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Using Arrays in Microsoft® Visual C#® 2013

  • 11/15/2013

Copying arrays

Arrays are reference types (remember that an array is an instance of the System.Array class). An array variable contains a reference to an array instance. This means that when you copy an array variable, you actually end up with two references to the same array instance, as demonstrated in the following example:

int[] pins = { 9, 3, 7, 2 };
int[] alias = pins; //  alias and pins refer to the same array instance

In this example, if you modify the value at pins[1], the change will also be visible by reading alias[1].

If you want to make a copy of the array instance (the data on the heap) that an array variable refers to, you have to do two things. First, you create a new array instance of the same type and the same length as the array you are copying. Second, you copy the data element by element from the original array to the new array, as in this example:

int[] pins = { 9, 3, 7, 2 };
int[] copy = new int[pins.Length];
for (int i = 0; i < pins.Length; i++)
    copy[i] = pins[i];

Note that this code uses the Length property of the original array to specify the size of the new array.

Copying an array is actually a common requirement of many applications—so much so that the System.Array class provides some useful methods that you can employ to copy an array rather than writing your own code. For example, the CopyTo method copies the contents of one array into another array given a specified starting index. The following example copies all the elements from the pins array to the copy array starting at element zero:

int[] pins = { 9, 3, 7, 2 };
int[] copy = new int[pins.Length];
pins.CopyTo(copy, 0);

Another way to copy the values is to use the System.Array static method named Copy. As with CopyTo, you must initialize the target array before calling Copy:

int[] pins = { 9, 3, 7, 2 };
int[] copy = new int[pins.Length];
Array.Copy(pins, copy, copy.Length);

Yet another alternative is to use the System.Array instance method named Clone. You can call this method to create an entire array and copy it in one action:

int[] pins = { 9, 3, 7, 2 };
int[] copy = (int[])pins.Clone();