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| <h4 class="subsection">25.3.3 Specifying Argp Parsers</h4> |
| |
| <p>The first argument to the <code>argp_parse</code> function is a pointer to a |
| <code>struct argp</code>, which is known as an <dfn>argp parser</dfn>: |
| |
| <!-- argp.h --> |
| <!-- GNU --> |
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| — Data Type: <b>struct argp</b><var><a name="index-struct-argp-3041"></a></var><br> |
| <blockquote><p>This structure specifies how to parse a given set of options and |
| arguments, perhaps in conjunction with other argp parsers. It has the |
| following fields: |
| |
| <dl> |
| <dt><code>const struct argp_option *options</code><dd>A pointer to a vector of <code>argp_option</code> structures specifying which |
| options this argp parser understands; it may be zero if there are no |
| options at all. See <a href="Argp-Option-Vectors.html#Argp-Option-Vectors">Argp Option Vectors</a>. |
| |
| <br><dt><code>argp_parser_t parser</code><dd>A pointer to a function that defines actions for this parser; it is |
| called for each option parsed, and at other well-defined points in the |
| parsing process. A value of zero is the same as a pointer to a function |
| that always returns <code>ARGP_ERR_UNKNOWN</code>. See <a href="Argp-Parser-Functions.html#Argp-Parser-Functions">Argp Parser Functions</a>. |
| |
| <br><dt><code>const char *args_doc</code><dd>If non-zero, a string describing what non-option arguments are called by |
| this parser. This is only used to print the ‘<samp><span class="samp">Usage:</span></samp>’ message. If |
| it contains newlines, the strings separated by them are considered |
| alternative usage patterns and printed on separate lines. Lines after |
| the first are prefixed by ‘<samp><span class="samp"> or: </span></samp>’ instead of ‘<samp><span class="samp">Usage:</span></samp>’. |
| |
| <br><dt><code>const char *doc</code><dd>If non-zero, a string containing extra text to be printed before and |
| after the options in a long help message, with the two sections |
| separated by a vertical tab (<code>'\v'</code>, <code>'\013'</code>) character. By |
| convention, the documentation before the options is just a short string |
| explaining what the program does. Documentation printed after the |
| options describe behavior in more detail. |
| |
| <br><dt><code>const struct argp_child *children</code><dd>A pointer to a vector of <code>argp_children</code> structures. This pointer |
| specifies which additional argp parsers should be combined with this |
| one. See <a href="Argp-Children.html#Argp-Children">Argp Children</a>. |
| |
| <br><dt><code>char *(*help_filter)(int </code><var>key</var><code>, const char *</code><var>text</var><code>, void *</code><var>input</var><code>)</code><dd>If non-zero, a pointer to a function that filters the output of help |
| messages. See <a href="Argp-Help-Filtering.html#Argp-Help-Filtering">Argp Help Filtering</a>. |
| |
| <br><dt><code>const char *argp_domain</code><dd>If non-zero, the strings used in the argp library are translated using |
| the domain described by this string. If zero, the current default domain |
| is used. |
| |
| </dl> |
| </p></blockquote></div> |
| |
| <p>Of the above group, <code>options</code>, <code>parser</code>, <code>args_doc</code>, and |
| the <code>doc</code> fields are usually all that are needed. If an argp |
| parser is defined as an initialized C variable, only the fields used |
| need be specified in the initializer. The rest will default to zero due |
| to the way C structure initialization works. This design is exploited in |
| most argp structures; the most-used fields are grouped near the |
| beginning, the unused fields left unspecified. |
| |
| <ul class="menu"> |
| <li><a accesskey="1" href="Argp-Option-Vectors.html#Argp-Option-Vectors">Options</a>: Specifying options in an argp parser. |
| <li><a accesskey="2" href="Argp-Parser-Functions.html#Argp-Parser-Functions">Argp Parser Functions</a>: Defining actions for an argp parser. |
| <li><a accesskey="3" href="Argp-Children.html#Argp-Children">Children</a>: Combining multiple argp parsers. |
| <li><a accesskey="4" href="Argp-Help-Filtering.html#Argp-Help-Filtering">Help Filtering</a>: Customizing help output for an argp parser. |
| </ul> |
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