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<h2><a name="binary_search" id="binary_search">binary_search</a></h2>
<div class="level2">

<p>
Syntax:
</p>
<pre class="c code c++" style="font-family:monospace;">    <span class="co2">#include &lt;algorithm&gt;</span>
    bool binary_search<span class="br0">&#40;</span> forward_iterator start<span class="sy0">,</span> forward_iterator end<span class="sy0">,</span> <span class="kw4">const</span> TYPE<span class="sy0">&amp;</span> val <span class="br0">&#41;</span><span class="sy0">;</span>
    bool binary_search<span class="br0">&#40;</span> forward_iterator start<span class="sy0">,</span> forward_iterator end<span class="sy0">,</span> <span class="kw4">const</span> TYPE<span class="sy0">&amp;</span> val<span class="sy0">,</span> Comp f <span class="br0">&#41;</span><span class="sy0">;</span></pre>
<p>
The binary_search() function searches from <code>start</code> to <code>end</code> for <code>val</code>. The elements
between <code>start</code> and <code>end</code> that are searched should be in ascending order as defined
by the &lt; operator. Note that a binary search will not work unless the elements
being searched are in order.
</p>

<p>
Only the &lt; operator should be defined for the values.  Two values <code>a</code> and <code>b</code> are
considered equal when <code>!(a&lt;b) &amp;&amp; !(b&lt;a)</code> is true.
</p>

<p>
If <code>val</code> is found, binary_search() returns true, otherwise false.
If the function <code>f</code> is specified, then it is used to compare elements instead of operator&lt; .
</p>

<p>
binary_search() runs in <a href="../../complexity.html" class="wikilink1" title="complexity">logarithmic time</a>.
</p>

<p>
For example, the following code uses binary_search() to determine if the
integers 0-9 are in an array of integers (nums[] should be sorted in ascending order):
</p>
<pre class="c code c++" style="font-family:monospace;">   <span class="kw4">int</span> nums<span class="br0">&#91;</span><span class="br0">&#93;</span> <span class="sy0">=</span> <span class="br0">&#123;</span> <span class="sy0">-</span>242<span class="sy0">,</span> <span class="sy0">-</span>1<span class="sy0">,</span> 0<span class="sy0">,</span> 5<span class="sy0">,</span> 8<span class="sy0">,</span> 9<span class="sy0">,</span> 11 <span class="br0">&#125;</span><span class="sy0">;</span>
   <span class="kw4">int</span> start <span class="sy0">=</span> <span class="nu0">0</span><span class="sy0">;</span>
   <span class="kw4">int</span> end <span class="sy0">=</span> <span class="nu0">7</span><span class="sy0">;</span>
&nbsp;
   <span class="kw1">for</span><span class="br0">&#40;</span> <span class="kw4">int</span> i <span class="sy0">=</span> <span class="nu0">0</span><span class="sy0">;</span> i <span class="sy0">&lt;</span> <span class="nu0">10</span><span class="sy0">;</span> i<span class="sy0">++</span> <span class="br0">&#41;</span> <span class="br0">&#123;</span>
     <span class="kw1">if</span><span class="br0">&#40;</span> binary_search<span class="br0">&#40;</span> nums<span class="sy0">+</span>start<span class="sy0">,</span> nums<span class="sy0">+</span>end<span class="sy0">,</span> i <span class="br0">&#41;</span> <span class="br0">&#41;</span> <span class="br0">&#123;</span>
       <a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0">&lt;&lt;</span> <span class="st0">&quot;nums[] contains &quot;</span> <span class="sy0">&lt;&lt;</span> i <span class="sy0">&lt;&lt;</span> endl<span class="sy0">;</span>
     <span class="br0">&#125;</span> <span class="kw1">else</span> <span class="br0">&#123;</span>
       <a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0">&lt;&lt;</span> <span class="st0">&quot;nums[] DOES NOT contain &quot;</span> <span class="sy0">&lt;&lt;</span> i <span class="sy0">&lt;&lt;</span> endl<span class="sy0">;</span>
     <span class="br0">&#125;</span>
   <span class="br0">&#125;</span></pre>
<p>
When run, this code displays the following output:
</p>
<pre class="code">
   nums[] contains 0
   nums[] DOES NOT contain 1
   nums[] DOES NOT contain 2
   nums[] DOES NOT contain 3
   nums[] DOES NOT contain 4
   nums[] contains 5
   nums[] DOES NOT contain 6
   nums[] DOES NOT contain 7
   nums[] contains 8
   nums[] contains 9</pre>
<p>
Related Topics: <a href="../../stl/algorithm/equal_range.html" class="wikilink1" title="stl:algorithm:equal_range">equal_range</a>, <a href="../../stl/algorithm/lower_bound.html" class="wikilink1" title="stl:algorithm:lower_bound">lower_bound</a>, <a href="../../stl/algorithm/partial_sort.html" class="wikilink1" title="stl:algorithm:partial_sort">partial_sort</a>, <a href="../../stl/algorithm/partial_sort_copy.html" class="wikilink1" title="stl:algorithm:partial_sort_copy">partial_sort_copy</a>, <a href="../../stl/algorithm/sort.html" class="wikilink1" title="stl:algorithm:sort">sort</a>, <a href="../../stl/algorithm/stable_sort.html" class="wikilink1" title="stl:algorithm:stable_sort">stable_sort</a>, <a href="../../stl/algorithm/upper_bound.html" class="wikilink1" title="stl:algorithm:upper_bound">upper_bound</a>
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