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| <div><h2 class="title"> |
| <a name="boost_lexical_cast"></a>Chapter 17. Boost.Lexical_Cast 1.0</h2></div> |
| <div><p class="copyright">Copyright © 2000-2005 Kevlin Henney</p></div> |
| <div><p class="copyright">Copyright © 2006-2010 Alexander Nasonov</p></div> |
| <div><p class="copyright">Copyright © 2011-2014 Antony |
| Polukhin</p></div> |
| <div><div class="legalnotice"> |
| <a name="boost_lexical_cast.legal"></a><p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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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| <div class="toc"> |
| <p><b>Table of Contents</b></p> |
| <dl class="toc"> |
| <dt><span class="section"><a href="boost_lexical_cast.html#boost_lexical_cast.motivation">Motivation</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/examples.html">Examples</a></span></dt> |
| <dd><dl> |
| <dt><span class="section"><a href="boost_lexical_cast/examples.html#boost_lexical_cast.examples.strings_to_numbers_conversion">Strings |
| to numbers conversion</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/examples.html#boost_lexical_cast.examples.numbers_to_strings_conversion">Numbers |
| to strings conversion</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/examples.html#boost_lexical_cast.examples.converting_to_string_without_dynamic_memory_allocation">Converting |
| to string without dynamic memory allocation</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/examples.html#boost_lexical_cast.examples.converting_part_of_the_string">Converting |
| part of the string</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/examples.html#boost_lexical_cast.examples.generic_programming__boost_fusion_">Generic |
| programming (Boost.Fusion)</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/examples.html#boost_lexical_cast.examples.generic_programming__boost_variant_">Generic |
| programming (Boost.Variant)</a></span></dt> |
| </dl></dd> |
| <dt><span class="section"><a href="boost_lexical_cast/synopsis.html">Synopsis</a></span></dt> |
| <dd><dl> |
| <dt><span class="section"><a href="boost_lexical_cast/synopsis.html#boost_lexical_cast.synopsis.lexical_cast">lexical_cast</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/synopsis.html#boost_lexical_cast.synopsis.bad_lexical_cast">bad_lexical_cast</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/synopsis.html#boost_lexical_cast.synopsis.try_lexical_convert">try_lexical_convert</a></span></dt> |
| </dl></dd> |
| <dt><span class="section"><a href="boost_lexical_cast/frequently_asked_questions.html">Frequently |
| Asked Questions</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/changes.html">Changes</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/performance.html">Performance</a></span></dt> |
| <dd><dl> |
| <dt><span class="section"><a href="boost_lexical_cast/performance.html#boost_lexical_cast.performance.tests_description">Tests |
| description</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/performance.html#boost_lexical_cast.performance.clang_version_3_0__tags_release_30_final_">Clang |
| version 3.0 (tags/RELEASE_30/final)</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/performance.html#boost_lexical_cast.performance.gnu_c___version_4_6_3">GNU |
| C++ version 4.6.3</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/performance.html#boost_lexical_cast.performance.gnu_c___version_4_5_3">GNU |
| C++ version 4.5.3</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/performance.html#boost_lexical_cast.performance.gnu_c___version_4_4_7">GNU |
| C++ version 4.4.7</a></span></dt> |
| <dt><span class="section"><a href="boost_lexical_cast/performance.html#boost_lexical_cast.performance.microsoft_visual_c___version_11_0">Microsoft |
| Visual C++ version 11.0</a></span></dt> |
| </dl></dd> |
| </dl> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="boost_lexical_cast.motivation"></a><a class="link" href="boost_lexical_cast.html#boost_lexical_cast.motivation" title="Motivation">Motivation</a> |
| </h2></div></div></div> |
| <p> |
| Sometimes a value must be converted to a literal text form, such as an <code class="computeroutput"><span class="keyword">int</span></code> represented as a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>, |
| or vice-versa, when a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> is interpreted as an <code class="computeroutput"><span class="keyword">int</span></code>. Such examples are common when converting |
| between data types internal to a program and representation external to a program, |
| such as windows and configuration files. |
| </p> |
| <p> |
| The standard C and C++ libraries offer a number of facilities for performing |
| such conversions. However, they vary with their ease of use, extensibility, |
| and safety. |
| </p> |
| <p> |
| For instance, there are a number of limitations with the family of standard |
| C functions typified by <code class="computeroutput"><span class="identifier">atoi</span></code>: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| Conversion is supported in one direction only: from text to internal data |
| type. Converting the other way using the C library requires either the |
| inconvenience and compromised safety of the <code class="computeroutput"><span class="identifier">sprintf</span></code> |
| function, or the loss of portability associated with non-standard functions |
| such as <code class="computeroutput"><span class="identifier">itoa</span></code>. |
| </li> |
| <li class="listitem"> |
| The range of types supported is only a subset of the built-in numeric types, |
| namely <code class="computeroutput"><span class="keyword">int</span></code>, <code class="computeroutput"><span class="keyword">long</span></code>, and <code class="computeroutput"><span class="keyword">double</span></code>. |
| </li> |
| <li class="listitem"> |
| The range of types cannot be extended in a uniform manner. For instance, |
| conversion from string representation to complex or rational. |
| </li> |
| </ul></div> |
| <p> |
| The standard C functions typified by <code class="computeroutput"><span class="identifier">strtol</span></code> |
| have the same basic limitations, but offer finer control over the conversion |
| process. However, for the common case such control is often either not required |
| or not used. The <code class="computeroutput"><span class="identifier">scanf</span></code> family |
| of functions offer even greater control, but also lack safety and ease of use. |
| </p> |
| <p> |
| The standard C++ library offers <code class="computeroutput"><span class="identifier">stringstream</span></code> |
| for the kind of in-core formatting being discussed. It offers a great deal |
| of control over the formatting and conversion of I/O to and from arbitrary |
| types through text. However, for simple conversions direct use of <code class="computeroutput"><span class="identifier">stringstream</span></code> can be either clumsy (with the |
| introduction of extra local variables and the loss of infix-expression convenience) |
| or obscure (where <code class="computeroutput"><span class="identifier">stringstream</span></code> |
| objects are created as temporary objects in an expression). Facets provide |
| a comprehensive concept and facility for controlling textual representation, |
| but their perceived complexity and high entry level requires an extreme degree |
| of involvement for simple conversions, and excludes all but a few programmers. |
| </p> |
| <p> |
| The <code class="computeroutput"><span class="identifier">lexical_cast</span></code> function template |
| offers a convenient and consistent form for supporting common conversions to |
| and from arbitrary types when they are represented as text. The simplification |
| it offers is in expression-level convenience for such conversions. For more |
| involved conversions, such as where precision or formatting need tighter control |
| than is offered by the default behavior of <code class="computeroutput"><span class="identifier">lexical_cast</span></code>, |
| the conventional <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">stringstream</span></code> approach is recommended. Where |
| the conversions are numeric to numeric, <a href="../../libs/numeric/conversion/doc/html/boost_numericconversion/improved_numeric_cast__.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">numeric_cast</span></code></a> |
| may offer more reasonable behavior than <code class="computeroutput"><span class="identifier">lexical_cast</span></code>. |
| </p> |
| <p> |
| For a good discussion of the options and issues involved in string-based formatting, |
| including comparison of <code class="computeroutput"><span class="identifier">stringstream</span></code>, |
| <code class="computeroutput"><span class="identifier">lexical_cast</span></code>, and others, see |
| Herb Sutter's article, <a href="http://www.gotw.ca/publications/mill19.htm" target="_top">The |
| String Formatters of Manor Farm</a>. Also, take a look at the <a class="link" href="boost_lexical_cast/performance.html" title="Performance">Performance</a> |
| section. |
| </p> |
| </div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"><p><small>Last revised: April 07, 2015 at 22:50:38 GMT</small></p></td> |
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