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Path: utzoo!watmath!clyde!rutgers!princeton!allegra!mit-eddie!rassilon
From: rassilon@mit-eddie.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Major bug in all(?) versions of MS-DOS.
Message-ID: <4774@mit-eddie.MIT.EDU>
Date: Sat, 7-Feb-87 20:15:56 EST
Article-I.D.: mit-eddi.4774
Posted: Sat Feb  7 20:15:56 1987
Date-Received: Mon, 9-Feb-87 02:27:56 EST
References: <4274@utah-cs.UUCP>
Reply-To: rassilon@eddie.MIT.EDU (Brian Preble
Organization: MIT, EE/CS Computer Facilities, Cambridge, MA
Lines: 33
Keywords: bug


In article <4274@utah-cs.UUCP> b-davis@utah-cs.UUCP (Brad Davis) writes:
>Here is a probable bug (or feature) in MS-DOS.  Does anyone know a
>work around (without closing the first file)?  Would Gordon Letwin at
>Microsoft care to comment?  This bug appears on PC-DOS 2.0, PC-DOS 3.0,
>and MS-DOS 3.1.  (Unix has no problems with this algorigthm.)
>
>The test goes like this:
>	Create a file with name 'xxx'.  Call this file FD1.
>	Write 80 bytes to FD1.
>	Open the file named 'xxx' a second time.  Call this file FD2.
>		Note that NO errors have happened yet.
>	Try to read 80 bytes from FD2.  No bytes are read.
>		Note that NO error is reported.
>	If in symdeb push to a new shell.  See that the file 'xxx' has
>		been created but has a size of 0.
>	Exit the program.  See that the file 'xxx' is now 80 bytes long.

I don't see any problem with this.  Remember, in most computers files are
not written too unless the buffer is full (which I don't think 80 bytes
fills) or you close the file.  From your code it appears that you are trying
to read from FD1 before closing it.  Yes, the file was created when you
originally opened it.  This is necessary to ensure that there is room on
the disk for at least one block and that you the disk/directory you are
attempting to write to actually exists.

One way of getting around this without closing the file is to do a 'flush'.
This, in essence, means checking to see if the buffer is empty and, if not,
writing it's contents to the disk.  How to force output in assembly I don't
know.  In TURBO Pascal I simply use the command FLUSH(filename).

					-- Rassilon
					   (rassilon@eddie.mit.edu)