C# structs and the heap question

[faustino Dina]

Hi,

I have a question about how C# handles struct. From the help, struct
variables are stored in the stack while class objects are stored in the
heap. Then what happens when I add a struct value to a colection?

struct MyStruct
{
public int X;
}

MyStruct s;

ArrayList list = new ArrayList();
list.Add(s);

In C/C++ store stack addresses on a global collection can lead to hard to
trace problems. But how C# works? In this case what is stored on the list
collection: struct, a reference to the stack or s is cloned into the heap
and that reference is added to the collection?

Thanks in advance
--
Faustino Dina
--------------------------------------------------------
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drop the first 'f' when mailing me.

--
Faustino Dina
--------------------------------------------------------
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[Mickey Williams [C# MVP]]

Instances of structs are not always stored on the stack -- rather struct
variables always directly contain their value. In your example, the struct
instances are boxed and allocated on the heap.
See http://www.yoda.arachsys.com/csharp/memory.html
--
Mickey Williams
Author, "Visual C# .NET Core Ref", MS Press
www.neudesic.com
www.servergeek.com

"faustino Dina" <ff****@matusa.com.mx> wrote in message
news:OD**************@TK2MSFTNGP09.phx.gbl...

Hi,

I have a question about how C# handles struct. From the help, struct
variables are stored in the stack while class objects are stored in the
heap. Then what happens when I add a struct value to a colection?

struct MyStruct
{
public int X;
}

MyStruct s;

ArrayList list = new ArrayList();
list.Add(s);

In C/C++ store stack addresses on a global collection can lead to hard to
trace problems. But how C# works? In this case what is stored on the list
collection: struct, a reference to the stack or s is cloned into the heap
and that reference is added to the collection?

Thanks in advance
--
Faustino Dina
--------------------------------------------------------
If my email address starts with two 'f'
drop the first 'f' when mailing me.

--
Faustino Dina
--------------------------------------------------------
If my email address starts with two 'f'
drop the first 'f' when mailing me.

[Jon Skeet [C# MVP]]

faustino Dina <ff****@matusa.com.mx> wrote:

I have a question about how C# handles struct. From the help, struct
variables are stored in the stack while class objects are stored in the
heap.
Unfortunately that's a rather simplistic approach.

See http://www.pobox.com/~skeet/csharp/memory.html

(For instance, a value type which is part of a reference type will
always be on the heap.)
Then what happens when I add a struct value to a colection?

struct MyStruct
{
public int X;
}

MyStruct s;

ArrayList list = new ArrayList();
list.Add(s);
This is actually a third case - here you're *boxing* the struct value.
This basically creates a strongly-typed object on the heap, containing
your value. To get it back as a value type, you need to unbox the
reference, which you do using casting syntax:

s = (MyStruct) list[0];
In C/C++ store stack addresses on a global collection can lead to hard to
trace problems. But how C# works? In this case what is stored on the list
collection: struct, a reference to the stack or s is cloned into the heap
and that reference is added to the collection?

Essentially the latter.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too