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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_convert.introduction"></a><a class="link" href="introduction.html" title="Introduction">Introduction</a>
</h2></div></div></div>
<p>
<span class="emphasis"><em>Boost.Convert</em></span> builds on the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code>
experience and takes those type conversion/transformation-related ideas further
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
to be applicable to a wider range of conversion-related deployment scenarios,
</li>
<li class="listitem">
to provide a more flexible, configurable and extendible type-conversion
framework,
</li>
<li class="listitem">
to provide generic consistent behavior,
</li>
<li class="listitem">
to <span class="emphasis"><em>unify and to uniformly deploy</em></span> various conversion
facilities <span class="emphasis"><em>through one consistent interface</em></span>.
</li>
</ul></div>
<p>
<span class="emphasis"><em>Boost.Convert</em></span> provides new and familiar conversion/transformation-related
functionality such as:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
means to deploy types that do not meet the <a href="http://en.cppreference.com/w/cpp/named_req/DefaultConstructible" target="_top"><span class="emphasis"><em>Default
Constructibility</em></span></a> requirement;
</li>
<li class="listitem">
four types of the conversion-failure <span class="emphasis"><em>detection</em></span>:
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
as part of the same process flow -- basic and generic;
</li>
<li class="listitem">
as a branched process flow -- exception-based and function-based;
</li>
</ul></div>
</li>
<li class="listitem">
the choice of immediate or delayed exception-throwing and non-throwing
conversion-failure <span class="emphasis"><em>processing</em></span>;
</li>
<li class="listitem">
flexibility of conversion-failure <span class="emphasis"><em>processing</em></span> via:
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
an exception thrown;
</li>
<li class="listitem">
the fallback value returned;
</li>
<li class="listitem">
the fallback function called;
</li>
</ul></div>
</li>
<li class="listitem">
support for standard algorithms.
</li>
</ul></div>
<p>
<span class="emphasis"><em>Boost.Convert</em></span> consists of two components:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">convert</span><span class="special">()</span></code>
interface;
</li>
<li class="listitem">
an extendible collection of pluggable converters.
</li>
</ul></div>
<p>
The <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">convert</span><span class="special">()</span></code>
interface
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
advertises, provides and ensures certain <span class="emphasis"><em>consistent behavior</em></span>;
</li>
<li class="listitem">
unifies and provides <span class="emphasis"><em>one consistent interface</em></span> to various
conversion facilities.
</li>
</ul></div>
<p>
The collection of pluggable converters is independent of the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">convert</span><span class="special">()</span></code> API facade and is designed to be <span class="emphasis"><em>extendible</em></span>
and extended over time. Currently the following converters are provided:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code>-based,
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">printf</span><span class="special">/</span><span class="identifier">scanf</span></code>-based,
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">strtol</span></code>-inspired,
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">stringstream</span></code>-based,
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span></code>-based.
</li>
</ul></div>
<p>
The converters provide new and familiar functionality and demonstrate how existing
and independent conversion facilities might be incorporated in to the <span class="emphasis"><em>Boost.Convert</em></span>
framework. For example, the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">stream</span></code>-based
converter draws on the standard <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">streams</span></code>
functionality and provides:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
string-to-type and type-to-string conversions;
</li>
<li class="listitem">
formatting support (<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">ios</span></code>-based
precision, base, upper/lower-case, scientific, etc.);
</li>
<li class="listitem">
support for different <code class="computeroutput"><span class="identifier">locale</span></code>s;
</li>
<li class="listitem">
<code class="computeroutput"><span class="keyword">char</span></code> and <code class="computeroutput"><span class="keyword">wchar_t</span></code>
support.
</li>
</ul></div>
<p>
The following code demonstrates conversion of an array of integers from their
textual <span class="emphasis"><em>hexadecimal</em></span> representation. It assigns -1 to those
which fail to convert:
</p>
<p>
</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">3</span><span class="special">&gt;</span> <span class="identifier">strs</span> <span class="special">=</span> <span class="special">{{</span> <span class="string">" 5"</span><span class="special">,</span> <span class="string">"0XF"</span><span class="special">,</span> <span class="string">"not an 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">ints</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">cstream</span> <span class="identifier">cnv</span><span class="special">;</span>
<span class="comment">// Configure converter to read hexadecimal, skip (leading) white spaces.</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">std</span><span class="special">::</span><span class="identifier">skipws</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">strs</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">strs</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">ints</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">apply</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cref</span><span class="special">(</span><span class="identifier">cnv</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_TEST</span><span class="special">(</span><span class="identifier">ints</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">3</span><span class="special">);</span> <span class="comment">// Number of values processed.</span>
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">ints</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="number">5</span><span class="special">);</span> <span class="comment">// " 5"</span>
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">ints</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="number">15</span><span class="special">);</span> <span class="comment">// "0XF"</span>
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">ints</span><span class="special">[</span><span class="number">2</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">// "not an int"</span>
</pre>
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