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<title>Chapter 1. The Boost Convert Library 2.0</title>
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<link rel="home" href="index.html" title="Chapter 1. The Boost Convert Library 2.0">
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<link rel="next" href="the_boost_convert_library/getting_started.html" title="Getting Started">
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<div class="spirit-nav"><a accesskey="n" href="the_boost_convert_library/getting_started.html"><img src="images/next.png" alt="Next"></a></div>
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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="convert"></a>Chapter 1. The Boost Convert Library 2.0</h2></div>
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<div><div class="author"><h3 class="author">
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<span class="firstname">Vladimir</span> <span class="surname">Batov</span>
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</h3></div></div>
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<div><p class="copyright">Copyright © 2009-2014 Vladimir Batov</p></div>
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<div><div class="legalnotice">
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<a name="convert.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></div>
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<div class="toc">
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<p><b>Table of Contents</b></p>
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<dl>
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<dt><span class="section"><a href="index.html#the_boost_convert_library.introduction">Introduction</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/getting_started.html">Getting Started</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/getting_serious.html">Getting Serious</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/convert_algorithms.html">Boost.Convert
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with Standard Algorithms</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/converters.html">Converters</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/__boost__lexical_cast__based_converter.html"><span class="emphasis"><em>boost::lexical_cast</em></span>-Based
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Converter</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/__std__stringstream__based_converter.html"><span class="emphasis"><em>std::stringstream</em></span>-Based
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Converter</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="the_boost_convert_library/__std__stringstream__based_converter.html#the_boost_convert_library.__std__stringstream__based_converter.formatting_support">Formatting
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Support</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/__std__stringstream__based_converter/locale_support.html">Locale
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Support</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/__std__stringstream__based_converter/integration_of_user_defined_types.html">Integration
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of User-Defined Types</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/__std__stringstream__based_converter/performance.html">Performance</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="the_boost_convert_library/type_requirements.html">Type Requirements</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/the___default_constructible__type_requirement.html">The
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<span class="emphasis"><em>Default Constructible</em></span> Type Requirement</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/other_conversions.html">Other Conversions</a></span></dt>
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<dt><span class="section"><a href="convert_reference.html">Convert Reference</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="convert_reference.html#header.boost.convert.api_hpp">Header <boost/convert/api.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/convert/lexical_cast_converter_hpp.html">Header <boost/convert/lexical_cast_converter.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/convert/safebool_hpp.html">Header <boost/convert/safebool.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/convert/sstream_converter_hpp.html">Header <boost/convert/sstream_converter.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/convert/string_sfinae_hpp.html">Header <boost/convert/string_sfinae.hpp></a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="the_boost_convert_library/motivation.html">Motivation</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/references.html">References</a></span></dt>
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<dt><span class="section"><a href="the_boost_convert_library/convert_acknowledgements.html">Acknowledgements</a></span></dt>
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<dt><span class="section"><a href="index/s15.html">Index</a></span></dt>
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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="the_boost_convert_library.introduction"></a><a class="link" href="index.html#the_boost_convert_library.introduction" title="Introduction">Introduction</a>
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</h2></div></div></div>
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<p>
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<span class="bold"><strong>Please note that the described framework is not part
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of the Boost library collection even though in this document it is referred
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to as <span class="emphasis"><em>Boost.Convert</em></span>. This is done in preparation for potential
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submission of the library to <span class="emphasis"><em>Boost</em></span>.</strong></span>
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</p>
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<p>
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<span class="emphasis"><em>Boost.Convert</em></span> builds on the <span class="emphasis"><em>boost::lexical_cast</em></span>
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design and experience and takes those conversion/transformation-related ideas
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further
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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to be applicable to a wider range of conversion-related deployment scenarios,
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</li>
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<li class="listitem">
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to provide a more flexible, extensible and configurable type-conversion
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framework.
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</li>
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</ul></div>
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<p>
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The <span class="emphasis"><em>boost::lexical_cast</em></span> framework essentially consists
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of:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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an API facade to deploy the relevant functionality uniformly and
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</li>
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<li class="listitem">
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the means to plug a particular type in to the <span class="emphasis"><em>boost::lexical_cast</em></span>
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framework; namely, <span class="emphasis"><em>operator>>(std::istream&)</em></span>
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and <span class="emphasis"><em>operator<<(std::ostream&)</em></span>).
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</li>
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</ul></div>
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<p>
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<span class="emphasis"><em>Boost.Convert</em></span> follows that successful design and also
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consists of two components:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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the API facade to provide simple, minimal and uniform deployment interface;
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</li>
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<li class="listitem">
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the extendible library of pluggable converters.
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</li>
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</ul></div>
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<p>
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The API facade implements new and familiar conversion/transformation-related
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behavior such as:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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flexible throwing, delayed-throwing and non-throwing failed-conversion
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behavior;
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</li>
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<li class="listitem">
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support for the fallback value to be returned when conversion/transformation
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fails;
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</li>
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<li class="listitem">
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two types of the conversion-failure check - quick/simple and generic;
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</li>
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<li class="listitem">
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means to deploy types that do no meet the <span class="emphasis"><em>Default Constructibility</em></span>
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requirement;
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</li>
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<li class="listitem">
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support for standard algorithms.
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</li>
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</ul></div>
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<p>
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The library of pluggable converters is independent of the <span class="emphasis"><em>Boost.Convert</em></span>
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API facade and is designed to be extended over time. With the current proposal
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two proof-of-the-concept converters are supplied -- string-to-type (and type-to-string)
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<span class="emphasis"><em>boost::lexical_cast</em></span>-based and <span class="emphasis"><em>std::stringstream</em></span>-based
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converters.
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</p>
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<p>
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The <span class="emphasis"><em>boost::lexical_cast</em></span>-based converter demonstrates how
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existing and independent conversion facilities might be incorporated in to
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the <span class="emphasis"><em>Boost.Convert</em></span> framework.
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</p>
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<p>
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The <span class="emphasis"><em>std::stringstream</em></span>-based converter draws on the standard
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<span class="emphasis"><em>std::streams</em></span> functionality and provides:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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string-to-type and type-to-string conversions;
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</li>
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<li class="listitem">
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formatting support based on standard manipulators (like <span class="emphasis"><em>std::hex</em></span>,
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<span class="emphasis"><em>std::scientific</em></span>, etc.);
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</li>
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<li class="listitem">
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support for different locales;
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</li>
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<li class="listitem">
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<span class="emphasis"><em>char</em></span> and <span class="emphasis"><em>wchar_t</em></span> support.
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</li>
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</ul></div>
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<p>
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For example, the following snippet converts an array of integers from their
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textual hexadecimal represention and assigns INT_MAX to those which fail to
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convert:
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</p>
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<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="number">5</span><span class="special">></span> <span class="identifier">strings</span> <span class="special">=</span> <span class="special">{{</span> <span class="string">"0XF"</span><span class="special">,</span> <span class="string">"0X10"</span><span class="special">,</span> <span class="string">"0X11"</span><span class="special">,</span> <span class="string">"0X12"</span><span class="special">,</span> <span class="string">"not int"</span> <span class="special">}};</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">integers</span><span class="special">;</span>
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<span class="identifier">boost</span><span class="special">::</span><span class="identifier">cstringstream_converter</span> <span class="identifier">cnv</span><span class="special">;</span> <span class="comment">// stringstream-based char converter</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span>
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<span class="identifier">strings</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>
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<span class="identifier">strings</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">back_inserter</span><span class="special">(</span><span class="identifier">integers</span><span class="special">),</span>
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<span class="identifier">convert</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">from</span><span class="special"><</span><span class="identifier">string</span><span class="special">>(</span><span class="identifier">ccnv</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">hex</span><span class="special">)).</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">INT_MAX</span><span class="special">));</span>
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</pre>
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<p>
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An interesting (yet to be explored) feature is that <span class="emphasis"><em>Boost.Convert</em></span>
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is not limited to string-to-type and type-to-string conversions. In fact, the
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<span class="emphasis"><em>Boost.Convert</em></span> API facade is type-agnostic. The plugged-in
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converter ultimately dictates what types and conversions are supported. Consequently,
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a wide range of conversion/transformation-related tasks can be addressed and
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deployed <span class="emphasis"><em>uniformly</em></span> by plugging-in special-purpose converters.
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For example, encryption by a string-to-string encrypting converter, etc.
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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: February 20, 2014 at 23:29:17 GMT</small></p></td>
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<td align="right"><div class="copyright-footer"></div></td>
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</tr></table>
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<hr>
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