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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="range.reference.utilities.sub_range"></a><a class="link" href="sub_range.html" title="Class sub_range">Class <code class="computeroutput"><span class="identifier">sub_range</span></code></a>
  28 </h4></div></div></div>
  29 <p>
  30           The <code class="computeroutput"><span class="identifier">sub_range</span></code> class inherits
  31           all its functionality from the <a class="link" href="iterator_range.html" title="Class iterator_range"><code class="computeroutput"><span class="identifier">iterator_range</span></code></a> class. The <code class="computeroutput"><span class="identifier">sub_range</span></code> class is often easier to use
  32           because one must specify the <a class="link" href="../../concepts/forward_range.html" title="Forward Range">Forward
  33           Range</a> template argument instead of an iterator. Moreover, the <code class="computeroutput"><span class="identifier">sub_range</span></code> class can propagate constness
  34           since it knows what a corresponding <code class="computeroutput"><span class="identifier">const_iterator</span></code>
  35           is.
  36         </p>
  37 <h5>
  38 <a name="range.reference.utilities.sub_range.h0"></a>
  39           <span class="phrase"><a name="range.reference.utilities.sub_range.synopsis"></a></span><a class="link" href="sub_range.html#range.reference.utilities.sub_range.synopsis">Synopsis</a>
  40         </h5>
  41 <p>
  42 </p>
  43 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
  44 <span class="special">{</span>
  45     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">ForwardRange</span> <span class="special">&gt;</span>
  46     <span class="keyword">class</span> <span class="identifier">sub_range</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">iterator_range</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">range_iterator</span><span class="special">&lt;</span><span class="identifier">ForwardRange</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="special">&gt;</span>
  47     <span class="special">{</span>
  48     <span class="keyword">public</span><span class="special">:</span>
  49         <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">range_value</span><span class="special">&lt;</span><span class="identifier">ForwardRange</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">value_type</span><span class="special">;</span>
  50         <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">range_iterator</span><span class="special">&lt;</span><span class="identifier">ForwardRange</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">iterator</span><span class="special">;</span>
  51         <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">range_iterator</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="identifier">ForwardRange</span><span class="special">&gt;::</span><span class="identifier">type</span>  <span class="identifier">const_iterator</span><span class="special">;</span>
  52         <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">range_difference</span><span class="special">&lt;</span><span class="identifier">ForwardRange</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">difference_type</span><span class="special">;</span>
  53         <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">range_size</span><span class="special">&lt;</span><span class="identifier">ForwardRange</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">size_type</span><span class="special">;</span>
  54         <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">range_reference</span><span class="special">&lt;</span><span class="identifier">ForwardRange</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">reference</span><span class="special">;</span>
  55         <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">range_reference</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="identifier">ForwardRange</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">const_reference</span><span class="special">;</span>
  56
  57     <span class="keyword">public</span><span class="special">:</span> <span class="comment">// construction, assignment</span>
  58         <span class="identifier">sub_range</span><span class="special">();</span>
  59
  60         <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">ForwardTraversalIterator</span> <span class="special">&gt;</span>
  61         <span class="identifier">sub_range</span><span class="special">(</span> <span class="identifier">ForwardTraversalIterator</span> <span class="identifier">Begin</span><span class="special">,</span> <span class="identifier">ForwardTraversalIterator</span> <span class="identifier">End</span> <span class="special">);</span>
  62
  63         <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">ForwardRange2</span> <span class="special">&gt;</span>
  64         <span class="identifier">sub_range</span><span class="special">(</span> <span class="identifier">ForwardRange2</span><span class="special">&amp;</span> <span class="identifier">r</span> <span class="special">);</span>
  65
  66         <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">ForwardRange2</span> <span class="special">&gt;</span>
  67         <span class="identifier">sub_range</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">Range2</span><span class="special">&amp;</span> <span class="identifier">r</span> <span class="special">);</span>
  68
  69         <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">ForwardRange2</span> <span class="special">&gt;</span>
  70         <span class="identifier">sub_range</span><span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">ForwardRange2</span><span class="special">&amp;</span> <span class="identifier">r</span> <span class="special">);</span>
  71
  72         <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">ForwardRange2</span> <span class="special">&gt;</span>
  73         <span class="identifier">sub_range</span><span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="keyword">const</span> <span class="identifier">ForwardRange2</span><span class="special">&amp;</span> <span class="identifier">r</span> <span class="special">);</span>
  74
  75         <span class="comment">// iterator accessors</span>
  76         <span class="identifier">const_iterator</span> <span class="identifier">begin</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>
  77         <span class="identifier">iterator</span> <span class="identifier">begin</span><span class="special">();</span>
  78         <span class="identifier">const_iterator</span> <span class="identifier">end</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>
  79         <span class="identifier">iterator</span> <span class="identifier">end</span><span class="special">();</span>
  80
  81         <span class="identifier">reference</span> <span class="identifier">front</span><span class="special">();</span>
  82         <span class="identifier">const_reference</span> <span class="identifier">front</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>
  83
  84         <span class="identifier">sub_range</span><span class="special">&amp;</span> <span class="identifier">advance_begin</span><span class="special">(</span><span class="identifier">difference_type</span> <span class="identifier">n</span><span class="special">);</span>
  85         <span class="identifier">sub_range</span><span class="special">&amp;</span> <span class="identifier">advance_end</span><span class="special">(</span><span class="identifier">difference_type</span> <span class="identifier">n</span><span class="special">);</span>
  86
  87         <span class="comment">// If traversal &gt;= bidirectional:</span>
  88         <span class="identifier">reference</span> <span class="identifier">back</span><span class="special">();</span>
  89         <span class="identifier">const_reference</span> <span class="identifier">back</span><span class="special">();</span>
  90
  91         <span class="comment">// If traversal &gt;= random-access:</span>
  92         <span class="identifier">reference</span> <span class="keyword">operator</span><span class="special">[](</span><span class="identifier">difference_type</span> <span class="identifier">n</span><span class="special">);</span>
  93         <span class="identifier">const_reference</span> <span class="keyword">operator</span><span class="special">[](</span><span class="identifier">difference_type</span> <span class="identifier">n</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  94
  95     <span class="keyword">public</span><span class="special">:</span>
  96         <span class="comment">// rest of interface inherited from iterator_range</span>
  97     <span class="special">};</span>
  98
  99 <span class="special">}</span> <span class="comment">// namespace 'boost'</span>
 100 </pre>
 101 <p>
 102         </p>
 103 <p>
 104           The class should be trivial to use as seen below. Imagine that we have
 105           an algorithm that searches for a sub-string in a string. The result is
 106           an iterator_range, that delimits the match. We need to store the result
 107           from this algorithm. Here is an example of how we can do it with and without
 108           <code class="computeroutput"><span class="identifier">sub_range</span></code>
 109         </p>
 110 <p>
 111 </p>
 112 <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">str</span><span class="special">(</span><span class="string">"hello"</span><span class="special">);</span>
 113 <span class="identifier">iterator_range</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">::</span><span class="identifier">iterator</span><span class="special">&gt;</span> <span class="identifier">ir</span> <span class="special">=</span> <span class="identifier">find_first</span><span class="special">(</span> <span class="identifier">str</span><span class="special">,</span> <span class="string">"ll"</span> <span class="special">);</span>
 114 <span class="identifier">sub_range</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span>               <span class="identifier">sub</span> <span class="special">=</span> <span class="identifier">find_first</span><span class="special">(</span> <span class="identifier">str</span><span class="special">,</span> <span class="string">"ll"</span> <span class="special">);</span>
 115 </pre>
 116 <p>
 117         </p>
 118 </div>
 119 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 120 <td align="left"></td>
 121 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2010 Thorsten Ottosen,
 122       Neil Groves<p>
 123         Distributed under the Boost Software License, Version 1.0. (See accompanying
 124         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>)
 125       </p>
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