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(libc.info)Argp Option Vectors

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Specifying Options in an Argp Parser
------------------------------------

   The `options' field in a `struct argp' points to a vector of `struct
argp_option' structures, each of which specifies an option that the
argp parser supports.  Multiple entries may be used for a single option
provided it has multiple names.  This should be terminated by an entry
with zero in all fields.  Note that when using an initialized C array
for options, writing `{ 0 }' is enough to achieve this.

 - Data Type: struct argp_option
     This structure specifies a single option that an argp parser
     understands, as well as how to parse and document that option.  It
     has the following fields:

    `const char *name'
          The long name for this option, corresponding to the long
          option `--NAME'; this field may be zero if this option _only_
          has a short name.  To specify multiple names for an option,
          additional entries may follow this one, with the
          `OPTION_ALIAS' flag set.  Note: Argp Option Flags.

    `int key'
          The integer key provided by the current option to the option
          parser.  If KEY has a value that is a printable ASCII
          character (i.e., `isascii (KEY)' is true), it _also_
          specifies a short option `-CHAR', where CHAR is the ASCII
          character with the code KEY.

    `const char *arg'
          If non-zero, this is the name of an argument associated with
          this option, which must be provided (e.g., with the
          `--NAME=VALUE' or `-CHAR VALUE' syntaxes), unless the
          `OPTION_ARG_OPTIONAL' flag (Note: Argp Option Flags) is
          set, in which case it _may_ be provided.

    `int flags'
          Flags associated with this option, some of which are referred
          to above.  Note: Argp Option Flags.

    `const char *doc'
          A documentation string for this option, for printing in help
          messages.

          If both the `name' and `key' fields are zero, this string
          will be printed tabbed left from the normal option column,
          making it useful as a group header.  This will be the first
          thing printed in its group.  In this usage, it's conventional
          to end the string with a `:' character.

    `int group'
          Group identity for this option.

          In a long help message, options are sorted alphabetically
          within each group, and the groups presented in the order 0,
          1, 2, ..., N, -M, ..., -2, -1.

          Every entry in an options array with this field 0 will
          inherit the group number of the previous entry, or zero if
          it's the first one.  If it's a group header with `name' and
          `key' fields both zero, the previous entry + 1 is the
          default.  Automagic options such as `--help' are put into
          group -1.

          Note that because of C structure initialization rules, this
          field often need not be specified, because 0 is the correct
          value.

Flags

Argp Option Flags. Flags for options.