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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="the_boost_algorithm_library.CXX14.mismatch"></a><a class="link" href="mismatch.html" title="mismatch">mismatch
  28       </a>
  29 </h3></div></div></div>
  30 <p>
  31         The header file 'mismatch.hpp' contains two variants of a the stl algorithm
  32         <code class="computeroutput"><span class="identifier">mismatch</span></code>. The algorithm finds
  33         the first point in two sequences where they do not match.
  34       </p>
  35 <p>
  36         Before (the proposed) C++14 the algorithm <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">mismatch</span></code>
  37         took three iterators and an optional comparison predicate. The first two
  38         iterators <code class="computeroutput"><span class="special">[</span><span class="identifier">first1</span><span class="special">,</span> <span class="identifier">last1</span><span class="special">)</span></code> defined a sequence, and the second one
  39         <code class="computeroutput"><span class="identifier">first2</span></code> defined the start
  40         of the second sequence. The second sequence was assumed to be the same length
  41         as the first.
  42       </p>
  43 <p>
  44         In C++14, two new variants were introduced, taking four iterators and an
  45         optional comparison predicate. The four iterators define two sequences <code class="computeroutput"><span class="special">[</span><span class="identifier">first1</span><span class="special">,</span> <span class="identifier">last1</span><span class="special">)</span></code> and <code class="computeroutput"><span class="special">[</span><span class="identifier">first2</span><span class="special">,</span> <span class="identifier">last2</span><span class="special">)</span></code>
  46         explicitly, rather than defining the second one implicitly. This leads to
  47         correct answers in more cases (and avoid undefined behavior in others).
  48       </p>
  49 <p>
  50         Consider the two sequences:
  51 </p>
  52 <pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">seq1</span> <span class="special">=</span> <span class="special">{</span> <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>
  53 <span class="keyword">auto</span> <span class="identifier">seq2</span> <span class="special">=</span> <span class="special">{</span> <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>
  54
  55 <span class="identifier">std</span><span class="special">::</span><span class="identifier">mismatch</span> <span class="special">(</span> <span class="identifier">seq1</span><span class="special">.</span><span class="identifier">begin</span> <span class="special">(),</span> <span class="identifier">seq1</span><span class="special">.</span><span class="identifier">end</span> <span class="special">(),</span> <span class="identifier">seq2</span><span class="special">.</span><span class="identifier">begin</span> <span class="special">());</span> <span class="comment">// &lt;3, 3&gt;</span>
  56 <span class="identifier">std</span><span class="special">::</span><span class="identifier">mismatch</span> <span class="special">(</span> <span class="identifier">seq2</span><span class="special">.</span><span class="identifier">begin</span> <span class="special">(),</span> <span class="identifier">seq2</span><span class="special">.</span><span class="identifier">end</span> <span class="special">(),</span> <span class="identifier">seq1</span><span class="special">.</span><span class="identifier">begin</span> <span class="special">());</span> <span class="comment">// Undefined behavior</span>
  57 <span class="identifier">std</span><span class="special">::</span><span class="identifier">mismatch</span> <span class="special">(</span> <span class="identifier">seq1</span><span class="special">.</span><span class="identifier">begin</span> <span class="special">(),</span> <span class="identifier">seq1</span><span class="special">.</span><span class="identifier">end</span> <span class="special">(),</span> <span class="identifier">seq2</span><span class="special">.</span><span class="identifier">begin</span> <span class="special">(),</span> <span class="identifier">seq2</span><span class="special">.</span><span class="identifier">end</span> <span class="special">());</span> <span class="comment">// &lt;3, 3&gt;</span>
  58 </pre>
  59 <p>
  60       </p>
  61 <p>
  62         The first N entries in <code class="computeroutput"><span class="identifier">seq2</span></code>
  63         are the same as the entries in <code class="computeroutput"><span class="identifier">seq1</span></code>
  64         - but that's not all that's in <code class="computeroutput"><span class="identifier">seq2</span></code>.
  65         In the second case, the algorithm will read past the end of <code class="computeroutput"><span class="identifier">seq1</span></code>, resulting in undefined behavior (large
  66         earthquake, incorrect results, pregnant cat, etc).
  67       </p>
  68 <p>
  69         However, if the two sequences are specified completely, it's clear that where
  70         the mismatch occurs.
  71       </p>
  72 <h5>
  73 <a name="the_boost_algorithm_library.CXX14.mismatch.h0"></a>
  74         <span class="phrase"><a name="the_boost_algorithm_library.CXX14.mismatch.interface"></a></span><a class="link" href="mismatch.html#the_boost_algorithm_library.CXX14.mismatch.interface">interface</a>
  75       </h5>
  76 <p>
  77         The function <code class="computeroutput"><span class="identifier">mismatch</span></code> returns
  78         a pair of iterators which denote the first mismatching elements in each sequence.
  79         If the sequences match completely, <code class="computeroutput"><span class="identifier">mismatch</span></code>
  80         returns their end iterators. One version uses <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">equal_to</span></code>
  81         to do the comparison; the other lets the caller pass predicate to do the
  82         comparisons.
  83       </p>
  84 <p>
  85 </p>
  86 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">InputIterator1</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">InputIterator2</span><span class="special">&gt;</span>
  87 <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">InputIterator1</span><span class="special">,</span> <span class="identifier">InputIterator2</span><span class="special">&gt;</span>
  88 <span class="identifier">mismatch</span> <span class="special">(</span> <span class="identifier">InputIterator1</span> <span class="identifier">first1</span><span class="special">,</span> <span class="identifier">InputIterator1</span> <span class="identifier">last1</span><span class="special">,</span>
  89            <span class="identifier">InputIterator2</span> <span class="identifier">first2</span><span class="special">,</span> <span class="identifier">InputIterator2</span> <span class="identifier">last2</span> <span class="special">);</span>
  90
  91 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">InputIterator1</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">InputIterator2</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">BinaryPredicate</span><span class="special">&gt;</span>
  92 <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">InputIterator1</span><span class="special">,</span> <span class="identifier">InputIterator2</span><span class="special">&gt;</span>
  93 <span class="identifier">mismatch</span> <span class="special">(</span> <span class="identifier">InputIterator1</span> <span class="identifier">first1</span><span class="special">,</span> <span class="identifier">InputIterator1</span> <span class="identifier">last1</span><span class="special">,</span>
  94            <span class="identifier">InputIterator2</span> <span class="identifier">first2</span><span class="special">,</span> <span class="identifier">InputIterator2</span> <span class="identifier">last2</span><span class="special">,</span> <span class="identifier">BinaryPredicate</span> <span class="identifier">pred</span> <span class="special">);</span>
  95 </pre>
  96 <p>
  97       </p>
  98 <h5>
  99 <a name="the_boost_algorithm_library.CXX14.mismatch.h1"></a>
 100         <span class="phrase"><a name="the_boost_algorithm_library.CXX14.mismatch.examples"></a></span><a class="link" href="mismatch.html#the_boost_algorithm_library.CXX14.mismatch.examples">Examples</a>
 101       </h5>
 102 <p>
 103         Given the container <code class="computeroutput"><span class="identifier">c1</span></code> containing
 104         <code class="computeroutput"><span class="special">{</span> <span class="number">0</span><span class="special">,</span> <span class="number">1</span><span class="special">,</span>
 105         <span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">,</span> <span class="number">14</span><span class="special">,</span> <span class="number">15</span> <span class="special">}</span></code>,
 106         and <code class="computeroutput"><span class="identifier">c2</span></code> containing <code class="computeroutput"><span class="special">{</span> <span class="number">1</span><span class="special">,</span>
 107         <span class="number">2</span><span class="special">,</span> <span class="number">3</span> <span class="special">}</span></code>, then
 108 </p>
 109 <pre class="programlisting"><span class="identifier">mismatch</span> <span class="special">(</span> <span class="identifier">c1</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>     <span class="identifier">c1</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>       <span class="identifier">c2</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">c2</span><span class="special">.</span><span class="identifier">end</span><span class="special">())</span> <span class="special">--&gt;</span> <span class="special">&lt;</span><span class="identifier">c1</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">c2</span><span class="special">.</span><span class="identifier">begin</span><span class="special">()&gt;</span> <span class="comment">// first elements do not match</span>
 110 <span class="identifier">mismatch</span> <span class="special">(</span> <span class="identifier">c1</span><span class="special">.</span><span class="identifier">begin</span><span class="special">()</span> <span class="special">+</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">c1</span><span class="special">.</span><span class="identifier">begin</span><span class="special">()</span> <span class="special">+</span> <span class="number">4</span><span class="special">,</span> <span class="identifier">c2</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">c2</span><span class="special">.</span><span class="identifier">end</span><span class="special">())</span> <span class="special">--&gt;</span> <span class="special">&lt;</span><span class="identifier">c1</span><span class="special">.</span><span class="identifier">begin</span><span class="special">()</span> <span class="special">+</span> <span class="number">4</span><span class="special">,</span> <span class="identifier">c2</span><span class="special">.</span><span class="identifier">end</span> <span class="special">()&gt;</span> <span class="comment">// all elements of `c2` match</span>
 111 <span class="identifier">mismatch</span> <span class="special">(</span> <span class="identifier">c1</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>       <span class="identifier">c1</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>       <span class="identifier">c2</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>   <span class="identifier">c2</span><span class="special">.</span><span class="identifier">end</span><span class="special">())</span> <span class="special">--&gt;</span> <span class="special">&lt;</span><span class="identifier">c1</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">c2</span><span class="special">.</span><span class="identifier">end</span><span class="special">()&gt;</span> <span class="comment">// empty sequences don't match at the end.</span>
 112 </pre>
 113 <p>
 114       </p>
 115 <h5>
 116 <a name="the_boost_algorithm_library.CXX14.mismatch.h2"></a>
 117         <span class="phrase"><a name="the_boost_algorithm_library.CXX14.mismatch.iterator_requirements"></a></span><a class="link" href="mismatch.html#the_boost_algorithm_library.CXX14.mismatch.iterator_requirements">Iterator
 118         Requirements</a>
 119       </h5>
 120 <p>
 121         <code class="computeroutput"><span class="identifier">mismatch</span></code> works on all iterators
 122         except output iterators.
 123       </p>
 124 <h5>
 125 <a name="the_boost_algorithm_library.CXX14.mismatch.h3"></a>
 126         <span class="phrase"><a name="the_boost_algorithm_library.CXX14.mismatch.complexity"></a></span><a class="link" href="mismatch.html#the_boost_algorithm_library.CXX14.mismatch.complexity">Complexity</a>
 127       </h5>
 128 <p>
 129         Both of the variants of <code class="computeroutput"><span class="identifier">mismatch</span></code>
 130         run in <span class="emphasis"><em>O(N)</em></span> (linear) time; that is, they compare against
 131         each element in the list once. If the sequence is found to be not equal at
 132         any point, the routine will terminate immediately, without examining the
 133         rest of the elements.
 134       </p>
 135 <h5>
 136 <a name="the_boost_algorithm_library.CXX14.mismatch.h4"></a>
 137         <span class="phrase"><a name="the_boost_algorithm_library.CXX14.mismatch.exception_safety"></a></span><a class="link" href="mismatch.html#the_boost_algorithm_library.CXX14.mismatch.exception_safety">Exception
 138         Safety</a>
 139       </h5>
 140 <p>
 141         Both of the variants of <code class="computeroutput"><span class="identifier">mismatch</span></code>
 142         take their parameters by value and do not depend upon any global state. Therefore,
 143         all the routines in this file provide the strong exception guarantee.
 144       </p>
 145 <h5>
 146 <a name="the_boost_algorithm_library.CXX14.mismatch.h5"></a>
 147         <span class="phrase"><a name="the_boost_algorithm_library.CXX14.mismatch.notes"></a></span><a class="link" href="mismatch.html#the_boost_algorithm_library.CXX14.mismatch.notes">Notes</a>
 148       </h5>
 149 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 150 <li class="listitem">
 151             If the sequences are equal (or both are empty), then mismatch returns
 152             the end iterators of both sequences.
 153           </li>
 154 <li class="listitem">
 155             The four iterator version of the routine <code class="computeroutput"><span class="identifier">mismatch</span></code>
 156             is part of the C++14 standard. When C++14 standard library implementations
 157             become available, the implementation from the standard library should
 158             be used.
 159           </li>
 160 </ul></div>
 161 </div>
 162 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 163 <td align="left"></td>
 164 <td align="right"><div class="copyright-footer">Copyright &#169; 2010-2012 Marshall Clow<p>
 165         Distributed under the Boost Software License, Version 1.0. (See accompanying
 166         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>)
 167       </p>
 168 </div></td>
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