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| <td width="85%" height="49"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Regular Expression Parser</b></font></td> |
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| <p><a name="regular_expression_parser"></a>Regular expressions are a form of pattern-matching |
| that are often used in text processing. Many users will be familiar with the |
| usage of regular expressions. Initially there were the Unix utilities grep, |
| sed and awk, and the programming language perl, each of which make extensive |
| use of regular expressions. Today the usage of such regular expressions is integrated |
| in many more available systems.</p> |
| <p>During parser construction it is often useful to have the power of regular |
| expressions available. The Regular Expression Parser was introduced, to make |
| the use of regular expressions accessible for Spirit parser construction.</p> |
| <p>The Regular Expression Parser <tt>rxstrlit</tt> has a single template type |
| parameter: an iterator type. Internally, <tt>rxstrlit</tt> holds the Boost Regex |
| object containing the provided regular expression. The <tt>rxstrlit</tt> attempts |
| to match the current input stream with this regular expression. The template |
| type parameter defaults to <tt>char const<span class="operators">*</span></tt>. |
| <tt>rxstrlit</tt> has two constructors. The first accepts a null-terminated |
| character pointer. This constructor may be used to build <tt>rxstrlit's</tt> |
| from quoted regular expression literals. The second constructor takes in a first/last |
| iterator pair. The function generator version is <tt>regex_p</tt>. </p> |
| <p>Here are some examples:</p> |
| <pre><code><span class=comment> </span><span class=identifier>rxstrlit</span><span class=special><>(</span><span class=string>"Hello[[:space:]]+[W|w]orld"</span><span class=special>) |
| </span><span class=identifier>regex_p</span><span class=special>(</span><span class=string>"Hello[[:space:]]+[W|w]orld"</span><span class=special>) |
| |
| </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>msg</span><span class=special>(</span><span class=string>"Hello[[:space:]]+[W|w]orld"</span><span class=special>); |
| rx</span><span class=identifier>strlit</span><span class=special><>(</span><span class=identifier>msg</span><span class=special>.</span><span class=identifier>begin</span><span class=special>(), </span><span class=identifier>msg</span><span class=special>.</span><span class=identifier>end</span><span class=special>());</span></code></pre> |
| <p>The generated parser object acts at the character level, thus an eventually |
| given skip parser is not used during the attempt to match the regular expression |
| (see <a href="faq.html#scanner_business">The Scanner Business</a>).</p> |
| <p>The Regular Expression Parser is implemented by the help of the <a href="http://www.boost.org/libs/regex/index.html">Boost |
| Regex++ library</a>, so you have to have some limitations in mind. </p> |
| <blockquote> |
| <p><img src="theme/bullet.gif" width="12" height="12"> Boost libraries have |
| to be installed on your computer and the Boost root directory has to be added |
| to your compiler <tt>#include<...></tt> search path. You can download |
| the actual version at the <a href="http://www.boost.org/">Boost web site</a>.</p> |
| <p><img src="theme/bullet.gif" width="12" height="12"> The Boost Regex library |
| requires the usage of bi-directional iterators. So you have to ensure this |
| during the usage of the Spirit parser, which contains a Regular Expression |
| Parser.</p> |
| <p><img src="theme/bullet.gif" width="12" height="12"> The Boost Regex library |
| is not a header only library, as Spirit is, though it provides the possibility |
| to include all of the sources, if you are using it in one compilation unit |
| only. Define the preprocessor constant <tt>BOOST_SPIRIT_NO_REGEX_LIB</tt> before |
| including the spirit Regular Expression Parser header, if you want to include |
| all the Boost Regex sources into this compilation unit. If you are using the |
| Regular Expression Parser in more than one compilation unit, you should not |
| define this constant and must link your application against the regex library |
| as described in the related documentation.</p> |
| </blockquote> |
| <p> <img src="theme/lens.gif" width="15" height="16"> See <a href="../example/fundamental/regular_expression.cpp">regular_expression.cpp</a> for a compilable example. This is part of the Spirit distribution.</p> |
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| <p class="copyright">Copyright © 2001-2002 Hartmut Kaiser<br> |
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| <font size="2">Use, modification and distribution is subject to the Boost Software |
| License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
| http://www.boost.org/LICENSE_1_0.txt)</font></p> |
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