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String Vs StringBuilder (C#)

, 1 May 2004
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An article on performance of String Vs StringBuilder and better places where each can be used

Introduction

This is my second article regarding performance. Most of the people use string everywhere in their code. Actually when doing string concatenation, do you know what exactly you are doing? It has a big drawback mainly in concatenation which can be overcome by StringBuilder. It will give a vast improvement in performance when you use concatenation of string over String.

What is the Exact Difference?

First we will look at what happens when you concatenate two strings. For a rough idea, think like this. In a loop, you are adding few numbers to get a string to give all the numbers.

string returnNumber = "";
for(int i = 0; i<1000; i++)
{ 
    returnNumber = returnNumber + i.ToString();
}

Here we are defining a string called returnNumber and after that, in the loop we are concatenating the old one with the new to get a string. Do you know when we do like that we are assigning it again and again? I mean it's really like assigning 999 new strings!

Actually the concatenation will create a new string returnNumber, with both old returnNumber and i.ToString(). If we think roughly, how will the performance of the code be? Can you imagine it? No one thinks about this when coding.

If we can have something which is to be defined only once and add all the strings into it, what can you say about the performance. That's what StringBuilder does.

StringBuilder returnNumber = new StringBuilder(10000);
for(int i = 0; i<1000; i++)
{ 
    returnNumber.Append(i.ToString());
}

We are creating a StringBuilder of length 10000 in memory where we can add all the strings. This surely won't create a new string each and every time. Actually we are creating a StringBinder, and whenever something is added it will get copied into that memory area. At the end, we can get the string by StringBuilder.ToString(). Here also, it won't create a new string. It will return a string instance that will point to the string inside the StringBuilder. See, how efficient this is?

To explain this in a practical manner, I'm not going to analyze IL code or Optimized JIT compiled code. You can see the differences by running the samples.

Why String? Can't Use StringBinder Everywhere?

No. You can't. When initializing a StringBuilder, you are going down in performance. Also many actions that you do with string can't be done with StringBinder. Actually it is used mostly for situations as explained above. Last week, I showed a person who used StringBuilder to just add two strings together! It's really nonsense. We must really think about the overhead of initialization. In my personal experience, a StringBuilder can be used where more than four or more string concatenations take place. Also if you try to do some other manipulation (like removing a part from the string, replacing a part in the string, etc.), then it's better not to use StringBuilder at those places. This is because we are anyway creating new strings. Another important issue. We must be careful to guess the size of StringBuilder. If the size which we are going to get is more than what is assigned, it must increase the size. This will reduce its performance.

History

  • 19th April, 2004: Article submitted

License

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

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About the Author

Chester Ragel
Web Developer
Singapore Singapore
No Biography provided

Comments and Discussions

 
GeneralMy vote of 3 Pinmembersibeesh17-Jul-14 7:28 
QuestionConfusion Regarding StringBuilder Class PinmemberSaddam Khan Ranjhani1-Apr-14 23:08 
SuggestionMemory PinmemberMember 1028141517-Sep-13 21:32 
GeneralMy vote of 5 PinmemberMember 950731410-Sep-13 21:44 
GeneralMy vote of 1 PinmemberMukesh_B18-Feb-13 22:26 
GeneralVote of 4 PinmemberIsmail482-Jan-13 2:09 
SuggestionThought I'd share, great way to automate Stringbuilder object creation PinmemberSuck League20-Oct-12 8:10 
GeneralMy vote of 3 PinmemberRyan Leeder24-May-12 19:00 
GeneralMy vote of 4 Pinmemberehab.abuzied23-May-12 3:23 
GeneralMy vote of 2 PinmemberSenthilkumar Elangovan6-Apr-12 10:45 
GeneralMy vote of 1 PinmemberMember 846447828-Dec-11 7:30 
GeneralMy vote of 4 Pinmemberawaisdar11-Dec-11 7:00 
GeneralMutable vs Immutable PinmemberVozzie230-Nov-10 3:37 
GeneralGood Article PinmemberShalinD27-Mar-10 19:30 
Generalthnx Pinmembergoher16-Feb-10 2:07 
GeneralStringBuilder Vs String PinmemberSuresh271298-Oct-07 21:11 
GeneralImprove Performance with Unnessary String Creation PinmemberCodeEnjoy2-Aug-07 2:59 
GeneralSome good Blog entries on .net String performance Pinmemberandy brummer29-Apr-04 6:54 
GeneralStringBuilder is OFTEN not faster PinmemberKenneth Beckett29-Apr-04 6:01 
GeneralRe: StringBuilder is OFTEN not faster Pinmemberkelvinninh29-Apr-04 6:25 
GeneralRe: StringBuilder is OFTEN not faster PinmemberThomas Freudenberg2-May-04 19:53 
GeneralRe: StringBuilder is OFTEN not faster PinmemberBrian Delahunty28-Jul-04 23:47 
GeneralRe: StringBuilder is OFTEN not faster PinmemberMagikos28-Sep-04 8:31 
GeneralRe: StringBuilder is OFTEN not faster Pinmemberjmelgaard17-Oct-07 4:17 
QuestionStringBinder? PinmemberThomas Freudenberg20-Apr-04 21:37 

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