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  26 <div class="titlepage"><div><div><h5 class="title">
  27 <a name="sort.single_thread.spreadsort.sort_hpp.string_sort"></a><a class="link" href="string_sort.html" title="String Sort">String
  28           Sort</a>
  29 </h5></div></div></div>
  30 <p>
  31             <code class="literal"><code class="computeroutput"><a class="link" href="../../../../boost/sort/spreadsort/string_s_idm46048202990736.html" title="Function template string_sort">string_sort</a></code></code>
  32             is a hybrid radix-based/comparison-based algorithm that sorts strings
  33             of characters (or arrays of binary data) in ascending order.
  34           </p>
  35 <p>
  36             The simplest version (no functors) sorts strings of items that can cast
  37             to an unsigned data type (such as an unsigned char), have a &amp;lt;
  38             operator, have a size function, and have a data() function that returns
  39             a pointer to an array of characters, such as a std::string. The functor
  40             version can sort any data type that has a strict weak ordering, via templating,
  41             but requires definitions of a get_char (acts like x[offset] on a string
  42             or a byte array), get_length (returns length of the string being sorted),
  43             and a comparison functor. Individual characters returned by get_char
  44             must support the != operator and have an unsigned value that defines
  45             their lexicographical order.
  46           </p>
  47 <p>
  48             This algorithm is not efficient for character types larger than 2 bytes
  49             each, and is optimized for one-byte character strings. For this reason,
  50             <a href="http://en.cppreference.com/w/cpp/algorithm/sort" target="_top">std::sort</a>
  51             will be called instead if the character type is of size &gt; 2.
  52           </p>
  53 <p>
  54             <code class="literal"><code class="computeroutput"><a class="link" href="../../../../boost/sort/spreadsort/string_s_idm46048202990736.html" title="Function template string_sort">string_sort</a></code></code>
  55             has a special optimization for identical substrings. This adds some overhead
  56             on random data, but identical substrings are common in real strings.
  57           </p>
  58 <p>
  59             reverse_string_sort sorts strings in reverse (decending) order, but is
  60             otherwise identical. <code class="literal"><code class="computeroutput"><a class="link" href="../../../../boost/sort/spreadsort/string_s_idm46048202990736.html" title="Function template string_sort">string_sort</a></code></code>
  61             is sufficiently flexible that it should sort any data type that <a href="http://en.cppreference.com/w/cpp/algorithm/sort" target="_top">std::sort</a>
  62             can, assuming the user provides appropriate functors that index into
  63             a key.
  64           </p>
  65 <p>
  66             <a href="../../../../../../doc/graph/windows_string_sort.htm" target="_top">Windows String Sort</a>
  67           </p>
  68 <p>
  69             <a href="../../../../../../doc/graph/osx_string_sort.htm" target="_top">OSX String Sort</a>
  70           </p>
  71 <div class="section">
  72 <div class="titlepage"><div><div><h6 class="title">
  73 <a name="sort.single_thread.spreadsort.sort_hpp.string_sort.stringsort_examples"></a><a class="link" href="string_sort.html#sort.single_thread.spreadsort.sort_hpp.string_sort.stringsort_examples" title="String Sort Examples">String
  74             Sort Examples</a>
  75 </h6></div></div></div>
  76 <p>
  77               See <a href="../../../../../../example/stringfunctorsample.cpp" target="_top">stringfunctorsample.cpp</a>
  78               for an example of how to sort structs using a string key and all functors:
  79             </p>
  80 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">lessthan</span> <span class="special">{</span>
  81   <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&amp;</span><span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&amp;</span><span class="identifier">y</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span>
  82     <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">a</span> <span class="special">&lt;</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">a</span><span class="special">;</span>
  83   <span class="special">}</span>
  84 <span class="special">};</span>
  85 </pre>
  86 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">bracket</span> <span class="special">{</span>
  87   <span class="keyword">inline</span> <span class="keyword">unsigned</span> <span class="keyword">char</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&amp;</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">offset</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span>
  88     <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">a</span><span class="special">[</span><span class="identifier">offset</span><span class="special">];</span>
  89   <span class="special">}</span>
  90 <span class="special">};</span>
  91 </pre>
  92 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">getsize</span> <span class="special">{</span>
  93   <span class="keyword">inline</span> <span class="identifier">size_t</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&amp;</span><span class="identifier">x</span><span class="special">)</span> <span class="keyword">const</span><span class="special">{</span> <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">a</span><span class="special">.</span><span class="identifier">size</span><span class="special">();</span> <span class="special">}</span>
  94 <span class="special">};</span>
  95 </pre>
  96 <p>
  97               and these functors are used thus:
  98             </p>
  99 <pre class="programlisting"><span class="identifier">string_sort</span><span class="special">(</span><span class="identifier">array</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">array</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">bracket</span><span class="special">(),</span> <span class="identifier">getsize</span><span class="special">(),</span> <span class="identifier">lessthan</span><span class="special">());</span>
 100 </pre>
 101 <p>
 102               See <a href="../../../../../../example/generalizedstruct.cpp" target="_top">generalizedstruct.cpp</a>
 103               for a working example of a generalized approach to sort structs by
 104               a sequence of integer, float, and multiple string keys using string_sort:
 105             </p>
 106 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">DATA_TYPE</span> <span class="special">{</span>
 107   <span class="identifier">time_t</span> <span class="identifier">birth</span><span class="special">;</span>
 108   <span class="keyword">float</span> <span class="identifier">net_worth</span><span class="special">;</span>
 109   <span class="identifier">string</span> <span class="identifier">first_name</span><span class="special">;</span>
 110   <span class="identifier">string</span> <span class="identifier">last_name</span><span class="special">;</span>
 111 <span class="special">};</span>
 112
 113 <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">birth_size</span> <span class="special">=</span> <span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">time_t</span><span class="special">);</span>
 114 <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">first_name_offset</span> <span class="special">=</span> <span class="identifier">birth_size</span> <span class="special">+</span> <span class="keyword">sizeof</span><span class="special">(</span><span class="keyword">float</span><span class="special">);</span>
 115 <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">uint64_t</span> <span class="identifier">base_mask</span> <span class="special">=</span> <span class="number">0xff</span><span class="special">;</span>
 116
 117 <span class="keyword">struct</span> <span class="identifier">lessthan</span> <span class="special">{</span>
 118   <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&amp;</span><span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&amp;</span><span class="identifier">y</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span>
 119     <span class="keyword">if</span> <span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">birth</span> <span class="special">!=</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">birth</span><span class="special">)</span> <span class="special">{</span>
 120       <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">birth</span> <span class="special">&lt;</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">birth</span><span class="special">;</span>
 121     <span class="special">}</span>
 122     <span class="keyword">if</span> <span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">net_worth</span> <span class="special">!=</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">net_worth</span><span class="special">)</span> <span class="special">{</span>
 123       <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">net_worth</span> <span class="special">&lt;</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">net_worth</span><span class="special">;</span>
 124     <span class="special">}</span>
 125     <span class="keyword">if</span> <span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">first_name</span> <span class="special">!=</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">first_name</span><span class="special">)</span> <span class="special">{</span>
 126       <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">first_name</span> <span class="special">&lt;</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">first_name</span><span class="special">;</span>
 127     <span class="special">}</span>
 128     <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">last_name</span> <span class="special">&lt;</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">last_name</span><span class="special">;</span>
 129   <span class="special">}</span>
 130 <span class="special">};</span>
 131
 132 <span class="keyword">struct</span> <span class="identifier">bracket</span> <span class="special">{</span>
 133   <span class="keyword">inline</span> <span class="keyword">unsigned</span> <span class="keyword">char</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&amp;</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">offset</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span>
 134     <span class="comment">// Sort date as a signed int, returning the appropriate byte.</span>
 135     <span class="keyword">if</span> <span class="special">(</span><span class="identifier">offset</span> <span class="special">&lt;</span> <span class="identifier">birth_size</span><span class="special">)</span> <span class="special">{</span>
 136       <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">bit_shift</span> <span class="special">=</span> <span class="number">8</span> <span class="special">*</span> <span class="special">(</span><span class="identifier">birth_size</span> <span class="special">-</span> <span class="identifier">offset</span> <span class="special">-</span> <span class="number">1</span><span class="special">);</span>
 137       <span class="keyword">unsigned</span> <span class="keyword">char</span> <span class="identifier">result</span> <span class="special">=</span> <span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">birth</span> <span class="special">&amp;</span> <span class="special">(</span><span class="identifier">base_mask</span> <span class="special">&lt;&lt;</span> <span class="identifier">bit_shift</span><span class="special">))</span> <span class="special">&gt;&gt;</span> <span class="identifier">bit_shift</span><span class="special">;</span>
 138       <span class="comment">// Handling the sign bit.  Unnecessary if the data is always positive.</span>
 139       <span class="keyword">if</span> <span class="special">(</span><span class="identifier">offset</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> <span class="special">{</span>
 140         <span class="keyword">return</span> <span class="identifier">result</span> <span class="special">^</span> <span class="number">128</span><span class="special">;</span>
 141       <span class="special">}</span>
 142
 143       <span class="keyword">return</span> <span class="identifier">result</span><span class="special">;</span>
 144     <span class="special">}</span>
 145
 146     <span class="comment">// Sort a signed float.  This requires reversing the order of negatives</span>
 147     <span class="comment">// because of the way floats are represented in bits.</span>
 148     <span class="keyword">if</span> <span class="special">(</span><span class="identifier">offset</span> <span class="special">&lt;</span> <span class="identifier">first_name_offset</span><span class="special">)</span> <span class="special">{</span>
 149       <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">bit_shift</span> <span class="special">=</span> <span class="number">8</span> <span class="special">*</span> <span class="special">(</span><span class="identifier">first_name_offset</span> <span class="special">-</span> <span class="identifier">offset</span> <span class="special">-</span> <span class="number">1</span><span class="special">);</span>
 150       <span class="keyword">unsigned</span> <span class="identifier">key</span> <span class="special">=</span> <span class="identifier">float_mem_cast</span><span class="special">&lt;</span><span class="keyword">float</span><span class="special">,</span> <span class="keyword">unsigned</span><span class="special">&gt;(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">net_worth</span><span class="special">);</span>
 151       <span class="keyword">unsigned</span> <span class="keyword">char</span> <span class="identifier">result</span> <span class="special">=</span> <span class="special">(</span><span class="identifier">key</span> <span class="special">&amp;</span> <span class="special">(</span><span class="identifier">base_mask</span> <span class="special">&lt;&lt;</span> <span class="identifier">bit_shift</span><span class="special">))</span> <span class="special">&gt;&gt;</span> <span class="identifier">bit_shift</span><span class="special">;</span>
 152       <span class="comment">// Handling the sign.</span>
 153       <span class="keyword">if</span> <span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">net_worth</span> <span class="special">&lt;</span> <span class="number">0</span><span class="special">)</span> <span class="special">{</span>
 154         <span class="keyword">return</span> <span class="number">255</span> <span class="special">-</span> <span class="identifier">result</span><span class="special">;</span>
 155       <span class="special">}</span>
 156       <span class="comment">// Increasing positives so they are higher than negatives.</span>
 157       <span class="keyword">if</span> <span class="special">(</span><span class="identifier">offset</span> <span class="special">==</span> <span class="identifier">birth_size</span><span class="special">)</span> <span class="special">{</span>
 158         <span class="keyword">return</span> <span class="number">128</span> <span class="special">+</span> <span class="identifier">result</span><span class="special">;</span>
 159       <span class="special">}</span>
 160
 161       <span class="keyword">return</span> <span class="identifier">result</span><span class="special">;</span>
 162     <span class="special">}</span>
 163
 164     <span class="comment">// Sort a string that is before the end.  This approach supports embedded</span>
 165     <span class="comment">// nulls.  If embedded nulls are not required, then just delete the "* 2"</span>
 166     <span class="comment">// and the inside of the following if just becomes:</span>
 167     <span class="comment">// return x.first_name[offset - first_name_offset];</span>
 168     <span class="keyword">const</span> <span class="keyword">unsigned</span> <span class="identifier">first_name_end_offset</span> <span class="special">=</span>
 169       <span class="identifier">first_name_offset</span> <span class="special">+</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">first_name</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>
 170     <span class="keyword">if</span> <span class="special">(</span><span class="identifier">offset</span> <span class="special">&lt;</span> <span class="identifier">first_name_end_offset</span><span class="special">)</span> <span class="special">{</span>
 171       <span class="keyword">int</span> <span class="identifier">char_offset</span> <span class="special">=</span> <span class="identifier">offset</span> <span class="special">-</span> <span class="identifier">first_name_offset</span><span class="special">;</span>
 172       <span class="comment">// This signals that the string continues.</span>
 173       <span class="keyword">if</span> <span class="special">(!(</span><span class="identifier">char_offset</span> <span class="special">&amp;</span> <span class="number">1</span><span class="special">))</span> <span class="special">{</span>
 174         <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
 175       <span class="special">}</span>
 176       <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">first_name</span><span class="special">[</span><span class="identifier">char_offset</span> <span class="special">&gt;&gt;</span> <span class="number">1</span><span class="special">];</span>
 177     <span class="special">}</span>
 178
 179     <span class="comment">// This signals that the string has ended, so that shorter strings come</span>
 180     <span class="comment">// before longer ones.</span>
 181     <span class="keyword">if</span> <span class="special">(</span><span class="identifier">offset</span> <span class="special">==</span> <span class="identifier">first_name_end_offset</span><span class="special">)</span> <span class="special">{</span>
 182       <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 183     <span class="special">}</span>
 184
 185     <span class="comment">// The final string needs no special consideration.</span>
 186     <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">last_name</span><span class="special">[</span><span class="identifier">offset</span> <span class="special">-</span> <span class="identifier">first_name_end_offset</span> <span class="special">-</span> <span class="number">1</span><span class="special">];</span>
 187   <span class="special">}</span>
 188 <span class="special">};</span>
 189
 190 <span class="keyword">struct</span> <span class="identifier">getsize</span> <span class="special">{</span>
 191   <span class="keyword">inline</span> <span class="identifier">size_t</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&amp;</span><span class="identifier">x</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span>
 192     <span class="keyword">return</span> <span class="identifier">first_name_offset</span> <span class="special">+</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">first_name</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="number">1</span> <span class="special">+</span>
 193       <span class="identifier">x</span><span class="special">.</span><span class="identifier">last_name</span><span class="special">.</span><span class="identifier">size</span><span class="special">();</span>
 194   <span class="special">}</span>
 195 <span class="special">};</span>
 196 </pre>
 197 <pre class="programlisting"><span class="identifier">string_sort</span><span class="special">(</span><span class="identifier">array</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">array</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">bracket</span><span class="special">(),</span> <span class="identifier">getsize</span><span class="special">(),</span> <span class="identifier">lessthan</span><span class="special">());</span>
 198 </pre>
 199 <p>
 200               Other examples:
 201             </p>
 202 <p>
 203               <a href="../../../../../../example/stringsample.cpp" target="_top">String sort.</a>
 204             </p>
 205 <p>
 206               <a href="../../../../../../example/reversestringsample.cpp" target="_top">Reverse string sort.</a>
 207             </p>
 208 <p>
 209               <a href="../../../../../../example/wstringsample.cpp" target="_top">Wide character string
 210               sort.</a>
 211             </p>
 212 <p>
 213               <a href="../../../../../../example/caseinsensitive.cpp" target="_top">Case insensitive string
 214               sort.</a>
 215             </p>
 216 <p>
 217               <a href="../../../../../../example/charstringsample.cpp" target="_top">Sort structs using
 218               a string key and indexing functors.</a>
 219             </p>
 220 <p>
 221               <a href="../../../../../../example/reversestringfunctorsample.cpp" target="_top">Sort structs
 222               using a string keynd all functors in reverse order.</a>
 223             </p>
 224 </div>
 225 </div>
 226 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 227 <td align="left"></td>
 228 <td align="right"><div class="copyright-footer">Copyright &#169; 2014-2017 Steven
 229       Ross, Francisco Tapia, Orson Peters<p>
 230         Distributed under the <a href="http://boost.org/LICENSE_1_0.txt" target="_top">Boost
 231         Software License, Version 1.0</a>.
 232       </p>
 233 </div></td>
 234 </tr></table>
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