Q158000: STL Sample for the nth_element Function

Article: Q158000
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): _IK
Last Modified: 05-MAY-2001

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The information in this article applies to:

- The Standard C++ Library, included with:
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, version 4.2 
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SUMMARY
=======

The sample code below illustrates how to use the nth_element STL function in
Visual C++.

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

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

     <algorithm>

Prototype
---------

     template<class RandomAccessIterator> inline
     void nth_element(RandomAccessIterator first,
                      RandomAccessIterator nth,
                      RandomAccessIterator last)

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 nth_element algorithm partitions the sequence [first..last) on the value
referenced by nth. All the elements less than or equal to the value are placed
before value and all elements greater than value are placed after value in the
sequence.

The non-predicate version of nth_element uses operator< for comparisons.

Sample Code
-----------

  ////////////////////////////////////////////////////////////////////// 
  // 
  // Compile options needed: /GX
  // 
  // nth_element.cpp : Illustrates how to use the nth_element
  //                   function.
  // 
  // Functions:
  // 
  //   nth_element : Partition the elements in a sequence by its nth
  //                 element.
  // 
  // 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
  #pragma warning(disable: 4786)

  #include <iostream>
  #include <algorithm>
  #include <functional>
  #include <vector><BR/>
  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 ;

      // Initialize vector Numbers
      Numbers[0] = 4 ;
      Numbers[1] = 10;
      Numbers[2] = 70 ;
      Numbers[3] = 30 ;
      Numbers[4] = 10;
      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

      cout << "Before calling nth_element\n" << endl ;

      // print content of Numbers
      cout << "Numbers { " ;
      for(it = start; it != end; it++)
          cout << *it << " " ;
      cout << " }\n" << endl ;

      // partition the elements by the 4th element
      nth_element(start, start+4, end) ;

      cout << "After calling nth_element\n" << endl ;

      cout << "Numbers { " ;
      for(it = start; it != end; it++)
          cout << *it << " " ;
      cout << " }\n" << endl ;
  }

  Program Output is:

  Before calling nth_element

  Numbers { 4 10 70 30 10 69 96 100  }

  After calling nth_element

  Numbers { 4 10 10 30 69 70 96 100  }

REFERENCES
==========

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

Additional query words: STL nth_element

======================================================================
Keywords          : _IK 
Technology        : kbVCsearch kbAudDeveloper kbVCLibrary
Version           : winnt:
Issue type        : kbhowto

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