Q193773: HOWTO: Detect File System Changes under Windows NT

Article: Q193773
Product(s): Microsoft FoxPro
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): 
Last Modified: 03-AUG-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 6.0 
-------------------------------------------------------------------------------

SUMMARY
=======

Windows NT provides the FindFirstChangeNotification() API function that allows
application programs to detect when changes occur in the file system. It can
detect when a file or directory is added, changed, deleted, and when a file's
size, attributes, or security descriptors change.

NOTE: This code is somewhat complex, and engineers may require some time to
familiarize themselves with the contents and concepts of the example.

MORE INFORMATION
================

1. Create a directory C:\TEST if a directory by that name does not already
  exist, or modify the variable lcPathSpec in the sample code to point to a
  directory of your choice.

2. Save and execute the following code. The code appears to 'hang' Visual FoxPro
  when it executes the call to the WaitForSingleObject() function. This line
  causes the application to enter a very processor-efficient wait state:

  

        DECLARE LONG WaitForSingleObject IN kernel32 ;
           INTEGER hHandle, ;
           INTEGER dwMilliseconds

        DECLARE LONG FindFirstChangeNotification IN kernel32 ;
           STRING lpPathName, ;
           INTEGER bWatchSubtree, ;
           INTEGER dwNotifyFilter AS LONG)

        DECLARE LONG FindNextChangeNotification IN kernel32 ;
           INTEGER hChangeHandle

        DECLARE LONG GetLastError IN kernel32
        DECLARE LONG FindCloseChangeNotification IN kernel32 ;
           INTEGER hChangeHandle

        * Only the second constant is demonstrated in this
        * example; the others are listed for convenience.

        * A file has been created, renamed or deleted.
        #DEFINE FILE_NOTIFY_CHANGE_FILE_NAME 0x01

        * Directory has been created, renamed or deleted.
        #DEFINE FILE_NOTIFY_CHANGE_DIR_NAME 0x02

        * A file's attribute (archive, read-only) has been changed.
        #DEFINE FILE_NOTIFY_CHANGE_ATTRIBUTES 0x04

        * A file's size has changed.
        #DEFINE FILE_NOTIFY_CHANGE_SIZE 0x08

        * A file's last write data has changed.
        #DEFINE FILE_NOTIFY_CHANGE_LAST_WRITE 0x10

        * A security descriptor for a directory or file has been changed.
        #DEFINE FILE_NOTIFY_CHANGE_SECURITY 0x100

        * Look for any changes - bitwise OR these values together.
        #DEFINE FILE_NOTIFY_ALL = FILE_NOTIFY_CHANGE_ATTRIBUTES BITOR ;
           FILE_NOTIFY_CHANGE_DIR_NAME BITOR ;
           FILE_NOTIFY_CHANGE_FILE_NAME BITOR ;
           FILE_NOTIFY_CHANGE_LAST_WRITE BITOR ;
           FILE_NOTIFY_CHANGE_SECURITY BITOR ;
           FILE_NOTIFY_CHANGE_SIZE

        #DEFINE INVALID_HANDLE_VALUE -1
        #DEFINE INFINITE 2147483647
        #DEFINE WAIT_FAILED 2147483647
        #DEFINE True -1
        #DEFINE False 0

        lcPathSpec = "C:\TEST"
        lbWatchSubtree = True

        * Watch for a directory added, changed or deleted beneath the
        * specified PathSpec.
        lihNotify = FindFirstChangeNotification(lcPathSpec, lbWatchSubtree, ;
           FILE_NOTIFY_CHANGE_DIR_NAME)

        IF lihNotify <= INVALID_HANDLE_VALUE
           MESSAGEBOX ("FindFirstChangeNotification failed. Error code: " + ;
              LTRIM(STR(GetLastError())))
           RETURN
        ELSE
        * Uncomment for debugging purposes.
        *   MessageBox ("FindFirstChangfeNotification instantiation ;
        *       succeeded. Handle is: " + ltrim(str(lihNotify)))
        ENDIF

        * Now, go into a wait state.
        * This is going to look like a hang, since the IDE is all in
        * one thread.
        liWaitReturn = WaitForSingleObject(lihNotify, INFINITE)
        IF liWaitReturn >= WAIT_FAILED
            MESSAGEBOX ("WaitForSingleObject failed. Error is: " + ;
               LTRIM(STR(GetLastError())))
           RETURN
        ELSE
            MESSAGEBOX ("Directory change in " + lcPathSpec + " occurred")
        ENDIF

        liWaitReturn = FindCloseChangeNotification(lihNotify)

3. In the Windows NT Explorer, create a new directory underneath C:\TEST, using
  File/New Folder. As soon as the directory is created, a message box appears
  in the Visual FoxPro application notifying you of the directory change.

REFERENCES
==========

"Advanced Windows", Jeffrey Richter, Microsoft Press, pages 664-687, Third
Edition 1997 ISBN: 1-57231-548-2

Additional query words: kbVFp600 kbAPI

======================================================================
Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbVFP600
Version           : WINDOWS:6.0
Issue type        : kbhowto

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.