Now let us see a practical use of union is data recovery programming. Let us take a little example. The following program is the small model of bad sector scanning program for a floppy disk drive (a: ) however it is not the complete model of bad sector scanning software

A practical use of a union in data recovery

Now let us see a practical use of union is data recovery programming. Let us take a little example. The following program is the small model of bad sector scanning program for a floppy disk drive (a: ) however it is not the complete model of bad sector scanning software.

Let us examine the program:

#include<dos.h>
#include<conio.h>
int main()
{
int rp, head, track, sector, status;
char *buf;

union REGS in, out;
struct SREGS s;
clrscr();

/* Reset the disk system to initialize to disk */
printf("\n Resetting the disk system....");

for(rp=0;rp<=2;rp++)
{

in.h.ah = 0;
in.h.dl = 0x00;

int86(0x13,&in,&out);
}

printf("\n\n\n Now Testing the Disk for Bad Sectors....");

/* scan for bad sectors */
for(track=0;track<=79;track++)
{

for(head=0;head<=1;head++)
{

for(sector=1;sector<=18;sector++)
{

in.h.ah = 0x04;
in.h.al = 1;
in.h.dl = 0x00;
in.h.ch = track;
in.h.dh = head;
in.h.cl = sector;
in.x.bx = FP_OFF(buf);
s.es = FP_SEG(buf);

int86x(0x13,&in,&out,&s);

if(out.x.cflag)
{

status=out.h.ah;
printf("\n track:%d Head:%d Sector:%d Status ==0x%X",track,head,sector,status);
}
}
}
}
printf("\n\n\nDone");
return 0;
}

Now let us see what its output will look like if there are bad sector in the floppy disk:

It may be a little bit difficult to understand functions and interrupts used in this program to verify the disk for bad sectors and resetting the disk system etc. but you need not to worry, we are going to learn all these things in BIOS and interrupt programming sections later in the next coming chapters.

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