scale the provided value by 1024, 1024^2 or 1024^3 respectively.
The scaled value is put into `unsigned_long_var`.
-`OPT_DATE(short, long, ×tamp_t_var, description)`::
- Introduce an option with date argument, see `approxidate()`.
- The timestamp is put into `timestamp_t_var`.
-
`OPT_EXPIRY_DATE(short, long, ×tamp_t_var, description)`::
Introduce an option with expiry date argument, see `parse_expiry_date()`.
The timestamp is put into `timestamp_t_var`.
The filename will be prefixed by passing the filename along with
the prefix argument of `parse_options()` to `prefix_filename()`.
-`OPT_ARGUMENT(long, description)`::
+`OPT_ARGUMENT(long, &int_var, description)`::
Introduce a long-option argument that will be kept in `argv[]`.
+ If this option was seen, `int_var` will be set to one (except
+ if a `NULL` pointer was passed).
`OPT_NUMBER_CALLBACK(&var, description, func_ptr)`::
Recognize numerical options like -123 and feed the integer as