C# `String.Substring()`: Extracting Substrings from Strings

Learn how to efficiently extract substrings from strings in C# using the `String.Substring()` method. This tutorial explains its different versions, demonstrates its usage with code examples, and highlights its applications in various string manipulation and text processing tasks.

Understanding and Using C#'s `String.Substring()` Method

Introduction

The `Substring()` method in C# is used to extract a portion (a substring) of a string. It's a fundamental string manipulation function used in many programming tasks.

Method Signatures

The `Substring()` method has two commonly used versions:

public string Substring(int startIndex);
public string Substring(int startIndex, int length);

Parameters

• startIndex: An integer representing the starting position (zero-based index) of the substring within the original string. The first character is at index 0.
• length (in the second version): An integer specifying the number of characters to include in the substring. If omitted (first version), the substring continues to the end of the original string.

Return Value

Both versions return a new string that is a copy of the extracted substring.

Example: Extracting Substrings

This example shows how to use both versions of `Substring()`.

using System;

public class StringExample {
    public static void Main(string[] args) {
        string s1 = "Hello C Sharp";

        string s2 = s1.Substring(6); //Start at index 6, go to end
        Console.WriteLine($"Substring 1: {s2}"); // Output: C Sharp

        string s3 = s1.Substring(0, 5); //Start at 0, take 5 characters
        Console.WriteLine($"Substring 2: {s3}"); // Output: Hello

    }
}

Substring 1: C Sharp
Substring 2: Hello
        

Explanation

In the example, s2 extracts the substring starting at index 6 (the "C" in "Hello C Sharp"), and s3 extracts the first 5 characters ( "Hello").

Important Note: Index Out Of Range

Be cautious! Providing an invalid startIndex or length will throw an `ArgumentOutOfRangeException`.

Conclusion

The `Substring()` method is a fundamental string utility. Understanding its usage and potential exceptions is essential for writing robust and error-free C# code.