Preventing Index Out of Range Error

Question

I want to write a check for some conditions without having to use try/catch and I want to avoid the possibilities of getting Index Out of Range errors

if (array.Element[0].Object.Length > 0 || array.Element[1].Object.Length > 0) //making sure there's at least one Object array that has values
 {                
    if (array.Element[0].Object[0].Item.Length != 0 || array.Element[1].Object[0].Item.Length != 0) //this is where I check that at least one of the Items (strings) is not empty
       {
           // execute code here
       }
 }

So the problem I am facing is that in the second check I need to see whether I have one Item that is not empty. However, If I don't have Element[1], I get the Index Out of Range exception. The problem is that there could be 2 Elements and one(or both) of them may have empty Object arrays. The code will have to be executed only if one of thos Item strings is not empty.

Hopefully, I explained it well. How do I go about avoiding getting that exception under any condition?

The two conditions in the first line are the same - presumably that's not intentional? — Jon Skeet, Apr 11 '12 at 20:48
I apologize, there should be two different conditions, I changed it. — Victor, Apr 11 '12 at 20:49

score 4 · Accepted Answer · edited May 23 '17 at 11:54

Alright, you need some better null checking and some more cautious code here.

if (array.Element[0].Object.Length > 0 || array.Element[1].Object.Length > 0) //making sure there's at least one Object array that has values
{                
   if (array.Element[0].Object[0].Item.Length != 0 || array.Element[1].Object[0].Item.Length != 0) //this is where I check that at least one of the Items (strings) is not empty
   {
       // execute code here
   }
}

is just unacceptable.

First, let's null check

if (array != null)
{
    if (array.Element != null)

for simplicity, you could use &&

if (array != null && array.Element != null)

then, inside that if, we use a for loop (since you're stuck on arrays) and null check it

for (int i = 0; i < array.Element; ++i)
{
    if (array.Element[i] != null && array.Element[i].Object != null)
    {

then, since you have nested arrays, we loop again. This is called a nested loop, and it's generally bad practice, I'll show you why it works in a second.

for (int o = 0; o < array.Element[i].Object.length; ++o)
{
    if (array.Element[i].Object[o] != null && !string.IsNullOrEmpty(array.Element[i].Object[o].Item))
    {

Now, with all of that ugly nested loopyness, we've found out that your Item is not null. On top of that, you have access to ALL of the potential values here, and can group them as you like. Here's how I would put the whole thing together for simplification.

List<string> arrayValues = new List<string>();
if (array != null && array.Element != null)
{
    for (int i = 0; i < array.Element.length; ++i)
    {
        //bool found = false;
        if (array.Element[i] != null && array.Element[i].Object != null)
        {
            for (int o = 0; o < array.Element[i].Object.length; ++o)
            {
                if (array.Element[i].Object[o] != null && !string.IsNullOrEmpty(array.Element[i].Object[o].Item))
                {
                    arrayValues.Add(array.Element[i].Object[o].Item);
                    //if you want to drop out here, you put a boolean in the bottom loop and break and then break out of the bottom loop if true
                    //found = true;
                     //break;
                }
            }
        }
        //if (found)
        //  break;
    }
}
if (arrayValues.Count > 0)
{
    //do stuff with arrayValues
}

Nicely done! When I start to need code like this is when I begin thinking whether my design is proper in the first place. I suspect the OP's design could benefit from some fundamental changes. — Kevin P. Rice, Apr 11 '12 at 21:22

score 1 · Answer 2 · edited Nov 08 '22 at 10:48

1

Could use a LINQ method ElementAtOrDefault(index)

so if the element is not found it will be null.

var currentElem = Elems.ElementAtOrDefault(i);

if(currentElem != null) 
     // do something
else
   // do something

edited Nov 08 '22 at 10:48

Mustafa Poya

2,615
5
22
36

answered Nov 04 '22 at 15:53

jber Ibra

11
1
1

score 0 · Answer 3 · answered Apr 11 '12 at 20:50

0

Could you do something like:

if(array.Element[0] != null || array.Element[1] != null){
    //execute code
}

answered Apr 11 '12 at 20:50

Ryan

1,135
1
13
28

I think this would still get that exception if `Element[1]` does not exist. – Victor Apr 11 '12 at 20:51

score 0 · Answer 4 · answered Apr 11 '12 at 20:53

0

Your code is probably subject to refactor.

I assume it can work this way:

var obj = array.Element.FirstOrDefault(x => x.Object.Length > 0);
if (obj != null)
{
  if (obj.Object[0].Item.Length != 0) 
  {
    // do whatever is necessary
  }
}

answered Apr 11 '12 at 20:53

nothrow

15,882
9
57
104

Kevin P. Rice · Answer 5 · 2012-04-11T21:11:48.643

Place both tests together using the short-circuit && so that the second test doesn't occur if the first fails:

object element0 = array.Element[0].Object;
object element1 = array.Element[1].Object;

// Ensure at least one Object array has a non-empty value.
if ((element0.Length > 0 && !string.IsNullOrEmpty((string)element0.Object[0].Item))
    || (element1.Length > 0 && !string.IsNullOrEmpty((string)element1.Object[1].Item)))
{
    // ...
}

I am presuming it is Object[1] causing the exception--you weren't clear on that. If it is Element[1] that causes the exception (or both), then you need to pre-test the length of the array:

if ((array.Element[0].Length != 0 && HasValue(array.Element[0].Object))
    || (array.Element[1].Length > 1 && HasValue(array.Element[1].Object)))
{
    // ...
}

// <summary>
// Returns true if the specified string array contains a non-empty value at
// the specified index.
// </summary>
private bool HasValue(System.Array array, int index)
{
    return array.Length > index && 
        !string.IsNullOrEmpty((string)array.Object[index].Item);
}

score 0 · Answer 6 · answered Apr 11 '12 at 21:05

I think you can put your check in right before your first if Check.

if (array.Length > 1 && array.Element[0].Object.Length > 0 || array.Element[1].Object.Length > 0) //making sure there's at least one Object array that has values
 {                
    if (array.Element[0].Object[0].Item.Length != 0 || array.Element[1].Object[0].Item.Length != 0) //this is where I check that at least one of the Items (strings) is not empty
       {
           // execute code here
       }
 }

This should just short-circuit out if your array doesn't have both Elements.

score 0 · Answer 7 · edited Oct 16 '13 at 09:05

0

for (long i = 0; i <= (output3.Length); i++)
{
    output1.WriteByte(output3[i]); -----> index out of range exception correct it
    output1.WriteByte(output3rx[i]);
}

edited Oct 16 '13 at 09:05

Bridge

29,818
9
60
82

answered Oct 16 '13 at 08:49

Dawit Selesh

1

1

"Index out of range exception correct it". Er, he was asking _how_ to do that. – S.L. Barth is on codidact.com Oct 16 '13 at 09:13

Preventing Index Out of Range Error

7 Answers7

Linked