Q157221: STL Sample for the Predicate Version of lower_bound Function

Article: Q157221
Product(s): Microsoft C Compiler
Version(s): winnt:4.2
Operating System(s): 
Keyword(s): _IK
Last Modified: 06-MAY-2001

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The information in this article applies to:

- The Standard C++ Library 
- Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
- Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
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SUMMARY
=======

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

MORE INFORMATION
================

Required Header
---------------

     <algorithm>

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.

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.
  // 
  // 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

REFERENCES
==========

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

Additional query words: STL lower_bound

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Keywords          : _IK 
Technology        : kbVCsearch kbAudDeveloper kbVC420 kbVC32bitSearch kbVCLibrary
Version           : winnt:4.2
Issue type        : kbhowto

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