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  26 <div class="titlepage"><div><div><h5 class="title">
  27 <a name="range.reference.adaptors.reference.map_keys"></a><a class="link" href="map_keys.html" title="map_keys">map_keys</a>
  28 </h5></div></div></div>
  29 <div class="toc"><dl class="toc"><dt><span class="section"><a href="map_keys.html#range.reference.adaptors.reference.map_keys.map_keys_example">map_keys
  30             example</a></span></dt></dl></div>
  31 <div class="informaltable"><table class="table">
  32 <colgroup>
  33 <col>
  34 <col>
  35 </colgroup>
  36 <thead><tr>
  37 <th>
  38                     <p>
  39                       Syntax
  40                     </p>
  41                   </th>
  42 <th>
  43                     <p>
  44                       Code
  45                     </p>
  46                   </th>
  47 </tr></thead>
  48 <tbody>
  49 <tr>
  50 <td>
  51                     <p>
  52                       Pipe
  53                     </p>
  54                   </td>
  55 <td>
  56                     <p>
  57                       <code class="computeroutput"><span class="identifier">rng</span> <span class="special">|</span>
  58                       <span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">::</span><span class="identifier">map_keys</span></code>
  59                     </p>
  60                   </td>
  61 </tr>
  62 <tr>
  63 <td>
  64                     <p>
  65                       Function
  66                     </p>
  67                   </td>
  68 <td>
  69                     <p>
  70                       <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">::</span><span class="identifier">keys</span><span class="special">(</span><span class="identifier">rng</span><span class="special">)</span></code>
  71                     </p>
  72                   </td>
  73 </tr>
  74 </tbody>
  75 </table></div>
  76 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  77 <li class="listitem">
  78                 <span class="bold"><strong>Precondition:</strong></span> The <code class="computeroutput"><span class="identifier">value_type</span></code> of the range is an instantiation
  79                 of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></code>.
  80               </li>
  81 <li class="listitem">
  82                 <span class="bold"><strong>Postcondition:</strong></span> For all elements
  83                 <code class="computeroutput"><span class="identifier">x</span></code> in the returned
  84                 range, <code class="computeroutput"><span class="identifier">x</span></code> is the result
  85                 of <code class="computeroutput"><span class="identifier">y</span><span class="special">.</span><span class="identifier">first</span></code> where <code class="computeroutput"><span class="identifier">y</span></code>
  86                 is the corresponding element in the original range.
  87               </li>
  88 <li class="listitem">
  89                 <span class="bold"><strong>Range Category:</strong></span> <a class="link" href="../../../concepts/single_pass_range.html" title="Single Pass Range">Single
  90                 Pass Range</a>
  91               </li>
  92 <li class="listitem">
  93                 <span class="bold"><strong>Range Return Type:</strong></span> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">select_first_range</span><span class="special">&lt;</span><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">rng</span><span class="special">)&gt;</span></code>
  94               </li>
  95 <li class="listitem">
  96                 <span class="bold"><strong>Returned Range Category:</strong></span> The range
  97                 category of <code class="computeroutput"><span class="identifier">rng</span></code>.
  98               </li>
  99 </ul></div>
 100 <div class="section">
 101 <div class="titlepage"><div><div><h6 class="title">
 102 <a name="range.reference.adaptors.reference.map_keys.map_keys_example"></a><a class="link" href="map_keys.html#range.reference.adaptors.reference.map_keys.map_keys_example" title="map_keys example">map_keys
 103             example</a>
 104 </h6></div></div></div>
 105 <p>
 106 </p>
 107 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">range</span><span class="special">/</span><span class="identifier">adaptor</span><span class="special">/</span><span class="identifier">map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 108 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">range</span><span class="special">/</span><span class="identifier">algorithm</span><span class="special">/</span><span class="identifier">copy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 109 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">assign</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 110 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iterator</span><span class="special">&gt;</span>
 111 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
 112 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">map</span><span class="special">&gt;</span>
 113 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">vector</span><span class="special">&gt;</span>
 114
 115 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">argc</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">argv</span><span class="special">[])</span>
 116 <span class="special">{</span>
 117     <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">assign</span><span class="special">;</span>
 118     <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">;</span>
 119
 120     <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">input</span><span class="special">;</span>
 121     <span class="keyword">for</span> <span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;</span> <span class="number">10</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span>
 122         <span class="identifier">input</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="identifier">i</span> <span class="special">*</span> <span class="number">10</span><span class="special">));</span>
 123
 124     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">copy</span><span class="special">(</span>
 125         <span class="identifier">input</span> <span class="special">|</span> <span class="identifier">map_keys</span><span class="special">,</span>
 126         <span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream_iterator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">,</span> <span class="string">","</span><span class="special">));</span>
 127
 128     <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 129 <span class="special">}</span>
 130 </pre>
 131 <p>
 132             </p>
 133 </div>
 134 <p>
 135             This would produce the output:
 136 </p>
 137 <pre class="programlisting"><span class="number">0</span><span class="special">,</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">,</span><span class="number">3</span><span class="special">,</span><span class="number">4</span><span class="special">,</span><span class="number">5</span><span class="special">,</span><span class="number">6</span><span class="special">,</span><span class="number">7</span><span class="special">,</span><span class="number">8</span><span class="special">,</span><span class="number">9</span><span class="special">,</span>
 138 </pre>
 139 <p>
 140           </p>
 141 </div>
 142 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 143 <td align="left"></td>
 144 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2010 Thorsten Ottosen,
 145       Neil Groves<p>
 146         Distributed under the Boost Software License, Version 1.0. (See accompanying
 147         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>)
 148       </p>
 149 </div></td>
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