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<title>Chapter 47. Boost.Xpressive</title>
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<div class="chapter">
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<div class="titlepage"><div>
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<div><h2 class="title">
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<a name="xpressive"></a>Chapter 47. Boost.Xpressive</h2></div>
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<div><div class="author"><h3 class="author">
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<span class="firstname">Eric</span> <span class="surname">Niebler</span>
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</h3></div></div>
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<div><p class="copyright">Copyright © 2007 Eric Niebler</p></div>
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<div><div class="legalnotice">
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<a name="xpressive.legal"></a><p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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</p>
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</div></div>
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<div class="toc">
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<p><b>Table of Contents</b></p>
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<dl class="toc">
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<dt><span class="section"><a href="xpressive.html#boost_xpressive.preface">Preface</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html">User's Guide</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.introduction">Introduction</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.installing_xpressive">Installing
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xpressive</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.quick_start">Quick Start</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#xpressive.user_s_guide.creating_a_regex_object">Creating
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a Regex Object</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.matching_and_searching">Matching
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and Searching</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.accessing_results">Accessing
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Results</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.string_substitutions">String
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Substitutions</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.string_splitting_and_tokenization">String
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Splitting and Tokenization</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.named_captures">Named Captures</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.grammars_and_nested_matches">Grammars
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and Nested Matches</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.semantic_actions_and_user_defined_assertions">Semantic
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Actions and User-Defined Assertions</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.symbol_tables_and_attributes">Symbol
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Tables and Attributes</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.localization_and_regex_traits">Localization
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and Regex Traits</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.tips_n_tricks">Tips 'N Tricks</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.concepts">Concepts</a></span></dt>
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<dt><span class="section"><a href="xpressive/user_s_guide.html#boost_xpressive.user_s_guide.examples">Examples</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="xpressive/reference.html">Reference</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.basic_regex_hpp">Header <boost/xpressive/basic_regex.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.match_results_hpp">Header <boost/xpressive/match_results.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.regex_actions_hpp">Header <boost/xpressive/regex_actions.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.regex_algorithms_hpp">Header <boost/xpressive/regex_algorithms.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.regex_compiler_hpp">Header <boost/xpressive/regex_compiler.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.regex_constants_hpp">Header <boost/xpressive/regex_constants.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.regex_error_hpp">Header <boost/xpressive/regex_error.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.regex_iterator_hpp">Header <boost/xpressive/regex_iterator.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.regex_primitives_hpp">Header <boost/xpressive/regex_primitives.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.regex_token_iterator_hpp">Header <boost/xpressive/regex_token_iterator.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.regex_traits_hpp">Header <boost/xpressive/regex_traits.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.sub_match_hpp">Header <boost/xpressive/sub_match.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.traits.c_regex_traits_hpp">Header <boost/xpressive/traits/c_regex_traits.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.traits.cpp_regex_traits_hpp">Header <boost/xpressive/traits/cpp_regex_traits.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.traits.null_regex_traits_hpp">Header <boost/xpressive/traits/null_regex_traits.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.xpressive_hpp">Header <boost/xpressive/xpressive.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.xpressive_dynamic_hpp">Header <boost/xpressive/xpressive_dynamic.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.xpressive_fwd_hpp">Header <boost/xpressive/xpressive_fwd.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.xpressive_static_hpp">Header <boost/xpressive/xpressive_static.hpp></a></span></dt>
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<dt><span class="section"><a href="xpressive/reference.html#header.boost.xpressive.xpressive_typeof_hpp">Header <boost/xpressive/xpressive_typeof.hpp></a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="boost_xpressive/acknowledgments.html">Acknowledgments</a></span></dt>
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<dt><span class="section"><a href="xpressive/appendices.html">Appendices</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="xpressive/appendices.html#boost_xpressive.appendices.appendix_1__history">Appendix
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1: History</a></span></dt>
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<dt><span class="section"><a href="xpressive/appendices.html#boost_xpressive.appendices.appendix_2__not_yet_implemented">Appendix
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2: Not Yet Implemented</a></span></dt>
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<dt><span class="section"><a href="xpressive/appendices.html#boost_xpressive.appendices.appendix_3__differences_from_boost_regex">Appendix
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3: Differences from Boost.Regex</a></span></dt>
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<dt><span class="section"><a href="xpressive/appendices.html#boost_xpressive.appendices.perf">Appendix 4: Performance
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Comparison</a></span></dt>
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<dt><span class="section"><a href="xpressive/appendices.html#xpressive.appendices.appendix_5__implementation_notes">Appendix
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5: Implementation Notes</a></span></dt>
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</dl></dd>
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</dl>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="boost_xpressive.preface"></a><a class="link" href="xpressive.html#boost_xpressive.preface" title="Preface">Preface</a>
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</h2></div></div></div>
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<div class="blockquote"><blockquote class="blockquote"><p>
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<span class="emphasis"><em>Wife:</em></span> New Shimmer is a floor wax!<br> <span class="emphasis"><em>Husband:</em></span>
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No, new Shimmer is a dessert topping!<br> <span class="emphasis"><em>Wife:</em></span> It's
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a floor wax!<br> <span class="emphasis"><em>Husband:</em></span> It's a dessert topping!<br>
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<span class="emphasis"><em>Wife:</em></span> It's a floor wax, I'm telling you!<br> <span class="emphasis"><em>Husband:</em></span>
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It's a dessert topping, you cow!<br> <span class="emphasis"><em>Announcer:</em></span> Hey,
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hey, hey, calm down, you two. New Shimmer is both a floor wax <span class="emphasis"><em>and</em></span>
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a dessert topping!
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</p></blockquote></div>
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<div class="blockquote"><blockquote class="blockquote"><p>
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<span class="bold"><strong><span class="emphasis"><em>-- Saturday Night Live</em></span></strong></span>
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</p></blockquote></div>
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<h3>
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<a name="boost_xpressive.preface.h0"></a>
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<span class="phrase"><a name="boost_xpressive.preface.description"></a></span><a class="link" href="xpressive.html#boost_xpressive.preface.description">Description</a>
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</h3>
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<p>
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xpressive is an advanced, object-oriented regular expression template library
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for C++. Regular expressions can be written as strings that are parsed at run-time,
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or as expression templates that are parsed at compile-time. Regular expressions
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can refer to each other and to themselves recursively, allowing you to build
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arbitrarily complicated grammars out of them.
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</p>
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<h3>
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<a name="boost_xpressive.preface.h1"></a>
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<span class="phrase"><a name="boost_xpressive.preface.motivation"></a></span><a class="link" href="xpressive.html#boost_xpressive.preface.motivation">Motivation</a>
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</h3>
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<p>
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If you need to manipulate text in C++, you have typically had two disjoint
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options: a regular expression engine or a parser generator. Regular expression
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engines (like <a href="../../libs/regex" target="_top">Boost.Regex</a>) are powerful
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and flexible; patterns are represented as strings which can be specified at
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runtime. However, that means that syntax errors are likewise not detected until
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runtime. Also, regular expressions are ill-suited to advanced text processing
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tasks such as matching balanced, nested tags. Those tasks have traditionally
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been handled by parser generators (like the <a href="http://spirit.sourceforge.net" target="_top">Spirit
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Parser Framework</a>). These beasts are more powerful but less flexible.
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They generally don't allow you to arbitrarily modify your grammar rules on
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the fly. In addition, they don't have the exhaustive backtracking semantics
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of regular expressions, which can make it more challenging to author some types
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of patterns.
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</p>
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<p>
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xpressive brings these two approaches seamlessly together and occupies a unique
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niche in the world of C++ text processing. With xpressive, you can choose to
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use it much as you would use <a href="../../libs/regex" target="_top">Boost.Regex</a>,
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representing regular expressions as strings. Or you can use it as you would
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use <a href="http://spirit.sourceforge.net" target="_top">Spirit</a>, writing your
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regexes as C++ expressions, enjoying all the benefits of an embedded language
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dedicated to text manipulation. What's more, you can mix the two to get the
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benefits of both, writing regular expression <span class="emphasis"><em>grammars</em></span>
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in which some of the regular expressions are statically bound -- hard-coded
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and syntax-checked by the compiler -- and others are dynamically bound and
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specified at runtime. These regular expressions can refer to each other recursively,
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matching patterns in strings that ordinary regular expressions cannot.
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</p>
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<h3>
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<a name="boost_xpressive.preface.h2"></a>
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<span class="phrase"><a name="boost_xpressive.preface.influences_and_related_work"></a></span><a class="link" href="xpressive.html#boost_xpressive.preface.influences_and_related_work">Influences
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and Related Work</a>
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</h3>
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<p>
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The design of xpressive's interface has been strongly influenced by John Maddock's
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<a href="../../libs/regex" target="_top">Boost.Regex</a> library and his <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1429.htm" target="_top">proposal</a>
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to add regular expressions to the Standard Library. I also drew a great deal
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of inspiration from Joel de Guzman's <a href="http://spirit.sourceforge.net" target="_top">Spirit
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Parser Framework</a>, which served as the model for static xpressive. Other
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sources of inspiration are the <a href="http://www.perl.com/pub/a/2002/06/04/apo5.html" target="_top">Perl
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6</a> redesign and <a href="http://research.microsoft.com/projects/greta" target="_top">GRETA</a>.
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(You can read a summary of the changes Perl 6 will bring to regex culture
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<a href="http://dev.perl.org/perl6/doc/design/syn/S05.html" target="_top">here</a>.)
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</p>
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</div>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"><p><small>Last revised: April 13, 2021 at 16:32:30 GMT</small></p></td>
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