Bios Interrupt under Optima++

   
  Using Optima++ I am trying to call a bios interruption (0x13) to read a sector(partition sec) of the hard drive.  Everything I code gives me always the same error: "intr_ is an undefined reference" at the Error Log.  

  YES, i86.h has an intr() prototype:
     _WCRTLINK extern void intr( int, union REGPACK * );
 
   (Thanks for the comment chensu)

What am I missing ???.  Here is part of my code:
   
    #include<i86.h>
    ...

    union REGPACK regs;
    unsigned char buffer[512];
                             // Will read head:0 cyl:0 sec:1
        regs.h.ah = 0x02;    // read function
        regs.h.al = 0x01;    // number of sectors to read
        regs.h.ch = 0x00;    // low 8 bits cylinder
        regs.h.cl = 0x01;    // sector + 2 high bits cylind
        regs.h.dh = 0x00;    // head number
        regs.h.dl = 0x80;    // drive letter (hard disk)

    #if defined(__386__)
        regs.x.ebx = FP_OFF(buffer);  // offset of buffer
    #else
        regs.w.bx = FP_OFF(buffer);   // offset if 16 bit
    #endif
        regs.w.es  = FP_SEG(buffer);  // segment of buffer
        intr( 0x13, ®s );          // bios call

  What I do not understand is why it compilies without errors in Borland C++.

 Thanks in advance:
 -eal-