Category : C Source Code
Archive   : INT24-TC.ZIP
Filename : ERROR.C

/* This file duplicates for Turbo C users the functions provided for
Turbo Pascal users by Bela Lubkin in the infamous INT24.ARC file.
It provides a neat and SIMPLE method of trapping all DOS critical
errors (interrupt 24 errors) and allowing the programmer to decide
how to proceed.

The "library" consists of one variable declaration and three function
declarations. The variable "int24errorcode" is an integer that our
interrupt 24 handler uses to store the last int24 error code. That's
all the handler does--it stores the DOS error code in int24errorcode,
and then returns to the program.

Needless to say, this handler does not do all that it could--Turbo C
provides a facility similar to DOS' infamous "Abort, Retry, Ignore?"
message. If you look at the example given on page 136 of the Turbo C
Reference Guide, you will notice that our int24 handler COULD tell
DOS to ABORT, RETRY, or IGNORE the process by returning the appropriate
value. This handler, on the other hand, leaves all that up to the
programmer--it just stores the error and returns to the program.

In order to turn on the interrupt 24 trapping, just say "int24on ();".
From this point on, a critical DOS error does not crash the program--
instead, our handler takes over and stores the error code in a variable.
Then, whenever you want to see what the current int24 code is, you should
use the function int24result(). You should not access the variable
int24errorcode directly, because it will not then be reset. The
function int24result() returns its current value and also resets it
to -1, which indicates no error has occurred.

The included file ERRTEST.C is a sample program showing how these
functions work. ERRTEST.EXE is that program compiled and linked to
these functions--you can run that or compile it yourself with the
file ERRTEST.PRJ. For the integrated version of Turbo C, just hit
Alt-P and return, and enter "ERRTEST". Then F9 will compile it for
you.

Again, this is hardly a full treatment of DOS critical errors--it
does, however, make it simple to see whether one has occurred. For
more information on this, see the Turbo c Reference guide entry for
the function harderr().

Turbo C provides no direct method of un-installing our interrupt
handler, but the original DOS handler is restored on program exit.
You could use the functions getvect() and setvect() for this purpose.

Here is a list of (decimal) error codes that int24result will return
and the errors that cause them:

Code Cause
____ ________________________________________

00 write-protect error
01 unknown unit
02 drive not ready
03 unknown command
04 data error (bad CRC)
05 bad request structure length
06 seek error
07 unknown media type
08 sector not found
09 printer out of paper
10 write fault
11 read fault
12 general failure


Marty Del Vecchio
8/19/87


*/


#include
#include

int int24errorcode = -1; /* Will hold our result code from int24 */
/* You should not access this directly, */
/* but through the function int24result() */

int handler (int errval, int ax, int bp, int si) /* This is the handler */
{
int24errorcode = errval; /* The handler simply stores the error code */
hardretn (-1); /* in int24result and returns to the program */
}

void int24on ()
{ /* This function installs our function as the */
harderr (handler); /* DOS interrupt 24 handler */
}

int int24result () /* This function returns the current value of */
{ int i; /* int24error and then sets it back to zero */
i = int24errorcode;
int24errorcode = -1;
return (i);
}