/*
file12 has the same effect as file10 and file11.
It eliminates the repeated read-from-f2 in main() by using
a variable, havec1, to remember what read-from-f1 returned.
*/

#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 safereadbyte(char *filename,FILE *f,char *result)
{
  if (fscanf(f,"%c",result) == 1) return 1;
  if (ferror(f)) die("read",filename);
  return 0;
}

int main(int argc,char **argv)
{
  FILE *f1;
  FILE *f2;
  char c1;
  char c2;
  int havec1;
  int havec2;

  if (argc < 3) {
    fprintf(stderr,"usage: file12 f1 f2\n");
    exit(100);
  }

  f1 = safefopen(argv[1],"r");
  f2 = safefopen(argv[2],"r");
  for (;;) {
    havec1 = safereadbyte(argv[1],f1,&c1);
    havec2 = safereadbyte(argv[2],f2,&c2);
    if (havec1 != havec2) exit_different();
    if (!havec1) exit_same();
    if (c1 != c2) exit_different();
  }
}