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 int86x()                Set Segment Registers and Execute Software Interrupt

 #include   <dos.h>

 int           int86x(intno,inregs,outregs,segregs);
 int           intno;                    Interrupt number
 union  REGS   *inregs;                  Register values going into call
 union  REGS   *outregs;                 Register values on return
 struct SREGS  *segregs;                 Segment-register values on call

    int86x() executes the 8086 software interrupt 'intno'; it is similar
    to int86(), but allows the DS and ES segment registers to be set. The
    general purpose registers are set to the values in 'inregs'; the DS
    and ES segment registers are set to the corresponding values in
    'segregs'.  On return, 'outregs' is set to the value of the registers
    after the interrupt has executed; DS is restored, the flags register
    is copied to the 'flags' field of 'outregs', and the 'cflag' field of
    'outregs' is set to the status of the system carry flag.

       Returns:     The value of the AX register after the system call.
                    If the 'cflag' field in 'outregs' is non-zero, an
                    error has occurred and '_doserrno' (defined in
                    <errno.h>) is set to the error code.

         Notes:     If the DS and ES registers don't need to be set,
                    int86() should be used. The values for the segment
                    registers can be obtained with the segread() function
                    or the FP_SEG() macro.

                    Use bdos(), bdosptr(), intdos() or intdosx() to
                    execute DOS system calls (interrupt 0x21).

                    The DS register is restored upon completion of the
                    int86x() call

   Portability:     MS-DOS only.

   -------------------------------- Example ---------------------------------

    The following statements read the boot sector (track 0, sector 1) of
    the disk in drive A: by calling BIOS interrupt 13h.

           #include <dos.h>    /* for int86x(), macros FP_SEG() and FP_OFF(),
                                  segread(), union REGS and struct SREGS */
           #include <stdio.h>  /* for printf() */
           #include <stdlib.h> /* for _doserrno */

           char buf [1024];

           main()
           {
               char far * bufptr;
               union REGS inregs, outregs;
               struct SREGS segregs;

               segread(&segregs);           /* set the segment registers */
               bufptr = (char far *) buf;   /* need a far pointer to 'buf' */
               segregs.es = FP_SEG(bufptr); /* ...to set the address of */
               inregs.x.bx = FP_OFF(bufptr);/* ...'buf' for the BIOS */
               inregs.h.ah = 2;             /* set BIOS function number */
               inregs.h.al = 1;             /* set # of sectors to read */
               inregs.h.ch = 0;             /* set track # of boot sector */
               inregs.h.cl = 1;             /* set sector # of boot sector */
               inregs.h.dh = 0;             /* set disk side number */
               inregs.h.dl = 0;             /* set drive number to A: */
               int86x(0x13, &inregs, &outregs, &segregs);  /* read sector */

               if (outregs.x.cflag)
                   printf("ERROR #%d: status = %d, # sectors read = %d\n",
                         _doserrno, outregs.h.ah, outregs.h.al);
           }