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| <TITLE>lower_bound()</TITLE> |
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| <H2>lower_bound()</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 determines the first valid position for an element in a sorted container</P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <algorithm> |
| |
| namespace std { |
| template <class ForwardIterator, class T> |
| ForwardIterator lower_bound(ForwardIterator start, |
| ForwardIterator finish, |
| const T& value); |
| |
| template <class ForwardIterator, class T, class Compare> |
| ForwardIterator lower_bound(ForwardIterator start, |
| ForwardIterator finish, |
| const T& value, |
| Compare comp); |
| } |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <P>The <SAMP>lower_bound()</SAMP> algorithm compares a supplied <SAMP>value</SAMP> to elements in a sorted sequence and returns the first position in the container at which <SAMP>value</SAMP> can be inserted without violating the container's ordering. There are two versions of the algorithm. The first uses <SAMP>operator<()</SAMP> to perform the comparison, and assumes that the sequence has been sorted using that operator. The second version lets you include a function object of type <SAMP>Compare</SAMP>, and assumes that <SAMP>comp</SAMP> is the function used to sort the sequence. The function object must be a binary predicate. </P> |
| <P>The return value of <SAMP>lower_bound()</SAMP> is the iterator for the first element in the container that is<I> greater than or equal to</I> <SAMP>value</SAMP>, or, when the comparison operator is used, the first element that does not satisfy the comparison function. Formally, the algorithm returns an iterator <SAMP>i</SAMP> in the range <SAMP>[start, finish)</SAMP> such that for any iterator <SAMP>j</SAMP> in the range <SAMP>[start, i)</SAMP> the following corresponding conditions hold: </P> |
| <P><SAMP>*j < value</SAMP></P> |
| <P>or</P> |
| <P><SAMP>comp(*j, value) == true</SAMP></P> |
| <A NAME="sec5"><H3>Complexity</H3></A> |
| <P><SAMP>lower_bound()</SAMP> performs at most <SAMP>log(finish - start) + 1</SAMP> comparisons.</P> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // ul_bound.cpp |
| // |
| |
| #include <vector> |
| #include <algorithm> |
| #include <functional> |
| #include <iostream> |
| |
| int main () |
| { |
| typedef std::vector<int, std::allocator<int> > Vector; |
| typedef Vector::const_iterator Iterator; |
| |
| const int a[] = { 0, 1, 2, 2, 3, 4, 5, 5, 5, 6, 7 }; |
| |
| // Set up a vector. |
| const Vector v (a, a + sizeof a / sizeof *a); |
| |
| // Try lower_bound variants. |
| Iterator it1 = std::lower_bound (v.begin (),v.end (), 3); |
| Iterator it2 = std::lower_bound (v.begin (),v.end (), 2, |
| std::less<int>()); |
| |
| // Try upper_bound variants. |
| Iterator it3 = std::upper_bound (v.begin (), v.end (), 3); |
| Iterator it4 = std::upper_bound (v.begin (), v.end (), 2, |
| std::less<int>()); |
| |
| std::cout << "\n\nThe upper and lower bounds of 3: ( " |
| << *it1 << " , " << *it3 |
| << " ]\n\n\nThe upper and lower bounds of 2: ( " |
| << *it2 << " , " << *it4 << " ]\n"; |
| |
| return 0; |
| } |
| |
| |
| |
| Program Output: |
| </PRE></UL> |
| <UL><PRE> |
| |
| The upper and lower bounds of 3: ( 3 , 4 ] |
| |
| |
| The upper and lower bounds of 2: ( 2 , 3 ] |
| </PRE></UL> |
| <A NAME="sec7"><H3>See Also</H3></A> |
| <P><SAMP><A HREF="upper-bound.html">upper_bound()</A></SAMP>, <SAMP><A HREF="equal-range.html">equal_range()</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 25.3.3.1</I></P> |
| |
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