Can reference types be allocated on stack?

Question

Consider following code:

class Point
{
   public int position;
}

here the int position will be allocated on heap even if it is a value type.

but my question is about the opposite scenario,consider following code:

struct Person
{
   public string name;
}

Here will string name be allocated on heap or stack?

TIA

you should read: [The Truth About Value Types](http://blogs.msdn.com/b/ericlippert/archive/2010/09/30/the-truth-about-value-types.aspx) btw, why do you care this ? — Selman Genç, Aug 18 '14 at 12:05
The pointer to the string will be on the stack and the string itself on the heap. — Enigmativity, Aug 18 '14 at 12:05
http://stackoverflow.com/questions/2031258/c-sharp-structs-classes-stack-heap-control, and int in first example won't be allocated on stack. — Eugene Podskal, Aug 18 '14 at 12:06
Current place for the article mentioned by @SelmanGenç is now https://ericlippert.com/2010/09/30/the-truth-about-value-types/ — zahir, Aug 27 '21 at 04:40

score 1 · Answer 1 · answered Feb 12 '15 at 16:22

Reference types actual instance object is allocated on the heap and its' reference variable, that references it is allocated on the stack.

Just as a brain teaser: When we take a value type cast it to a reference type, for example and object (everything is an object in .net ) or and interface (reference type) it's implementing then value type is boxed, meaning copied to the heap and it's being referenced from the stack. If we cast the object back to value type , it's being unboxed back to a value type and copied entirely to the stack. Some people tend to wrongly consider this scenario as a reference type allocated on the heap.

score 0 · Answer 2 · answered Aug 18 '14 at 12:06

0

No. The reference to the string will be allocated where ever Person is allocated. The string itself will be allocated on the heap. Infact everytime you say new T where T is a class the object will be allocated on the heap.

answered Aug 18 '14 at 12:06

Esben Skov Pedersen

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You mean that in the second example if the Person was class,would both the reference of the string and string data be positioned on heap? – Code Geek Aug 18 '14 at 12:11
No Person is a struct. The thing about structs is that they are not always allocated on the stack. They are allocated inline where ever they are used which can be in a class or stack or another struct. – Esben Skov Pedersen Aug 18 '14 at 12:13
I've drawn an image to tell you what i've understood until now. http://www.pixentral.com/pics/1lgTw2M0rd68InSHj0ILKa1Cy1vYx0.png – Code Geek Aug 18 '14 at 12:50

Геннадий Ефимов · Answer 3 · 2021-10-04T05:53:55.263

in your case - string allocates on heap.

but reference types can be allocated on stack.

for exemplar, arrays can be allocated as:

private static void Main(string[] args)
        {
            unsafe
            {
                const int size = 123;
                var mgmtArray = new long[size];
                mgmtArray[0] = 12345;

                void* refAddr = Unsafe.AsPointer(ref mgmtArray);

                long mgmtArrAddr = *(long*)refAddr;
                long mtAddr = *(long*)mgmtArrAddr;
                long arrSize = ((int*)mgmtArrAddr)[2];

                Console.WriteLine("Addr ref: {0:x}", (long)refAddr);
                Console.WriteLine("Mgmt array addr: {0:x}", mgmtArrAddr);
                Console.WriteLine("MT: {0:X}", mtAddr);
                Console.WriteLine($"{nameof(arrSize)}: {arrSize}");

                long* stackPtr = stackalloc long[size * 2];

                stackPtr[0] = 0; //sync block
                stackPtr[1] = mtAddr;
                ((int*)stackPtr)[4] = size;
                stackPtr++;

                long** stackPtrRef = &stackPtr;

                var pointer = new MgmtPointer<long[]>(Unsafe.Read<long[]>(stackPtrRef));

                long[] arrayOnStack = Unsafe.Read<long[]>(stackPtrRef);

                arrayOnStack[0] = 54321;

                Console.WriteLine("-----");

                Console.WriteLine($"In heap: {mgmtArray[0]}"); //12345
                Console.WriteLine($"In stack: {arrayOnStack[0]}"); //54321
                Console.WriteLine($"arrayOnStack len: {arrayOnStack.Length}");
            }
        }

for other reference types also, but with some changes.

Can reference types be allocated on stack?

3 Answers3