C# - StringBuilder

In C#, the string type is immutable. It means a string cannot be changed once created. For example, a new string, "Hello World!" will occupy a memory space on the heap. Now, by changing the initial string "Hello World!" to "Hello World! from Tutorials Teacher" will create a new string object on the memory heap instead of modifying an original string at the same memory address. This behavior would hinder the performance if the original string changed multiple times by replacing, appending, removing, or inserting new strings in the original string.

To solve this problem, C# introduced the StringBuilder in the System.Text namespace. The StringBuilder doesn't create a new object in the memory but dynamically expands memory to accommodate the modified string.

Creating a StringBuilder Object

You can create an object of the StringBuilder class using the new keyword and passing an initial string. The following example demonstrates creating StringBuilder objects.

using System.Text; // include at the top
            
StringBuilder sb = new StringBuilder(); //string will be appended later
//or
StringBuilder sb = new StringBuilder("Hello World!");

Optionally, you can also specify the maximum capacity of the StringBuilder object using overloaded constructors, as shown below.

StringBuilder sb = new StringBuilder(50); //string will be appended later
//or
StringBuilder sb = new StringBuilder("Hello World!", 50);

Above, C# allocates a maximum of 50 spaces sequentially on the memory heap. This capacity will automatically be doubled once it reaches the specified capacity. You can also use the capacity or length property to set or retrieve the StringBuilder object's capacity.

You can iterate the using for loop to get or set a character at the specified index.

StringBuilder sb = new StringBuilder("Hello World!");

for(int i = 0; i < sb.Length; i++)
    Console.Write(sb[i]); // output: Hello World!

Retrieve String from StringBuilder

The StringBuilder is not the string. Use the ToString() method to retrieve a string from the StringBuilder object.

StringBuilder sb = new StringBuilder("Hello World!");

var greet = sb.ToString(); //returns "Hello World!"

Add/Append String to StringBuilder

Use the Append() method to append a string at the end of the current StringBuilder object. If a StringBuilder does not contain any string yet, it will add it. The AppendLine() method append a string with the newline character at the end.

StringBuilder sb = new StringBuilder();
sb.Append("Hello ");
sb.AppendLine("World!");
sb.AppendLine("Hello C#");
Console.WriteLine(sb);

Append Formated String to StringBuilder

Use the AppendFormat() method to format an input string into the specified format and append it.

StringBuilder sbAmout = new StringBuilder("Your total amount is ");
sbAmout.AppendFormat("{0:C} ", 25);

Console.WriteLine(sbAmout);//output: Your total amount is $ 25.00

Insert String into StringBuilder

Use the Insert() method inserts a string at the specified index in the StringBuilder object.

StringBuilder sb = new StringBuilder("Hello World!");
sb.Insert(5," C#"); 

Console.WriteLine(sb); //output: Hello C# World!

Remove String in StringBuilder

Use the Remove() method to remove a string from the specified index and up to the specified length.

StringBuilder sb = new StringBuilder("Hello World!",50);
sb.Remove(6, 7);

Console.WriteLine(sb); //output: Hello

Replace String in StringBuilder

Use the Replace() method to replace all the specified string occurrences with the specified replacement string.

StringBuilder sb = new StringBuilder("Hello World!");
sb.Replace("World", "C#");

Console.WriteLine(sb);//output: Hello C#!