HOWTO: Use NTFS Alternate Data Streams

Last reviewed: November 26, 1997
Article ID: Q105763

The information in this article applies to:

Microsoft Win32 Application Programming Interface (API) included with: - Microsoft Windows NT versions 3.1, 3.5, 3.51, 4.0

SUMMARY

The documentation for the NTFS file system states that NTFS supports multiple streams of data; however, the documentation does not address the syntax for the streams themselves.

The Windows NT Resource Kit documents the stream syntax as follows:

   filename:stream

Alternate data streams are strictly a feature of the NTFS file system and may not be supported in future file systems. However, NTFS will be supported in future versions of Windows NT.

Future file systems will support a model based on OLE 2.0 structured storage (IStream and IStorage). By using OLE 2.0, an application can support multiple streams on any file system and all supported operating systems (Windows, Macintosh, Windows NT, and Win32s), not just Windows NT.

MORE INFORMATION

The following sample code demonstrates NTFS streams:

Sample Code

   #include <windows.h>
   #include <stdio.h>

   void main( )
   {
      HANDLE hFile, hStream;
      DWORD dwRet;

      hFile = CreateFile( "testfile",
                       GENERIC_WRITE,
                    FILE_SHARE_WRITE,
                                NULL,
                         OPEN_ALWAYS,
                                   0,
                                NULL );
      if( hFile == INVALID_HANDLE_VALUE )
         printf( "Cannot open testfile\n" );
      else
          WriteFile( hFile, "This is testfile", 16, &dwRet, NULL );

      hStream = CreateFile( "testfile:stream",
                                GENERIC_WRITE,
                             FILE_SHARE_WRITE,
                                         NULL,
                                  OPEN_ALWAYS,
                                            0,
                                         NULL );
      if( hStream == INVALID_HANDLE_VALUE )
         printf( "Cannot open testfile:stream\n" );
      else
         WriteFile(hStream, "This is testfile:stream", 23, &dwRet, NULL);
   }

The file size obtained in a directory listing is 16, because you are looking only at "testfile", and therefore

   type testfile

produces the following:

   This is testfile

However

   type testfile:stream

produces the following:

   The filename syntax is incorrect

In order to view what is in testfile:stream, use:

   more < testfile:stream

   -or-

   mep testfile:stream

where "mep" is the Microsoft Editor available in Win32 SDK.

Keywords          : BseFileio
Version           : winnt:3.1,3.5,3.51,4.0;
Platform          : winnt
Issue type        : kbhowto

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Last reviewed: November 26, 1997
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