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<H2>lower_bound</H2>
<HR><PRE> Algorithm</PRE><HR>
<A NAME="Summary"><H3>Summary</H3></A>
<P>Determine the first valid position for an element in a sorted container.</P>
<H3>Contents</H3>
<UL>
<A HREF="#Synopsis"><LI>Synopsis</LI></A>
<A HREF="#Description"><LI>Description</LI></A>
<A HREF="#Complexity"><LI>Complexity</LI></A>
<A HREF="#Example"><LI>Example</LI></A>
<A HREF="#Warning"><LI>Warning</LI></A>
<A HREF="#See Also"><LI>See Also</LI></A>
</UL>
<A NAME="Synopsis"><H3>Synopsis</H3></A>
<PRE>template <class ForwardIterator, class T></PRE>
<PRE> ForwardIterator <B>lower_bound</B>(ForwardIterator first,
ForwardIterator last,
const T& value);
template <class ForwardIterator, class T, class Compare>
ForwardIterator <B>lower_bound</B>(ForwardIterator first,
ForwardIterator last,
const T& value, Compare comp);
</PRE>
<A NAME="Description"><H3>Description</H3></A>
<P>The <B><I>lower_bound</B></I> algorithm compares a supplied <SAMP>value</SAMP> to elements in a sorted container and returns the first postition in the container that <SAMP>value</SAMP> can occupy without violating the container's ordering. There are two versions of the algorithm. The first uses the less than operator (<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>Compare</SAMP> is the function used to sort the sequence. The function object must be a binary predicate. </P>
<P><B><I>lower_bound</B></I>'s return value 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>[first, last)</SAMP> such that for any iterator <SAMP>j</SAMP> in the range <SAMP>[first, i)</SAMP> the following corresponding conditions hold: </P>
<PRE>*j < value</PRE>
<PRE></PRE><P>or </P>
<PRE> comp(*j, value) == true</PRE>
<PRE></PRE>
<A NAME="Complexity"><H3>Complexity</H3></A>
<P><B><I>lower_bound</B></I> performs at most <SAMP>log(last - first) + 1</SAMP> comparisons.</P>
<A NAME="Example"><H3>Example</H3></A>
<PRE>//
// ul_bound.cpp
//
#include <vector>
#include <algorithm>
#include <iostream.h>
int main()
{
typedef vector<int>::iterator iterator;
int d1[11] = {0,1,2,2,3,4,2,2,2,6,7};
// Set up a vector
vector<int> v1(d1,d1 + 11);
// Try lower_bound variants
iterator it1 = <B>lower_bound</B>(v1.begin(),v1.end(),3);
// it1 = v1.begin() + 4
iterator it2 =
<B>lower_bound</B>(v1.begin(),v1.end(),2,less<int>());
// it2 = v1.begin() + 4
// Try upper_bound variants
iterator it3 = upper_bound(v1.begin(),v1.end(),3);
// it3 = vector + 5
iterator it4 =
upper_bound(v1.begin(),v1.end(),2,less<int>());
// it4 = v1.begin() + 5
cout << endl << endl
<< "The upper and lower bounds of 3: ( "
<< *it1 << " , " << *it3 << " ]" << endl;
cout << endl << endl
<< "The upper and lower bounds of 2: ( "
<< *it2 << " , " << *it4 << " ]" << endl;
return 0;
}
Output :
The upper and lower bounds of 3: ( 3 , 4 ]
The upper and lower bounds of 2: ( 2 , 3 ]
</PRE>
<A NAME="Warning"><H3>Warning</H3></A>
<P>If your compiler does not support default template parameters then you need to always supply the <SAMP>Allocator</SAMP> template argument. For instance you'll have to write:</P>
<PRE>vector<int,allocator></PRE>
<PRE></PRE><P>instead of:</P>
<PRE>vector<int></PRE>
<A NAME="See Also"><H3>See Also</H3></A>
<P><A HREF="upp_0967.htm"><B><I>upper_bound</B></I></A>, <A HREF="equ_3232.htm"><B><I>equal_range</B></I></A></P>
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