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<h4 class="subsection">25.3.4 Specifying Options in an Argp Parser</h4>

<p>The <code>options</code> field in a <code>struct argp</code> points to a vector of
<code>struct argp_option</code> 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 <code>{ 0 }</code> is enough to achieve this.

<!-- argp.h -->
<!-- GNU -->
<div class="defun">
&mdash; Data Type: <b>struct argp_option</b><var><a name="index-struct-argp_005foption-3042"></a></var><br>
<blockquote><p>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:

          <dl>
<dt><code>const char *name</code><dd>The long name for this option, corresponding to the long option
&lsquo;<samp><span class="samp">--</span><var>name</var></samp>&rsquo;; this field may be zero if this option <em>only</em>
has a short name.  To specify multiple names for an option, additional
entries may follow this one, with the <code>OPTION_ALIAS</code> flag
set.  See <a href="Argp-Option-Flags.html#Argp-Option-Flags">Argp Option Flags</a>.

          <br><dt><code>int key</code><dd>The integer key provided by the current option to the option parser.  If
<var>key</var> has a value that is a printable <span class="sc">ascii</span> character (i.e.,
<code>isascii (</code><var>key</var><code>)</code> is true), it <em>also</em> specifies a short
option &lsquo;<samp><span class="samp">-</span><var>char</var></samp>&rsquo;, where <var>char</var> is the <span class="sc">ascii</span> character
with the code <var>key</var>.

          <br><dt><code>const char *arg</code><dd>If non-zero, this is the name of an argument associated with this
option, which must be provided (e.g., with the
&lsquo;<samp><span class="samp">--</span><var>name</var><span class="samp">=</span><var>value</var></samp>&rsquo; or &lsquo;<samp><span class="samp">-</span><var>char</var> <var>value</var></samp>&rsquo;
syntaxes), unless the <code>OPTION_ARG_OPTIONAL</code> flag (see <a href="Argp-Option-Flags.html#Argp-Option-Flags">Argp Option Flags</a>) is set, in which case it <em>may</em> be provided.

          <br><dt><code>int flags</code><dd>Flags associated with this option, some of which are referred to above. 
See <a href="Argp-Option-Flags.html#Argp-Option-Flags">Argp Option Flags</a>.

          <br><dt><code>const char *doc</code><dd>A documentation string for this option, for printing in help messages.

          <p>If both the <code>name</code> and <code>key</code> 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
&lsquo;<samp><span class="samp">:</span></samp>&rsquo; character.

          <br><dt><code>int group</code><dd>Group identity for this option.

          <p>In a long help message, options are sorted alphabetically within each
group, and the groups presented in the order 0, 1, 2, <small class="dots">...</small>, <var>n</var>,
&minus;<var>m</var>, <small class="dots">...</small>, &minus;2, &minus;1.

          <p>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 <code>name</code> and <code>key</code> fields both zero, the
previous entry + 1 is the default.  Automagic options such as
&lsquo;<samp><span class="samp">--help</span></samp>&rsquo; are put into group &minus;1.

          <p>Note that because of C structure initialization rules, this field often
need not be specified, because 0 is the correct value. 
</dl>
        </p></blockquote></div>

<ul class="menu">
<li><a accesskey="1" href="Argp-Option-Flags.html#Argp-Option-Flags">Flags</a>:      Flags for options. 
</ul>

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