Q40549: QB.EXE May Overwrite File Allocation Table If Floppy Switched

Article: Q40549
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist4.00 buglist4.00b buglist4.50 b_basiccom | mspl13_basic
Last Modified: 23-JAN-1989

Microsoft has duplicated the following problem in QuickBASIC Versions
4.00, 4.00b, and 4.50 and to the QB.EXE program that is shipped with
the Microsoft BASIC Compiler Versions 6.00 and 6.00b for MS-DOS and MS
OS/2.

QB.EXE can damage a floppy disk's File Allocation Table (FAT) if the
following steps occur:

1. A program OPENs a disk file.

2. The disk file is aborted with CTRL+BREAK before the file is ever
   closed.

3. The floppy running QB.EXE is replaced with a different floppy disk.

4. You exit QB.EXE.

The program example shown below will cause QB.EXE to overwrite the
File Allocation Table after the following steps are executed:

1. QB.EXE is executed from a floppy disk.

2. The program is started and then interrupted with a CTRL+BREAK.

3. A different disk is put into the drive from which QB.EXE was
   executed.

4. The QuickBASIC QB.EXE editor is exited (such as with ALT+F+X).

The overwrite may occur whether the file is opened with RANDOM access
or SEQUENTIAL access.

Microsoft is currently researching this problem and will post more
information as it becomes available.

To work around the problem, do one of the following after breaking out
of the program:

1. Go to the immediate window and issue the command CLOSE.

2. Exit QuickBASIC before switching disks.

This program does not cause any problem with versions of Microsoft
QuickBASIC earlier than Version 4.00.

The following is a code example:

OPEN "test.dat" FOR OUTPUT AS #1
FOR i = 1 TO 10000
    PRINT #1, i
NEXT

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