#define _POSIX_C_SOURCE 200809L

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
  FILE * cur_in_file;
  int i; char c;

  int using_unbuffered_output;

  int error_occurred;

  while((c = getopt(argc, argv, "u")) != -1) {
    if(c == 'u') {
      using_unbuffered_output = 1;
    }
  }

  if(argc == 1 || optind == argc) {
    cur_in_file = stdin;
    for(c = fgetc(cur_in_file); c != EOF; c = fgetc(cur_in_file)) {
      if(using_unbuffered_output) {
	      write(1, &c, 1);
      }
      else {
	      fprintf(stdout, "%c", c);
      }
    }
    fclose(cur_in_file);
  }
  
  for(i = optind; i < argc; i++) {
    if(argv[i][0] == '-' && argv[i][1] == '\0') {
      cur_in_file = stdin;
    }
    else {
      cur_in_file = fopen(argv[i], "r");
      if(cur_in_file == NULL) {
	      fprintf(stderr, "%s: %s: No such file or directory\n", argv[0], argv[i]);
	      error_occurred = 1;
      }
    }
    for(c = fgetc(cur_in_file); c != EOF; c = fgetc(cur_in_file)) {
      if(using_unbuffered_output) {
	      write(1, &c, 1);
      }
      else {
	      fprintf(stdout, "%c", c);
      }
    }
    fclose(cur_in_file);
  }

  if(error_occurred) {
    return 1;
  }
  else {
    return 0;
  }
}