C# "Get" Not Working Correctly

Question

I'm trying to make a swap operation. But when i tried to swap, it changes temp and the orginal array. The codes are here.

    private int[] currentNumbers;

    currentNumbers = new int[7] { 0, 1, 2, 3, 4, 5, 6 };

    public int[] getNumbers()
    {
        return currentNumbers;
    }

    int[] temp;
    int[] ux = numbers.getNumbers();

    int i=1, j=2;

    temp = swap(i, j, ux);

    public int[] swap(int i,int j,int[] u) {
        int t = u[i];
        u[i] = u[j];
        u[j] = t;
        return u;
    }

That code blocks changed ux array as planned. But changed currentNumbers. I don't want swap in orginal array. What can i do about that? Any ideas?

"Correctly" and "how I wish it worked" aren't the same thing. — Preston Guillot, Dec 08 '13 at 20:28
See http://stackoverflow.com/questions/1533757/is-int-a-reference-type-or-a-value-type — Sam Leach, Dec 08 '13 at 20:34
@SLaks "int[] ux = numbers.getNumbers();" already gets the array like copying. But there is no set method and i changed only ux array not currentNumbers. — mgkrks, Dec 08 '13 at 20:36
@MügeKarakaş No, it doesn't, it returns a reference to the same array that `currentNumbers` is a reference to. — Preston Guillot, Dec 08 '13 at 20:36
I've never seen such a thing before. Thanks for answering all guys. — mgkrks, Dec 08 '13 at 20:42
@MügeKarakaş: Wrong. C# never copies reference types for you. — SLaks, Dec 08 '13 at 20:58

score 2 · Accepted Answer · answered Dec 08 '13 at 20:31

Expanding on what SLaks said, your .getNumbers() function isn't returning a copy of the array, it's returning a reference directly to currentNumbers. If you want to return a new copy every time and not modify currentNumbers, you should use Array.Copy.

int[] ux;
Array.Copy(numbers.getNumbers(), ux, numbers.getNumbers.Length)

There are probably more optimal ways to do this, but this will get you what you want!

score 1 · Answer 2 · answered Dec 08 '13 at 20:29

1

You should use clone method in getNumbers method. http://msdn.microsoft.com/en-us/library/system.array.clone%28v=vs.110%29.aspx

answered Dec 08 '13 at 20:29

Leon Borko

198
2
13

score 1 · Answer 3 · edited May 23 '17 at 12:29

1

Your problem is that arrays in c# are passed by reference, so you need to copy that array in another one, apply changes to that array, and then return it.

Check this answer for more details Passing Arrays by Value and by Reference

edited May 23 '17 at 12:29

Community

1
1

answered Dec 08 '13 at 20:34

prole92

56
5

2

The array *reference* is passed *by value* - it's a minor distinction with different consequences. See http://msdn.microsoft.com/en-us/library/8b0bdca4.aspx – Preston Guillot Dec 08 '13 at 20:41

C# "Get" Not Working Correctly

3 Answers3