14 at 18:33
Despite of this It still doesn't work, but I handled that kind of exception. – user3692826 Dec 04 '14 at 18:36

juharr · Accepted Answer · 2014-12-04T18:50:38.767

Because you are passing 5 as the _index to your constructor the following if condition will be true

if(_index > (stringArray.Length - 1) || _index < 0)

because the length of the array is 2 an 5 > 1. This causes the code to throw the IndexOutOfRangeException which stops the constructor from returning an instance of the object. Additionally if you do not have a try-catch around the new myClass(5) then the exception will bubble up and cause your running application to crash.

score 0 · Answer 3 · answered Dec 04 '14 at 18:32

0

You have a typo in your code. You need to get the length of the array not the string.

The line of code should:

 if(_index > (stringArray.Length - 1) || _index < 0)

answered Dec 04 '14 at 18:32

Black Frog

11,595
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IndexOutOfRange in Constructor C#

3 Answers3