File extension. A file has an optional extension—it occurs at the end of the file name. With the VB.NET Path.GetExtension Function we acquire the extension.

Function notes. We then make decisions based on the result String of Path.GetExtension. This function has some interesting behavior.

In this example, you can see that the string literal contains a Windows file system path. Next, the extension is extracted by invoking the Path.GetExtension method.

Imports System.IO

Module Module1
    Sub Main()
        ' Input path.
        Dim p As String = "C:\Users\Sam\Documents\Test.txt"
        ' Get extension.
        Dim extension As String = Path.GetExtension(p)

        ' Display extension.
        Console.WriteLine(extension)
        Console.WriteLine(".txt" = extension)
    End Sub
End Module
.txt
True

When using Path.GetExtension, developers may assume the period is not included in the extension string. We can use a string literal (like ".txt") to compare.

Summary. With Path.GetExtension we reliably determine what the extension of a file name or path is. Many inputs are accepted by this function. It allows for many different formats of paths.