/*
file13 has the same effect as file10, file11, and file12.
It uses fgetc() instead of fscanf().

d1 in file13.c, the result of getchar(), fgetc(), safefgetc(), etc.,
is a combination of c1 and havec1 in file12.c:

   havec1   c1   d1   situation
        0    ?   -1   end of file (or error, eliminated by safefgetc)
        1    0    0   the byte we just read was a 0
        1    1    1   the byte we just read was a 1
        1    2    2   the byte we just read was a 2
        	      ...
        1   65   65   the byte we just read was a 65 ('A')
        1   66   66   the byte we just read was a 66 ('B')
        	      ...
        1  255  255   the byte we just read was a 255

Note that d1 is an int, not a char;
a char does not have enough room for -1, 0, 1, ..., 255.
Note also that safefgetc() is returning only one value,
so it doesn't need call-by-reference as safegetbyte() did,
although it still uses pointers for filename and f.

Can you rewrite safefgetc() to use fscanf(),
and rewrite safegetbyte() to use fgetc()?
*/

#include <stdio.h>
#include <errno.h>
#include <string.h>

void die(char *operation,char *filename)
{
  fprintf(stderr,"fatal: unable to %s %s: %s\n"
    ,operation,filename,strerror(errno));
  exit(111);
}

void exit_same(void)
{
  printf("The files have the same contents.\n");
  exit(0);
}

void exit_different(void)
{
  printf("The files have different contents.\n");
  exit(0);
}

FILE *safefopen(char *filename,char *how)
{
  FILE *f = fopen(filename,how);
  if (!f) die("open",filename);
  return f;
}

int safefgetc(char *filename,FILE *f)
{
  int result = fgetc(f);
  if (result != -1) return result;
  if (ferror(f)) die("read",filename);
  return -1;
}

int main(int argc,char **argv)
{
  FILE *f1;
  FILE *f2;
  int d1;
  int d2;

  if (argc < 3) {
    fprintf(stderr,"usage: file13 f1 f2\n");
    exit(100);
  }

  f1 = safefopen(argv[1],"r");
  f2 = safefopen(argv[2],"r");
  for (;;) {
    d1 = safefgetc(argv[1],f1);
    d2 = safefgetc(argv[2],f2);
    if (d1 != d2) exit_different();
    if (d1 == EOF) exit_same();
  }
}