reference in object Type in c#

Question

3.33/5 (3 votes)

See more:

I create two variable with object type , i initialized variable "d" ;then i assign
variable "d" to variable "h".finally changed value variable "d",but variable "h" do not change while object is reference type and "h" must be change with new value?

C#

object d = 5;
object h = d;
d = 9;        //h variable do not change!!

Posted 29-Jan-12 5:58am

User 7427435

Updated 29-Jan-12 6:41am

Sander Rossel

v4

Add a Solution

Comments

[no name] 29-Jan-12 13:52pm

Since my solution is incorrect, I'm deleting it. Apologies :)

2 solutions

Solution 2

I have to disagree with the answer by J_N above: value Types are boxed, and unboxed: see: [^].

A reference Type remains a reference Type: consider this simple example:

C#

public class SomeClass
{
    public string someString { get; set; }
}

Now execute this code:

SomeClass sClass = new SomeClass();

SomeClass dClass = sClass;

sClass.someString = "hello";

dClass.someString = "goodbye";

And set a break-point right after the last statement in the code.

You will see that changing the string value of the Property 'someString in 'dClass which has been set equal to the instance of 'sClass: also changes the string value of the Property 'someString in 'sClass.

This is because both the instance of 'sClass, and the pointer to the instance of 'sClass held in 'dClass: are both references to the same underlying Object.

Posted 29-Jan-12 7:10am

BillWoodruff

Updated 29-Jan-12 7:12am

v2

Comments

Wonde Tadesse 29-Jan-12 13:18pm

5+

Sergey Alexandrovich Kryukov 29-Jan-12 13:54pm

I have a mixed feeling: you have a number of good points, but they and your examples do not address the confusion of OP at all, because you only work with System.String, which is a reference type.

To be more accurate, a note on your first statement: it's correct, but there is no any unboxing in the OP's code, only boxing.

So, you post is kind of out of topic. But maybe reading it just would be a useful exercise for OP in near future. So... I voted 4 this time.
--SA

BillWoodruff 29-Jan-12 16:08pm

I'd really appreciate knowing from the evaluator who down-voted this answer -16 points, what the reason was for that.

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Accepted Answer · 2012-01-29T07:11:00

The type of your variables is a reference type System.Object (and object is an alias in language), a common base of all types. What happens with primitive types like integers?

Working with reference types, you store two objects: the variable itself stored in a variable, and the reference points to some object stored in heap. When you assign, reference is changed, object is not.

A variable has some compile-time type which never changes and is defined only by a declaration. Its compile-time type never changes, but run-time type can be changed during run time. All variable of the type System.Object are assignment-compatible with any type (on the right of the assignment operator), but non-reference types are boxes, see http://en.wikipedia.org/wiki/Boxing_%28computer_science%29#Boxing[^], http://msdn.microsoft.com/en-us/library/yz2be5wk.aspx[^].

Here is what happened:

In fist line, a boxed form of 5 is created and assigned to d.

In second line, h is done referentially equal to d. You obtain one single boxed form of 5 referenced by the two variables.

In third line, a boxed form of 9 is created and assigned to d. It created a brand new reference, not modified a previously created boxed form.

Assignment to variable of reference types in general case change the reference, not the value of anything.

The boxed object is immutable from the standpoint of the language, but in principle you can modify it using Reflection.

—SA