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STL Sample for the Predicate Version of lower_bound Function

Retired KB ArticleThis article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
Article ID:157221
Last Review:November 18, 2003
Revision:2.0
This article was previously published under Q157221
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SUMMARY

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

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MORE INFORMATION

Required Header

   <algorithm>
				

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Prototype

   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 original version in the header file. They have been modified to improve readability.

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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.

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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.
// 
// Written by Kalindi Sanghrajka
// of Microsoft Product Support Services,
// Software Core Developer Support.
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
////////////////////////////////////////////////////////////////////// 

// 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, allocator<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 ;
}
				
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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REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

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APPLIES TO
The Standard C++ Library
Microsoft Visual C++ 4.2 Enterprise Edition
Microsoft Visual C++ 4.2 Professional Edition

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Keywords: 
kbhowto KB157221

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