MaylorTaylor
MaylorTaylor

String Vs. String Builder

03 Oct 2018

What is the difference between string and string builder in C#

TLDR;

String is Immutable and StringBuilder is Mutable

To go in more depth…

String:

  • under System namespace
  • immutable (read-only) instance
  • performance degrades when continuous change of value occures
  • thread safe

StringBuilder: (mutable string)

  • under System.Text namespace
  • mutable instance
  • shows better performance since new changes are made to existing instance

String

The String class is in the System namespace. A string instance is immutable. You cannot change it after it was created. Any operation that appears to change the string instead returns a new instance.

A string is a sequential collection of characters that is used to represent text. A String object is a sequential collection of System.Char objects that represent a string; a System.Char object corresponds to a UTF-16 code unit. The value of the String object is the content of the sequential collection of System.Char objects, and that value is immutable (that is, it is read-only). For more information about the immutability of strings, see the Immutability and the StringBuilder class. The maximum size of a String object in memory is 2GB, or about 1 billion characters.

Consider using the String class under these conditions:

  • When the number of changes that your app will make to a string is small. In these cases, StringBuilder might offer negligible or no performance improvement over String.

  • When you are performing a fixed number of concatenation operations, particularly with string literals. In this case, the compiler might combine the concatenation operations into a single operation.

  • When you have to perform extensive search operations while you are building your string. The StringBuilder class lacks search methods such as IndexOf or StartsWith. You’ll have to convert the StringBuilder object to a String for these operations, and this can negate the performance benefit from using StringBuilder. For more information, see the Searching the text in a StringBuilder object section.

String example

string string1 = "This is a string created by assignment.";
Console.WriteLine(string1);
string string2a = "The path is C:\\PublicDocuments\\Report1.doc";
Console.WriteLine(string2a);
string string2b = @"The path is C:\PublicDocuments\Report1.doc";
Console.WriteLine(string2b);
// The example displays the following output:
// This is a string created by assignment.
// The path is C:\PublicDocuments\Report1.doc
// The path is C:\PublicDocuments\Report1.doc

StringBuilder

The StringBuilder class is in the System.Text namespace. It represents a mutable string of characters, such as one you’re constructing piece-wise, or where you change lots of things while building the string.

Consider using the StringBuilder class under these conditions:

  • When you expect your app to make an unknown number of changes to a string at design time (for example, when you are using a loop to concatenate a random number of strings that contain user input).

  • When you expect your app to make a significant number of changes to a string.

StringBuilder Example

using System;
using System.Text;

public sealed class App
{
    static void Main()
    {
        // Create a StringBuilder that expects to hold 50 characters.
        // Initialize the StringBuilder with "ABC".
        StringBuilder sb = new StringBuilder("ABC", 50);

        // Append three characters (D, E, and F) to the end of the StringBuilder.
        sb.Append(new char[] { 'D', 'E', 'F' });

        // Append a format string to the end of the StringBuilder.
        sb.AppendFormat("GHI{0}{1}", 'J', 'k');

        // Display the number of characters in the StringBuilder and its string.
        Console.WriteLine("{0} chars: {1}", sb.Length, sb.ToString());

        // Insert a string at the beginning of the StringBuilder.
        sb.Insert(0, "Alphabet: ");

        // Replace all lowercase k's with uppercase K's.
        sb.Replace('k', 'K');

        // Display the number of characters in the StringBuilder and its string.
        Console.WriteLine("{0} chars: {1}", sb.Length, sb.ToString());
    }
}

// This code produces the following output.
//
// 11 chars: ABCDEFGHIJk
// 21 chars: Alphabet: ABCDEFGHIJK

References