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| <TITLE>binary_search()</TITLE> |
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| <H2>binary_search()</H2> |
| <P><B>Library:</B> <A HREF="2-9.html">Algorithms</A></P> |
| |
| <PRE><HR><B><I>Function</I></B><HR></PRE> |
| |
| <UL> |
| <LI><A HREF="#sec1">Local Index</A></LI> |
| <LI><A HREF="#sec2">Summary</A></LI> |
| <LI><A HREF="#sec3">Synopsis</A></LI> |
| <LI><A HREF="#sec4">Description</A></LI> |
| <LI><A HREF="#sec5">Complexity</A></LI> |
| <LI><A HREF="#sec6">Example</A></LI> |
| <LI><A HREF="#sec7">See Also</A></LI> |
| <LI><A HREF="#sec8">Standards Conformance</A></LI> |
| </UL> |
| <A NAME="sec1"><H3>Local Index</H3></A> |
| No Entries |
| <A NAME="sec2"><H3>Summary</H3></A> |
| <P>Algorithm that performs a binary search for a value</P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <algorithm> |
| |
| namespace std { |
| template <class ForwardIterator, class T> |
| bool |
| binary_search(ForwardIterator start, ForwardIterator finish, |
| const T& value); |
| template <class ForwardIterator, class T, class Compare> |
| bool |
| binary_search(ForwardIterator start, ForwardIterator finish, |
| const T& value, Compare comp); |
| } |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <P>The <SAMP>binary_search()</SAMP> algorithm, like the related algorithms <SAMP><A HREF="equal-range.html">equal_range()</A></SAMP>, <SAMP><A HREF="lower-bound.html">lower_bound()</A></SAMP>, and <SAMP><A HREF="upper-bound.html">upper_bound()</A></SAMP>, performs a binary search on a range of ordered values. All binary search algorithms have two variations. The first variation uses the <SAMP>operator<</SAMP> to perform the comparison, and assumes that the sequence has been sorted using that operator. The second variation allows you to specify a function object of type <SAMP>Compare</SAMP>, which it assumes was the function used to sort the sequence. The function object must be a binary predicate. </P> |
| <P>The <SAMP>binary_search()</SAMP> algorithm returns <SAMP>true</SAMP> if a sequence contains an element equivalent to the argument <SAMP>value</SAMP>. The first variation of <SAMP>binary_search()</SAMP> returns <SAMP>true</SAMP> if the sequence contains at least one element that is equal to the search value. The second variation of the <SAMP>binary_search()</SAMP> algorithm returns <SAMP>true</SAMP> if the sequence contains at least one element that satisfies the conditions of the comparison function. Formally, <SAMP>binary_search()</SAMP> returns <SAMP>true</SAMP> if there is an iterator <SAMP>i</SAMP> in the range <SAMP>[start, finish)</SAMP> that satisfies the corresponding conditions:</P> |
| <P><SAMP>!(*i < value) && !(value < *i) </SAMP></P> |
| <P>or </P> |
| <P><SAMP>comp(*i, value) == false && comp(value, *i) == false</SAMP></P> |
| <A NAME="sec5"><H3>Complexity</H3></A> |
| <P><SAMP>binary_search()</SAMP> performs at most <SAMP>log(finish - start) + 2 </SAMP>comparisons.</P> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // b_search.cpp |
| // |
| |
| #include <algorithm> // for copy, sort |
| #include <deque> // for deque |
| #include <functional> // for less |
| #include <iostream> // for cout, endl, ostream_iterator |
| |
| |
| |
| int main () |
| { |
| // Typedefs for convenience. |
| typedef std::deque<short, std::allocator<short> > deque; |
| |
| typedef std::ostream_iterator<deque::value_type, char, |
| std::char_traits<char> > os_iter; |
| |
| const deque::value_type arr[] = { |
| 0, 1, 2, 2, 3, 4, 2, 2, 6, 7 |
| }; |
| |
| // Populate and sort the container. |
| deque d (arr + 0, arr + sizeof arr / sizeof *arr); |
| std::sort (d.begin (), d.end ()); |
| |
| // Try binary_search variants. |
| bool b1 = std::binary_search (d.begin (), d.end (), 3); |
| bool b2 = std::binary_search (d.begin (), d.end (), 11, |
| std::less<int>()); |
| |
| // Output results. |
| std::cout << "Container contents: "; |
| std::copy (d.begin (), d.end (), |
| os_iter (std::cout, " ")); |
| |
| std::cout << "\nThe number 3 was " |
| << ("NOT found" + b1 * 4); |
| |
| std::cout << "\nThe number 11 was " |
| << ("NOT found" + b2 * 4) << std::endl; |
| |
| return 0; |
| } |
| |
| Program Output: |
| Container contents: 0 1 2 2 2 2 3 4 6 7 |
| The number 3 was found |
| The number 11 was NOT found |
| </PRE></UL> |
| <A NAME="sec7"><H3>See Also</H3></A> |
| <P><SAMP><A HREF="equal-range.html">equal_range()</A></SAMP>, <SAMP><A HREF="lower-bound.html">lower_bound()</A></SAMP>, <SAMP><A HREF="upper-bound.html">upper_bound()</A></SAMP></P> |
| <A NAME="sec8"><H3>Standards Conformance</H3></A> |
| <P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.3.4</I></P> |
| |
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