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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">// <3, 3></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">// <3, 3></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"><</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="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">InputIterator1</span><span class="special">,</span> <span class="identifier">InputIterator2</span><span class="special">></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"><</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">></span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">InputIterator1</span><span class="special">,</span> <span class="identifier">InputIterator2</span><span class="special">></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">--></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">c2</span><span class="special">.</span><span class="identifier">begin</span><span class="special">()></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">--></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">end</span> <span class="special">()></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">--></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="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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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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