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<title>Boost.Convert with Standard Algorithms</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="the_boost_convert_library.convert_algorithms"></a><a class="link" href="convert_algorithms.html" title="Boost.Convert with Standard Algorithms">Boost.Convert
with Standard Algorithms</a>
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<p>
The following code demonstrates a failed attempt to convert a few strings with
<span class="emphasis"><em>boost::lexical_cast</em></span>:
</p>
<pre class="programlisting"><span class="identifier">array</span><span class="special">&lt;</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="number">5</span><span class="special">&gt;</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>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">integers</span><span class="special">;</span>
<span class="keyword">try</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span>
<span class="identifier">strings</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>
<span class="identifier">strings</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>
<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>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;,</span> <span class="identifier">_1</span><span class="special">));</span>
<span class="identifier">BOOST_ASSERT</span><span class="special">(!</span><span class="string">"We should not be here"</span><span class="special">);</span>
<span class="special">}</span>
<span class="keyword">catch</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span class="special">&amp;)</span>
<span class="special">{</span>
<span class="comment">// No strings converted.</span>
<span class="special">}</span>
</pre>
<p>
The first take by <span class="emphasis"><em>boost::convert</em></span> is more successful but
still not quite satisfactory (your mileage may vary) as conversion is interrupded
when <span class="emphasis"><em>boost::convert</em></span> comes across an invalid input:
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special">&lt;</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="number">5</span><span class="special">&gt;</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>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">integers</span><span class="special">;</span>
<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>
<span class="keyword">try</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span>
<span class="identifier">strings</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>
<span class="identifier">strings</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>
<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>
<span class="identifier">convert</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;::</span><span class="identifier">from</span><span class="special">&lt;</span><span class="identifier">string</span><span class="special">&gt;(</span><span class="identifier">cnv</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">BOOST_ASSERT</span><span class="special">(!</span><span class="string">"We should not be here"</span><span class="special">);</span>
<span class="special">}</span>
<span class="keyword">catch</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span class="special">&amp;)</span>
<span class="special">{</span>
<span class="comment">// Only the first four strings converted. Failed to convert the last one.</span>
<span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">integers</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="number">15</span><span class="special">);</span>
<span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">integers</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="number">16</span><span class="special">);</span>
<span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">integers</span><span class="special">[</span><span class="number">2</span><span class="special">]</span> <span class="special">==</span> <span class="number">17</span><span class="special">);</span>
<span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">integers</span><span class="special">[</span><span class="number">3</span><span class="special">]</span> <span class="special">==</span> <span class="number">18</span><span class="special">);</span>
<span class="special">}</span>
</pre>
<p>
And at last a fully working version (with a conversion-failure fallback value
provided):
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special">&lt;</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="number">5</span><span class="special">&gt;</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>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">integers</span><span class="special">;</span>
<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>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span>
<span class="identifier">strings</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>
<span class="identifier">strings</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>
<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>
<span class="identifier">convert</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;::</span><span class="identifier">from</span><span class="special">&lt;</span><span class="identifier">string</span><span class="special">&gt;(</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="number">1</span><span class="special">));</span>
<span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">integers</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="number">15</span><span class="special">);</span>
<span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">integers</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="number">16</span><span class="special">);</span>
<span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">integers</span><span class="special">[</span><span class="number">2</span><span class="special">]</span> <span class="special">==</span> <span class="number">17</span><span class="special">);</span>
<span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">integers</span><span class="special">[</span><span class="number">3</span><span class="special">]</span> <span class="special">==</span> <span class="number">18</span><span class="special">);</span>
<span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">integers</span><span class="special">[</span><span class="number">4</span><span class="special">]</span> <span class="special">==</span> <span class="special">-</span><span class="number">1</span><span class="special">);</span> <span class="comment">// Failed conversion</span>
</pre>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2009-2014 Vladimir Batov<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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