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Checking whether a file is already in use or not.

Posted on 2003-12-09
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Last Modified: 2013-11-20
Hi,

I am trying to write a rotuine, which will check whether a given file is already in use or not.

For writing this, I am using the routine, OpenFile with OF_SHARE_EXCLUSIVE mode.

When OpenFile is used on a file which is already opened by any other application, then it is returning error message (as it should) which is indicating that the file is already in use.

This seems to work fine only with Binary files.

when a text based file ( with extensions .txt, .cpp, .c and etc) , is opened by another applicaiton (for e.g. if file.c is opened in MSDEV) OpenFile is still able to get access to the file in OF_SHARE_EXCLUSIVE mode. Even from windows explorer also, the text based files opened in any other application can be deleted or modified without any problem.

Can someone tell me a way of checking both Text Based files and Binary files which are already in use ?

Thanks!
Gangisetti

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Question by:gangisetti
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5 Comments
 
LVL 9

Accepted Solution

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Priyesh earned 100 total points
ID: 9909972
Try this:

      HANDLE hFile = CreateFile("c:\\1.txt", GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL) ;
      if(hFile == INVALID_HANDLE_VALUE)
      {
            LPVOID lpMsgBuf;
            if (!FormatMessage(
                  FORMAT_MESSAGE_ALLOCATE_BUFFER |
                  FORMAT_MESSAGE_FROM_SYSTEM |
                  FORMAT_MESSAGE_IGNORE_INSERTS,
                  NULL,
                  GetLastError(),
                  MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language
                  (LPTSTR) &lpMsgBuf,
                  0,
                  NULL ))
            {
               // Handle the error.
               return TRUE ;
            }

            // Process any inserts in lpMsgBuf.
            // ...

            // Display the string.
            AfxMessageBox((LPCTSTR)lpMsgBuf) ;

            // Free the buffer.
            LocalFree( lpMsgBuf ) ;
      }

If any open handles exists to the above file, there will be an OS error.  This is true for all files. Editors might just read the file into memory and then close handle, that's why you could delete the file even when it is open in an editor.

If this does not work for you, you can look into file/ directory watch (NT and higher)
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LVL 48

Expert Comment

by:AlexFM
ID: 9910039
>> when a text based file ( with extensions .txt, .cpp, .c and etc) , is opened by another applicaiton (for e.g. if file.c is opened in MSDEV) OpenFile is still able to get access to the file in OF_SHARE_EXCLUSIVE mode.

This happens because Visual Studio doesn't keep opened file handle. It opens file only to load it into memory and to save it. So, your program is OK.
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