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From: jcmorris@mwunix.mitre.org (Joe Morris)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Help.  End of Diskette VS EOF
Message-ID: <116585@linus.mitre.org>
Date: 9 Aug 90 15:32:36 GMT
References: <1990Aug9.004845.16663@sun.soe.clarkson.edu>
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Reply-To: jcmorris@mwunix.mitre.org (Joe Morris)
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In a recent article levericw@clutx.clarkson.edu (Allanon) writes:
>I would like to know if a C program will return different error codes if
>it reaches the end of a file or reaches the end of a diskette, are these
>two things the same or can I tell them apart.

Unless the application which writes the file leaves some out-of-band information
about the ending status, there is no way to distinguish the cases.  By 
definition a file ends when the forward pointer in the FAT is the EOF flag,
and DOS does not define the concept of a multi-volume file.  One could
probably be devised which would provide a multiplex interrupt hook to
let the writing program mark EOV instead of EOF, and let the reader know
which one terminated the read, but there's nothing there now.  (Microsoft,
are you reading this?)

Programs like BACKUP have a separate file for the out-of-band signals such as
disk number and EOF/EOV status.  DOS has nothing to do with the ability
of these programs to carry large files across multiple volumes.  

For your particular application what is needed is a special dump/restore type
of program.  There's gotta be someone who has written such a beastie...