Member Avatar for gicio

Hi!

Im very interesting in when to use exactly the StringBuilder?

For example for something like this?:

String strTest1 = This;
String strTest2 = Test;
StringBuilder stbTest = new StringBuilder();
stbTest.Append(strTest1). Append(is a ). Append(stbTest);


can someone provide some sample codes when to use a StringBuilder?

And can someone tell me his experience about the performance of a StringBuilder?


Regards,


gicio

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  • Latest Post Latest Post by jujubee

Dani AI

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Short answer: prefer a StringBuilder when the code makes many incremental edits to a text (for example, concatenating inside large loops, assembling multi‑MB output, or stitching together lots of user input). As noted, strings in .NET are immutable, so repeated “modifications” create new string objects and extra allocations; using a mutable builder avoids that churn. (learn.microsoft.com)

Practical heuristics: if the number of pieces is fixed and small, the + operator, string interpolation or String.Concat is simpler and often optimized by the compiler. If combining many elements from a collection, string.Join will usually be faster than iteratively appending because it can size the final buffer once. If the number of concatenations depends on input size (loops, file lines, user data), lean on a builder. These tradeoffs and examples are discussed in the C# string/concatenation guide. (learn.microsoft.com)

Concrete tips that save time and memory: initialize the builder with an estimated capacity (constructor or EnsureCapacity) to avoid repeated reallocations; call ToString() only once when finished; reuse a builder with Clear() if reusing makes sense but beware that retained capacity keeps memory around; don’t rely on StringBuilder for heavy substring searches since it lacks IndexOf‑style APIs — convert to string for robust searching or regex work. The runtime’s capacity behavior and the EnsureCapacity/Capacity options are documented in the StringBuilder reference. (learn.microsoft.com)

For extreme, allocation‑sensitive paths, consider modern low‑allocation APIs (spans and the string.Create pattern) or write streaming code so the whole file/text is never held in memory; these APIs let code construct text with fewer temporaries on supported runtimes. Always measure the real scenario (Stopwatch or a micro‑benchmark) — algorithm and I/O strategy often dwarfs string‑allocation costs. (learn.microsoft.com)

Notes tied to the thread: ’s caution about overhead for small strings is correct; ’s CSV import story is typical when code naively builds huge strings in loops — often the biggest win is streaming or using a proper CSV parser rather than just switching builders.

Recommended Answers

All 12 Replies

Member Avatar for Tekmaven

StringBuilder should be used when putting together large, complex strings. Do not use it for working with small strings - StringBuilder has a lot of overhead and isn't worth the performance loss.

Member Avatar for Dani

It seems to me as if gicio might indeed be using it for large strings, and is just providing these small "test" strings as an example to learn how to use it.

Member Avatar for jackster

From my experience, if you are manipulating very large strings, such as imported from a 2MB text file you have to use StringBuilder.

To give you an example, to import a csv file of 30,000 records, when i used a string to store the data took over 2 mins to process (and used a lot of computer resources.

with StringBuilder, it tool just a few seconds to process.

jack

It seems to me as if gicio might indeed be using it for large strings, and is just providing these small "test" strings as an example to learn how to use it.

Member Avatar for Tekmaven

Why would you store all of that in a string? LOL

That's why we have things like DataSets...

Member Avatar for jackster

Why would you store all of that in a string? LOL

That's why we have things like DataSets...

Can you convert directly from a cvs file to a datatable?

I imported the cvs, into a string builder, then from that I manually converted it to a datatable by splitting it at the commans and end of lines.

is there an easier way?

Member Avatar for Decency

well from my experience you better not using the StringBuilder its full of over head, now if you are really dealing with very large strings you better use data sets or design a small data structure that accepts Object and proccess your data with.

Member Avatar for jackster

how could u turna string straight to a dataaset

Member Avatar for SPYRO

It has nothing to do with the text size.
The difference is that the string value is immutable.
Methods that appear to modify a string actually return a new string containing the modification.

Here is a simple example:

string s1 = "World";
string s2 = s1.Insert(0, "Hello ");
label1.Text = object.ReferenceEquals(s1, s2).ToString();

StringBuilder sb1 = new StringBuilder("World");
StringBuilder sb2 = sb1.Insert(0, "Hello ");
label2.Text = object.ReferenceEquals(sb1, sb2).ToString();

Result:
label1.Text is “false
label2.Text is “true

s1 and s2 reference different objects, while sb1 and sb2 reference the same object.

Conclusion:
Use a StringBuilder if you have significant modifications of the text (to build a string)

Member Avatar for markjuggles

I agree with SPYRO.

This is ultimately an issue of efficiency. If a program is constantly making minor string modifications without a StringBuilder, there will be a lot of unused object references which get garbage collected (eventually).

If you are working on a large number of items with several string manipulations each, the computer's performance might suffer. To get around this, manipulate the strings in a StringBuilder. There will be far fewer objects created.

Mark

Member Avatar for Iron_Cross

how could u turna string straight to a dataaset

I recently wrote a program that did exactly that. It imported a .csv file into a dataset then exported all the data to a SQL Server 2000 DB. I would give you the source, except there is a lot happening in there that doesn't apply to this so it would be confusing.

Basically what I did was I read one line of text at a time, then I divided that text by the commas. Then I used each of those "cells" as the data for a datatable that I just looped over at the same time I was looping over the CSV file.

Member Avatar for SethWebster

SPYRO is right. Any time that you are processing in a loop to build a string, or as some of you have stated, manipulating a large string, StringBuilder is the way.

The overhead of StringBuilder is nothing when compared to the overhead created by a loop that run through 1000 iterations, and creates a 1000 string objects (or more).

StringBuilder = 1 object for entire operation.

Seth Webster

Member Avatar for jujubee

What spyro said -
the number of times you need to add/modify the string is the cause of overhead -

here is its basic usage:
//add reference
using System.Text

//create string builder
StringBuilder sb = new StringBuilder();
//add items to it
sb.Append("some text");
sb.Append(" more text");
...
//output contents, in this case to the lblOutput label
lblOutput.Text=sb.ToString();

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