4DOS24H - DOS CRITICAL ERROR HANDLER

for JP SOFTWARE 4DOS utility



Author : Patrick Philippot - 1990


This software is released to the Public Domain. Since this
program is 4DOS specific, JP Software is herewith authorized to
include this utility in the 4DOS package without any claim from me.

This software is free. This means that nobody can charge any
amount of money for 4DOS24H. In any form, for any reason.

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WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING!


THIS PROGRAM WILL WORK ONLY IF 4DOS IS INSTALLED. IT ALSO
REQUIRES DOS VERSION 3.0 OR ABOVE.


4DOS24H has been written to illustrate the good behaviour of
4DOS regarding the handling of INT 24H. With COMMAND.COM it's
impossible to write such a TSR because the INT 24H vector address is
not taken from the PSP (although the DOS technical reference claims
COMMAND.COM does so) but from a hard-coded value in COMMAND.COM
itself.

4DOS behaves (almost) exactly like described in the DOS
Technical Reference. This made possible to write this utility.

4DOS24H is a replacement for the standard DOS Critical Error
Handler which issues the "Abort, Retry, Ignore, Fail ?" message.
The standard handler has some weaknesses. First of all the above
prompt overwrites any data on the screen and doesn't restore the
user screen. This is not important while at the DOS prompt but very
unpleasant when a critical error happens within an application.
Moreover, the standard handler doesn't give much information about
the error which occured.

4DOS24H fixes these two problems.

When an error occurs, a window is opened prompting for a user
response. As soon as the user has entered his response the screen is
restored.

4DOS24H gives additional information about what happened:

The "Disk Error" field is set to Y or N to indicate whether
the error is related to a disk drive.

In case of a disk error three additional fields are set:

Error type: D --> indicates a DOS area error
T --> indicates a FAT area error
R --> indicates a ROOT directory error
F --> indicates a FILES area error

Read/Write R --> indicates a READ error
W --> indicates a WRITE error

Drive The letter indicates which drive is
in error

If the error occured on a character device, the device driver
name is also displayed.

Finally, a text is displayed giving additional details about the
error which occured.

If the user enters a response which is not allowed, 4DOS24H
automatically translates it to a valid one. This is why you must have
DOS 3.0 or above.

4DOS24H takes no parameter. Just load it from your autoexec.bat
or from the DOS command line.

4DOS24H will be really useful for applications that don't
process DOS critical errors themselves.

This version of 4DOS24H can be loaded high using QEMM or 386 MAX
(tested with QEMM).


LIMITATIONS:
************

1. Graphics mode are not supported. In that case 4DOS24H calls
the standard interrupt handler.

2. 40 columns text modes are not supported.

3. The code can be optimized. The source code is also available.
Feel free to study it and to suggest modifications/enhancements. This
is quick and dirty code. To understand it you'll need at least a DOS
Technical Reference or the Duncan "Bible". You'll also need to read
the related discussion in 4DOS FORUM on Compuserve (GO PCVENB).


Have fun!

Patrick Philippot - 10/20/90
France
CIS : 72561,3532