I know what struct is but haven't seen such use of it. 
Can any one explain to me in more details what that code do ?

```
static struct option const long_options[] =
{
  {"all", no_argument, NULL, 'a'},
  {"kernel-name", no_argument, NULL, 's'},
  {"sysname", no_argument, NULL, 's'},  /* Obsolescent.  */
  {"nodename", no_argument, NULL, 'n'},
  {"kernel-release", no_argument, NULL, 'r'},
  {"release", no_argument, NULL, 'r'},  /* Obsolescent.  */
  {"kernel-version", no_argument, NULL, 'v'},
  {"machine", no_argument, NULL, 'm'},
  {"processor", no_argument, NULL, 'p'},
  {"hardware-platform", no_argument, NULL, 'i'},
  {"operating-system", no_argument, NULL, 'o'},
  {GETOPT_HELP_OPTION_DECL},
  {GETOPT_VERSION_OPTION_DECL},
  {NULL, 0, NULL, 0}
};

```