/*
file10 f1 f2 compares the file named f1 to the file named f2.
It prints a message saying whether the files have the same contents.
If it has any trouble reading the files,
it prints an error message on stderr and exits.
*/

#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);
}

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

  if (argc < 3) {
    fprintf(stderr,"usage: file10 f1 f2\n");
    exit(100);
  }

  f1 = fopen(argv[1],"r");
  if (!f1) die("open",argv[1]);

  f2 = fopen(argv[2],"r");
  if (!f2) die("open",argv[2]);

  for (;;)
    if (fscanf(f1,"%c",&c1) == -1)
      if (ferror(f1))
        die("read",argv[1]);
      else /* end of file on f1 */
        if (fscanf(f2,"%c",&c2) == -1)
          if (ferror(f2))
            die("read",argv[2]);
          else
            exit_same(); /* end of file on both f1 and f2 */
        else
          exit_different(); /* end of file on f1, but not f2 */
    else
      if (fscanf(f2,"%c",&c2) == -1)
        if (ferror(f2))
          die("read",argv[2]);
        else
          exit_different(); /* end of file on f2, but not f1 */
      else
        if (c1 != c2)
          exit_different();
}