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<div class="titlepage"><div><div><h3 class="title">
<a name="the_boost_algorithm_library.CXX14.mismatch"></a><a class="link" href="mismatch.html" title="mismatch">mismatch
      </a>
</h3></div></div></div>
<p>
        The header file 'mismatch.hpp' contains two variants of a the stl algorithm
        <code class="computeroutput"><span class="identifier">mismatch</span></code>. The algorithm finds
        the first point in two sequences where they do not match.
      </p>
<p>
        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>
        took three iterators and an optional comparison predicate. The first two
        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
        <code class="computeroutput"><span class="identifier">first2</span></code> defined the start
        of the second sequence. The second sequence was assumed to be the same length
        as the first.
      </p>
<p>
        In C++14, two new variants were introduced, taking four iterators and an
        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>
        explicitly, rather than defining the second one implicitly. This leads to
        correct answers in more cases (and avoid undefined behavior in others).
      </p>
<p>
        Consider the two sequences:
</p>
<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>
<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>

<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>
<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>
<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>
</pre>
<p>
      </p>
<p>
        The first N entries in <code class="computeroutput"><span class="identifier">seq2</span></code>
        are the same as the entries in <code class="computeroutput"><span class="identifier">seq1</span></code>
        - but that's not all that's in <code class="computeroutput"><span class="identifier">seq2</span></code>.
        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
        earthquake, incorrect results, pregnant cat, etc).
      </p>
<p>
        However, if the two sequences are specified completely, it's clear that where
        the mismatch occurs.
      </p>
<h5>
<a name="the_boost_algorithm_library.CXX14.mismatch.h0"></a>
        <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>
      </h5>
<p>
        The function <code class="computeroutput"><span class="identifier">mismatch</span></code> returns
        a pair of iterators which denote the first mismatching elements in each sequence.
        If the sequences match completely, <code class="computeroutput"><span class="identifier">mismatch</span></code>
        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>
        to do the comparison; the other lets the caller pass predicate to do the
        comparisons.
      </p>
<p>
</p>
<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>
<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>
<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>
           <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="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>
<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>
<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>
           <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>
</pre>
<p>
      </p>
<h5>
<a name="the_boost_algorithm_library.CXX14.mismatch.h1"></a>
        <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>
      </h5>
<p>
        Given the container <code class="computeroutput"><span class="identifier">c1</span></code> containing
        <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>
        <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>,
        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>
        <span class="number">2</span><span class="special">,</span> <span class="number">3</span> <span class="special">}</span></code>, then
</p>
<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>
<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>
<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>
</pre>
<p>
      </p>
<h5>
<a name="the_boost_algorithm_library.CXX14.mismatch.h2"></a>
        <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
        Requirements</a>
      </h5>
<p>
        <code class="computeroutput"><span class="identifier">mismatch</span></code> works on all iterators
        except output iterators.
      </p>
<h5>
<a name="the_boost_algorithm_library.CXX14.mismatch.h3"></a>
        <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>
      </h5>
<p>
        Both of the variants of <code class="computeroutput"><span class="identifier">mismatch</span></code>
        run in <span class="emphasis"><em>O(N)</em></span> (linear) time; that is, they compare against
        each element in the list once. If the sequence is found to be not equal at
        any point, the routine will terminate immediately, without examining the
        rest of the elements.
      </p>
<h5>
<a name="the_boost_algorithm_library.CXX14.mismatch.h4"></a>
        <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
        Safety</a>
      </h5>
<p>
        Both of the variants of <code class="computeroutput"><span class="identifier">mismatch</span></code>
        take their parameters by value and do not depend upon any global state. Therefore,
        all the routines in this file provide the strong exception guarantee.
      </p>
<h5>
<a name="the_boost_algorithm_library.CXX14.mismatch.h5"></a>
        <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>
      </h5>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            If the sequences are equal (or both are empty), then mismatch returns
            the end iterators of both sequences.
          </li>
<li class="listitem">
            The four iterator version of the routine <code class="computeroutput"><span class="identifier">mismatch</span></code>
            is part of the C++14 standard. When C++14 standard library implementations
            become available, the implementation from the standard library should
            be used.
          </li>
</ul></div>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2010-2012 Marshall Clow<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        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>)
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