Building strings

[Daniel Grunwald]

Assume you're building a string from 100000 characters using +=. Assuming one += call per character. On the first concatenation, you're copying 2 characters (first+second character) (= 4 byte). On the second concatenation, you're copying 3 characters (= 6 byte). On the third concatenation, you're copying 4 characters (= 8 byte). You see how this continues - you're effectively copying the first characters a lot of times. In total, you'll copy 10 GB of data for just 100000 characters resulting in a tiny 200 KB string. In comparison, StringBuilder will internally have to copy at most 400 KB to build that string.

[Guffa]

Using += works fine as long as you have a small (and limited) number of strings, but it scales really badly. The execution time increases exponetially with the number of string that you add. Here's a guy with the same problem a while back: String manipulation performance issue[^] Creating a string of 383000 characters by using += required moving 75 GB of data, so there is no wonder that it took over a minute to create it. Using a StringBuilder reduces the execution time with something like 99.999%. As an experiment in optimisation I also attempted to reduce the execution time without using a StringBuilder, and managed to reduce it by about 96%. :)

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[Johann Gerell]

Guffa wrote:

As an experiment in optimisation I also attempted to reduce the execution time without using a StringBuilder, and managed to reduce it by about 96%.

You've said 'A', I wait for 'B'... ;)

-- The Blog: Bits and Pieces

[Guffa]

I already said both A and B a long time ago. Look in the thread that I linked to.

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[Johann Gerell]

Ah! Now I see it - you didn't mention in the post that your 96% fix was in that thread... ;P

-- The Blog: Bits and Pieces

[Ennis Ray Lynch Jr]

My favorite issue with StringBuilder. 99% if the time I have seen it used are as follows: StringBuilder sb = new StringBuilder(); ... do sb.Append("Some Text" + i.ToString() + "some more text" + abc.ToString()); while return sb.ToString();

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On two occasions I have been asked [by members of Parliament], 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question. - Charles Babbage

[Guffa]

Lol. And to explain to the great masses that has not yet grasped the power of the StringBuilder, this is the way to use it: sb.Append("Some Text").Append(i).Append("some more text").Append(abc); :)

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[Alois Kraus]

If you have to alter very big strings StringBuilder is the way to go. But for small strings the border where StringBuilder is faster than the String.xxx functions becomes a moving target: http://www.codeproject.com/useritems/StringBuilder_vs_String.asp Yours, Alois Kraus

[Jorgen Sigvardsson]

The reason why this is the case is that strings in .NET (just like in Java), are immutable objects. That means that the underlying memory buffer is locked, and will not allow modifications. String s = "ab"; s += "c"; is equivalent to String s = "ab"; s = s + "c" which in turn is equivalent to String s = "ab"; String temp = s + "c"; s = temp;. Each append generates a new object. StringBuilder however, is a mutable object, meaning that the underlying character array is modified when you issue an append command - no temporary objects are created. The reason why strings are immutable is that you can do a fair amount of optimizations on strings, which will improve performance - given that you do not misuse them of course. :)

-- Presented in doublevision (where drunk)

[Pascal Ganaye]

I think I read somewhere that StringBuilder is not a class that you could write in managed C# or VB. It is managed C# but It uses string internals which are not available to us. This result in a much better memory management. I had a look at the source, and I believe it is an awfully long winded. Anyway It is MUCH better than using +. This said I have seen people using StringBuilder to concatenate 2 strings and show the result in a message box. I think it is a bit over the top, stringbuilder beat the + operator when .append is used repeatidly on the same stringbuilder. What the point of saving 0.1 millisecond to display a messagebox. Overall in the long run code clarity is as important as speed, I would recommend to use stringbuilder when you concatenate 3 items or more.

[Judah Gabriel Himango]

So they have the thread safe StringBuffer and the non-thread safe StringBuilder, both with identical functionality. Yeah, that's not confusing. :rolleyes:

Tech, life, family, faith: Give me a visit. I'm currently blogging about: God-as-Judge, God-as-Forgiver The apostle Paul, modernly speaking: Epistles of Paul Judah Himango

[GaryWoodfine]

MS probably copied it from Java :-)

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"a fool will not learn from a wise man, but a wise man will learn from a fool" "It is hard to fail, but it is worse never to have tried to succeed." - Theodore Roosevelt "Success is going from failure to failure without losing your enthusiasm." - Winston Churchill

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My Website || My Blog

[Zac Howland]

V. wrote:

but this is a microsoft site

*looks around* I don't recall seeing anywhere that stated this site ONLY dealt with Microsoft products. In fact, I've seen several questions/comments on here dealing with compiling code with Intel C++, GCC, and Borland ... and even some using Linux ;P

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week Zac

[Zac Howland]

cykophysh39 wrote:

MS probably copied it from Java

Not likely. StringBuilder was part of .Net long before Java 1.5 was released. Sun and Microsoft are going back and forth with their library support, so don't be surprised when you see similar classes doing similar things coming from both of them. When one does it, the other will soon copy it.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week Zac

[David Stone]

There's a lot of stuff like that in Java. ArrayList<T> and Vector<T> are interchangeable. One of them is thread safe. Go figure.

Once you wanted revolution
Now you're the institution
How's it feel to be the man?

[Judah Gabriel Himango]

David Stone wrote:

There's a lot of stuff like that in Java. ArrayList and Vector are interchangeable. One of them is thread safe. Go figure.

:doh:

Tech, life, family, faith: Give me a visit. I'm currently blogging about: God-as-Judge, God-as-Forgiver The apostle Paul, modernly speaking: Epistles of Paul Judah Himango

[Nitron]

Zac Howland wrote:

and even some using Linux

soapbox! :-D

~Nitron.

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