What are the differences between using int[][] and int[,]? [duplicate]

Answer 1

Here's a good comparison

Basically int[][] is a "jagged" array, it looks like this:

[] -> [1, 2, 3]
[] -> [1, 2]
[] -> [1, 2, 3, 4]

While int[,] is a multidimentional array which always has the same width and height:

[1, 2, 3, 4
 5, 6, 7, 8
 9, 1, 2, 3]

Each have their uses depending on what you're trying to accomplish.

Answer 2

One thing to consider about a jagged array is that you are allocating non-contiguous chunks of memory. This is a good thing if you have a large array of large objects. I've seen SomeThing[n,n] create StackOverflow issues, but SomeThing[n][n] be ok.

Also, if an object gets > 85,000 bytes it goes to the LOH (Large Object Heap). .NET Collections and the Large Object Heap (LOH)

Answer 3

int[][] is an array of arrays or "jagged" array: you can use this when you want different sizes in the second dimension. For example, the first sub array can have 5 elements and the second can have 42.

int[,] is a two dimensional array: The second dimension is the same through out the array. With int[7, 42] the second dimension is 42 for all 7 lines.

Answer 4

you can see int[][] as to (int[])[] (int[]) is a object

Answer 5

The best way to understand the difference is to look at two ways to create an nxn matrix:

const int n = 8, m = 8;

int[,] matrix1 = new int[n,m];

int[][] matrix2 = new int[n][];
for (int i = 0; i < matrix2.Length; i++) { matrix2[i] = new int[m]; }

matrix1[1,1] = matrix2[2][2];

As you can see the second one is a bit more involved because you need the for-loop to fully create it. It is often called a jagged array because the 2nd order arrays do not need to be all of the same length.

Answer 6

The difference here is that the first sample, int[][] creates a jagged array, while the second creates a rectangular array (of dimension 2). In a jagged array each "column" can be of a different size. In a true multidimensional array, each "column" (in a dimension) is the same size. For more complete information see the Array section of the C# Programming Guide.