Predicate Version of lower_bound (STL Sample)

The sample code below illustrates how to use the the predicate version of the lower_bound STL function in Visual C++.

Required Header:
<algorithm>

template<class ForwardIterator, class T, class Compare> 
     inline ForwardIterator lower_bound(ForwardIterator first, ForwardIterator last,
     const T& value, Compare compare)

Note: The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.

Description:
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.

Sample Code:

//////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
// lower_bound.cpp : Illustrates how to use the lower_bound
//                   function.
//
// Functions:
//
//    lower_bound : Return the lower bound within a range.
//
//////////////////////////////////////////////////////////////////////

// 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 is:

Numbers { 4 10 10 30 69 70 96 100  }

First location element 10 can be inserted in Numbers is: 1