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| <h3 class="section">25.3 Parsing Program Options with Argp</h3> |
| |
| <p><a name="index-argp-_0028program-argument-parser_0029-3032"></a><a name="index-argument-parsing-with-argp-3033"></a><a name="index-option-parsing-with-argp-3034"></a> |
| <dfn>Argp</dfn> is an interface for parsing unix-style argument vectors. |
| See <a href="Program-Arguments.html#Program-Arguments">Program Arguments</a>. |
| |
| <p>Argp provides features unavailable in the more commonly used |
| <code>getopt</code> interface. These features include automatically producing |
| output in response to the ‘<samp><span class="samp">--help</span></samp>’ and ‘<samp><span class="samp">--version</span></samp>’ options, as |
| described in the GNU coding standards. Using argp makes it less likely |
| that programmers will neglect to implement these additional options or |
| keep them up to date. |
| |
| <p>Argp also provides the ability to merge several independently defined |
| option parsers into one, mediating conflicts between them and making the |
| result appear seamless. A library can export an argp option parser that |
| user programs might employ in conjunction with their own option parsers, |
| resulting in less work for the user programs. Some programs may use only |
| argument parsers exported by libraries, thereby achieving consistent and |
| efficient option-parsing for abstractions implemented by the libraries. |
| |
| <p><a name="index-argp_002eh-3035"></a>The header file <samp><span class="file"><argp.h></span></samp> should be included to use argp. |
| |
| <h4 class="subsection">25.3.1 The <code>argp_parse</code> Function</h4> |
| |
| <p>The main interface to argp is the <code>argp_parse</code> function. In many |
| cases, calling <code>argp_parse</code> is the only argument-parsing code |
| needed in <code>main</code>. |
| See <a href="Program-Arguments.html#Program-Arguments">Program Arguments</a>. |
| |
| <!-- argp.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: error_t <b>argp_parse</b> (<var>const struct argp *argp, int argc, char **argv, unsigned flags, int *arg_index, void *input</var>)<var><a name="index-argp_005fparse-3036"></a></var><br> |
| <blockquote><p>The <code>argp_parse</code> function parses the arguments in <var>argv</var>, of |
| length <var>argc</var>, using the argp parser <var>argp</var>. See <a href="Argp-Parsers.html#Argp-Parsers">Argp Parsers</a>. |
| |
| <p>A value of zero is the same as a <code>struct argp</code>containing all |
| zeros. <var>flags</var> is a set of flag bits that modify the parsing |
| behavior. See <a href="Argp-Flags.html#Argp-Flags">Argp Flags</a>. <var>input</var> is passed through to the argp |
| parser <var>argp</var>, and has meaning defined by <var>argp</var>. A typical |
| usage is to pass a pointer to a structure which is used for specifying |
| parameters to the parser and passing back the results. |
| |
| <p>Unless the <code>ARGP_NO_EXIT</code> or <code>ARGP_NO_HELP</code> flags are included |
| in <var>flags</var>, calling <code>argp_parse</code> may result in the program |
| exiting. This behavior is true if an error is detected, or when an |
| unknown option is encountered. See <a href="Program-Termination.html#Program-Termination">Program Termination</a>. |
| |
| <p>If <var>arg_index</var> is non-null, the index of the first unparsed option |
| in <var>argv</var> is returned as a value. |
| |
| <p>The return value is zero for successful parsing, or an error code |
| (see <a href="Error-Codes.html#Error-Codes">Error Codes</a>) if an error is detected. Different argp parsers |
| may return arbitrary error codes, but the standard error codes are: |
| <code>ENOMEM</code> if a memory allocation error occurred, or <code>EINVAL</code> if |
| an unknown option or option argument is encountered. |
| </p></blockquote></div> |
| |
| <ul class="menu"> |
| <li><a accesskey="1" href="Argp-Global-Variables.html#Argp-Global-Variables">Globals</a>: Global argp parameters. |
| <li><a accesskey="2" href="Argp-Parsers.html#Argp-Parsers">Parsers</a>: Defining parsers for use with <code>argp_parse</code>. |
| <li><a accesskey="3" href="Argp-Flags.html#Argp-Flags">Flags</a>: Flags that modify the behavior of <code>argp_parse</code>. |
| <li><a accesskey="4" href="Argp-Help.html#Argp-Help">Help</a>: Printing help messages when not parsing. |
| <li><a accesskey="5" href="Argp-Examples.html#Argp-Examples">Examples</a>: Simple examples of programs using argp. |
| <li><a accesskey="6" href="Argp-User-Customization.html#Argp-User-Customization">Customization</a> |
| Users may control the ‘<samp><span class="samp">--help</span></samp>’ output format. |
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