What to Know About Value Types and Reference Types in C#
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by Brendan Enrick
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Reference Assignment

One of the hardest concepts for people to understand when it comes to reference types is assignment. It is often difficult to realize how assignments work with reference types. The problem with this is that a lot of people assume that value types and reference types handle assignment in the same way. This is wrong. Assignments with value types copy the value stored in the memory location. Reference types merely copy the reference to the value.

Basic assignment of reference types

When you assign a variable which is a reference type to another variable of the same type, it does not duplicate the values. What happens behind the scenes is that the pointer to the memory location is duplicated.

In the following code I create two variables; both of them are strings. The first one I start by giving a string value. The second one I start by assigning null. I then assign it to the first variable. In the accompanying illustration you can see what changes after the assignment.

Listing 1: Reference Assignment

string myName = "Brendan";
string authorName = null;
 
authorName = myName;

Figure 2: Reference Assignment

It is important to notice here that we have not copied the data. All we have done is copied that reference. This means that we are pointing at the exact same data for both variables. I have seen many people run into problems where they assumed that an assignment with reference type variables worked the same way as value types. They assume the value has been duplicated. A dangerous assumption since they may alter the value not realizing it alters both.


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User Comments

Title: feedback   
Name: vishal
Date: 2012-12-27 3:12:57 AM
Comment:
super awesome articles
Title: What to Know About Value Types and Reference Types in C#   
Name: Venkatesh
Date: 2012-09-26 4:02:32 AM
Comment:
hi ur explanation is very super.Figure 2: Reference Assignment
doesnt display please correct


thanks
Title: What to Know About Value Types and Reference Types in C#   
Name: sreenath
Date: 2012-03-06 12:27:36 AM
Comment:
very easy to understand doing a good job......
Title: What to Know About Value Types and Reference Types in C#   
Name: Rakesh Kumar chouhan
Date: 2011-03-03 11:47:38 PM
Comment:
thansks alot...Very Easy to understand
Title: Feedback   
Name: Sneha Bhavar
Date: 2010-08-30 1:20:15 AM
Comment:
this article is very useful one in respect of c.net platform as for beginners
Title: Compliments   
Name: Pramod Bhat
Date: 2010-02-17 9:08:20 AM
Comment:
Hey brendan,

This article is superb.especially the examples with pictures.I tried a lot to understand the diff btwn value vs reference types.But, After I read this article, now no more confusion..!!! thanks a lot
Title: RE: Need Help   
Name: Brendan Enrick
Date: 2009-11-23 1:41:48 PM
Comment:
Thanks saurabh. I am glad you found the article useful. I have written a blog post which should help explain the behavior you're seeing in your code.

http://brendan.enrick.com/blog/a-quick-answer-about-reference-types/
Title: Need Help   
Name: saurabh
Date: 2009-11-17 1:37:35 AM
Comment:
Title: Need Help
Name: saurabh
Date: 11/17/2009 1:32:18 AM
Comment:
First of all the article is excellent.
But why the following program produces output as:: abc:xyz
it should produce xyz:xyz.
I am confused...Plz help
The Code:

string myName = "abc";
string authorName = null;
authorName = myName;
authorName = "xyz";
Console.WriteLine("{0}:{1}",myName,authorName);
Console.ReadLine();
The Actual Output:
abc:xyz
The Expected Output:
xyz:xyz

as it's areference type only one copy is shared between references.
Title: Need Help   
Name: saurabh
Date: 2009-11-17 1:32:18 AM
Comment:
First of all the article is excellent.
But why the following program produces output as:: abc:xyz
it should produce zyx:zyx.
I am confused...Plz help
The Code:

string myName = "abc";
string authorName = null;
authorName = myName;
authorName = "zyx";
Console.WriteLine("{0}:{1}",myName,authorName);
Console.ReadLine();
The Actual Output:
abc:zyx
The expected Output:
xyz:xyz
Title: Best Explaination   
Name: MIten Shah
Date: 2009-11-04 11:41:38 PM
Comment:
Excellent article help me lot about understand value type and reference type
Title: Fantasic Work   
Name: Dinakran.U
Date: 2009-09-17 5:40:55 AM
Comment:
Tnx for the explantion.
Itz really gud:)
Thank u so much,Sir:)
Title: Best foundation for Value and Reference Types   
Name: Kannan
Date: 2009-08-22 6:10:06 AM
Comment:
Enrick,
This article is very useful yaar. Now I am clear with Value and ReferenceTypes...
Title: Easy and clear   
Name: Alessandro Camargo
Date: 2009-07-27 6:53:50 AM
Comment:
Excellent article easy to understand and very helpfull.

Thanks,
Title: clear understanding of value type and reference type   
Name: haritha ponnam
Date: 2009-03-03 12:44:59 AM
Comment:
hi Thanq verymuch u have given good artical it is givindg clear explanyion. now i am clear about boxing and unboxing, nullable values and much clear abt stack and heap.Thax again
Regards,
Haritha Ponnam
Title: What to Know About Value Types and Reference Types in C#   
Name: DombaX
Date: 2008-12-19 9:50:34 AM
Comment:
Excellent.. Tx...
Title: ggf   
Name: jagan nagabilli
Date: 2008-11-28 12:13:48 AM
Comment:
excellent article.....its really helps us alot..thanz author
Title: RE: Reference Assignment   
Name: Brendan Enrick
Date: 2008-11-13 10:44:30 AM
Comment:
@Horus Thanks Horus, hmm I can't believe I forgot to mention the immutability of strings. Thanks for mentioning it.
Title: Reference Assignment   
Name: Horus
Date: 2008-11-13 10:15:44 AM
Comment:
Good articel. You have to be careful with your example in the chapter 'Reference Assignment' thought. The assignment in the example works exact the way it is illustrated, but the text after the figure is only true for reference types that aren't strings. Strings are implemented as immutable and will automatically created a new instance if they are changed. So a change of 'myName' would create an independent instance with 'myName' pointing to it and authorName would keep its pointer to the old instance and so its value would remain unchanged.
Title: Value Types & Reference types   
Name: Vishal Khot
Date: 2008-10-14 4:54:15 AM
Comment:
great yaar
i am really happy by the fact that there are people who has the
tremendous capacity like you to explain the matter
it was very good & thorough explaination
great man
keep doing this
Title: Thanxx Brother   
Name: Muhammad Atif Javed
Date: 2008-09-25 2:37:18 AM
Comment:
You'r posted article is very very nice. I learned a lot from this article. This article is written in very easy words with easy to understand examples and this this will clear my concepts about value types and reference types.
Title: very helpful   
Name: Sivakumar
Date: 2008-09-10 2:55:16 AM
Comment:
Very very helpful
Good for every one.....
Title: Very very helpful   
Name: Poornima
Date: 2008-09-05 2:04:04 PM
Comment:
It is a fantastic article written in very simple language which makes it easy for beginners like me to understand.I understood everything explained in the article and Now i think I can make some sense out of the big fat C# books which I was trying to read in the first place.After struggling through complicated articles and ebooks this was like a breath of fresh air.Thanks a ton
Title: A Good Article for Beginners.   
Name: Ahsan
Date: 2008-07-09 1:19:11 AM
Comment:
It is really a very nice article for the beginners to get very Good Concept on Value Type and Reference Type.

Thanks for providing such a clear explanation.
Title: Very informative   
Name: Prince
Date: 2008-07-09 1:03:24 AM
Comment:
It was really informative. All concepts are well described except nullable which i couldn't make out :) Thanks for sharing this.
Title: Good Article   
Name: suchi banerjee
Date: 2008-07-09 12:37:57 AM
Comment:
It is a very good article. Probably you could have added a little more i.e. Cloning.
Title: RE: Good Article   
Name: Brendan
Date: 2008-07-08 8:57:35 AM
Comment:
@Ravi Chougule

Thanks, I was trying to keep it simple and easy enough for beginners to understand. I am quite happy to hear that it is also valuable for you.
Title: Good Article   
Name: Ravi Chougule
Date: 2008-07-08 5:59:37 AM
Comment:
This is really good atrticle for all...not just beginners.
Thank you






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