How To Use NTFS Alternate Data Streams

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This article was previously published under Q105763

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.

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MORE INFORMATION

The following sample code demonstrates NTFS streams:

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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: