1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Flexibility and Adaptability to Change</title> 5<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Chapter 1. Boost.Convert 2.0"> 8<link rel="up" href="../getting_started.html" title="Getting Started"> 9<link rel="prev" href="../getting_started.html" title="Getting Started"> 10<link rel="next" href="basic_conversion_failure_detection.html" title="Basic Conversion-Failure Detection"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="../getting_started.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../getting_started.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="basic_conversion_failure_detection.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="boost_convert.getting_started.flexibility_and_adaptability_to_change"></a><a class="link" href="flexibility_and_adaptability_to_change.html" title="Flexibility and Adaptability to Change">Flexibility 28 and Adaptability to Change</a> 29</h3></div></div></div> 30<div class="blockquote"><blockquote class="blockquote"><p> 31 <span class="bold"><strong><span class="emphasis"><em>"There is nothing more constant than 32 change" Heraclitus</em></span></strong></span> 33 </p></blockquote></div> 34<p> 35 Sooner or later (during initial development or in the maintenance phase) 36 flexibility and adaptability become important. Deployment of <span class="emphasis"><em>Boost.Convert</em></span> 37 helps to adjust and to change in line with the evolution of the requirements. 38 For example, if the program flow would benefit from the non-throwing behavior, 39 then: 40 </p> 41<p> 42</p> 43<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">;</span> 44<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span><span class="special">;</span> 45<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">convert</span><span class="special">;</span> 46</pre> 47<p> 48 </p> 49<p> 50</p> 51<pre class="programlisting"><span class="comment">// Does not throw. Returns fallback value (-1) when failed.</span> 52<span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"uhm"</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">lexical_cast</span><span class="special">()).</span><span class="identifier">value_or</span><span class="special">(-</span><span class="number">1</span><span class="special">);</span> 53 54<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="special">-</span><span class="number">1</span><span class="special">);</span> <span class="comment">// Conversion failed. 'i' assigned the fallback value.</span> 55</pre> 56<p> 57 </p> 58<p> 59 Or, if the component is identified as too slow, then the performance could 60 be improved with minimal effort by replacing the converter: 61 </p> 62<p> 63</p> 64<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">convert</span><span class="special">/</span><span class="identifier">strtol</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 65<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">convert</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 66</pre> 67<p> 68 </p> 69<p> 70</p> 71<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">lexical_cast</span> <span class="identifier">cnv1</span><span class="special">;</span> 72<span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">strtol</span> <span class="identifier">cnv2</span><span class="special">;</span> 73<span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">spirit</span> <span class="identifier">cnv3</span><span class="special">;</span> 74 75<span class="keyword">int</span> <span class="identifier">i1</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"123"</span><span class="special">,</span> <span class="identifier">cnv1</span><span class="special">).</span><span class="identifier">value</span><span class="special">();</span> 76<span class="keyword">int</span> <span class="identifier">i2</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"123"</span><span class="special">,</span> <span class="identifier">cnv2</span><span class="special">).</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// Two times faster than lexical_cast.</span> 77<span class="keyword">int</span> <span class="identifier">i3</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"123"</span><span class="special">,</span> <span class="identifier">cnv3</span><span class="special">).</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// Four times faster than lexical_cast.</span> 78</pre> 79<p> 80 </p> 81<p> 82 If, instead, the requirements change to support more input formats or to 83 require a certain output format, then, again, that could be accommodated 84 with: 85 </p> 86<p> 87</p> 88<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">convert</span><span class="special">/</span><span class="identifier">stream</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 89</pre> 90<p> 91 </p> 92<p> 93</p> 94<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">cstream</span> <span class="identifier">cnv</span><span class="special">;</span> 95 96<span class="keyword">try</span> 97<span class="special">{</span> 98 <span class="keyword">int</span> <span class="identifier">i1</span> <span class="special">=</span> <span class="identifier">lexical_cast</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">" 123"</span><span class="special">);</span> <span class="comment">// Does not work.</span> 99 <span class="identifier">BOOST_TEST</span><span class="special">(!</span><span class="string">"Never reached"</span><span class="special">);</span> 100<span class="special">}</span> 101<span class="keyword">catch</span> <span class="special">(...)</span> <span class="special">{}</span> 102 103<span class="keyword">int</span> <span class="identifier">i2</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">" 123"</span><span class="special">,</span> <span class="identifier">cnv</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">skipws</span><span class="special">)).</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// Success</span> 104<span class="identifier">string</span> <span class="identifier">s1</span> <span class="special">=</span> <span class="identifier">lexical_cast</span><span class="special"><</span><span class="identifier">string</span><span class="special">>(</span><span class="number">12.34567</span><span class="special">);</span> 105<span class="identifier">string</span> <span class="identifier">s2</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special"><</span><span class="identifier">string</span><span class="special">>(</span><span class="number">12.34567</span><span class="special">,</span> <span class="identifier">cnv</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">fixed</span><span class="special">)(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">setprecision</span><span class="special">(</span><span class="number">3</span><span class="special">))).</span><span class="identifier">value</span><span class="special">();</span> 106<span class="identifier">string</span> <span class="identifier">s3</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special"><</span><span class="identifier">string</span><span class="special">>(</span><span class="number">12.34567</span><span class="special">,</span> <span class="identifier">cnv</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">scientific</span><span class="special">)(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">setprecision</span><span class="special">(</span><span class="number">3</span><span class="special">))).</span><span class="identifier">value</span><span class="special">();</span> 107<span class="identifier">string</span> <span class="identifier">expected</span> <span class="special">=</span> <span class="identifier">local</span><span class="special">::</span><span class="identifier">is_msc</span> <span class="special">?</span> <span class="string">"1.235e+001"</span> <span class="special">:</span> <span class="string">"1.235e+01"</span><span class="special">;</span> 108 109<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">i2</span> <span class="special">==</span> <span class="number">123</span><span class="special">);</span> <span class="comment">// boost::cnv::cstream. Successful conversion of " 123".</span> 110<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">s1</span> <span class="special">==</span> <span class="string">"12.34567"</span><span class="special">);</span> <span class="comment">// boost::lexical_cast. Precision is not configurable.</span> 111<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">s2</span> <span class="special">==</span> <span class="string">"12.346"</span><span class="special">);</span> <span class="comment">// boost::cnv::cstream. Precision was set to 3. Fixed.</span> 112<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">s3</span> <span class="special">==</span> <span class="identifier">expected</span><span class="special">);</span> <span class="comment">// boost::cnv::cstream. Precision was set to 3. Scientific.</span> 113</pre> 114<p> 115 </p> 116</div> 117<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 118<td align="left"></td> 119<td align="right"><div class="copyright-footer">Copyright © 2009-2016 Vladimir Batov<p> 120 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>. 121 </p> 122</div></td> 123</tr></table> 124<hr> 125<div class="spirit-nav"> 126<a accesskey="p" href="../getting_started.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../getting_started.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="basic_conversion_failure_detection.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 127</div> 128</body> 129</html> 130
