#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>


int main(int argc, char **argv)
  {
   char fname[50];          // Holds disk image file name
   int fd;                  // UNIX file descriptor
   int numbytesread;        // actual no of bytes read from file
   unsigned char buf[5120]; // character buffer
   int pos, seekpos;        // pos = desired byte position, sekkpos = actual
   int blocknum;            // block number to seek to
   int perline = 16;        // number of values (bytes printed per line
   unsigned short int val;  // holds int value of two bytes
   int i,j;
   
 /* 
  * Get file name from command line if supplied, otherwise prompt for it
  */
   if(argc == 2)
     {
      strcpy(fname, argv[1]);
     }	 
   else
     {
      printf("Enter name of file to open: ");
      scanf("%s", fname);
     }
	    
   printf("\nOpening %s\n", fname);
   fd = open(fname, O_RDONLY);
	       
   if(fd <= 0)
     {
      printf("Something bad happened opening file - bye\n");
      exit(1);
     }

 /* 
  * The following three lines aren't necessary here, but shows how to move 
  * the file pointer to the start of block number 'blocknum'
  */
   blocknum = 0;
   pos = blocknum * 512;
   seekpos = lseek(fd, pos, SEEK_SET);

   numbytesread = read(fd, buf, 512);
   printf("Read %d bytes from file\n\n", numbytesread);

 /*
  * Headings for table
  */
   printf("StartByte|");
   for(j = perline -1; j >= 0; j--)
      printf("%3d ", j);
   printf(" |\n");
   printf(" Dec Hex |");
   for(j = perline -1; j >= 0; j--)
      printf(" %02X ", j);
   printf(" |\n");
   for(j = 0; j < 75; j++)
      printf("_");
   printf("|\n");
 
 /*
  * Print out block, "perline" values per line. Both hex and character values
  * are printed.
  */
   for(i = 0; i < numbytesread; i+=perline)
     {
      printf("%4d %03X |", i, i);
      for(j = i + perline - 1; j >= i; j--)
         printf(" %02X ", buf[j]);
      printf( " |\n         |");

      for(j = i + perline - 1; j >= i; j--)
        {
         if(buf[j] < 32 || buf[j] > 126)
            printf("  . ");
         else
            printf("  %c ",buf[j]);
        }  // END for j
      printf( " |\n         |");

      for(j = i + perline - 1; j >= i; j-=2)
        {
         val = buf[j] << 8 | buf[j-1];
         printf("  %5d ", val);
        }
      printf(" |\n\n");

     }  // END for i
   
   printf("\n");
   
  } //END main