lower_bound (3C++std) - Tru64 UNIX
Standard C++ LibraryCopyright 1996, Rogue Wave Software, Inc. NAME
lower_bound - Determine the first valid position for an element in a
sorted container.
SYNOPSIS
template <class ForwardIterator, class T>
ForwardIterator lower_bound(ForwardIterator first,
ForwardIterator last,
const T& value);
template <class ForwardIterator, class T, class Compare>
ForwardIterator lower_bound(ForwardIterator first,
ForwardIterator last,
const T& value, Compare comp);
DESCRIPTION
The lower_bound algorithm compares a supplied value to elements in a sorted
container and returns the first position in the container that value can
occupy without violating the container's ordering. There are two versions
of the algorithm. The first uses the less than operator (operator<) 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 Compare, and assumes that Compare is the function used to sort the
sequence. The function object must be a binary predicate.
lower_bound's return value is the iterator for the first element in the
container that is greater than or equal to value, or, when the comparison
operator is used, the first element that does not satisfy the comparison
function. Formally, the algorithm returns an iterator i in the range
[first, last) such that for any iterator j in the range [first, i) the
following corresponding conditions hold:
*j < value
or
comp(*j, value) == true
COMPLEXITY
lower_bound performs at most log(last - first) + 1 comparisons.
EXAMPLE
//
// 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 = lower_bound(v1.begin(),v1.end(),3);
// it1 = v1.begin() + 4
iterator it2 =
lower_bound(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 ]
WARNING
If your compiler does not support default template parameters then you need
to always supply the Allocator template argument. For instance you'll have
to write:
vector<int,allocator<int> >
instead of:
vector<int>
SEE ALSO
upper_bound, equal_range
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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