Determining the number of bytes used by a variable

Question

I have the following array:

byte[][] A = new byte[256][];

Each element of this array references another array.

A[n] = new byte[256];

However, most elements reference the same array. In fact, array A only references two or three unique arrays.

Is there an easy way to determine how much memory the entire thing uses?

Answer 1

If your question is to find out the number of unique 1D arrays, you could do:

A.Distinct().Count()

This should do because equality of arrays works on reference-equality by default.

But perhaps you're looking for:

A.Distinct().Sum(oneDimArray => oneDimArray.Length) * sizeof(byte)

Of course, "number of bytes used by variables" is a somewhat imprecise term. In particular, the above expression doesn't account for the storage of the variable A, references in the jagged array, overhead, alignment etc.

EDIT: As Rob points out, you may need to filter null references out if the jagged-array can contain them.

You can estimate the cost of storing the references in the jagged-array with (unsafe context):

A.Length * sizeof(IntPtr) 

Answer 2

I don't believe there's any built in functionality.

Whipped this up very quickly, haven't tested it throughly however;

void Main()
{
    byte[][] a = new byte[256][];
    var someArr = new byte[256];
    a[0] = someArr;
    a[1] = someArr;
    a[2] = new byte[256];
    getSize(a).Dump();
}

private long getSize(byte[][] arr)
{
    var hashSet = new HashSet<byte[]>();
    var size = 0;
    foreach(var innerArray in arr)
    {
        if(innerArray != null)
            hashSet.Add(innerArray);
    }

    foreach (var array in hashSet)
    {
        size += array.Length * sizeof(byte);
    }
    return size;
}