A demo usging mmap() to read a file

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#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;  }