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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. |
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| <!-- argp.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — 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 |
| ‘<samp><span class="samp">--</span><var>name</var></samp>’; 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 ‘<samp><span class="samp">-</span><var>char</var></samp>’, 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 |
| ‘<samp><span class="samp">--</span><var>name</var><span class="samp">=</span><var>value</var></samp>’ or ‘<samp><span class="samp">-</span><var>char</var> <var>value</var></samp>’ |
| 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 |
| ‘<samp><span class="samp">:</span></samp>’ 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>, |
| −<var>m</var>, <small class="dots">...</small>, −2, −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 |
| ‘<samp><span class="samp">--help</span></samp>’ are put into group −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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