A demo usging mmap() to read a file

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

  int main (int argc, char *argv[])
  {
          struct stat sb;
          off_t len;
          char *p;
          int fd;

          if (argc < 2) {
                  fprintf (stderr, "usage: %s <file>\n", argv[0]);
                  return 1;
          }

          fd = open (argv[1], O_RDONLY);
          if (fd == -1) {
                  perror ("open");
                  return 1;
          }

          if (fstat (fd, &sb) == -1) {
                  perror ("fstat");
                  return 1;
          }

          if (!S_ISREG (sb.st_mode)) {
                  fprintf (stderr, "%s is not a file\n", argv[1]);
                  return 1;
          }

          p = mmap (0, sb.st_size, PROT_READ, MAP_SHARED, fd, 0);
          if (p == MAP_FAILED) {
                  perror ("mmap");
                  return 1;
          }

          if (close (fd) == -1) {
                  perror ("close");
                  return 1;
          }

          for (len = 0; len < sb.st_size; len++)
                  putchar (p[len]);

          if (munmap (p, sb.st_size) == -1) {
                  perror ("munmap");
                  return 1;
          }

          return 0;
  }