Article
11/18/2011

DateTime.ToFileTime Method

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Converts the value of the current DateTime object to a Windows file time.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Function ToFileTime As Long

public long ToFileTime()

Return Value

Type: System.Int64
The value of the current DateTime object expressed as a Windows file time.

Exceptions

Exception	Condition
ArgumentOutOfRangeException	The resulting file time would represent a date and time before 12:00 midnight January 1, 1601 C.E. UTC.

Remarks

A Windows file time is a 64-bit value that represents the number of 100-nanosecond intervals that have elapsed since 12:00 midnight, January 1, 1601 A.D. (C.E.) Coordinated Universal Time (UTC). Windows uses a file time to record when an application creates, accesses, or writes to a file.

The ToFileTime method uses the Kind property to determine whether the current DateTime object is a local time, a UTC time, or an unspecified kind of time which is treated as a local time.

Notes to Callers

Ordinarily, the FromFileTime method restores a DateTime value that was saved by the ToFileTime method. However, the two values may differ under the following conditions:

If the serialization and deserialization of the DateTime value occur in different time zones. For example, if a DateTime value with a time of 12:30 P.M. in the U.S. Eastern Time zone is serialized, and then deserialized in the U.S. Pacific Time zone, the original value of 12:30 PM is adjusted to 9:30 A.M. to reflect the difference between the two time zones.

If the DateTime value that is serialized represents an invalid time in the local time zone. In this case, the ToFileTime method adjusts the restored DateTime value so that it represents a valid time in the local time zone.

For example, the transition from standard time to daylight saving time occurs in the U.S. Pacific Time zone on March 14, 2010, at 2:00 A.M., when the time advances by one hour, to 3:00 A.M. This hour interval is an invalid time, that is, a time interval that does not exist in this time zone. The following example shows that when a time that falls within this range is converted to a long integer value by the ToFileTime method and is then restored by the FromFileTime method, the original value is adjusted to become a valid time. You can determine whether a particular date and time value may be subject to modification by passing it to the TimeZoneInfo.IsInvalidTime method, as the example illustrates.

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim date1 As New DateTime(2010, 3, 14, 2, 30, 0)
      outputBlock.Text += String.Format("Invalid Time: {0}", TimeZoneInfo.Local.IsInvalidTime(date1)) & vbCrLf
      Dim ft As Long = date1.ToFileTime()
      Dim date2 As DateTime = DateTime.FromFileTime(ft)
      outputBlock.Text += String.Format("{0} -> {1}", date1, date2) & vbCrLf
   End Sub
End Module
' The example displays the following output:
'       Invalid Time: True
'       3/14/2010 2:30:00 AM -> 3/14/2010 3:30:00 AM

using System;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      DateTime date1 = new DateTime(2010, 3, 14, 2, 30, 00);
      outputBlock.Text += String.Format("Invalid Time: {0}",
                        TimeZoneInfo.Local.IsInvalidTime(date1)) + "\n";
      long ft = date1.ToFileTime();
      DateTime date2 = DateTime.FromFileTime(ft);
      outputBlock.Text += String.Format("{0} -> {1}", date1, date2) + "\n";
   }
}
// The example displays the following output:
//       Invalid Time: True
//       3/14/2010 2:30:00 AM -> 3/14/2010 3:30:00 AM

Examples

The following example demonstrates the ToFileTime method.

Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

   outputBlock.Text &= "Enter the file path:" & vbCrLf
   Dim filePath As String
   filePath = System.Console.ReadLine()

   If System.IO.File.Exists(filePath) Then
      Dim fileCreationDateTime As System.DateTime
      fileCreationDateTime = System.IO.File.GetCreationTime(filePath)

      Dim fileCreationFileTime As Long
      fileCreationFileTime = fileCreationDateTime.ToFileTime()

      outputBlock.Text &= String.Format("{0} in file time is {1}.", _
                               fileCreationDateTime, _
                               fileCreationFileTime) & vbCrLf
   Else
      outputBlock.Text &= String.Format("{0} is an invalid file", filePath) & vbCrLf
   End If
End Sub

public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
   outputBlock.Text += "Enter the file path:" + "\n";
   string filePath = System.Console.ReadLine();

   if (System.IO.File.Exists(filePath))
   {
      System.DateTime fileCreationDateTime =
         System.IO.File.GetCreationTime(filePath);

      long fileCreationFileTime = fileCreationDateTime.ToFileTime();

      outputBlock.Text += String.Format("{0} in file time is {1}.",
                         fileCreationDateTime,
                         fileCreationFileTime) + "\n";
   }
   else
   {
      outputBlock.Text += String.Format("{0} is an invalid file", filePath) + "\n";
   }
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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