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The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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/* HARDERR.C illustrates handling of hardware errors using functions:
 *      _harderr            _hardresume         _hardretn
 */
 
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <direct.h>
#include <string.h>
#include <dos.h>
#include <bios.h>
 
void _far hhandler( unsigned deverr, unsigned doserr, unsigned _far *hdr );
int _bios_str( char *p );
 
void main()
{
    /* Install our hard error handler. */
    _harderr( hhandler );
 
    /* Test it. */
    printf( "Make sure there is no disk in drive A:\n" );
    printf( "Press a key when ready...\n" );
    getch();
    if( mkdir( "a:\test" ) )
    {
        printf( "Failed" );
        exit( 1 );
    }
    else
    {
        printf( "Succeeded" );
        rmdir( "a:test" );
        exit( 0 );
    }
}
 
/* Handler to deal with hard error codes. Since DOS is not reentrant,
 * it is not safe to use DOS calls for doing I/O within the DOS Critical
 * Error Handler (int 24h) used by _harderr. Therefore, screen output and
 * keyboard input must be done through the BIOS.
 */
void _far hhandler( unsigned deverr, unsigned doserr, unsigned _far *hdr )
{
    int ch;
    static char buf[200], tmpbuf[10];
 
    /* Copy message to buffer, then use BIOS to print it. */
    strcpy( buf, "\n\rDevice error code: " );
    strcat( buf, itoa( deverr, tmpbuf, 10 ) );
    strcat( buf, "\n\rDOS error code:    " );
    strcat( buf, itoa( doserr, tmpbuf, 10 ) );
    strcat( buf, "\n\r(R)etry, (F)ail, or (Q)uit? " );
 
    /* Use BIOS to write strings and get a key. */
    _bios_str( buf );
    ch = _bios_keybrd( _KEYBRD_READ ) & 0x00ff;
    _bios_str( "\n\r" );
 
    switch( ch )
    {
        case 'R':
        case 'r':       /* Try again */
        default:
            _hardresume( _HARDERR_RETRY );
        case 'Q':
        case 'q':       /* Quit program */
 
            /* The following statement may fail in the PWB environment
             * because of conflicts with PWB's hard error handler. The
             * Quit selection falls through to the Fail selection. You
             * can remove the comment to enable this line if you wish to
             * test from the command line.
            _hardresume( _HARDERR_ABORT );
             */
        case 'F':
        case 'f':       /* Return to DOS with error code */
            _hardretn( doserr );
 
    }
}
 
/* Display a string using BIOS interrupt 0x0e (Write TTY). Return length
 * of string displayed.
 */
int _bios_str( char *p )
{
    union REGS inregs, outregs;
    char *start = p;
 
    inregs.h.ah = 0x0e;
    for( ; *p; p++ )
    {
        inregs.h.al = *p;
        int86( 0x10, &inregs, &outregs );
    }
    return p - start;
}