What part of an array local variable is stored on the stack? And which part is on the heap?

Question

Suppose we have the following code:

void method() {
    int[] test = new int[3];
    test[0] = 0;
    test[1] = 1;
    test[2] = 2;
}

From what I read from Jon Skeet's post on SO, the new int[3] part is equivalent to:

public class ArrayInt3 {
    public readonly int length = 3;
    public int value0;
    public int value1;
    public int value2;
}

So does that mean test (a reference to ArrayInt3) is on the stack? And does that mean ArrayInt3 is on the heap? And I suppose value0, value1, and value2 are on the heap as well (i.e. 0, 1, 2 in this example)?

So in total, there is 4 objects on the heap, correct?

Sotirios Delimanolis · Accepted Answer · 2014-09-24T15:57:23.867

1

There will be no object on the stack. On the stack, there will be a reference value to the single int[] object stored in the heap.

You have to start making the distinction between objects, variables, and values.

Local variables are part of the method stackframe, which is on the stack. So the reference value to the int[] will be stored in the variable, on the stack.

edited Sep 24 '14 at 15:57

answered Sep 24 '14 at 15:52

Sotirios Delimanolis

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@SomeRandomGuy Those are not objects. First, `ArrayInt3` is a type. The rest are values. They are part of the single `int[]` object. They are not independent. – Sotirios Delimanolis Sep 24 '14 at 15:55
@SomeRandomGuy If they were initialized, they would be 4 reference values pointing to 4 other objects on the heap. – Sotirios Delimanolis Sep 24 '14 at 15:55
@SomeRandomGuy No, there is a single object on the heap, the `int[]` object. – Sotirios Delimanolis Sep 24 '14 at 15:56
Assuming value0, value1, and value2 are initialized, then what do we have on the heap exactly? value0, value1, value2, and ArrayInt3, right? I apologize for asking this poorly. – SomeRandomGuy Sep 24 '14 at 15:57
@SomeRandomGuy You'll have memory allocated for an instance of type `ArrayInt3`. That memory will be large enough to fit exactly those fields and their value. – Sotirios Delimanolis Sep 24 '14 at 15:58
Okay this is a poor example but if we assume instead of ints, they were objects like House objects, it would be 3 House objects on the heap + ArrayInt3 object on the heap? – SomeRandomGuy Sep 24 '14 at 16:02
@SomeRandomGuy Yes, the `ArrayInt3` object would have enough memory allocated for 3 reference values, each referencing a `House` object, all on the heap. – Sotirios Delimanolis Sep 24 '14 at 16:03
Thank you. Sorry for the confusion. – SomeRandomGuy Sep 24 '14 at 16:04

What part of an array local variable is stored on the stack? And which part is on the heap?

1 Answers1