What is wrong with this Custom Compare function

Question

I was trying to debug a problem and ran into this issue. Maybe somebody can explain it to me. This is the code in question

public int Compare(CustomClass rt1, CustomClass rt2)
{
     if (rt1 == null & rt2 == null)
                return 0;
     if (rt1 == null)
                return -1;
     if (rt2 == null)
                return 1;
     if (rt1.yPos < rt2.yPos)
                return -1;
     if (rt1.yPos == rt2.yPos)
     {
                if (rt1.xPos < rt2.xPos)
                    return -1;
                if (rt1.xPos == rt2.xPos)
                    return 0;
     }
     return 1;
}

The error I was getting was: IComparer (or the IComparable methods it relies upon) did not return zero when Array.Sort called x. CompareTo(x).

To make it even more interesting, the error would not occur if I ran it from VS in debug mode. Only if I put it in release mode AND hit "start without debugging". Anybody have any ideas why this would happen? I fixed the problem by adding an "if(rt1 == rt2) return 0;" line to the beginning of the function, but would really like to know what is going on.

Extra info: Yes, this implements the IComparer class

Could you give us some context? Is there threading involved? Serialization? Anything else interesting? — John Fisher, Oct 20 '09 at 19:19
And your class implements `IComparer`, and is being passed to the array method? — Marc Gravell, Oct 20 '09 at 19:28
Your right. I've deleted my answer. I also think that this `if (rt1 == null & rt2 == null)` doesn't cause the problem. — bruno conde, Oct 20 '09 at 20:08
the single & is being caused by the markup here. It is a double & in the code — Kevin, Oct 20 '09 at 20:13

score 2 · Answer 1 · edited Oct 20 '09 at 20:07

2

your missing an amperstand (&) (is this a typo?)

if (rt1 == null & rt2 == null) // oops!
if (rt1 == null && rt2 == null) // like this....

edited Oct 20 '09 at 20:07

Steven Sudit

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answered Oct 20 '09 at 19:27

Muad'Dib

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score 0 · Answer 2 · answered Oct 20 '09 at 19:28

0

Sometimes a sort algorithm will end up comparing an object to itself. When this happened, it triggered the code:

if (rt1 == null)
    return -1;

It was this that caused the error. You've got to be sure that you have all cases covered.

And if those x,y values represent points, you might want to check this article on sorting them: http://www.c-sharpcorner.com/UploadFile/mgold/SortedDictionarySample06202007142815PM/SortedDictionarySample.aspx

answered Oct 20 '09 at 19:28

Michael Dillon

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If it is comparing to itself, why would `rt1` be `null`, and it not have already triggered the `return 0` case? – Marc Gravell Oct 20 '09 at 19:31
I'm assuming that the first if statement is the bit that he added to get rid of the error message. – Michael Dillon Oct 20 '09 at 19:33
1

The OP says that was "`if(rt1 == rt2) return 0;`". – Marc Gravell Oct 20 '09 at 19:43

What is wrong with this Custom Compare function

2 Answers2