Access Cookbook, 2nd Edition [Electronic resources] نسخه متنی

Recipe 11.11 Set File Date and Time Stamps

11.11.1 Problem

Access makes it easy to
retrieve the modification date and time for files on disk, using the
FileDateTime function. In one application, though, you need to be
able to reset the last-modification date of files manually; the
Access FileCopy function doesn't reset file date and
time stamps, and you'd like copied files to have the
current time. Is there a Windows API call that allows you to set file
date and time stamps?

11.11.2 Solution

Windows provides the GetFileTime and
SetFileTime API functions. Both work with three different date/time
values: date of creation, date of last access, and date of last
write. You want to preserve the date of creation and update the dates
of last access and update. The code shown in this example will allow
you to do this.

The sample form, frmTimeStamp, allows you to
select a filename. The function then displays the date and time of
last modification for the file, as shown in Figure 11-13. In addition, you can set a new file date,
time, or both (the function retains whichever setting you
don't change, if you just change one).

Figure 11-13. frmTimeStamp shows a selected file's modification date and time

To set file date and time information in your own applications,
follow these steps:

1. Import the module basTimeStamp from
   

   11-11.MDB . This module includes the type
   definitions and Windows API declarations you'll
   need, as well as a VBA function to convert dates and times as
   retrieved from the API call into date/time values that Access can
   understand. If you want to use this sample form in your own
   applications, you'll also need to import
   basFillList, which includes functions to retrieve
   the list of files.

2. To set the modification-date information for a specific file, call
   the acbSetFileDateTime function, passing it a filename and a
   date/time value as parameters. For example, the following code will
   change the last-modification time and date for
   

   C:\AUTOEXEC.BAT to the current date and time:

   blnOK = acbSetFileDateTime("C:\AUTOEXEC.BAT", Now)

11.11.3 Discussion

The

acbSetFileDateTime function consists of
three basic steps. Its source code is:

Public Function acbSetFileDateTime( _
strFileName As String, varDate As Date) As Boolean
Dim hFile As Long
Dim of As OFSTRUCT
Dim st As SYSTEMTIME
Dim ftCreation As FILETIME
Dim ftLastAccess As FILETIME
Dim ftLastWrite As FILETIME
Dim ftLocal As FILETIME
Dim blnOK As Boolean
st.wYear = Year(varDate)
st.wMonth = Month(varDate)
st.wDay = Day(varDate)
st.wHour = Hour(varDate)
st.wMinute = Minute(varDate)
st.wSecond = Second(varDate)
hFile = OpenFile(strFileName, of, OF_READWRITE)
If hFile > 0 Then
blnOK = GetFileTime(hFile, ftCreation, ftLastAccess, ftLastWrite)
If blnOK Then blnOK = SystemTimeToFileTime(st, ftLastWrite)
If blnOK Then blnOK = LocalFileTimeToFileTime(ftLastWrite, ftLocal)
If blnOK Then blnOK = SetFileTime(hFile, ftCreation, ftLocal, ftLocal)
CloseHandle hFile
End If
acbSetFileDateTime = blnOK
End Function

The first step the function takes is to copy the date information
from the Access Date-type variable into a structure that the API can
use:

' In the declarations section:
Private Type SYSTEMTIME
wYear As Integer
wMonth As Integer
wDayOfWeek As Integer
wDay As Integer
wHour As Integer
wMinute As Integer
wSecond As Integer
wMilliseconds As Integer
End Type
' In the function:
Dim st As SYSTEMTIME
st.wYear = Year(varDate)
st.wMonth = Month(varDate)
st.wDay = Day(varDate)
st.wHour = Hour(varDate)
st.wMinute = Minute(varDate)
st.wSecond = Second(varDate)

Next, the function must open the requested file with read/write
access so that it can write to the file's time
stamp:

hFile = OpenFile(strFileName, of, OF_READWRITE)

If this succeeds, the function then retrieves the current time
stamps, converts the system time structure to a file time structure,
converts that time from local time to the internal generalized time
that Windows uses, and finally sets the file time:

blnOK = GetFileTime(hFile, ftCreation, ftLastAccess, ftLastWrite)
If blnOK Then blnOK = SystemTimeToFileTime(st, ftLastWrite)
If blnOK Then blnOK = LocalFileTimeToFileTime(ftLastWrite, ftLocal)
If blnOK Then blnOK = SetFileTime(hFile, ftCreation, ftLocal, ftLocal)
CloseFileHandle hFile

The function sets both the time of last access and the time of last
write to be the date and time you've specified.

When you select the Set button on the sample form, Access executes
the following procedure:

Private Sub cmdSetTime_Click( )
Dim varDate As Date
Dim strDate As String
Dim strTime As String
strDate = IIf(IsNull(Me.txtNewDate), Me.txtDate, Me.txtNewDate)
strTime = IIf(IsNull(Me.txtNewTime), Me.txtTime, Me.txtNewTime)
varDate = CVDate(strDate & " " & strTime)
If Not acbSetFileDateTime(GetPath( ), varDate) Then
MsgBox "Unable to set the file date!"
Else
Me.txtDate = Format(varDate, "Short Date")
Me.txtTime = Format(varDate, "Short Time")
End If
End Sub

This procedure retrieves the dates you've typed on
the form, converts them to an Access date/time value, and then sets
the date for the file you've selected. Note that the
example uses the existing date or time for any value you
didn't enter. Because the Set button
isn't enabled unless you enter at least the date or
the time, there's no need to worry about when
they're both null.

Unless you take the extra step of
converting the passed-in date/time value from local time to the
internal time Windows uses (Greenwich Mean Time), the time you set
will be off by the difference in time zones between your time and the
standardized time. The call to LocalTimeToFileTime
takes care of this for you. Of course, this counts on the local time
having been set correctly on the local system.