The Problem

I recently found several bugs in my own programs relating to the way I had been interpreting the creation time of files. All of these bugs resulted from some variation of the following sequence of events:

• Create file C:\temp\MyFile
• Delete file C:\temp\MyFile
• Create file C:\temp\MyFile

My [false] assumption was that the creation time of MyFile is always equal to the last time it was created. This was, after all, the “creation time”. One program of mine, for example, writes and deletes a particular log file once per day—why then was I finding instances where this file had a creation date several months old? In short, the answer is that I was not setting it.

Some Background

The .NET Class Library description of the CreationTime property [of the FileInfo class] is somewhat cryptic (Fig. 1). Does this mean the property gets the time when the object is instantiated—e.g. by calling New FileInfo(), or the time when the underlying file is created—e.g. by calling FileInfo.Create()? It turns out that neither is true. However, it is true that this property sets the time when the underlying file is created.

The Test

In order to test this suspicious property I wanted to remove the .NET Framework from the equation. The logic was that if I could show how the OS should act apart from the .NET Framework, then I could illustrate the bug. I ran a series of tests employing Windows Explorer: I created and deleted files from the same directory, using the file property dialog to examine the timestamps placed on these activities by the OS. Following the Windows Explorer test, I created a simple console app (Fig. 2) that would create and delete the same file 16 times.

The Results

I was once again surprised by the results (Tables 1-2). Though the patterns varied between replications of my test, Windows Explorer demonstrated the same behaviors I had seen in my own apps. It left file creation attributes unchanged after many manipulations. Even a full system reboot after step 2 (i.e. Delete File, Create File), for example, did not change the File Creation Time established in step 1 (Original Create).

The Microsoft product references for both XP and Win2K3 include some details about the way NTFS works. Although File Creation Time is not mentioned in either article, the following statement is made in both regarding the Last Update Time attribute:

NTFS does not update a file’s directory entry when all in-memory references to that file are gone

Although my testing showed that the file attributes seem to catch up eventually, after certain types of manipulations, my experience in the real-world shows that File Creation Time can go unchecked for literally months. Hence, it would seem the only solution to this problem is to  set the Creation Time attribute explicitly whenever a file is created.

Appendix A: Test Results

Appendix B: VB.NET code

    Sub Main(ByVal Args() As String)
        Dim fi As System.IO.FileInfo
        Dim fs As System.IO.FileStream
        fi = New System.IO.FileInfo(Args(0))
        If Not fi.Exists Then
            fs = fi.Create
            fs.Close()
            'fi.CreationTime = Now ' THIS IS THE LINE YOU NEED
        End If
        fi.Refresh()
        Console.WriteLine(fi.CreationTime.ToString)
        Dim i As Integer = 0
        For i = 0 To 15
            fi.Delete()
            fi.Refresh()
            fs = fi.Create
            fs.Close()
            'fi.CreationTime = Now ' THIS IS THE LINE YOU NEED
            fi.Refresh()
            Console.WriteLine(fi.CreationTime.ToString)
        Next

        fi.Delete()
        fi.Refresh()
    End Sub