Path.ChangeExtension

This modifies a path string. It can, for example, change a file ending in a ".txt" extension to end in the ".html" extension.

Use ChangeExtension with string arguments such as ".txt". You can use null to remove the entire extension. This makes it unnecessary to write custom string methods.

First, we use Path.ChangeExtension to change the extension of a path string in the program's memory. The Path class does not access the disk or persist the change.

using System.IO;

class Program
{
    static void Main()
    {
        // The file name.
        string path = "test.txt";

        // Make sure the file exists.
        File.WriteAllText(path, "Tutorial file");

        // Change the path name to have a new extension in memory.
        string changed = Path.ChangeExtension(path, ".html");

        // Create file with the new extension name.
        File.WriteAllText(changed, "Changed file");
    }
}
test.txt
test.html

Remove extension

We can remove the extension by providing null. Because the Path class has no RemoveExtension method, providing null is the clearest way to remove the extension.

using System;
using System.IO;

class Program
{
    static void Main()
    {
        string original = "file.txt";
        Console.WriteLine(Path.ChangeExtension(original, ""));
        Console.WriteLine(Path.ChangeExtension(original, null));
    }
}
file.
file

A summary

We used the Path.ChangeExtension method. This method receives 2 parameters: the path string you want to change, and the new extension including the leading period.