Remove or replace a substring from a string in C#

This article illustrates the different techniques to remove or replace a substring from a string in C#.

The standard solution to remove a substring from a string is using the String.Remove() method. It returns a new string in which a specified number of characters from the string are deleted. The following sample illustrates the use of the Remove() method.

using System;

public class Example

{

public static void Main()

{

String s = "ABCDEF";

int start = 3;

int length = 2;

s = s.Remove(start, length);

Console.WriteLine(s); // ABCF

}

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The above code throws System.ArgumentOutOfRangeException if the length refers to a location outside the string. This can be handled by simply performing the length check.

using System;

public class Example

{

public static void Main()

{

String s = "ABCDEF";

int start = 5;

int length = 2;

s = s.Remove(start, Math.Min(length, s.Length - start));

Console.WriteLine(s); // ABCDE

}

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In order to replace a portion of a string with another string, you can invoke the String.Insert() method on the resultant string, as shown below:

using System;

public class Example

{

public static void Main()

{

String s = "ABCDEF";

int start = 5;

int length = 2;

string replacement = "XX";

s = s.Remove(start, Math.Min(length, s.Length - start))

.Insert(start, replacement);

Console.WriteLine(s); // ABCDEXX

}

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It’s better to create a string extension method, ReplaceAt(), which replaces the characters in the current string beginning at the specified position, with the replacement string.

using System;

public static class StringExtensions

{

public static string ReplaceAt(this string s, int start, int length, string replacement)

{

return s.Remove(start, Math.Min(length, s.Length - start))

.Insert(start, replacement);

}

public class Example

{

public static void Main()

{

String s = "ABCDEF";

int start = 5;

int length = 2;

string replacement = "XX";

s = s.ReplaceAt(start, length, replacement);

Console.WriteLine(s); // ABCDEXX

}

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Here’s an alternative method using the StringBuilder class. The benefit of using StringBuilder is that it considerably improves the code’s readability.

using System;

using System.Text;

public static class StringExtensions

{

public static string ReplaceAt(this string s, int start, int length, string replacement)

{

var sb = new StringBuilder(s);

sb.Remove(start, Math.Min(length, s.Length - start));

sb.Insert(start, replacement);

return sb.ToString();

}

public class Example

{

public static void Main()

{

String s = "ABCDEF";

int start = 5;

int length = 2;

string replacement = "XX";

s = s.ReplaceAt(start, length, replacement);

Console.WriteLine(s); // ABCDEXX

}

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That’s all about removing or replacing a substring from a string in C#.

Remove or replace a substring from a string in C#

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