Q158001: STL Sample for the partial_sort Function

Article: Q158001
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 partial_sort STL function in
Visual C++.

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

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

     <algorithm>

Prototype
---------

     template<class RandomAccessIterator> inline
     void partial_sort(RandomAccessIterator first,
                       RandomAccessIterator middle,
                       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 partial_sort algorithm sorts the smallest N elements, where N = middle -
first of the sequence [first, last). The remaining elements end up in the range
[middle..last) in an undefined order.

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

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

  ////////////////////////////////////////////////////////////////////// 
  // 
  // Compile options needed: /GX
  // 
  // partial_sort.cpp : Illustrates how to use the partial_sort
  //                    function.
  // 
  // Functions:
  // 
  //    partial_sort : Sort the smallest N elements in a sequence.
  // 
  // 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>
  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] = 7;

      start = Numbers.begin() ;   // location of first
                                  // element of Numbers

      end = Numbers.end() ;       // one past the location
                                  // last element of Numbers

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

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

      // sort the smallest 4 elements in the sequence
      partial_sort(start, start+4, end) ;

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

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

  Program Output is:

  Before calling partial_sort

  Numbers { 4 10 70 30 10 69 96 7  }

  After calling partial_sort

  Numbers { 4 7 10 10 70 69 96 30  }

REFERENCES
==========

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

Additional query words: STL partial_sort

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

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