DateTime DateTime Format File String.Format

Filename, date

A VB.NET program can be used to generate a report on a daily basis. But where should it store this report? Sometimes a file (named with the current day) is a good place.

By using some common String and DateTime functions, we can generate a file name for each day. Some surrounding characters can also be added.

An example

To begin, we place some code in the Main subroutine—this is run when the program is started. There are 3 parts to the codex ample.

Part 1 We generate the file name by calling String.Format. We specify a format string with year, month and day chars.

Part 2 We build up the full path for the output file name. You can change this to point to a folder on your computer.

Part 3 We write a file using the full name and path we generated. The contents also contain the date.

Imports System.IO

Module Program
    Sub Main()

        ' Part 1: generate file name from date.
        Dim name As String = String.Format("log-{0:yyyy-MM-dd}.txt", DateTime.Now)

        ' Part 2: get full path for file.
        Dim path As String = "C:\\programs\\" + name

        ' Part 3: write file with date in file name.
        File.WriteAllText(path, "Today is " + DateTime.Today.ToString())
        Console.WriteLine("DONE")

    End Sub
End Module
DONE

Notes, output

Let us consider the output of the program in the year 2020. I tested that the file name is correct. And the file contents also matches the current day (when tested).

File:     log-2020-06-19.txt
Contents: Today is 6/19/2020 12:00:00 AM

Programming languages like VB.NET are often used for server-based applications, or for data analysis. Writing a daily file (from the results of a run) is a common requirement.