2-dimensional table copy

[april86]

Hello everyone! I'm new to C# and i have a question:

If there is a two-dimensional table of objects A , can i copy it to another table B by simply assigning A to B?

e.g
public Object[,] A;
A= new Object[ 10, 10];

public Object[,] B ;
B= A;

Does this work?

Thanks!

[tm123456789]

Hi there,

The example that you gave would result in Array variables A and B pointing to the same array (and therefore the same objects). The code below proves this:

 
    // Declare and initialise array A
    Object[,] A;
    A = new Object[10, 10];
 
    // Set a value
    A[2, 4] = "Hi there";
 
    // Declare another array, B
    Object[,] B;
 
    // Set B's reference to array A (shallow copy - same as Clone())
    B = A;
 
    // Array variables A and B now point to the same array, 
    // and therefore, the same objects.
 
    Console.WriteLine("A[2,4]={0}\nB[2,4]={1}",
        A[2, 4], B[2, 4]);
 
    // Change a value in A
    A[2, 4] = "A new value";
 
    // See if the value in A has affected
    // the value in B.
    Console.WriteLine("A[2,4]={0}\nB[2,4]={1}",
                    A[2, 4], B[2, 4]);
 
    // Do the references of A and B match?
    Console.WriteLine("Does A[2,4] reference "
            + "the same object as B[2,4]? Answer={0}",
            (Object.ReferenceEquals(A[2, 4], B[2, 4])
            == true) ? "Yes" : "No");
 
 

Arrays are reference types (not Value types). Reference types simply refer to objects, they do not hold the value of an object. Thus in the example, assigning B with the value of A simply means that B is assigned a copy of A's reference to an array. They both then refer to the same array.

It is important to understand that variable B is not provided with a fresh stand alone copy of the array that variable A refers to. Both variables now refer to the same array and thus the same objects in the array.

The only way to get a completely stand alone copy of a two-dimensional array and its elements is to manually copy every element in the array to a new array.

Be careful when hand copying array elements. If the array holds value types (such as int, long, char etc) then simply assigning them to a location in the new array will work fine. However, if (like in the example above) the array contains reference types (Objects) then obtaining a shallow copy of each element raises the same problem as the array copy issue - i.e. you'll be copying the references to objects and not copying the objects themselves.

Each object in the array will have to be DEEP copied using ICloneable interface.

I refer you to:

http://www.thescripts.com/forum/thread233829.html

Hope this helps a bit.

[april86]

Thanks a lot, this helps!