C# program to get the extension of a file in C#

The Path.GetExtension() method in C# is used to extract the file extension from a file path. This method is part of the System.IO namespace and returns the extension portion of the path string, including the period (.).

Syntax

Following is the syntax for using Path.GetExtension() method −

public static string GetExtension(string path)

Parameters

• path: A string containing the file path from which to get the extension.

Return Value

The method returns a string containing the extension of the specified path (including the period), or an empty string if the path has no extension.

Using Path.GetExtension() with File Paths

Example

Here is a basic example showing how to get file extensions −

using System;
using System.IO;

class Program {
    static void Main(string[] args) {
        string myPath = "D:\new\quiz.txt";
        string extension = Path.GetExtension(myPath);
        Console.WriteLine("File path: " + myPath);
        Console.WriteLine("Extension: " + extension);
    }
}

The output of the above code is −

File path: D:\new\quiz.txt
Extension: .txt

Using Path.GetExtension() with Different File Types

Example

This example demonstrates getting extensions from various file types −

using System;
using System.IO;

class Program {
    static void Main(string[] args) {
        string[] filePaths = {
            "document.pdf",
            "image.jpg",
            "data.csv",
            "program.cs",
            "fileWithoutExtension",
            "archive.tar.gz"
        };

        foreach (string path in filePaths) {
            string extension = Path.GetExtension(path);
            Console.WriteLine($"File: {path} | Extension: '{extension}'");
        }
    }
}

The output of the above code is −

File: document.pdf | Extension: '.pdf'
File: image.jpg | Extension: '.jpg'
File: data.csv | Extension: '.csv'
File: program.cs | Extension: '.cs'
File: fileWithoutExtension | Extension: ''
File: archive.tar.gz | Extension: '.gz'

Handling Edge Cases

Example

This example shows how the method handles various edge cases −

using System;
using System.IO;

class Program {
    static void Main(string[] args) {
        string[] testCases = {
            "C:\folder\file.txt",
            "file.txt",
            ".hiddenfile",
            "folder",
            "",
            null
        };

        foreach (string testCase in testCases) {
            try {
                string extension = Path.GetExtension(testCase);
                Console.WriteLine($"Path: '{testCase}' | Extension: '{extension}'");
            }
            catch (Exception ex) {
                Console.WriteLine($"Path: '{testCase}' | Error: {ex.GetType().Name}");
            }
        }
    }
}

The output of the above code is −

Path: 'C:\folder\file.txt' | Extension: '.txt'
Path: 'file.txt' | Extension: '.txt'
Path: '.hiddenfile' | Extension: ''
Path: 'folder' | Extension: ''
Path: '' | Extension: ''
Path: '' | Error: ArgumentNullException

Common Use Cases

Conclusion

The Path.GetExtension() method provides a reliable way to extract file extensions from paths in C#. It handles various edge cases and returns the extension including the period, making it essential for file type validation and processing operations.