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<!-- This is a @section so that it's at the same level as getopt and argp -->
<h5 class="subsubsection">25.3.12.1 Parsing of Suboptions</h5>

<p>Having a single level of options is sometimes not enough.  There might
be too many options which have to be available or a set of options is
closely related.

   <p>For this case some programs use suboptions.  One of the most prominent
programs is certainly <code>mount</code>(8).  The <code>-o</code> option take one
argument which itself is a comma separated list of options.  To ease the
programming of code like this the function <code>getsubopt</code> is
available.

<!-- stdlib.h -->
<div class="defun">
&mdash; Function: int <b>getsubopt</b> (<var>char **optionp, const char* const *tokens, char **valuep</var>)<var><a name="index-getsubopt-3097"></a></var><br>
<blockquote>
        <p>The <var>optionp</var> parameter must be a pointer to a variable containing
the address of the string to process.  When the function returns the
reference is updated to point to the next suboption or to the
terminating &lsquo;<samp><span class="samp">\0</span></samp>&rsquo; character if there is no more suboption available.

        <p>The <var>tokens</var> parameter references an array of strings containing the
known suboptions.  All strings must be &lsquo;<samp><span class="samp">\0</span></samp>&rsquo; terminated and to mark
the end a null pointer must be stored.  When <code>getsubopt</code> finds a
possible legal suboption it compares it with all strings available in
the <var>tokens</var> array and returns the index in the string as the
indicator.

        <p>In case the suboption has an associated value introduced by a &lsquo;<samp><span class="samp">=</span></samp>&rsquo;
character, a pointer to the value is returned in <var>valuep</var>.  The
string is &lsquo;<samp><span class="samp">\0</span></samp>&rsquo; terminated.  If no argument is available
<var>valuep</var> is set to the null pointer.  By doing this the caller can
check whether a necessary value is given or whether no unexpected value
is present.

        <p>In case the next suboption in the string is not mentioned in the
<var>tokens</var> array the starting address of the suboption including a
possible value is returned in <var>valuep</var> and the return value of the
function is &lsquo;<samp><span class="samp">-1</span></samp>&rsquo;. 
</p></blockquote></div>

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