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| <h4 class="subsection">25.3.5 Argp Parser Functions</h4> |
| |
| <p>The function pointed to by the <code>parser</code> field in a <code>struct |
| argp</code> (see <a href="Argp-Parsers.html#Argp-Parsers">Argp Parsers</a>) defines what actions take place in response |
| to each option or argument parsed. It is also used as a hook, allowing a |
| parser to perform tasks at certain other points during parsing. |
| |
| <p>Argp parser functions have the following type signature: |
| |
| <p><a name="index-argp-parser-functions-3048"></a> |
| <pre class="smallexample"> error_t <var>parser</var> (int <var>key</var>, char *<var>arg</var>, struct argp_state *<var>state</var>) |
| </pre> |
| <p class="noindent">where the arguments are as follows: |
| |
| <dl> |
| <dt><var>key</var><dd>For each option that is parsed, <var>parser</var> is called with a value of |
| <var>key</var> from that option's <code>key</code> field in the option |
| vector. See <a href="Argp-Option-Vectors.html#Argp-Option-Vectors">Argp Option Vectors</a>. <var>parser</var> is also called at |
| other times with special reserved keys, such as <code>ARGP_KEY_ARG</code> for |
| non-option arguments. See <a href="Argp-Special-Keys.html#Argp-Special-Keys">Argp Special Keys</a>. |
| |
| <br><dt><var>arg</var><dd>If <var>key</var> is an option, <var>arg</var> is its given value. This defaults |
| to zero if no value is specified. Only options that have a non-zero |
| <code>arg</code> field can ever have a value. These must <em>always</em> have a |
| value unless the <code>OPTION_ARG_OPTIONAL</code> flag is specified. If the |
| input being parsed specifies a value for an option that doesn't allow |
| one, an error results before <var>parser</var> ever gets called. |
| |
| <p>If <var>key</var> is <code>ARGP_KEY_ARG</code>, <var>arg</var> is a non-option |
| argument. Other special keys always have a zero <var>arg</var>. |
| |
| <br><dt><var>state</var><dd><var>state</var> points to a <code>struct argp_state</code>, containing useful |
| information about the current parsing state for use by |
| <var>parser</var>. See <a href="Argp-Parsing-State.html#Argp-Parsing-State">Argp Parsing State</a>. |
| </dl> |
| |
| <p>When <var>parser</var> is called, it should perform whatever action is |
| appropriate for <var>key</var>, and return <code>0</code> for success, |
| <code>ARGP_ERR_UNKNOWN</code> if the value of <var>key</var> is not handled by this |
| parser function, or a unix error code if a real error |
| occurred. See <a href="Error-Codes.html#Error-Codes">Error Codes</a>. |
| |
| <!-- argp.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Macro: int <b>ARGP_ERR_UNKNOWN</b><var><a name="index-ARGP_005fERR_005fUNKNOWN-3049"></a></var><br> |
| <blockquote><p>Argp parser functions should return <code>ARGP_ERR_UNKNOWN</code> for any |
| <var>key</var> value they do not recognize, or for non-option arguments |
| (<var>key</var><code> == ARGP_KEY_ARG</code>) that they are not equipped to handle. |
| </p></blockquote></div> |
| |
| <p>A typical parser function uses a switch statement on <var>key</var>: |
| |
| <pre class="smallexample"> error_t |
| parse_opt (int key, char *arg, struct argp_state *state) |
| { |
| switch (key) |
| { |
| case <var>option_key</var>: |
| <var>action</var> |
| break; |
| ... |
| default: |
| return ARGP_ERR_UNKNOWN; |
| } |
| return 0; |
| } |
| </pre> |
| <ul class="menu"> |
| <li><a accesskey="1" href="Argp-Special-Keys.html#Argp-Special-Keys">Keys</a>: Special values for the <var>key</var> argument. |
| <li><a accesskey="2" href="Argp-Parsing-State.html#Argp-Parsing-State">State</a>: What the <var>state</var> argument refers to. |
| <li><a accesskey="3" href="Argp-Helper-Functions.html#Argp-Helper-Functions">Functions</a>: Functions to help during argp parsing. |
| </ul> |
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