#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <sys/stat.h>

int main(int argc, char* argv[])
{
  char *buf;
  int i;

  if (argc < 2 ) {
    printf("Usage: mmapEx <filename>\n");
    exit(0);
  }

  int fd = open(argv[1], O_RDONLY);

  if ( fd < 0 ) {
    printf("Unable to open file %s\n", argv[1]);
    exit(0);
  }
  struct stat s;
  fstat(fd, &s);
  buf = mmap(NULL, s.st_size, PROT_READ, MAP_PRIVATE, fd, 0);

  printf("\n\n*** File %s Backwards ***\n\n", argv[1]);
  for(i = s.st_size - 1; i >= 0; i--) {
    printf("%c", buf[i]);
  }
  printf("\n");

  printf("\n\n*** Now Forwards ***\n\n");
  for(i = 0; i < s.st_size; i++) {
    printf("%c", buf[i]);
  }
  printf("\n");

  printf("\n\n*** Now output whole file with one write
  statement.***\n\n");
  write(1, buf, s.st_size);

  return 0;
}