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  21 <div class="chapter">
  22 <div class="titlepage"><div>
  23 <div><h2 class="title">
  24 <a name="convert"></a>Chapter&#160;1.&#160;Boost.Convert 2.0</h2></div>
  25 <div><div class="author"><h3 class="author">
  26 <span class="firstname">Vladimir</span> <span class="surname">Batov</span>
  27 </h3></div></div>
  28 <div><p class="copyright">Copyright &#169; 2009-2016 Vladimir Batov</p></div>
  29 <div><div class="legalnotice">
  30 <a name="convert.legal"></a><p>
  31         Distributed under the Boost Software License, Version 1.0. See copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>.
  32       </p>
  33 </div></div>
  34 </div></div>
  35 <div class="toc">
  36 <p><b>Table of Contents</b></p>
  37 <dl class="toc">
  38 <dt><span class="section"><a href="index.html#boost_convert.rationale">Rationale</a></span></dt>
  39 <dt><span class="section"><a href="boost_convert/introduction.html">Introduction</a></span></dt>
  40 <dt><span class="section"><a href="boost_convert/getting_started.html">Getting Started</a></span></dt>
  41 <dd><dl>
  42 <dt><span class="section"><a href="boost_convert/getting_started.html#boost_convert.getting_started.basic_deployment">Basic
  43       Deployment</a></span></dt>
  44 <dt><span class="section"><a href="boost_convert/getting_started/flexibility_and_adaptability_to_change.html">Flexibility
  45       and Adaptability to Change</a></span></dt>
  46 <dt><span class="section"><a href="boost_convert/getting_started/basic_conversion_failure_detection.html">Basic
  47       Conversion-Failure Detection</a></span></dt>
  48 </dl></dd>
  49 <dt><span class="section"><a href="boost_convert/error_detection.html">Better Error Detection</a></span></dt>
  50 <dt><span class="section"><a href="boost_convert/default_converter.html">Default Converter</a></span></dt>
  51 <dt><span class="section"><a href="boost_convert/alternative_interface.html">Alternative Interface</a></span></dt>
  52 <dt><span class="section"><a href="boost_convert/converters.html">Converters</a></span></dt>
  53 <dt><span class="section"><a href="boost_convert/integration_of_user_types.html">Integration of
  54     User-Defined Types</a></span></dt>
  55 <dt><span class="section"><a href="boost_convert/algorithms.html">Boost.Convert with Standard Algorithms</a></span></dt>
  56 <dt><span class="section"><a href="boost_convert/performance.html">Performance</a></span></dt>
  57 <dd><dl>
  58 <dt><span class="section"><a href="boost_convert/performance.html#boost_convert.performance.converters_compared">Converters
  59       Compared</a></span></dt>
  60 <dt><span class="section"><a href="boost_convert/performance/boost_convert_overhead.html">Boost.Convert
  61       Overhead</a></span></dt>
  62 <dt><span class="section"><a href="boost_convert/performance/the_bigger_picture.html">The Bigger
  63       Picture</a></span></dt>
  64 </dl></dd>
  65 <dt><span class="section"><a href="boost_convert/other_conversions.html">Beyond Basic Conversions</a></span></dt>
  66 <dt><span class="section"><a href="boost_convert/converters_detail.html">Converters in Detail</a></span></dt>
  67 <dd><dl>
  68 <dt><span class="section"><a href="boost_convert/converters_detail.html#boost_convert.converters_detail.lexical_cast_converter"><span class="emphasis"><em>boost::cnv::lexical_cast</em></span>
  69       Converter</a></span></dt>
  70 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter.html"><span class="emphasis"><em>boost::cnv::stream</em></span>
  71       Converter</a></span></dt>
  72 <dd><dl>
  73 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter.html#boost_convert.converters_detail.stream_converter.formatting_support">Formatting
  74         Support</a></span></dt>
  75 <dd><dl>
  76 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter.html#boost_convert.converters_detail.stream_converter.formatting_support.numeric_base">Numeric
  77           Base</a></span></dt>
  78 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter.html#boost_convert.converters_detail.stream_converter.formatting_support.field_width__fill_character_and_adjustment">Field
  79           Width, Fill Character and Adjustment</a></span></dt>
  80 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter.html#boost_convert.converters_detail.stream_converter.formatting_support.leading_whitespace_characters">Leading
  81           Whitespace Characters</a></span></dt>
  82 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter.html#boost_convert.converters_detail.stream_converter.formatting_support.format_of_boolean_values">Format
  83           of Boolean Values</a></span></dt>
  84 </dl></dd>
  85 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter/locale_support.html">Locale
  86         Support</a></span></dt>
  87 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter/supported_string_types.html">Supported
  88         String Types</a></span></dt>
  89 <dd><dl>
  90 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter/supported_string_types.html#boost_convert.converters_detail.stream_converter.supported_string_types.wide_string">Wide
  91           String</a></span></dt>
  92 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter/supported_string_types/custom_string_types.html">Custom
  93           String Types</a></span></dt>
  94 </dl></dd>
  95 <dt><span class="section"><a href="boost_convert/converters_detail/stream_converter/the___default_constructible__type_requirement.html">The
  96         <span class="emphasis"><em>Default Constructible</em></span> Type Requirement</a></span></dt>
  97 </dl></dd>
  98 <dt><span class="section"><a href="boost_convert/converters_detail/strtol_converter.html"><span class="emphasis"><em>boost::cnv::strtol</em></span>
  99       Converter</a></span></dt>
 100 <dd><dl>
 101 <dt><span class="section"><a href="boost_convert/converters_detail/strtol_converter.html#boost_convert.converters_detail.strtol_converter.basic_deployment">Basic
 102         Deployment</a></span></dt>
 103 <dt><span class="section"><a href="boost_convert/converters_detail/strtol_converter/formatting_support.html">Formatting
 104         Support</a></span></dt>
 105 <dd><dl>
 106 <dt><span class="section"><a href="boost_convert/converters_detail/strtol_converter/formatting_support.html#boost_convert.converters_detail.strtol_converter.formatting_support.numeric_base__bin__oct__dec__hex_">Numeric
 107           Base (bin, oct, dec, hex)</a></span></dt>
 108 <dt><span class="section"><a href="boost_convert/converters_detail/strtol_converter/formatting_support/field_width__fill_character_and_adjustment.html">Field
 109           Width, Fill Character and Adjustment</a></span></dt>
 110 <dt><span class="section"><a href="boost_convert/converters_detail/strtol_converter/formatting_support/leading_whitespace_characters.html">Leading
 111           Whitespace Characters</a></span></dt>
 112 <dt><span class="section"><a href="boost_convert/converters_detail/strtol_converter/formatting_support/floating_point_precision.html">Floating-Point
 113           Precision</a></span></dt>
 114 </dl></dd>
 115 <dt><span class="section"><a href="boost_convert/converters_detail/strtol_converter/supported_string_types.html">Supported
 116         String Types</a></span></dt>
 117 <dd><dl>
 118 <dt><span class="section"><a href="boost_convert/converters_detail/strtol_converter/supported_string_types.html#boost_convert.converters_detail.strtol_converter.supported_string_types.wide_string">Wide
 119           String</a></span></dt>
 120 <dt><span class="section"><a href="boost_convert/converters_detail/strtol_converter/supported_string_types/custom_string_types.html">Custom
 121           String Types</a></span></dt>
 122 </dl></dd>
 123 </dl></dd>
 124 </dl></dd>
 125 <dt><span class="section"><a href="boost_convert/design_notes.html">Design
 126     Notes</a></span></dt>
 127 <dd><dl>
 128 <dt><span class="section"><a href="boost_convert/design_notes.html#boost_convert.design_notes.requirements">Requirements</a></span></dt>
 129 <dt><span class="section"><a href="boost_convert/design_notes/converter_signature.html">Converter
 130       Signature</a></span></dt>
 131 <dt><span class="section"><a href="boost_convert/design_notes/user_interface_signature.html">User
 132       Interface Signature</a></span></dt>
 133 </dl></dd>
 134 <dt><span class="section"><a href="boost_convert/supporting_tools.html">Supporting Tools</a></span></dt>
 135 <dd><dl>
 136 <dt><span class="section"><a href="boost_convert/supporting_tools.html#boost_convert.supporting_tools.boost__cnv__range">boost::cnv::range</a></span></dt>
 137 <dt><span class="section"><a href="boost_convert/supporting_tools/boost__cnv__is_range.html">boost::cnv::is_range</a></span></dt>
 138 <dt><span class="section"><a href="boost_convert/supporting_tools/boost_declare_has_member.html">BOOST_DECLARE_HAS_MEMBER</a></span></dt>
 139 <dt><span class="section"><a href="boost_convert/supporting_tools/boost_declare_is_callable.html">BOOST_DECLARE_IS_CALLABLE</a></span></dt>
 140 <dt><span class="section"><a href="boost_convert/supporting_tools/boost__cnv__is_cnv.html">boost::cnv::is_cnv</a></span></dt>
 141 </dl></dd>
 142 <dt><span class="section"><a href="boost_convert/supported_compilers.html">Supported Compilers</a></span></dt>
 143 <dt><span class="section"><a href="boost_convert/acknowledgements.html">Acknowledgements</a></span></dt>
 144 <dt><span class="section"><a href="boost_convert_c___reference.html">Boost.Convert C++ Reference</a></span></dt>
 145 <dd><dl>
 146 <dt><span class="section"><a href="boost_convert_c___reference.html#header.boost.convert_hpp">Header &lt;boost/convert.hpp&gt;</a></span></dt>
 147 <dd><dl></dl></dd>
 148 <dt><span class="section"><a href="header/boost/convert/base_hpp.html">Header &lt;boost/convert/base.hpp&gt;</a></span></dt>
 149 <dd><dl></dl></dd>
 150 <dt><span class="section"><a href="header/boost/convert/lexical_cast_hpp.html">Header &lt;boost/convert/lexical_cast.hpp&gt;</a></span></dt>
 151 <dd><dl></dl></dd>
 152 <dt><span class="section"><a href="header/boost/convert/parameters_hpp.html">Header &lt;boost/convert/parameters.hpp&gt;</a></span></dt>
 153 <dt><span class="section"><a href="header/boost/convert/printf_hpp.html">Header &lt;boost/convert/printf.hpp&gt;</a></span></dt>
 154 <dd><dl></dl></dd>
 155 <dt><span class="section"><a href="header/boost/convert/spirit_hpp.html">Header &lt;boost/convert/spirit.hpp&gt;</a></span></dt>
 156 <dd><dl></dl></dd>
 157 <dt><span class="section"><a href="header/boost/convert/stream_hpp.html">Header &lt;boost/convert/stream.hpp&gt;</a></span></dt>
 158 <dd><dl></dl></dd>
 159 <dt><span class="section"><a href="header/boost/convert/strtol_hpp.html">Header &lt;boost/convert/strtol.hpp&gt;</a></span></dt>
 160 <dd><dl></dl></dd>
 161 <dt><span class="section"><a href="header/boost/make_default_hpp.html">Header &lt;boost/make_default.hpp&gt;</a></span></dt>
 162 <dd><dl></dl></dd>
 163 </dl></dd>
 164 <dt><span class="section"><a href="index/s18.html">Index</a></span></dt>
 165 </dl>
 166 </div>
 167 <div class="section">
 168 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 169 <a name="boost_convert.rationale"></a><a class="link" href="index.html#boost_convert.rationale" title="Rationale">Rationale</a>
 170 </h2></div></div></div>
 171 <p>
 172       I was using textual configuration files extensively and was also processing
 173       and preparing considerable amounts of data in XML. Consequently, I had a need
 174       for an <span class="emphasis"><em>extendible</em></span> library that would provide a <span class="emphasis"><em>uniform</em></span>
 175       interface to convert various data between their internal binary representations
 176       and external (predominantly textual) representations.
 177     </p>
 178 <p>
 179       The <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code> library (with its orthogonal
 180       and extendible design) looked very promising compared to others (see <a href="http://www.gotw.ca/publications/mill19.htm" target="_top">The String Formatters of Manor
 181       Farm</a> by H. Sutter for the discussion of alternatives). Unfortunately,
 182     </p>
 183 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 184 <li class="listitem">
 185           many deployed user types simply did not meet <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code>
 186           requirements (namely, <a href="http://en.cppreference.com/w/cpp/named_req/DefaultConstructible" target="_top"><span class="emphasis"><em>Default
 187           Constructibility</em></span></a>);
 188         </li>
 189 <li class="listitem">
 190           failure to convert a user-provided configuration parameter was not that
 191           rare or exceptional to justify the hassle and the overhead of exception
 192           processing; consequently, additional flexibility (<span class="emphasis"><em>if</em></span>,
 193           <span class="emphasis"><em>when</em></span> and <span class="emphasis"><em>how</em></span>) in handling conversion
 194           failures was needed;
 195         </li>
 196 <li class="listitem">
 197           additional conversion-related functionality (such as formatting and locale
 198           support) were needed.
 199         </li>
 200 </ul></div>
 201 <p>
 202       The original hope was to see <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code>
 203       extended to be applicable to a wider range of deployment scenarios. However,
 204       after discussions with Kevlin Henney (the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code>
 205       author) and in the Boost Developers forum it was collectively decided that
 206       the desired extensions were not compatible with the original design and the
 207       idea of what <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code> embodied and, therefore, a new
 208       component with richer interface and functionality was needed. That decision
 209       resulted in the development of <span class="emphasis"><em>Boost.Convert</em></span> described
 210       in this document.
 211     </p>
 212 </div>
 213 </div>
 214 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 215 <td align="left"><p><small>Last revised: December 10, 2019 at 00:23:44 GMT</small></p></td>
 216 <td align="right"><div class="copyright-footer"></div></td>
 217 </tr></table>
 218 <hr>
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