/* inittable.c -- It is called with the command
      % inittable filename
   where filename is the name of an existing file 
   with at least NCOUNT person records. It inserts a '\0'
   at the end of each field of each record.
 */
#include <stdio.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define NAMESIZE 26
struct person { // In each fielt I leave space for an extra character
  char ssn[10];
  char name[NAMESIZE];
  char grade[3]; // A, A-, B+, B, B-, C+, C, C-, D+, D, D-, F, I
};
#define NCOUNT 20
struct moo {
  struct person a[NCOUNT];
};

void main(int argc, char *argv[])
{
  struct moo *ptr;
  int k;
  int fd;

  if (argc != 2) {
    printf("Usage: %s filename\n", argv[0]);
    exit(0);
  }

  if ((fd = open(argv[1], O_RDWR | O_CREAT, 
		 S_IRWXU | S_IRWXG | S_IRWXO  )) < 0){
    fprintf(stderr, "Error opening mapped file\n");
    exit(1);
  }

  if ((ptr = (struct moo *)mmap(0, sizeof(struct moo), PROT_READ | PROT_WRITE, 
		  MAP_SHARED, fd, 0)) == (struct moo *)MAP_FAILED) {
    fprintf(stderr, "Error in mmap\n");
    exit(1);
  }

  close(fd);

  for (k=0; k < NCOUNT; ++k) {
    // insert '\0's in k-th record
    (ptr->a[k]).ssn[9] = '\0';
    (ptr->a[k]).name[NAMESIZE-1] = '\0';
    (ptr->a[k]).grade[2] = '\0';
  }
  
  if (munmap((void *)ptr, sizeof(struct moo)) < 0){
    fprintf(stderr, "Error in munmap\n");
    exit(1);
  }
}