259 lines
39 KiB
HTML
259 lines
39 KiB
HTML
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
|
|
<title>Boost.Convert with Standard Algorithms</title>
|
|
<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
|
|
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
|
|
<link rel="home" href="../index.html" title="Chapter 1. Boost.Convert 2.0">
|
|
<link rel="up" href="../index.html" title="Chapter 1. Boost.Convert 2.0">
|
|
<link rel="prev" href="integration_of_user_types.html" title="Integration of User-Defined Types">
|
|
<link rel="next" href="performance.html" title="Performance">
|
|
</head>
|
|
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
|
|
<table cellpadding="2" width="100%"><tr>
|
|
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
|
|
<td align="center"><a href="../../../../../index.html">Home</a></td>
|
|
<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td>
|
|
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
|
|
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
|
|
<td align="center"><a href="../../../../../more/index.htm">More</a></td>
|
|
</tr></table>
|
|
<hr>
|
|
<div class="spirit-nav">
|
|
<a accesskey="p" href="integration_of_user_types.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="performance.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
|
|
</div>
|
|
<div class="section">
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
<a name="boost_convert.algorithms"></a><a class="link" href="algorithms.html" title="Boost.Convert with Standard Algorithms">Boost.Convert with Standard Algorithms</a>
|
|
</h2></div></div></div>
|
|
<p>
|
|
The following code demonstrates a failed attempt (and one of the reasons <span class="emphasis"><em>Boost.Convert</em></span>
|
|
has been developed) to convert a few <code class="computeroutput"><span class="identifier">string</span></code>s
|
|
to <code class="computeroutput"><span class="keyword">int</span></code>s with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code>:
|
|
</p>
|
|
<p>
|
|
</p>
|
|
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="number">3</span><span class="special">></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"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">ints</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">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">bind</span><span class="special">(</span><span class="identifier">boost</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="identifier">string</span><span class="special">>,</span> <span class="identifier">_1</span><span class="special">));</span>
|
|
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="number">0</span> <span class="special">&&</span> <span class="string">"Never reached!"</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">&)</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">0</span><span class="special">);</span> <span class="comment">// No strings converted.</span>
|
|
<span class="special">}</span>
|
|
</pre>
|
|
<p>
|
|
</p>
|
|
<p>
|
|
If the exception-throwing behavior is the desired behavior, then <span class="emphasis"><em>Boost.Convert</em></span>
|
|
supports that. In addition, it also supports a non-throwing process-flow:
|
|
</p>
|
|
<p>
|
|
</p>
|
|
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="number">3</span><span class="special">></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"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">ints</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"><</span><span class="keyword">int</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>
|
|
|
|
<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="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="special">-</span><span class="number">1</span><span class="special">);</span> <span class="comment">// Failed conversion does not throw.</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="special">-</span><span class="number">1</span><span class="special">);</span> <span class="comment">// Failed conversion does not throw.</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">// Failed conversion does not throw.</span>
|
|
</pre>
|
|
<p>
|
|
</p>
|
|
<p>
|
|
Deploying <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">cstream</span></code>
|
|
with better formatting capabilities yields better results with exception-throwing
|
|
and non-throwing process-flows still supported:
|
|
</p>
|
|
<p>
|
|
</p>
|
|
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="number">3</span><span class="special">></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"><</span><span class="keyword">int</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">cstream</span> <span class="identifier">cnv</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">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"><</span><span class="keyword">int</span><span class="special">>(</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">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">BOOST_TEST</span><span class="special">(</span><span class="number">0</span> <span class="special">&&</span> <span class="string">"Never reached!"</span><span class="special">);</span>
|
|
<span class="special">}</span>
|
|
<span class="keyword">catch</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">bad_optional_access</span> <span class="keyword">const</span><span class="special">&)</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">2</span><span class="special">);</span> <span class="comment">// Only the first two strings converted.</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="comment">// "not an int" causes the exception thrown.</span>
|
|
<span class="special">}</span>
|
|
</pre>
|
|
<p>
|
|
</p>
|
|
<p>
|
|
</p>
|
|
<pre class="programlisting"><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"><</span><span class="keyword">int</span><span class="special">>(</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">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">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="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="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="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">// Failed conversion</span>
|
|
</pre>
|
|
<p>
|
|
</p>
|
|
<div class="important"><table border="0" summary="Important">
|
|
<tr>
|
|
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td>
|
|
<th align="left">Important</th>
|
|
</tr>
|
|
<tr><td align="left" valign="top">
|
|
<p>
|
|
One notable difference in the deployment of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">cstream</span></code> with algorithms is the use of
|
|
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cref</span></code> (or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cref</span></code>
|
|
in C++11).
|
|
</p>
|
|
<p>
|
|
It needs to be remembered that with standard algorithms the deployed converter
|
|
needs to be <a href="http://en.cppreference.com/w/cpp/concept/TriviallyCopyable" target="_top">copyable</a>
|
|
or <a href="http://en.cppreference.com/w/cpp/concept/MoveAssignable" target="_top">movable
|
|
(C++11)</a> and is, in fact, copied or moved by the respective algorithm
|
|
before being used. Given that <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cstringstream</span></code>
|
|
is not copyable, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">cstream</span></code>
|
|
is not copyable either. That limitation is routinely worked-around using
|
|
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">ref</span></code> or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cref</span></code>.
|
|
</p>
|
|
</td></tr>
|
|
</table></div>
|
|
<p>
|
|
And now an example of algorithm-based integer-to-string formatted conversion
|
|
with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">hex</span></code>, <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">uppercase</span></code>
|
|
and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">showbase</span></code> formatting applied:
|
|
</p>
|
|
<p>
|
|
</p>
|
|
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="number">3</span><span class="special">></span> <span class="identifier">ints</span> <span class="special">=</span> <span class="special">{{</span> <span class="number">15</span><span class="special">,</span> <span class="number">16</span><span class="special">,</span> <span class="number">17</span> <span class="special">}};</span>
|
|
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">strs</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="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">uppercase</span><span class="special">)(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">showbase</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">ints</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">ints</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">strs</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"><</span><span class="identifier">string</span><span class="special">>(</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">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs</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="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="string">"0XF"</span><span class="special">);</span> <span class="comment">// 15</span>
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="string">"0X10"</span><span class="special">);</span> <span class="comment">// 16</span>
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs</span><span class="special">[</span><span class="number">2</span><span class="special">]</span> <span class="special">==</span> <span class="string">"0X11"</span><span class="special">);</span> <span class="comment">// 17</span>
|
|
</pre>
|
|
<p>
|
|
</p>
|
|
<h4>
|
|
<a name="boost_convert.algorithms.h0"></a>
|
|
<span class="phrase"><a name="boost_convert.algorithms.forced__emphasis_typein__emphasis__vs__deduced"></a></span><a class="link" href="algorithms.html#boost_convert.algorithms.forced__emphasis_typein__emphasis__vs__deduced">Forced
|
|
<span class="emphasis"><em>TypeIn</em></span> vs. Deduced</a>
|
|
</h4>
|
|
<p>
|
|
So far it was sufficient to explicitly specify only one type to <code class="computeroutput"><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"><</span><span class="identifier">TypeOut</span><span class="special">></span></code>
|
|
-- the target <span class="emphasis"><em>TypeOut</em></span> type. The source <span class="emphasis"><em>TypeIn</em></span>
|
|
type has been provided implicitly through the algorithm and often it all just
|
|
works (as the examples above demonstrate). However, at times more control is
|
|
needed regarding the <span class="emphasis"><em>TypeIn</em></span> type and <code class="computeroutput"><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">()</span></code> provides
|
|
such control via explicit specification of <span class="emphasis"><em>TypeIn</em></span> --
|
|
<code class="computeroutput"><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"><</span><span class="identifier">TypeOut</span><span class="special">,</span> <span class="identifier">TypeIn</span><span class="special">></span></code>.
|
|
</p>
|
|
<p>
|
|
The following example demonstrates an interesting issue related to the <span class="emphasis"><em><code class="computeroutput"><span class="identifier">change</span></code></em></span> class introduced in <a class="link" href="integration_of_user_types.html" title="Integration of User-Defined Types">Integration of User-Defined
|
|
Types</a>. The class is essentially a glorified <span class="emphasis"><em><code class="computeroutput"><span class="keyword">enum</span></code></em></span>, a user-friendly convenience
|
|
wrapper around the actual <span class="emphasis"><em><code class="computeroutput"><span class="keyword">enum</span>
|
|
<span class="identifier">value_type</span> <span class="special">{</span>
|
|
<span class="identifier">no</span><span class="special">,</span> <span class="identifier">up</span><span class="special">,</span> <span class="identifier">dn</span>
|
|
<span class="special">}</span></code></em></span>. In the example an array
|
|
of <span class="emphasis"><em><code class="computeroutput"><span class="identifier">change</span></code></em></span>
|
|
values (<code class="computeroutput"><span class="identifier">chgs1</span></code>) is sensibly
|
|
converted to readable "no", "up" and "dn" strings
|
|
(<code class="computeroutput"><span class="identifier">strs1</span></code>) when an array of <span class="emphasis"><em><code class="computeroutput"><span class="identifier">change</span><span class="special">::</span><span class="identifier">value_type</span></code></em></span> values (<code class="computeroutput"><span class="identifier">chgs2</span></code>) converts to obscure "0",
|
|
"1" and "2" (<code class="computeroutput"><span class="identifier">strs2</span></code>).
|
|
</p>
|
|
<p>
|
|
</p>
|
|
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="identifier">change</span><span class="special">,</span> <span class="number">3</span><span class="special">></span> <span class="identifier">chgs1</span> <span class="special">=</span> <span class="special">{{</span> <span class="identifier">change</span><span class="special">::</span><span class="identifier">no</span><span class="special">,</span> <span class="identifier">change</span><span class="special">::</span><span class="identifier">up</span><span class="special">,</span> <span class="identifier">change</span><span class="special">::</span><span class="identifier">dn</span> <span class="special">}};</span>
|
|
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="identifier">change</span><span class="special">::</span><span class="identifier">value_type</span><span class="special">,</span> <span class="number">3</span><span class="special">></span> <span class="identifier">chgs2</span> <span class="special">=</span> <span class="special">{{</span> <span class="identifier">change</span><span class="special">::</span><span class="identifier">no</span><span class="special">,</span> <span class="identifier">change</span><span class="special">::</span><span class="identifier">up</span><span class="special">,</span> <span class="identifier">change</span><span class="special">::</span><span class="identifier">dn</span> <span class="special">}};</span>
|
|
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">strs1</span><span class="special">;</span>
|
|
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">strs2</span><span class="special">;</span>
|
|
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">strs3</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="identifier">std</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span><span class="identifier">chgs1</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">chgs1</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">strs1</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"><</span><span class="identifier">string</span><span class="special">>(</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="comment">// Deduced TypeIn is 'change'</span>
|
|
|
|
<span class="identifier">std</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span><span class="identifier">chgs2</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">chgs2</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">strs2</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"><</span><span class="identifier">string</span><span class="special">>(</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="comment">// Deduced TypeIn is 'change::value_type'</span>
|
|
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs1</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="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs1</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="string">"no"</span><span class="special">);</span>
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs1</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="string">"up"</span><span class="special">);</span>
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs1</span><span class="special">[</span><span class="number">2</span><span class="special">]</span> <span class="special">==</span> <span class="string">"dn"</span><span class="special">);</span>
|
|
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs2</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="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs2</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="string">"0"</span><span class="special">);</span>
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs2</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="string">"1"</span><span class="special">);</span>
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs2</span><span class="special">[</span><span class="number">2</span><span class="special">]</span> <span class="special">==</span> <span class="string">"2"</span><span class="special">);</span>
|
|
</pre>
|
|
<p>
|
|
</p>
|
|
<p>
|
|
The <code class="computeroutput"><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"><</span><span class="identifier">TypeOut</span><span class="special">,</span> <span class="identifier">TypeIn</span><span class="special">></span></code> with forced (rather than deduced) <span class="emphasis"><em>TypeIn</em></span>
|
|
comes to the rescue and converts the array of <span class="emphasis"><em><code class="computeroutput"><span class="identifier">change</span><span class="special">::</span><span class="identifier">value_type</span></code></em></span>
|
|
values (<code class="computeroutput"><span class="identifier">chgs2</span></code>) to sensible
|
|
"no", "up" and "dn" (<code class="computeroutput"><span class="identifier">strs3</span></code>):
|
|
</p>
|
|
<p>
|
|
</p>
|
|
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span><span class="identifier">chgs2</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">chgs2</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">strs3</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"><</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">change</span><span class="special">>(</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">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs3</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="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs3</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="string">"no"</span><span class="special">);</span>
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs3</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="string">"up"</span><span class="special">);</span>
|
|
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">strs3</span><span class="special">[</span><span class="number">2</span><span class="special">]</span> <span class="special">==</span> <span class="string">"dn"</span><span class="special">);</span>
|
|
</pre>
|
|
<p>
|
|
</p>
|
|
<div class="note"><table border="0" summary="Note">
|
|
<tr>
|
|
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
|
|
<th align="left">Note</th>
|
|
</tr>
|
|
<tr><td align="left" valign="top"><p>
|
|
For demonstration purposes the example above is made as simple as possible
|
|
and, consequently, the described "issue" could probably be addressed
|
|
by other means. Still, do not let my inability to come up with a better (complex
|
|
but short and succulent) example get in the way of appreciating the described
|
|
functionality. I do not expect it to be used often but it is here when you
|
|
need it.
|
|
</p></td></tr>
|
|
</table></div>
|
|
</div>
|
|
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
|
<td align="left"></td>
|
|
<td align="right"><div class="copyright-footer">Copyright © 2009-2016 Vladimir Batov<p>
|
|
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>.
|
|
</p>
|
|
</div></td>
|
|
</tr></table>
|
|
<hr>
|
|
<div class="spirit-nav">
|
|
<a accesskey="p" href="integration_of_user_types.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="performance.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
|
|
</div>
|
|
</body>
|
|
</html>
|