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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documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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─────Run-Time Library───────────────────────────────────────────────────────
 
/* SYSCALL.C illustrates system calls to DOS and BIOS interrupts using
 * functions:
 *      _intdos          _intdosx         _bdos                   (DOS-only)
 *      _int86           _int86x          _segread
 *
 * The _int86x call is not specifically shown in the example, but
 * it is the same as _intdosx, except that an interrupt number must be
 * supplied.
 */
 
#include <dos.h>
#include <stdio.h>
#define LPT1 0
 
union _REGS inregs, outregs;
struct _SREGS segregs;
 
void main()
{
    char __far *buffer = "Dollar-sign terminated string\n\r\n\r$";
    char __far *p;
 
    /* Get DOS version using DOS function 0x30. */
    inregs.h.ah = 0x30;
    _intdos( &inregs, &outregs );
    printf( "\nMajor: %d\tMinor: %d\tOEM number: %d\n\n",
        outregs.h.al, outregs.h.ah, outregs.h.bh );
 
    /* Print a $-terminated string on the screen using DOS function 0x9. */
    inregs.h.ah = 0x9;
    inregs.x.dx = _FP_OFF( buffer );
    segregs.ds = _FP_SEG( buffer );
    _intdosx( &inregs, &outregs, &segregs );
 
    _segread( &segregs );
    printf( "Segments:\n\tCS\t%.4x\n\tDS\t%.4x\n\tES\t%.4x\n\tSS\t%.4x\n\n",
            segregs.cs, segregs.ds, segregs.es, segregs.ss );
 
    /* Make sure printer is available. Fail if any error bit is on,
     * or if either operation bit is off.
     */
    inregs.h.ah = 0x2;
    inregs.x.dx = LPT1;
    _int86( 0x17, &inregs, &outregs );
    if(  (outregs.h.ah & 0x29) || !(outregs.h.ah & 0x80) ||
                                  !(outregs.h.ah & 0x10) )
        printf( "Printer not available." );
    else
    {
        /* Output a string to the printer using DOS function 0x5. */
        for( p = buffer; *p != '$'; p++ )
            _bdos( 0x05, *p, 0 );
 
        /* Do print screen. */
        inregs.h.ah = 0x05;
        _int86( 0x05, &inregs, &outregs );
    }
}
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