How can we know whether a file is read or not

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    How can we know whether a file is read or not

    how can we know whether a particular file is read or not using c programming.

    for an example:

    the file name = abcd.txt

    the status of the file should be 0 if the person has not opened it and it should be changed to 1 after any one reads it

    how can we do this

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    Guest Sebastiani's Avatar
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    Check the time stamp, perhaps?

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    and the hat of wrongness Salem's Avatar
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    > how can we know whether a particular file is read or not using c programming.
    In general, you can't.

    Some file systems maintain a "last access", but that could mean anything (not just reading).
    Then there is the problem of if the filesystem is mounted read-only, in which case the last access time directory entries won't be updated.

    Then there is the whole "boot another OS" and read the file issue, not to mention "bypass the file system and read the raw disk" issue.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    On Windows, I saw some Windows API functions that you could subscribe to which notify you when a file is accessed. I forget their names, but you can look them up. I'm not sure about UNIX though.
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

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    spurious conceit MK27's Avatar
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    Quote Originally Posted by cpjust View Post
    I'm not sure about UNIX though.
    Hmmm. This came up tangentially today. There is a Glib function, g_io_add_watch(), which can be used with a "socket, pipe, or file". I've used it with a socket, but not a file; I would assume something has to be added to the file to trigger, but you never know.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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