C++ Programming Code Examples
C++ > Visual C++ 5.0 Standard C++ Library Code Examples
The lower bound algorithm returns the first location in the sequence that value
The lower bound algorithm returns the first location in the sequence that value
lower_bound
Header
<algorithm>
template<class ForwardIterator, class T> inline
ForwardIterator lower_bound(ForwardIterator first, ForwardIterator last, const T& value)
The lower_bound algorithm returns the first location in the sequence that value can be inserted such that the order of the sequence is maintained. lower_bound returns an iterator positioned at the location that value can be inserted in the range [first..last), or returns last if no such position exists. lower_bound assumes the range [first..last) is sorted using operator<.
template<class ForwardIterator, class T, class Compare> inline
ForwardIterator lower_bound(ForwardIterator first, ForwardIterator last, const T& value, Compare compare)
The lower_bound algorithm returns the first location in the sequence that value can be inserted such that the order of the sequence is maintained. lower_bound returns an iterator positioned at the location that value can be inserted in the range [first..last), or returns last if no such position exists. This version assumes the range [first..last) is sorted sequentially using the compare function.
Samples
Sample for Non-Predicate Version
// disable warning C4786: symbol greater than 255 character,
// okay to ignore this warning
#pragma warning(disable: 4786)
#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
using namespace std;
void main()
{
const int VECTOR_SIZE = 8 ;
// Define a template class vector of int
typedef vector<int > IntVector ;
//Define an iterator for template class vector of strings
typedef IntVector::iterator IntVectorIt ;
IntVector Numbers(VECTOR_SIZE) ;
IntVectorIt start, end, it, location ;
// Initialize vector Numbers
Numbers[0] = 4 ;
Numbers[1] = 10;
Numbers[2] = 10 ;
Numbers[3] = 30 ;
Numbers[4] = 69 ;
Numbers[5] = 70 ;
Numbers[6] = 96 ;
Numbers[7] = 100;
start = Numbers.begin() ; // location of first
// element of Numbers
end = Numbers.end() ; // one past the location
// last element of Numbers
// print content of Numbers
cout << "Numbers { " ;
for(it = start; it != end; it++)
cout << *it << " " ;
cout << " }\n" << endl ;
// return the first location at which 10 can be inserted
// in Numbers
location = lower_bound(start, end, 10) ;
cout << "First location element 10 can be inserted in Numbers is: "
<< location - start << endl ;
}
Program Output
Numbers { 4 10 10 30 69 70 96 100 }
First location element 10 can be inserted in Numbers is: 1
Sample for Predicate Version
// disable warning C4786: symbol greater than 255 character,
// okay to ignore this warning
#pragma warning(disable: 4786)
#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
using namespace std;
void main()
{
const int VECTOR_SIZE = 8 ;
// Define a template class vector of int
typedef vector<int > IntVector ;
//Define an iterator for template class vector of strings
typedef IntVector::iterator IntVectorIt ;
IntVector Numbers(VECTOR_SIZE) ;
IntVectorIt start, end, it, location ;
// Initialize vector Numbers
Numbers[0] = 4 ;
Numbers[1] = 10;
Numbers[2] = 70 ;
Numbers[3] = 10 ;
Numbers[4] = 30 ;
Numbers[5] = 69 ;
Numbers[6] = 96 ;
Numbers[7] = 100;
start = Numbers.begin() ; // location of first
// element of Numbers
end = Numbers.end() ; // one past the location
// last element of Numbers
//sort Numbers using the function object less<int>()
//lower_bound assumes that Numbers is sorted
//using the "compare" (less<int>() in this case)
//function
sort(start, end, less<int>()) ;
// print content of Numbers
cout << "Numbers { " ;
for(it = start; it != end; it++)
cout << *it << " " ;
cout << " }\n" << endl ;
// return the first location at which 10 can be inserted
// in Numbers
location = lower_bound(start, end, 10, less<int>()) ;
cout << "First location element 10 can be inserted in Numbers is: "
<< location - start << endl ;
}
Program Output
Numbers { 4 10 10 30 69 70 96 100 }
First location element 10 can be inserted in Numbers is: 1
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Return iterator to lower bound. Returns an iterator pointing to the first element in the range [first,last) which does not compare less than val. The elements are compared using operator< for the first version, and comp for the second. The elements in the range shall already be sorted according to this same criterion (operator< or comp), or at least partitioned with respect to val. The function optimizes the number of comparisons performed by comparing non-consecutive elements of the sorted range, which is specially efficient for random-access iterators. Unlike upper_bound, the value pointed by the iterator returned by this function may also be equivalent to val, and not only greater.
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