Is string a value type or Reference type..

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Hi Everyone,

I am a newbie to C#.Can anyone tell me whether string is a value type or reference type in C#.net.Some sources say ..it is a value type, some say it is Refernce type and some say it is a reference type but acts like a value type..so confused..Kinldy help me how "String" behaves in C#?

regards
Chaithanya M

Posted 13-Apr-11 5:18am

M.CHAITHANYA

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5 solutions

Solution 3

I think in the context you are asking it is a value type. The code below will explain better than my sentences I think...

void Test(){
   string s = "A";//set string to A
   Change(s);
   //if s was reference type
   //   s would = "B"
   //if a was value type
   //   s would = "A" still

   //s will = "A" hence it is value type
}

void Change(string s){
   s = B";
}

Posted 13-Apr-11 5:23am

musefan

Comments

Olivier Levrey 13-Apr-11 11:47am

You are right, in this case string behaves like a value type, although it is not. My 5 anyway.

Solution 6

Not sure if this has been posted yet, but here is the definition from the MSDN site:

http://msdn.microsoft.com/en-us/library/362314fe%28VS.71%29.aspx[^]

You're right, the string type is confusing (because it seems to be both a reference AND a value type). But this is how MS is defining it.

Dre---

Posted 13-Apr-11 16:49pm

DRAYKKO

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Sergey Alexandrovich Kryukov · Accepted Answer · 2011-04-13T05:27:00

This is a reference type but simulating value semantic in all aspects. For example, when you compare two referentially different strings, comparison (==) can be true — they are compared by the content. However, this is easy part: you can implement your own identity rules overriding System.Object.Equals, System.Object.GetHashCode (required) and optionally define custom operators "==" and "!=".

You can understand the essence of working with string references if you look at the properties system.String.Intern and system.String.IsInterned:
http://msdn.microsoft.com/en-us/library/system.string.intern.aspx[^],
http://msdn.microsoft.com/en-us/library/system.string.isinterned.aspx[^].

One important practical issue with the strings: they are immutable (in contrast to mutable arrays). Therefore, for performance reasons one should never use "+" in cycles. For this (and many other) purposes, use System.Text.StringBuilder.

—SA

Olivier Levrey · Accepted Answer · 2011-04-13T05:44:00

Solution 5

Check MSDN: string (C# reference)[^]

The second line states:
Although string is a reference type, the equality operators (== and !=) are defined to compare the values of string objects, not references. This makes testing for string equality more intuitive.

So it is a reference type but with some value-type behaviour ;)

Posted 13-Apr-11 5:44am

Olivier Levrey

Comments

TweakBird 13-Apr-11 13:22pm

MSDN is always great reference. My 5.

Olivier Levrey 13-Apr-11 15:16pm

Thank you E$w@r

TweakBird 13-Apr-11 15:19pm

Welcome

walterhevedeich · Accepted Answer · 2011-04-13T05:21:00

Solution 2

Take a look here Strings[^]

Posted 13-Apr-11 5:21am

walterhevedeich

Comments

RaviRanjanKr 13-Apr-11 11:37am

Good Link! My 5

walterhevedeich 13-Apr-11 12:36pm

Thanks

Olivier Levrey 13-Apr-11 11:48am

Interesting link. My 5.

walterhevedeich 13-Apr-11 12:37pm

Thanks.

TweakBird 13-Apr-11 13:20pm

Good Link. My 5

walterhevedeich 14-Apr-11 1:09am

Thanks.

TweakBird 14-Apr-11 12:20pm

Welcome

M.CHAITHANYA 14-Apr-11 0:19am

Hi walerhevedeich,

The statement(taken from the link provided by you) :"the code s = s.Replace ("foo", "bar"); doesn't change the contents of the string that s originally referred to - it just sets the value of s to a new string, which is a copy of the old string but with "foo" replaced by "bar". " ,Does it mean s is pointed to new strin g values which is stored in the heap.If it is so what happens to the old value,will the old pointer will be wiped .

Regards
chaithanya M

walterhevedeich 14-Apr-11 0:46am

Yes you are right. Since string is a reference type, they are all stored in the heap. As for the old values, these are marked for garbage collection, which happens periodically. Unless you are doing N million s.Replace on your code(which I dont think will happen :) ), you dont need to worry about memory pressure, and you can trust GC to do its work.

M.CHAITHANYA 14-Apr-11 0:51am

Hi Walterhevedeich,

If it so..what is the need of creating a new memory where the new value resides ,Instead the old memory can be used by replacing the old string with the new string right?

RegardsChaithanya

walterhevedeich 14-Apr-11 1:08am

Its because strings are immutable, meaning, they can not be changed. There are many reasons why they were designed that way. As for your second statement, about replacing the old memory, StringBuilder behaves exactly that way. You can refer to http://www.codeproject.com/KB/cs/StringBuilder_vs_String.aspx for more info about strings vs. stringbuilders.

M.CHAITHANYA 14-Apr-11 1:32am

Hi walterhevedeich,
I agree with your words..But if we conider the case below:
String s1;
s1="A";
string s2;
s2="B";
s1=s2
Now,is it like s1 has two references one pointig to A and one pointing to B in heap or will it point to only B?what way it is done?

Regards
Chaithanya M

walterhevedeich 14-Apr-11 1:56am

In this case, a new string with the value of s2 will be created and will be assigned to s1. its old value "A" will now be orphaned and be marked for garbage collection. Note though that changing the value of s2(s2="C") will not change s1 since s1 has his own value.

nilesh.d.mankar 6-Jul-11 1:57am

hi walterhevedeich/Chaitanya,

the whole discussion is realy very awesome!!!!

walterhevedeich 6-Jul-11 1:59am

Im glad it helped. :)

Is string a value type or Reference type..

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