List gives "Array index is out of range" for no reason

Question

Hi!

How can this possibly give the forementioned error?

 RaycastHit2D[] hit;
 hit = Physics2D.RaycastAll (position, transform.right);
 for(int i = 0; i < hit.Length; i++){
     if(hit[i+1] != null){
         Debug.Log(hit[i+1].collider.name);
         secondTarget = hit[i+1].transform;
         break;
     }
 }

The code compiles, but it give a runtime error and doesnt function correctly.

Answer 1

Best Answer

Answer by fafase · Jun 02, 2014 at 06:15 PM

First off, nothing happens for no reason in a computer, particularly with such a beginner error.

 if(hit.Length > i){
     Debug.Log(hit[i+1].collider.name);
     secondTarget = hit[i+1].transform;
     break;
 }

So you have an array and you want to perform the action if the i is smaller than hit.Length.

Consider your length to be 10, you list is from 0 to 9. So on the run when i is 9, it is smaller than 10 but you use i + 1 in the method trying to access the index 10 that is out of bound.

See, there is always a reason, even if a bug, the bug has a reason. Computers are dumb.

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jetty112 · Jun 02, 2014 at 08:08 PM 0

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Yea i noticed that myself, i edited the code, to what i meant it to be. What is weird, is that the hit[i+1] is not null but it still gives this error (index is out of range)

Sorry for the wrong code at first.

Blayer98 · Jun 02, 2014 at 09:05 PM 0

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Just read through it again, it might be likely that performing that action when i is smaller than hit length is the problem.

Also, did you get any script errors when saving? Are you not able to use play mode?

Answer 2

Answer by rutter · Jun 02, 2014 at 09:08 PM

Classic "off by one" error.

Your loop runs from 0 to Length.

Inside the loop, you access i+1. On the last iteration, i+1 is out of bounds.

You can fix this by checking if i is equal to Length-1 before accessing the array, or by changing your loop so that it runs from 0 to Length-1.

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Clockmagnet · Jun 26, 2014 at 01:00 PM 0

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Usually Length used in cycles without "-1", you just shouldn't check if counter <= Length. Maybe I'm wrong, but i consider "Length-1" as bad tone in this case. We can just put i < length.

List gives "Array index is out of range" for no reason

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