DateTimeOffset.FromFileTime(Int64) 方法

定义

将指定的 Windows 文件时间转换为等效的本地时间。Converts the specified Windows file time to an equivalent local time.

public:
 static DateTimeOffset FromFileTime(long fileTime);
public static DateTimeOffset FromFileTime (long fileTime);
static member FromFileTime : int64 -> DateTimeOffset
Public Shared Function FromFileTime (fileTime As Long) As DateTimeOffset

参数

fileTime
Int64

以计时周期表示的 Windows 文件时间。A Windows file time, expressed in ticks.

返回

一个对象,表示偏移量被设置为本地时间偏移量的 fileTime 的日期和时间。An object that represents the date and time of fileTime with the offset set to the local time offset.

异常

filetime 小于零。filetime is less than zero.

-或--or- filetime 大于 DateTimeOffset.MaxValue.Ticksfiletime is greater than DateTimeOffset.MaxValue.Ticks.

示例

下面的示例使用 Windows API 检索 WordPad 可执行文件的 Windows 文件时间。The following example uses the Windows API to retrieve the Windows file times for the WordPad executable.

using System;
using System.IO;
using System.Runtime.InteropServices;

public struct FileTime
{
   public uint dwLowDateTime;
   public uint dwHighDateTime;

   public static implicit operator long(FileTime fileTime)
   {
      long returnedLong;
      // Convert 4 high-order bytes to a byte array
      byte[] highBytes = BitConverter.GetBytes(fileTime.dwHighDateTime);
      // Resize the array to 8 bytes (for a Long)
      Array.Resize(ref highBytes, 8); 

      // Assign high-order bytes to first 4 bytes of Long
      returnedLong = BitConverter.ToInt64(highBytes, 0); 
      // Shift high-order bytes into position
      returnedLong = returnedLong << 32;
      // Or with low-order bytes
      returnedLong = returnedLong | fileTime.dwLowDateTime;
      // Return long 
      return returnedLong;
   }
}

public class FileTimes
{
   private const int OPEN_EXISTING = 3;
   private const int INVALID_HANDLE_VALUE = -1;
      
   [DllImport("Kernel32.dll", CharSet = CharSet.Unicode)]
   private static extern int CreateFile(string lpFileName, 
                                       int dwDesiredAccess, 
                                       int dwShareMode, 
                                       int lpSecurityAttributes, 
                                       int dwCreationDisposition, 
                                       int dwFlagsAndAttributes, 
                                       int hTemplateFile);

   [DllImport("Kernel32.dll")]
   private static extern bool GetFileTime(int hFile, 
                                          out FileTime lpCreationTime, 
                                          out FileTime lpLastAccessTime, 
                                          out FileTime lpLastWriteTime);

   [DllImport("Kernel32.dll")]
   private static extern bool CloseHandle(int hFile); 

   public static void Main()
   {
      // Open file %windir%\write.exe
      string winDir = Environment.SystemDirectory; 
      if (! (winDir.EndsWith(Path.DirectorySeparatorChar.ToString())))
         winDir += Path.DirectorySeparatorChar; 
      winDir += "write.exe";

      // Get file time using Windows API
      //
      // Open file
      int hFile = CreateFile(winDir, 0, 0, 0, OPEN_EXISTING, 0, 0);
      if (hFile == INVALID_HANDLE_VALUE)
      {
         Console.WriteLine("Unable to access {0}.", winDir);
      }   
      else
      {
         FileTime creationTime, accessTime, writeTime;
         if (GetFileTime(hFile, out creationTime, out accessTime, out writeTime)) 
         {
            CloseHandle(hFile);
            long fileCreationTime = (long) creationTime;
            long fileAccessTime = accessTime;
            long fileWriteTime = (long) writeTime;

            Console.WriteLine("File {0} Retrieved Using the Windows API:", winDir);
            Console.WriteLine("   Created:     {0:d}", DateTimeOffset.FromFileTime(fileCreationTime).ToString());
            Console.WriteLine("   Last Access: {0:d}", DateTimeOffset.FromFileTime(fileAccessTime).ToString());
            Console.WriteLine("   Last Write:  {0:d}", DateTimeOffset.FromFileTime(fileWriteTime).ToString());
            Console.WriteLine();
         }   
      }
      
      // Get date and time, convert to file time, then convert back
      FileInfo fileInfo = new FileInfo(winDir);
      DateTimeOffset infoCreationTime, infoAccessTime, infoWriteTime;
      long ftCreationTime, ftAccessTime, ftWriteTime;
      
      // Get dates and times of file creation, last access, and last write
      infoCreationTime = fileInfo.CreationTime;
      infoAccessTime = fileInfo.LastAccessTime;
      infoWriteTime = fileInfo.LastWriteTime;
      // Convert values to file times
      ftCreationTime = infoCreationTime.ToFileTime();
      ftAccessTime = infoAccessTime.ToFileTime();
      ftWriteTime = infoWriteTime.ToFileTime();
      
      // Convert file times back to DateTimeOffset values
      Console.WriteLine("File {0} Retrieved Using a FileInfo Object:", winDir);
      Console.WriteLine("   Created:     {0:d}", DateTimeOffset.FromFileTime(ftCreationTime).ToString());
      Console.WriteLine("   Last Access: {0:d}", DateTimeOffset.FromFileTime(ftAccessTime).ToString());
      Console.WriteLine("   Last Write:  {0:d}", DateTimeOffset.FromFileTime(ftWriteTime).ToString()); 
   }
}
// The example produces the following output:
//    File C:\WINDOWS\system32\write.exe Retrieved Using the Windows API:
//       Created:     10/13/2005 5:26:59 PM -07:00
//       Last Access: 3/20/2007 2:07:00 AM -07:00
//       Last Write:  8/4/2004 5:00:00 AM -07:00
//    
//    File C:\WINDOWS\system32\write.exe Retrieved Using a FileInfo Object:
//       Created:     10/13/2005 5:26:59 PM -07:00
//       Last Access: 3/20/2007 2:07:00 AM -07:00
//       Last Write:  8/4/2004 5:00:00 AM -07:00
Imports System.IO

Public Structure FileTime
   Public dwLowDateTime As UInteger
   Public dwHighDateTime As UInteger

   Public Shared Widening Operator CType(fileTime As FileTime) As Long
      Dim returnedLong As Long
      ' Convert 4 high-order bytes to a byte array
      Dim highBytes() As Byte = BitConverter.GetBytes(fileTime.dwHighDateTime)
      ' Resize the array to 8 bytes (for a Long)
      ReDim Preserve highBytes(7)

      ' Assign high-order bytes to first 4 bytes of Long
      returnedLong = BitConverter.ToInt64(highBytes, 0) 
      ' Shift high-order bytes into position
      returnedLong = returnedLong << 32
      ' Or with low-order bytes
      returnedLong = returnedLong Or fileTime.dwLowDateTime
      ' Return Long 
      return returnedLong
   End Operator
End Structure

Module modMain
   Private Const OPEN_EXISTING As Integer = 3
   
   Private Const INVALID_HANDLE_VALUE As Integer = -1
      
   Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" ( _
                            ByVal lpFileName As String, _
                            ByVal dwDesiredAccess As Integer, _
                            ByVal dwShareMode As Integer, _
                            ByVal lpSecurityAttributes As Integer, _
                            ByVal dwCreationDisposition As Integer, _
                            ByVal dwFlagsAndAttributes As Integer, _
                            ByVal hTemplateFile As Integer) _
           As Integer

   Private Declare Function GetFileTime Lib "Kernel32"( _
                            hFile As Integer, _
                            ByRef lpCreationTime As FileTime, _
                            ByRef lpLastAccessTime As FileTime, _
                            ByRef lpLastWriteTime As FileTime) _
            As Boolean 

   Private Declare Function CloseHandle Lib "Kernel32" ( _
                            hFile As Integer) _
           As Boolean
                        
   Public Sub Main()
      ' Open file %windir%\write.exe
      Dim winDir As String = Environment.SystemDirectory 
      If Not winDir.EndsWith(Path.DirectorySeparatorChar) Then _
         winDir += Path.DirectorySeparatorChar 
      windir += "write.exe"

      ' Get file time using Windows API
      '
      ' Open file
      Dim hFile As Integer = CreateFile(winDir, 0, 0, 0, _
                                       OPEN_EXISTING, 0, 0)
      If hFile = INVALID_HANDLE_VALUE Then
         Console.WriteLine("Unable to access {0}.", winDir)
      Else
         Dim creationTime, accessTime, writeTime As FileTime
         If GetFileTime(hFile, creationTime, accessTime, writeTime) Then
            CloseHandle(hFile)
            Dim fileCreationTime As Long = CType(creationTime, Long)
            Dim fileAccessTime As Long = CType(accessTime, Long)
            Dim fileWriteTime As Long = CType(writeTime, Long)

            Console.WriteLine("File {0} Retrieved Using the Windows API:", winDir)
            Console.WriteLine("   Created:     {0:d}", DateTimeOffset.FromFileTime(fileCreationTime).ToString())
            Console.WriteLine("   Last Access: {0:d}", DateTimeOffset.FromFileTime(fileAccessTime).ToString())
            Console.WriteLine("   Last Write:  {0:d}", DateTimeOffset.FromFileTime(fileWriteTime).ToString())
            Console.WriteLine() 
         End If   
      End If
      
      ' Get date and time, convert to file time, then convert back
      Dim fileInfo As New FileInfo(winDir)
      Dim infoCreationTime, infoAccessTime, infoWriteTime As DateTimeOffset
      Dim ftCreationTime, ftAccessTime, ftWriteTime As Long
      
      ' Get dates and times of file creation, last access, and last write
      infoCreationTime = fileInfo.CreationTime
      infoAccessTime = fileInfo.LastAccessTime
      infoWriteTime = fileInfo.LastWriteTime
      ' Convert values to file times
      ftCreationTime = infoCreationTime.ToFileTime()
      ftAccessTime = infoAccessTime.ToFileTime()
      ftWriteTime = infoWriteTime.ToFileTime()
      
      ' Convert file times back to DateTimeOffset values
      Console.WriteLine("File {0} Retrieved Using a FileInfo Object:", winDir)
      Console.WriteLine("   Created:     {0:d}", DateTimeOffset.FromFileTime(ftCreationTime).ToString())
      Console.WriteLine("   Last Access: {0:d}", DateTimeOffset.FromFileTime(ftAccessTime).ToString())
      Console.WriteLine("   Last Write:  {0:d}", DateTimeOffset.FromFileTime(ftWriteTime).ToString()) 
   End Sub
End Module
' The example produces the following output:
'    File C:\WINDOWS\system32\write.exe Retrieved Using the Windows API:
'       Created:     10/13/2005 5:26:59 PM -07:00
'       Last Access: 3/20/2007 2:07:00 AM -07:00
'       Last Write:  8/4/2004 5:00:00 AM -07:00
'    
'    File C:\WINDOWS\system32\write.exe Retrieved Using a FileInfo Object:
'       Created:     10/13/2005 5:26:59 PM -07:00
'       Last Access: 3/20/2007 2:07:00 AM -07:00
'       Last Write:  8/4/2004 5:00:00 AM -07:00

注解

Windows 文件时间是一个64位的值,它表示自公元1900年1月 1601 1 日午夜12:00 之后经过的100纳秒间隔数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. 公元协调世界时(UTC)。(C.E.) Coordinated Universal Time (UTC). 当应用程序创建、访问或写入到文件时,Windows 将使用文件时间来记录。Windows uses a file time to record when an application creates, accesses, or writes to a file.

Windows 文件时间通过调用 GetFileTime 函数(该函数将返回 FILETIME 结构)直接通过 Windows API 进行访问。A Windows file time is directly accessible through the Windows API by calling the GetFileTime function, which returns a FILETIME structure. 单个函数参数是要检索其文件时间信息的文件的句柄。The single function parameter is the handle of the file whose file time information is to be retrieved. 文件句柄是通过调用 CreateFile 函数来检索的。The file handle is retrieved by calling the CreateFile function. FILETIME 结构的 dwHighDateTime 成员包含文件时间的四个高序位字节,其 dwLowDateTime 成员包含四个低序位字节。The FILETIME structure's dwHighDateTime member contains the four high-order bytes of the file time, and its dwLowDateTime member contains the four low-order bytes. 下面的示例演示了如何检索 Windows 文件时间值并将其转换为 DateTimeOffset 值。The example that follows illustrates how to retrieve Windows file time values and convert them to DateTimeOffset values.

还可以通过调用 DateTime.ToFileTimeDateTime.ToFileTimeUtc 方法,并通过调用 DateTimeOffset.ToFileTime 方法从 DateTimeOffset 值创建 Windows 文件时间值 DateTime 值。Windows file time values can also be created from DateTime values by calling the DateTime.ToFileTime and DateTime.ToFileTimeUtc methods, and from DateTimeOffset values by calling the DateTimeOffset.ToFileTime method.

适用于