File size

Sometimes in VB.NET programs we want to get the number of bytes in a file. FileInfo can return the file size. This value is a Long, but can usually be safely to an Integer.

We create a new FileInfo instance with a file name. We then access the Length property to get a byte size of the file.

Example

First, to begin using FileInfo, it helps to import System.IO. We construct the FileInfo instance by passing a file name to its constructor.

Imports System.IO

Module Module1

    Sub Main()
        ' Get file info for test.txt.
        ' ... Create this file in Visual Studio and select Copy If Newer on its properties.
        Dim info As New FileInfo("test.txt")

        ' Get length of the file.
        Dim length As Long = info.Length

        ' Add more characters to the file.
        File.AppendAllText("test.txt", " More characters.")

        ' Get another file info.
        ' ... Then get the length.
        Dim info2 As New FileInfo("test.txt")
        Dim length2 As Long = info2.Length

        ' Show how the size changed.
        Console.WriteLine("Before and after: {0}, {1}", length, length2)
        Console.WriteLine("Size increase: {0}", length2 - length)
    End Sub

End Module
Before and after: 3, 20
Size increase: 17

Program notes

The initial file was only 3 bytes in length, while the file after the append operation was 20 bytes. This means the file increased in size by 17 bytes.

We looked at how you can obtain the size of a file using VB.NET. Further, we demonstrated how this measurement changes as the file is mutated on the disk.