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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. |
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| <!-- stdlib.h --> |
| <div class="defun"> |
| — 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 ‘<samp><span class="samp">\0</span></samp>’ 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 ‘<samp><span class="samp">\0</span></samp>’ 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 ‘<samp><span class="samp">=</span></samp>’ |
| character, a pointer to the value is returned in <var>valuep</var>. The |
| string is ‘<samp><span class="samp">\0</span></samp>’ 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 ‘<samp><span class="samp">-1</span></samp>’. |
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